title graphic

PART 4
Specific Equipment

Order of Presentation

SG Radar
SC, SK Radars
Mark 3, Mark 4 Radars
SA Radar
SL Radar
SO Radar
SF Radar
SJ Radar
SD Radar
SU Radar
ST Radar
SR Radar
SP Radar
VD Remote Indicator
VF Remote Indicator
VG Remote Indicator
OBU Echo Box


Part 4
SG Radar

CONTROLS 4-SG-2
  Range and train indicator 4-SG-2
  Identification and function 4-SG-2
   
TURNING ON AND OFF 4-SG-4
  Turning on 4-SG-4
  Turning off 4-SG-4
   
CALIBRATION 4-SG-5
  Calibration of the range counters 4-SG-5
  External calibration 4-SG-6
   
OPERATIONAL TECHNIQUE 4-SG-6
  Tuning the receiver 4-SG-6
    Land echo  
    Ship echo  
    Sea-return  
    Meter  
  Long-range search or large target search 4-SG-7
  Close-range search or small target search 4-SG-7
  Station keeping 4-SG-8
  Auxiliary fire control 4-SG-8
  Navigation 4-SG-9
  Composition 4-SG-9
    Type and number of ships  
    Aircraft  
    Land  
    False echoes  
    PPI echoes  
  Jamming and deception 4-SG-11
   
PERFORMANCE 4-SG-12
  Maximum reliable range 4-SG-12
  Minimum range 4-SG-12
  Accuracy 4-SG-12
  Resolution 4-SG-12
TROUBLES 4-SG-12

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SG RADAR

CONTROLS

Range and train indicator.

Working with the SG, the operator is concerned primarily with the range and train indicator unit from which he can control the entire radar gear. A close-up of this unit is shown in figure 4-SG-1.

All the controls on the range and train indicator may be divided into three groups: power, operating, and pre-set. All the power controls are grouped on the left and extend from top to bottom of the unit, except for the dial lights switch, which is at the far right of the pre-set group. The second group, operating controls, extend along the center of the panel. The third group is the bottom row of pre-set controls.

Identification and function.

It is important to be able to identify, and to know the functions of all of the controls. For ease in locating and identifying, all controls in figure 4 SG-1 are either numbered or lettered.

  1. The switch marked A is the remote control for the main-power switch at the transmitter-receiver unit.

  2. Meter B is identical to one located on the transmitter-receiver unit, and indicates line voltage. This meter should read between 110 and 120 volts AC. If it does not, call the maintenance man.

  3. The other meter, C, indicates transmitter current when switch K is in NORMAL position. Transmitter current as indicated on meter C is controlled by the setting of the variac (E). The variac should be set so that the transmitter current reading on meter C is between 15 and 25 milliamperes. If this reading cannot be attained, notify the maintenance man. With Switch K in MONITOR or RECEIVER TUNE position, meter C duplicates respectively RF. monitor and tuning indicator meter readings at the transmitter and receiver

Drawing of the front of the range and train indicator unit.
Figure 4 SG-1. Range and train indicator unit.

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    unit. When switch K is an the RECEIVER TUNE position, it should read from 30 to 40 depending upon how well the receiver is tuned. The receiver should be tuned for maximum meter deflection. The meter reading in the MONITOR position will vary from time to time according to the way it is adjusted by the maintenance man. The operator should check the value at the start of his watch, and periodically thereafter, in order to determine whether any changes occur. The maintenance man should be notified immediately of any change.

  1. The radiation switch D controls intermittent and continuous operation of the transmitter. For intermittent operation, switch D must be held in KEY position, as there is a spring action that automatically returns the switch to OFF position. LOCK position is for continuous operation.

  2. Variac (E) controls the power supplied to the transmitter.

  3. The scope (F) is the range scope. Ranges are read directly on the range counters (G). A modified method for quick and approximate readings is to place a calibrated scotch tape scale on the "A" scope below the sweep. The same can be done at the PPI (I) by drawing with india ink 5,000-yard circles for the 15,000-yard range; then, on the 75,000-yard range, these circles will be 25.000 yards apart.

  4. -8. Bearing is read on indicator H and PPI (I). True bearing is read from the outer scale, while relative bearing is read from the inner dial, when synchro switch (J) is in NORMAL position. If ship's gyrocompass repeater system should fail, switch J must be thrown to EMERGENCY for equipment to operate, giving relative beatings only on the outer dial.

  1. When the radar is operating, switch K is in the NORMAL position. The other positions, RECEIVER TUNE and MONITOR, are for purposes stated in 3 above.

  2. Receiver sensitivity is controlled remotely by the operator through receiver gain control (L).

  3. Receiver's tuning is controlled remotely by the operator with receiver tune control (M) This is set for maximum return signals.

  4. The range crank (N) is geared to the range counters and also moves the step in the time base on the range scope. Thus, lining up the step with the blip on the range scope, the range of the target can be read directly from the range counters.

  5. There are two range scales. 15,000 yards and 75,000 yards. Switch P permits the operator to select either of the two ranges.

  6. Switch Q allows the operator to receive either signals or range markers on the range scope and PPI. Normally this switch is on SIGNALS. In order to insure that the gear will give accurate ranges, the operator must cheek frequently (at least once each watch) the range calibration by switching range markers to the scope. This procedure is described later, in the section on Calibration.

  7. The antenna's rotation may be controlled either manually or automatically by switch R. From its center position moving switch R to right gives automatic clockwise rotation; moving it to left gives automatic counterclockwise rotation. There are four positions for four speeds on either side of center.

  8. Remote range switch (T) and remote bearing switch (U) permit transmission of ranges and bearings, respectively, to range and bearing indicators located on the bridge, gun control, torpedo control, and plotting rooms. At these stations there are selector switches for cutting in either range and/or bearing indicators. As a rule, remote range and bearing are always in the ON position at the range and train indicator and OFF at the selector switches when bearings or ranges are not desired.

  9. As a safety precaution against overloading the transmitter, there is a relay which trips during any overload condition. This relay can be reset by the operator by pushing reset button (V).

  10. Switch W will determine the positions OFF, INTERMITTENT, and CONTINUOUS operation for IFF equipment when it is installed,

  11. Switch X adjusts the IFF gain.

  12. Range focus (1), permits the operator to adjust the sweep on the range scope, permitting a sharp, even trace for the entire width of the scope. This setting is made on installing a new tube.

  13. 15,000-yard zero set (2) adjusts the calibration for the lower end of this range scale.

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  1. 15,000-yard limit set (3) adjusts the calibration for the upper end of this range scale.

  2. 75,000-yard zero set (4) adjusts the calibration for the lower end of this range scale.

  3. 75,000-yard limit set (5) adjusts the calibration for the upper end of this range scale.

  4. Pulse frequency (6) controls the pulse repetition frequency. There are three adjustments, A, B, and C, which are used to reduce interference from other radars of approximately the same frequency. The control (6) is set on the letter giving the minimum interference. This control also is used for identifying second-sweep echoes. More will he said about this in the technique section.

  5. PPI focus (7) permits the operator to adjust the sweep on the PPI for a sharp, even trace.

  6. Dial lights switch (8) controls the intensity of lights on the PPI, bearing dial, and counters. Pilot lights switch (9) controls light intensity for the red and amber lights opposite the stand-by and radiation switches (this control has been omitted on later models).

  7. There are five screwdriver adjustments with which the operator should not tamper once the set is operating normally.

      H center adjustment (12) centers the time base on the range scope from right to left.

      V center adjustment (13) centers the up and down position of the time base on the scope.

      PPI anode 2 (16) adjusts the sweep and signal intensity of the PPI screen.

      PPI intensity (15) adjusts the intensity of the signal.

      Marker amplitude (14) adjusts the height of the range markers, which should be from 3/4 inch to 1 inch in height.

  8. There are two fuses with which the operator should he familiar. These fuses are located on the front panel near the transmitter current meter (C). One is marked INDICATOR F-902 (10), and the other is marked BEARING CONTROL F-901 (11). If, for any reason, the antenna or indicator should stop functioning, the operator should check these fuses before sending for the maintenance man There is a further description of these fuses in the section on Operational Technique. So far the controls on the range and train indicator unit have been identified. The operator should become so familiar with these controls that he can make any adjustment automatically, even in complete darkness.

TURNING ON AND OFF

Turning on.

Let us assume that the transmitter and receiver unit are ready for operation. When starting the gear for the first time, check to see that the controls are set as follows:

  1. Turn the main-line power at the remote control switch (A) to STANDBY.

  2. Set the radiation switch (D) in the OFF position.

  3. Turn the variac (E) to zero (extreme counterclockwise).

  4. Place synchro switch (J) on NORMAL position.

  5. Turn receiver gain (L) down.

  6. Throw signal-markers switch (Q) to SIGNALS.

  7. Turn bearing switch (R) to NORMAL.

  8. Set rec-tune, normal, monitor switch (K) to NORMAL.

Steps 1 through 8 represent the normal settings of the range and train indicator unit when equipment is on STANDBY, and from which the SG can be placed in operation as follows:

  1. Turn the standby-on switch (A) to the ON position. The amber pilot light will indicate that power is available. Check the line voltage on meter (B), which should read between 110 and 120 volts.

  2. Throw the radiation switch (D) to LOCK position. After about one minute, the red pilot light will glow, indicating that the transmitter is ready.

  3. Turn the variac (F) slowly to the right until the transmitter current meter reads 25 milliamperes or less.

  4. Turn the receiver gain control (L) up until about 3/8-inch grass appears on the range scope.

  5. Start antenna rotation by turning the switch (R) to right or left.

Turning off.

In order to shut down the equipment the above procedure should be reversed.

  1. Stop antenna rotation by turning switch (R) to the center position, leaving antenna on 000° relative bearing.

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  1. Turn receiver gain control (L) down.

  2. Return variac (F) to zero (extreme counterclockwise).

  3. Turn radiation switch OFF.

  4. Throw the power switch (A) to STANDBY.

CALIBRATION

Calibration of the range counters.

To make sure that the equipment will give accurate range readings, the operator should check the calibration of the range counters at least once every watch (every four hours). To do this, the range selector switch (P) is first set to the 15,000-yard position and the signal-markers switch (Q) to the MARKERS position. Markers representing divisions of 5,000 yards appear along the time base on the range scope. The operator now turns the range crank (N) until the 15,000-yard marker just begins to "pull down" into the step. The diagram in figure 4 SG-2 illustrates how the step should appear when adjusted to the correct position. If accurate, the range counters should read exactly 15,000 yards. Next, the step is lined up with the center of the 5,000-yard marker. Now, the counter should read exactly 5,000 yards.

The operator also checks the counters on the 75,000-yard range scale. Then, if the selector switch is in the 75,000-yard position, a series of markers will appear on the time base, each representing distances of 5,000 yards. The appearance of these markers will vary somewhat on different installations, and this difference must be clearly understood if the calibration is to he done correctly. The zero marker may or may not

Under, over and correct calibration at 15,000- and 75,000-yard ranges scales.
Figure 4 SG-2. Correct calibration at 15,000- and 75,000-yard ranges scales.

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be visible at the left end of the time base. However, there should not be any confusion as to whether the first visible marker represents zero or 5,000 yards. If the zero marker appears, it will just he seen at the extreme left end of the time base. lithe first visible marker is some distance from the beginning of the time base, it is the 5,000-yard marker.

The step is first lined up with the center of the 5,000-yard marker, and the range counters should read exactly 5,000 yards. Next, the step is cranked until the 75,000-yard marker begins to drop down. The counters should read exactly 75,000 yards. The 75,000-yard marker will be the sixteenth or fifteenth, depending on whether the zero marker is, or is not visible.

If the calibration of the range counters is not correct, the operator will perform the following operations:

  1. Turn the signal-markers switch (Q) to MARKERS.

  2. Set the range switch (P) to the 15,000-yard position.

  3. Turn the range crank (N) until the range counter reads exactly 15,000 yards on the lower scale. Unlock the 15,000-yard limit set control (3), and adjust it until the top of the fourth range marker at the far right just begins to "pull down" into the step. Lock the control in this position.

  4. Change the range switch (P) to the 75,000yard position. If the range crank has not been move], the top counter will read 75,000 yards. Unlock the 75,000-yard limit set control (5), and turn it until the 75,000-yard marker (fifteenth or sixteenth from the left) begins to "pull down" into the step. Then lock the control again.

  5. Turn the range crank (N) until the top counter reads 5,000. Unlock the 75,000-yard zero set control (4), and adjust it until the 5,000-yard marker (first or second from the left) begins to drop. Lock the control.

  6. Switch to the 15.000-yard range, and turn the range crank until the bottom counters read 5,000. Now unlock the 15,000-yard zero set control (2) and adjust it until the 5,000-yard marker begins to drop. Lock the control.

  7. Re-check the upper limits on both range scales.

External calibration.

It is important that the external calibration of the set he checked periodically. This may be done by using one of three methods. It may be determined by comparison with fire-control radar, by ranging on some target whose distance can he determined precisely, or by observation of a double range echo. A double range echo is a false echo that will sometimes appear on the same bearing as a target, but at twice the range of that target. These echoes are most evident when the target ship is on a parallel course, close abeam, and large. If the real echo appears at 800 yards and the double range echo appears at 1,800 yards, the correct range of the target will he the difference between the two, or 1,000 yards. Since, in this example, your radar measured the range as 800 yards, the set's individual, constant error would be 200 yards, making all ranges low by that amount.

Be sure the set has been warmed up and calibrated carefully before trying to determine its error. When determined, the error can be compensated in calibration. Thus, to compensate for the error in the above example, set the range dial to 5,200 yards, and 15,200 yards instead of 5,000 yards and 15,000 yards,-line up the first and third range marks with the step as before. Now all ranges read on the 15,000-yard scale will he 200 yards higher and therefore correct. Make the same compensation on 75,000-yard scale.

OPERATIONAL TECHNIQUE

Tuning the receiver.

The operator has only one tuning control to adjust. This control is the knob marked receiver-tune (M) located next to the range crank.

When the set is turned on from the stand-by condition, it takes about twenty minutes for the oscillator frequency to become stable. The tuning will have to be adjusted frequently if the set is to be used during this first 20 minutes. After this "warm-up" time the tuning will be fairly stable, but should be checked at least every half hour, or by each new operator. Experience will indicate how often your particular set must he tuned. Some sets require more frequent tuning than others.

The following procedures are used to tune the receiver:

Land echo. The best method is to tune on a land echo. Stop the antenna in order to get a good steady land echo on the "A" scope. Turn the gain down to where the echo is not saturated (to where it is about half of its maximum height). Then adjust the receiver-tune control (M) until the signal is at its maximum height. The technique for determining maximum signal height is to turn the tuning control rapidly when approaching the maximum height, going a little beyond and a little under maximum signal, and

4-SG-6


then estimating the mean (average) setting between these two points. During tuning, always keep the signal below saturation by adjusting the receiver gain control (L), and make the setting rapidly.

Ship echo. The next method is similar to the foregoing but is not so effective. Tune on an echo from another ship. The same procedure is used; however, trouble will be experienced because the echo will bounce up and down. Tuning on an echo of this type requires a certain amount of skill and experience.

Sea-return. Another method, which, under certain conditions such as especially heavy weather is better than tuning on ship echoes, is to tune for maximum sea-return.

The sea-return consists of many bouncing echoes which extend out, sometimes as far as 6,000 yards. The operator should operate the set on the short-range scale, watch the "A" scope, and tune for the point where overall sea-return is highest and extends out to the greatest range. An illustration of how sea-return should appear is shown in figure 4 SG-3.

Meter. If there are no echoes or sea-return available for tuning, throw the receiver tune-normal-monitor switch (M) to the RECEIVER TUNE position. Then tune for the highest reading on the transmitter current meter (C), using the receiver tune (M) control. Do not fail to return switch to NORMAL after tuning, since in receiver tune position, ranges will be 500 yards off.

Sea Return Signal (Poor Timing) at the left A; (Some Signal in A After Adjusting Rec. Tuning Control) B
Fig. 4 SG-3. Sea-return on the "A" scope using 15,000 yard range scale.

Long-range search or large target search.

The "A" scope will show targets at greater ranges than the PPI; therefore, it is necessary that the "A" scope he used in the long-range search. The PPI is, however, much easier to watch, and once a target appears on it, there will he little chance of the operator missing the echo.

Because of the above considerations, a long-range search should use both the "A" and PPI scopes, with the following procedure:

Switch to the 75,000-yard scale and adjust the receiver gain for about 3/8-inch of grass on the "A" scope. Then, for approximately five minutes, search with the antenna on automatic rotation at the slowest speed. The operator should watch the PPI for two antenna sweeps, then the "A" scope for two sweeps, then the PPI for two more, and so on for the rest of the five minutes. At the end of this time, switch to hand rotation and make a slow hand rotation of a full 360°, watching the "A" scope very carefully. After this, repeat the automatic rotation search.

The speed used for automatic rotation is 4 rpm in the first position. Some ships have changed this so that the first position now has an antenna rotation speed of 1 or 2 rpm. If the set aboard your ship does not have a rotation as slow as this, the technician can easily change it to the desired speed. When this adjustment has been made, the operator can use the second speed of rotation, 4 rpm, for normal search, and lie can use the first speed in place of the hand search.

Close-range search or small target search.

This type of search is primarily intended to detect surfaced submarines, periscopes, or PT boats, although it has other functions. The following procedure should he used.

Switch the range to the 15,000-yard scale. The search is conducted by watching the PPI scope, using an antenna speed of 1 or 2 rpm, (or 4 rpm if that is the slowest available).

Two conditions requiring special attention are likely to be encountered in this type of search. The first is sea-return, which may extend to 1,000 or 2,000 yards, and in rough weather to 6,000 yards. With the receiver gain up to its normal value, targets at close range will be hidden in this sea-return. To detect, or to get bearings and ranges on targets under these conditions, it is necessary to reduce receiver gain. It should be borne in mind, however, that the gain is reduced only when checking these close targets, and then only for a very short time, since the gain must be up if the small echoes from submarines are to be detected.

The other thing requiring consideration on this range is the saturated echo. Targets at such short ranges give strong echoes. On the "A" scope these echoes are saturated; that is, they have flat tops. To get an accurate range on this type echo, the range dial should be cranked to a point at which one-half of the

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flat top drops off into the step. The illustration in figure 4 SG-4 shows the correct means of ranging on a saturated pip.

To get an accurate bearing on these strong echoes, the PPI should be used. Rapidly rotate the antenna back and forth so that the entire echo is visible on the PPI; then quickly stop the antenna so as to bisect the echo.

Station keeping.

For station keeping, it is not usually necessary to obtain extremely accurate ranges and bearings. In normal steaming, ranges and bearings to the guide ship may he obtained with sufficient accuracy for keeping station without stopping the antenna rotation. The PPI scope is used to approximate the bearing. The bearing is read off the scale surrounding the PPI by mentally drawing a line from the PPI center through the target to the scale. The range may be approximated by several different methods. The best method is to mark permanent 5,000-yard circles on the PPI with India ink-, and to estimate range in relation to these. A second method is to switch the signal-markers switch to MARKERS. As the antenna rotates, 5,000-yard circles will remain for a few seconds after the switch is turned back to SIGNALS. The range to the target may be estimated by noting its position relative to the marker circles. The third method is to put a piece of scotch tape on the "A" scope and ink a scale of ranges on it. Then, as the antenna sweeps by the target, the operator watches for the pip to jump up on the range scope and obtains the range from the scotch tape. A new rotating scale device is being placed on the PPI's of many of the SC's in the Elect. The range and bearing of target may be estimated by simply rotating the scale to coincide with the target. This device has two disadvantages: first, the range scale is inaccurate; second, it obscures the view of the PPI. A more satisfactory device is under development.

The above-mentioned methods of approximations are usually satisfactory for normal station keeping. While taking a new station, or during formation changes, it will usually be necessary to get accurate ranges and bearings in the normal way.

Radar was not meant to supersede regular station keeping methods. Since such use cuts down the search efficiency, employment of radar for station keeping should be kept to the absolute minimum.

Auxiliary fire control.

The SG may he called upon for fire-control work, especially torpedo fire-control on destroyers. There is always the possibility that the fire-control radars may be put out of commission, making it necessary to use the SG to obtain accurate bearings and ranges to be used in the computers. This can best be done by stopping the antenna. However, since such procedure cuts down the efficiency of the search, tracking should be carried on without stopping the antenna unless accuracy is absolutely vital. It is recommended that at least one 360° sweep be made per minute while tracking, to guard against surprise.

Shell splashes can be picked up when the antenna is trained in the direction of fire. On the "A" scope the echo will jump up rapidly, and a quick estimation of range difference between it aid the target echo may he made. If the antenna is rapidly rotated back and forth by hand so as to cover a small sector near the target, the splashes may appear on the PPI. It is

Three illustrations of Over, Correct and Under Ranging.
Figure 4 SG-4 Correct method for ranging on a saturated signal on the 15,000-yard range scale.

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possible to do very rough spotting in both range and deflection by estimation from the PPI.

Navigation.

The SG is extremely useful to the navigator, particularly when operating in close waters. The navigator who is always cognizant of the ship's position will he able to give the operator the approximate bearing, distance, and expected time of contact with land. From his chart lie will be able to tell if the land rises abruptly out of the water, or, in case the land is low lying near the beach, whether or not it rises farther inland.

Land that rises at the water's edge to considerable height is excellent for radar purposes since the closest land appearing on the PPI in this case, is usually the beach. The chart should always be checked for the possibility of inland mountains appearing; first, by checking the altitude of mountain peaks against the altitude of the shore line, and second, by checking the outline of the shore from the chart against the outline from the PPI. In eases of this type of land, the outlines will be almost identical, and comparison with the chart may be used to fix the ship's position. Almost all the islands in the Aleutians are of this type.

Another type of situation involves a low-lying shore line and inland mountains. When contact is first made, only the mountains will appear on the PPI, since the low shore will be below the horizon. With this type of land it would be a dangerous mistake to assume that the beach is the closest contact. Failure to remember this may result in the ship's grounding. For this same reason, unless your knowledge of the contour of the land justifies it, never depend on bearing tangents for fixing your position.

The best fixes are not necessarily obtained from a large group of random ranges and bearings, or from the closest land. The best method is to obtain a few accurate ranges and bearings of small prominent objects. Isolated rocks, small distinct islands, and isolated mountain peaks are excellent for obtaining fixes. The prominent points may be chosen from the chart. If the ranges and bearings obtained on two or three of them plot in at the same point, it is safe to assume that that point is your position.

Always remember to make use of the contours of the land when employing radar for navigation. By closely examining the echo of the "A" scope for multiple peaks and other peculiarities, the echo may be more definitely fixed to some position on the chart.

Islands in the mid-Pacific are very flat, and rise only a few feet above sea level. These islands are usually bounded by coral reefs and shoals, so extreme caution must be observed while using radar navigational fix taken close to them. Lack of small prominent points on these islands makes it difficult to obtain reliable fixes.

Sometimes it is possible to detect shoals on the radar screens, if the shoals are close enough to the surface to cause a disturbance in the water. The signal appearing on the radar screen would be much the same as a "wake" signal obtained from another ship. However, shoals are very treacherous and ships should not rely upon radar to detect them.

Composition.

When a contact is detected on the SG, it is extremely important that certain facts be determined about its composition. Ability to obtain these facts comes largely from experience, but the following hints may be of value.

Type and number of ships. The range of initial contact is the best indication of target size. Fixed antenna height results in ships of a certain size usually having a certain maximum range. Thus, on a ship where it is usual to contact battleships at 40,000 yards and destroyers at 25,000 yards, first contact at 38,000 yards would indicate a ship of battleship size.

Echoes from large ships will he much steadier than those from small ships, and will usually appear thicker on the "A" scope. On first contact or at great distance, the "A" scope should be used for determining the number of ships in a contacted group. Turn the receiver gain down, and examine the top of the echo for multiple peaks, counting as many as possible. It should be remembered that when contact is first made, only the large ships will appear, since the smaller ones will still be out of range.

Aircraft. Pips from aircraft will appear quite erratic, the echo fluctuating rapidly on the "A" scope. On the PPI they are apt to appear very strongly on the antenna sweep, be absent on the next sweep, and appear at some other position on the next sweep. They may be recognized by their fluctuating echo and rapid change of position.

Land. Land echoes are steady and are likely to be quite wide. When plotted on the DRT, their position will remain stationary.

False echoes. Various types of false echoes are encountered with the SG. They are not caused by trouble in the equipment, and are not truly false for they are actually caused by some reflecting surface. They are, however, considered false because they indicate objects in which we are not interested.

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Multiple-reflection echoes are caused by the beam reflecting between several ships in a group before returning to the antenna. The bearing of the echo will be the same as one of the ships. Because of the changing position of the ships, this type of echo will disappear very quickly.

In close formations, double-range echoes are quite common. They are caused by the returning echo reflecting off the searching ship, again reflecting off the target, and finally reaching the antenna. This type of false echo may be recognized by three factors; first, it will always be at the same bearing as one of the large targets; second, it will be at exactly twice the range of the large targets; and third, it will vary rapidly in amplitude.

Second-sweep echoes result from long-range echoes arriving back after the next sweep has started. With a pulse rate of 1,000 c.p.s., there is time for 81 miles of range between each pulse and sweep. Thus, for an echo to appear on the second sweep it must be over 81 miles away. Trouble will be experienced with this type of echo only when there is high land over 81 miles away. In order to know when second-sweep echoes are likely to be encountered, the operator should be constantly aware of the ship's position in relation to land. To check this type of false echo, the pulse rate should be changed. If the echo is of the second-sweep type, it will shift in range or disappear entirely. Although these echoes are rare, they should be recognized and understood. Figure 4 SG-5 shows a graphic representation of how the second-sweep echo pip will shift its position on the "A" scope as the pulse frequency is varied.

Another type of false echo results from reflection off some part of the ships structure. These echoes occur when the mast or superstructure is in the path of the radiated beam. The energy reflects off the interfering structure, hits the target, and returns by the same route. The false echo will be at the same range as some real target and on the bearing of the

Second-sweep echoes.
Figure 4 SG-5. Second-sweep echoes.

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interfering structure. The SG also has side lobes 60° to 70° on either side of the main lobe. They will often show up on a large target which is within 5,000 yards.

PPI echoes. When cruising in close formation with other ships, the picture that appears on the PPI will give the impression that we can determine the course of each individual ship simply by observing the PPI. This is definitely not true; although all the ships are on a similar course, each appears on the PPI to be on a different one because of the curved pip resulting from the radial sweep.

Jamming and deception.

There is no doubt that the enemy considers our radar an extremely dangerous weapon, and consequently it is only reasonable to expect him to try every means possible to make it less effective. He may use two tactics to do this: jamming and/or deception. Every operator should learn how to recognize these countermeasures, and expect them when in combat zones.

When the enemy broadcasts radio signals intending that our radar receive them, and they show a confusing pattern on the screen, it is called jamming. Use of dummy targets (tinfoil, kites, balloons, etc.) is called deception. More precise definitions are sometimes given, but these are satisfactory for this discussion.

The SG radar can be jammed, and it will show echoes from the tinfoil the enemy sometimes throws out to confuse the operator. The operator should not become alarmed when either of these things happen.

If you were suddenly confronted with jamming without previous experience, it would appear impossible to work through. However, it is not really that serious if the following procedure is carried out:

  1. DF on the jamming.

  2. Use available anti-jamming devices on receiver when provided.

  3. Try moving the gain control up and down.

  4. Try changing the receiver local oscillator tuning.

  5. Keep operating.

  6. Report the type and bearing of jamming to CIC.

The first reason for obtaining a bearing on the jamming is to determine whether or not it could be accidental interference. Jamming will not only be directional, but its true bearing will not be changed by any sudden change in your ship's course. Interference originating aboard your own ship will either be non-directional and appear on all bearings, or else it will always be on some certain relative bearing regardless of own-ships course changes.

Try moving the gain control up and down. This is probably one of the most important countermeasures that can be taken, and the one most commonly overlooked because of its simplicity.

In most cases, except when effective noise modulated jamming is being encountered, there is a setting of the gain control with which it is possible to range on a target in the presence of heavy jamming. If there are several echoes on the same bearing, the best setting for each echo is different. Of course it is more difficult to obtain these ranges because of the distortion of the echo produced by jamming, but it is, after all, possible to obtain the desired information. The extra effort is worth while because the enemy would not be jamming unless he were trying to conceal something important.

Two general methods of using the gain control, both of which should be tried, are as follows:

  1. Reduce setting; this prevents overload of radar receiver; echoes are visible "riding on top" of the jamming pattern.

  2. Increase setting; this limits (or clips) jamming; echoes are visible as a break in the base line.

Try changing receiver local oscillator tuning. When you change the rec. tune, you lose some of the height of the desired echo. However, if the jammer is not exactly on your radar frequency, there is a chance that you will detune the jamming signal more than the echo signal. Considerable improvement can sometimes be obtained in this way. Try "swinging" the rec. tune dial in both directions to see which direction brings the greatest improvement. Note the correct setting of the rec. tune dial so that it can be returned to its normal position when no jam is present, or if detuning does not help.

Keep operating. Even if the jamming is extremely effective, keep trying and do not turn your radar off. Turning your radar off informs the enemy that his jamming is effective, and certainly makes the radar completely worthless. The effectiveness of the jamming may change from time to time, so if you are persistent enough some information may be obtainable.

Report the nature and bearing of jamming to CIC. Recognizing the type may be difficult because nonsynchronous patterns sometimes appear blurred beyond recognition. Inasmuch as knowledge of jamming type* may possibly help identify the jammer


* See Part 3, Defense Against Jamming and Deception.

4-SG-11


in some cases, this information should he reported if possible. If the equipment is provided with an anti-jamming receiver, the jamming may be reduced sufficiently for reading targets without any detuning of the receiver. Detuning should be undertaken as a last resort, and then should be done very carefully and cautiously; otherwise all targets may be lost and the procedure made completely ineffective. No special method is offered for setting the controls of the AJ receiver, except that they should be varied for minimum jamming, the gain control coming first, and then the A\TC control.

Above all, never turn off the radar.

When jamming and/or deception is encountered, full 360° search must be continued. However, the antenna should be stopped for short intervals from time to time, in order to try reading through the jamming (using the "A" scope). You also must be prepared for any diversionary tactics, for the enemy may or may not use jamming and/or deception to divert your attention from the bearing of the main attacking forces. This problem is simplified somewhat when similar but separate radars are used for reading through jamming and for searching.

PERFORMANCE

Maximum reliable range.

Ranges in surface craft obtained with the SG are dependent on the antenna height. Expected ranges with a typical antenna height should he of value to the new operator.

The results listed below are maximum reliable ranges for a 90-foot antenna.

Accuracy.

Resolution.

Assuming two targets to be on the same bearing, the SG can distinguish between them at short ranges when they are separated by no more than 300 yards; at longer ranges approximately 500 yards separation is needed. At any range, too high gain tends to cause the pips to merge, and reduces discriminatory power. In general, the SG is able to discriminate in range between two targets separated by 300 yards or more on the "A" scope, and 500 yards on the PPI.

With respect to bearing, a comparable minimum limit exists and is expressed in angular rather than linear measurement. Since the transmitted beam does not travel along a single line, but has an angular spread, it can be seen that if there are two targets at the same range, one in the center of the beam pattern and the other in the edge, an echo will be returned from the target in the center and from the target in the edge, and these will appear as one echo. By reducing receiver gain it will often be possible to distinguish both targets. At normal ranges the angular separation necessary for target discrimination in bearing is 5° using the "A" scope, and 9° using the PPI.

TROUBLES

Major troubles are handled by the technicians but time will be saved if the operator is able to recognize some of the minor breakdowns.

If the sweep traces on the "A" and PPI scopes suddenly go out, the indicator fuse next to the "A" scope should be checked,


Type of target.   SG   SG-A and SG-1

BB, CV, Large auxiliaries   35,000-45,000 yards   45,000-55,000 yards
CA, CL, Medium auxiliaries   28,000-35,000 yards   30,000-40,000 yards
DD, DM, AV, PC   18,000-30,000 yards   25,000-35,000 yards
Submarines   9,000-12,000 yards   11,000-15,000 yards
Submarine periscope   2,000-4,000 yards   2,000- 4,000 yards
Large planes (altitude 1000'-3000')
PBM, PBY, PBZ
  20,000-35,000 yards   20,000-40,000 yards
Small planes (altitude 1000'-3000')
SOC, OSZU, SBD, F4F
  10,000-15,000 yards   12,000-21,000 yards
 
Minimum range.   SG   SG-A and SG-1

Ship   600 yards   600 yards
Plane   1,000 yards   1,200 yards

4-SG-12


If the antenna and "bug" will not turn when the antenna is switched to automatic rotation, the bearing fuse next to the "A" scope should be checked.

If the red light goes out, sweeps disappear, and the plate current drops to zero, the overload relay probably has kicked out. Torn the high-voltage variac all the way down, press the overload reset, wait for the red light to come on, and then turn up the variac to the proper value.

When ranges appear to be 500 yards too high, the receiver-tune- normal monitor switch should be checked to see if it is on NORMAL position.

If the sweeps on either scope appear fuzzy, their respective focus controls should be adjusted.

There are certain occurrences which are entirely normal on the SG but which might be interpreted as troubles by the new operator.

If the synchro excitation to the antenna control motor should fail, the operator will be able to detect the trouble almost immediately. When the synchro supply goes out, the antenna will stop rotating, even though the "bug" continues to rotate and the sweep continues on the PPI. However, the picture on the "A" scope will stay constant because the antenna is not rotating, and the picture on the PPI will appear as a series of markers described through 360°. When this condition exists, the operator should do the following:

  1. Shift the switch on the gyro-control panel from the forward gyro to the after gyro supply or vice versa.

  2. If this does not correct the situation, shift the synchro switch on the R and T indicator from NORMAL to EMERGENCY and continue to operate, reading relative bearing only on the outer dial.

If the synchro excitation should fail while at sea, and there are no targets on the screen, it will be difficult to detect what is wrong. The operator might detect the trouble by close observation of the "A" scope for changes in sea-return signals. If there seem to be no changes in the signals the operator should have someone cheek visually to see if the antenna is rotating.

Sometimes targets will be obscured by radar interference. This appears as either a series of dots, or as a series of radial lines on the PPI. There is not much that can be done to correct the situation: however, changing the pulse rate sometimes changes the interference pattern so as to make it less objectionable. When interference is severe, use the "A" scope.

4-SG-13


[B L A N K   PAGE]

4-SG-14


Part 4
SG-1b Radar

CONTROLS

Range and Train Indicator

In order to take advantage of new developments in radar, a major modification has been authorized for radars of the SG series. The resulting modernization of SG-1 produces the SG-1b radar. A line drawing of the range and train indicator is shown in figure 4 SG-6. Only those controls which have been added or have taken on new or additional functions are lettered and discussed in this section. See SG radar page 4-SG-2 and those following for description of all other controls. For ease in locating and identifying, control to be discussed are lettered in figure 4 SG-6.

Fig. 4 SG-6. Range and train indicator
Figure 4 SG-6. Range and train indicator.

(1) The switch marked (A) is the battle short switch. One of these switches is also provided on the transmitter. Normally these switches should be in the OFF position to provide interlock protection for personnel who may open the units without cutting off the power. During battle or other critical times these switches may be turned on thereby short circuiting the interlocks and insuring continuous operation.

(2) The range scope sweep expansion (B) permits expansion of any part of the A-scope trace enabling echoes and IFF responses to be spread out and examined more closely. The sweep expansion control

4-SG-15


(B) is operative whenever the IFF switch (D) is turned on.

(3) Switch (C) turns on the range step of the A-scope and the range mark on the PPI. See sections under OPERATIONAL TECHNIQUE for discussion of taking ranges and bearings without the necessity of stopping the antenna.

(4) Switch (D) is the same IFF switch described under CONTROLS, page 4-SG-3 and labeled (W) on figure 4 SG-1. In this modification it has the added function of enabling operation of the sweep expansion control (B) described above.

Switches (E), (F), and (G) are called A-J (anti-jamming) controls. The functions of these switches will be described more fully under OPERATIONAL TECHNIQUE.

(5) Switch (E) labeled STC (Sensitivity Time Control) controls the circuit which reduces the gain of the receiver from zero range to approximately 5,000 yards range, thus reducing the effect of sea return.

(6) Switch (F) labeled IAVC (Instantaneous Automatic Volume Control) controls the circuit which reduces the effect of interference, pulse type jamming, and return from clouds by reducing the gain on the receiver for each individual echo and allowing it to return to normal between echoes on the time base.

(7) Switch (G) labeled FTC (Fast Time Constant) aids in separating closely bunched targets by sharpening and narrowing video pulses so that heavy wide echoes become sharp narrow pips and do not clutter up the time base.

(8) Control (H) is the hand crank which rotates the cursor (I) on the PPI tube enabling the operator to read bearings from the dial beneath the cursor (I) without stopping the antenna.

TURNING ON AND OFF

This modification has made no changes necessary in the turning on and off procedure outlined on pages 4-SG-4 and 4-SG-5.

CALIBRATION

Calibration procedure is the same as outlined on pages 4-SG-5 and 4-SG-6. Since the range markers and range step have been considerably sharpened, greater care than before will be required to insure accurate setting of the calibration controls.

OPERATIONAL TECHNIQUE

Read the section titled "OPERATIONAL TECHNIQUE," pages 4-SG-6 through 4-SG-12.

Included in the following discussion are only those points of operation that are basically different from that described in the above named pages and new techniques made possible by the addition of new circuits and their controls.

Determination of Range

Two features have been added to improve range determination.

(1) The range step on the A-scope has been considerably sharpened to facilitate accurate reading.

(2) A range spot has been provided on the PPI sweep so that the accurate range of a target may be determined from this scope without stopping the antenna. The range spot moves with the range step on the range scope (A-scope).

To determine range on the PPI tube, rotate the range crank until the range spot coincides with the center of the target on the screen. The range counters will then indicate the accurate range to the target.

Determination of Bearing

The determination of bearing is greatly facilitated by the hand operated cursor (I) on the PPI. The cursor is rotated by means of the hand crank (H) until it bisects the target, after which, bearings can be read on the illuminated dial surrounding the PPI tube. Thus bearings can be taken without stopping the antenna.

Station Keeping

On other models of the SG series sea return clutter on the A-scope and PPI obscured nearby echoes. Station keeping was best accomplished by reducing the gain to the point where the sea return did not interfere. This procedure interrupted normal search and was avoided whenever possible. When the STC switch (E) is on, sea return is diminished enough to allow station keeping to be accomplished and at the same time keeping a gain setting that is best for search. The STC circuit eliminates sea return without seriously affecting echoes from nearby targets.

Composition

Composition on a particular target can best be obtained by setting the range step just to the left of the target pip on the A-scope and switching on

4-SG-16


the IFF switch (E). This enables the operator to operate the sweep expansion control (B) and spread the target over a greater length of the sweep. By reducing the gain and turning on the FTC switch (G) a more accurate estimate of the number of peaks can be made on the echo. This is not fool proof and cannot be expected to take the place of an experienced operator. It will, however, enable an inexperienced operator to obtain more accurate estimates of composition.

Jamming and Interference

When the radar is being jammed, the receiver gain and receiver tune are the most important controls for combatting the jamming. See 4-SG-11 for a full discussion of how to use the above named controls.

Switches (F) and (G), IAVC and FTC respectively, should be turned on during the presence of jamming and interference of a pulse nature. These circuits act to differentiate or sharpen received impulses from jamming and interference as well as impulses from targets. Since ordinary jamming and interference represent pulses of fairly long duration, their effect can be considerably reduced by such differentiation or sharpening. As land masses and other large targets are also differentiated, care must be taken in interpreting the echoes when IAVC and TC are used.

During normal operation, these switches should be left in the OFF position.

PERFORMANCE

See page 4-SG-12.

TROUBLES

See pages 4-SG-12 and 4-SG-13.

In the SG-1b the 500 yard error in range reading caused by the receiver tune-normal-monitor switch not being in the NORMAL position has been eliminated.

4-SG-17


[B L A N K   PAGE]

4-SG-18


PART 4
SC-SK RADAR

CONTROLS 4-SC/SK-2
  Control unit 4-SC/SK-2
  Receiver unit 4-SC/SK-3
  Indicator unit 4-SC/SK-3
  PPI unit 4-SC/SK-4
  Preamplifier Unit 4-SC/SK-4
   
TURNING ON AND OFF 4-SC/SK-4
  Turning on 4-SC/SK-4
  Turning off 4-SC/SK-4
   
CALIBRATION 4-SC/SK-4
  Calibrating the range scope 4-SC/SK-4
  Calibrating the PPI 4-SC/SK-4
  Modification of PPI scope 4-SC/SK-6
   
OPERATIONAL TECHNIQUE 4-SC/SK-6
  Tuning the receiver 4-SC/SK-6
  Long-range search 4-SC/SK-6
  Searching over land 4-SC/SK-6
  Multiple-target tracking 4-SC/SK-7
  Fighter-director tracking 4-SC/SK-7
  Fire-control liaison 4-SC/SK-7
  Composition 4-SC/SK-7
  Jamming and deception 4-SC/SK-8
   
PERFORMANCE 4-SC/SK-9
  Maximum reliable range 4-SC/SK-9
  Minimum range 4-SC/SK-9
  Accuracy 4-SC/SK-9
  Resolution 4-SC/SK-9
   
TROUBLES 4-SC/SK-10

4-SC/SK-1


SC-SK RADAR

The SC radar is now obsolete and will not be dealt with in this discussion. The controls on the control unit and the receiver indicator unit, which the operator uses, are the same as those of the SC-1. The SC-1 radar is a modification of the SC. The transmitter was re-designed to increase the power output, and the antenna was modified. A preamplifier unit has been added to most sets.

The SC-2 radar is similar to the SC-1, but incorporates a few modifications. The sweep circuit has been revised, and the antenna has been re-designed, with a directional IFF antenna included. A PPI unit has also been added. The SK radar at present is an SC-2 with an antenna four times as large. The SC-2 or SK radars are composed of six units, as follows:

  1. The control unit.
  2. The receiver indicator unit.
  3. The transmitter.
  4. The preamplifier.
  5. The plan position Indicator unit.
  6. The antenna, together with transmission line and duplexer units.

The operator is concerned principally with the first two units, and possibly with the fourth, and the duplexer unit of the sixth. Ordinarily, the technician tunes the transmitter, preamplifier, duplexer, and receiver. The operator checks the tuning of the receiver at the beginning of his watch.

CONTROLS

Control unit.

  1. Main power switch: controls power to all units.

  2. Transmitter-plate voltage: this switch, when snapped on, applies all power to the transmitter. As it is turned clockwise, it increases the high voltage applied to the transmitter tubes.

  3. Relative-true bearing switch: when on TRUE the antenna is controlled by the ship's gyro system. Relative bearings are read on the outer dial, and true bearings on the inner dial of bearing indicator (M). When on RELATIVE, the antenna is controlled by power from the set. This maintains antenna control in the event that gyro power fails. Only relative bearings to the outer dial may then be read.

Figure 4 SC/SK-1. Receiver, indicator and control unit.
Figure 4 SC/SK-1. Receiver, indicator and control unit.

4-SC/SK-2


  1. Remote bearing indicator switch: applies control power to remote bearing repeaters.

  2. Remote bearing mark: buzzer or horn switch to notify remote station when readings may be taken.

  3. Automatic-manual toggle switch: power switch to slewing motor, which gives automatic antenna rotation.

  4. Antenna-control switch: center position is off. Right gives clockwise rotation. Left gives counterclockwise rotation. Speed is controlled by the amount of turning.

  5. Hand crank: for antenna control.

  1. BL power switch; may or may not be used.

  2. Sweep: local-PH; PPI position used when in sector search. Local position is the normal operating position.

  3. Overload relay reset.

  4. Bearing indicator: inner dial--true; outer dial--relative.

  5. Brightness control of bearing indicator light.

  1. Brightness control of pilot lights.

  2. Transmitter pilot light.

  3. BL power pilot light.

Receiver unit.

AA.  Radio frequency tuning control.

XX.  Local oscillator tuning control.

BB.  Receiver gain control.

Indicator unit.

CC.  Receive-calibrate switch.

DD.  Dial light brightness control: controls brightness of the pilot lights and range-counter lights on the indicator unit.

EE.  Brilliance control: controls brightness of the trace.

FF.  Focus control: controls width of the trace.

GG.  Astigmatism control: controls uniformity of focus along length of the sweep.

HH.  IFF gain control.

JJ.  Calibrate maximum.

KK.  Calibrate frequency.

LL.  Calibrate minimum.

MM.  Challenge switch for IFF: puts the IFF system into operation from standby.

NN.  Synchronizing switch: EXTERNAL-INTERNAL: normal operating position on EXTERNAL. Brings synchronizing pulse from transmitter to the indicator. INTERNAL position may be used for adjusting sweep and calibrating frequency when high voltage has not been turned up.

PP.  Crystal switch.

QQ.  Range step height control.

SS.  Vertical trace centering control.

TT.  Range crank.

UU.  Horizontal sweep centering control.

VV.  Synchronizing pulse gain control.

WW.  Range selector switch:

Drawing of the plan position indicator and its switches.
Figure 4 SC/SK-2. Plan position indicator.

4-SC/SK-3


VV.  Remote range mark: remote alarm switch,

ZZ.  Power switch for receiver indicator unit.

PPI unit.

  1. Mark-IFF switch: normal operating position on IFF. When on MARK, range step is shown on PPI.

  2. Dimmer control for PPI bearing dial light.

  3. PPI power switch.

  4. Brilliance control.

  5. Bearing indicator switch; RADAR-PPI: when on RADAR, bug follows the antenna; when on PPI, bug follows the yoke (cursor).

  6. Focus control.

  7. Bearing indicator adjustment control: for synchronizing bug reading and cursor reading, when operating bearing indicator switch is in the PPI position. Depress knob and set cursor (bearing blade) to read with the bug, then release knob to again engage the cursor.

  8. Sector search control: in normal position, which is DOWN, clockwise rotation of the control increases the sector. Counterclockwise rotation narrows the sector. When pulled UP to engage the cursor, the sector may be rotated by rotating the cursor.

  9. Sector search off-on switch.

  10. Remote alarm button.

  11. Relative-true switch for PPI.

  12. Calibration control.

  13. Range selector switch:

      Range 1-20 miles
      Range 2-75 miles
      Range 3-200 miles

  14. Centering control: controls only centering of sweep along axis of sweep.

Preamplifier unit.

  1. All controls on the preamplifier unit are tuning controls.

TURNING ON AND OFF

Turning on.

  1. Turn the main power switch (A) ON. The dial light of the bearing indicator will light, and the amplidyne motor will start.

  2. Turn the transmitter plate voltage variac to 10. The pilot light (R) will light up and the filaments in the transmitter oscillator and power supply will glow.

  3. Turn ON receiver indicator power switch (ZZ). Pilot light (RR) and the lights on the range counter will light. After a few seconds, a trace will be seen on the range scope, unless the brilliance control (EE) is fully counterclockwise.

  4. Turn ON the power switch of the PPI unit. The lamp for the bearing glass will light.

  5. After waiting a half minute, the filaments of the transmitter tubes will be hot, and the plate voltage variac (B) should be turned slowly up to between 70 and 100. This value is determined by the technician.

  6. Turn on BL power switch (J).

  7. Start the antenna rotating by setting switch (F) on AUTOMATIC, and switch (G) to give a slow rotation of the antenna.

  8. Turn up PPI intensity control (4) until a trace appears.

  9. Adjust focus (6) to get fine uniform trace.

  10. Center sweep with control (14). This adjustment should be made so that the beginning of the sweep starts at the same point regardless of the bearing. That is, there is no overlap of the sweep and no open portion. If the center of the sweep is not at the center of the scope, the technician must make internal adjustments.

Turning off.

  1. Turn down (CCW) PPI intensity control (4).
  2. Turn off power switch for PPI unit.
  3. Turn off BL power switch (J).
  4. Turn off automatic switch (F).
  5. Turn switch G to OFF position.
  6. Turn off receiver indicator power switch (ZZ).
  7. Turn plate voltage variac fully CCW.
  8. Turn off main power switch (A).

CALIBRATION

Calibrating the range scope.

  1. Turn switch (CC) to CALIBRATE.

  2. Turn switch (WW) to Range 1.

  3. Adjust brilliance (FE), focus (FF), and astigmatism (GG) for a fine uniform trace. These controls interact one on the other, and must he adjusted together.

  4. Turn crystal switch (PP) to ON. A "figure of eight" with the lower half clipped will now he observed on the "A" scope. If this figure is not observed:

  5. Release lock and adjust (KK)--frequency

4-SC/SK-4


    calibration so that a stationary figure of eight is observed. Lock control. (See fig. 4 SC/SK-3.)

  1. Turn crystal switch (PP) to OFF.

  2. Crank (TT) so that 2,000 yards is observed on the first range counter.

    Figure of eight determines when calibration pips are 2,000 yards apart.
    Figure 4 SC/SK-3. Figure of eight determines when calibration pips are 2,000 yards apart.

  3. Release lock on calibrate minimum (LL) and adjust position of range step with (LL) so that the top of the second marker just begins to drop. (See fig. 4 SC/SK-4.)

  4. Crank (TT) so that counter reads 20,000 yards.

  5. Release lock and adjust calibrate maximum (JJ) so that the top of the eleventh marker begins to drop.

  6. Check the 2,000-yard setting and if it has changed, repeat step 9.

  7. Check the 20,000-yard setting. If either (JJ) or (LL) is changed, it affects the other. Keep checking until no further adjustment is necessary; lock both controls.

  8. Turn (CC) to RECEIVE.
    This method of calibration differs from that given in the instructional manual.
    We use this method for three reasons:

    1. To make the calibration and ranging uniform on SC-2 and SG, the center of the range mark and the center of the target pip are used.

    2. It is easier to range on the center of a pip than on the leading edge.

    3. This introduction of error compensates for a range error on SC radars when calibrated against fire-control radar.

Calibrating the PPI.

The PPI unit must never be calibrated until the "A" scope has been calibrated, since it is dependent on the accuracy of the calibration of the "A" scope.

  1. Turn the mark-IFF switch (1) to MARK.

  2. Set the range selector (WW) to Range 2, and set the counter to 60 miles.

  3. Set the PPI range selector (13) to Range 2.

  4. With the antenna rotating rapidly, a circle will appear on the PPI scope. Set calibrate control (12) so that the inboard edge of the trace corresponds with the 60-mile ring on the scope face.

  5. Set the range counter to 30 miles and check the calibration. If the internal calibration of the set is correct, the PPI will be calibrated for all three range scales.

Pattern for calibrating minimum range on range 1.
Figure 4 SC/SK-4. Pattern for calibrating minimum range on range 1.

4-SC/SK-5


Modification of PPI scope.

With the orange filter glass on the PPI, the range marks are so far from the screen that errors of several miles in range are possible because of parallax. The authorized revision should be made, whereby the filter glass is removed and the range lines made directly on the face of the PPI scope. This is (lone with a drafting compass and India ink as outlined below.

  1. Make a center for the drafting compass out of a small piece of plastiglass in which you have drilled a shallow hole to hold the compass point.

  2. Secure this center to the center of the PPI scope with scotch tape.

  3. Using the radii of the range circles on the filter, ink solid circles on the scope face. To facilitate direct reading of the 75-mile range scale, ink in two dashed circles evenly spaced between the solid circles.

Direct reading of the PPI on the 75-mile range scale is now easy and accurate. The solid circles are 15 miles apart. The dashed circles are 5 miles apart. The range of any indication may he read accurately to the nearest mile. Bearings are read by bisecting the indication with the cursor, and reading the bearing on the illuminated indicator.

OPERATIONAL TECHNIQUE

Tuning the receiver.

The technician will have the transmitter tuned for maximum power output and it should not be touched by the operators.

The preamplifier and receiver are also tuned by the technician, and only slight adjustments need he made by the operator. Care should be taken when tuning on a bobbing echo that increase in echo height results from tuning adjustments and not from bobbing of the echo. Tune for maximum results from tuning adjustments and not from bobbing of the echo. Tune for maximum echo height by going a little over and then a little under maximum. Jockey back and forth rapidly, and stop between the two points, a little over and a little under, for optimum tuning. If land echoes are available, they should be used for tuning. In any event, all operators should know the dial settings of the receiver for maximum echo height.

Long-range search.

Long-range search, so called, is essentially search for initial contacts at any range. It will he conducted either when there are no indications on the screen at all, or when there are one or more target indications on the screen which have been identified and are of interest to the CIC watch officer only, as to their general position. The CIC officer will get most of the information he desires from his repeater scope, but a rough plot should also he kept. Readings every three minutes are usually sufficient for this plot.

The range scale used on the scopes will depend on the tactical situation. In a carrier task force, initial contact at the longest range is highly desirable. Two methods of search are possible:

  1. PPI scope on 200-mile range scale, and "A" scope on 75-mile range scale, or

  2. PPI scope on 75-mile range scale, and "A" scope on 375-mile range scale.

When using the first method, most careful watch is made on the PPI scope with occasional search on the "A" scope. As the PPI is the less tiring scope to observe, most operators prefer this method.

The alternate method employs the closer watch of the "A" scope with occasional search on the PPI scope. The advantage of this method is that if a contact is made within 75 miles, tracking may be begun immediately on the PPI without changing scale.

If the task force has no air support, 75-mile warning of approaching aircraft is sufficient, and both scopes may be operated on the 75-mile range.

The receiver gain setting should he such as to give approximately 3/8-inch of grass on the range scope when the operator is giving his attention to the PPI scope. This should he reduced to between 1/16- and 1/8-inch when attention is given to the range scope.

The antenna should he rotated at a rate of approximately 1½revolutions per minute. A plot should be started on the first indication no matter how weak the signal. On the next sweep of the antenna, it may be stopped, the blip on the range scope studied to determine composition, and the plane challenged with IFF equipment. Normally this pause in continuous rotation should not take more than 15 seconds,

Searching over land.

If search must be made over land, target pips will be mixed with the land pips. However, planes will give echoes which bob up and down more rapidly and irregularly than the land pips. Also, the plane pip will move with respect to the land pips. When faced with the problem of searching over land, the antenna may he stopped for a few seconds to determine whether the pip is actually behaving as a plane echo or as a land echo. Bearings cannot be obtained very accurately, but the bearing of maximum swing of the

4-SC/SK-6


pip should be reported. Land masses may cause the pip to be higher on a bearing a few degrees to one side of the actual target bearing, and so maximum pip height may not give the correct indication-it is the maximum bounce that counts. The approximate bearings secured are well worth the effort to get them.

The operator must remember to keep searching. He should not find one target and "camp on it" from then on.

Multiple-target tracking.

Multiple-target tracking should be done exclusively on the PPI. In the large majority of cases, the 75-mile scale is the proper scale for multiple-target tracking. Rapid ranges and bearings may be accurately obtained on targets at from 10 to 80 miles, and a good search for new targets at ranges up to 80 miles is maintained. The antenna rotation speed should be increased to 2 rpm, and half of the targets reported for each revolution. Gain setting should be for 3/8-inch of grass on the range scope. All ranges and bearings are read from the PP 1.

Fighter-director tracking.

To a good operator, there s no essential difference between multiple-target tracking and ID tracking. With the antenna rotating at 2 rpm, reports can be given on the intercept planes and bogies at 30-second intervals, by reporting these targets on every revolution of the antenna, if desired by the fighter director officer. A good track can be kept on all other targets by reporting them every other revolution, giving one minute reports to the plotter. Ranges and bearings should come directly from the PPI operating on the 75-mile range with the gain set for 3/8-inch of grass on the range scope.

It may happen in certain instances during night attacks, that the gunnery officer or assistant gunnery officer will want to man the PPI himself. He will then be in a position to direct AA fire rapidly, and the information will not be delayed by going through CIC and plotting.

Fire-control liaison.

Fire-control liaison may be conducted on the 75-mile range with normal gain setting at about ten miles, provided there are not many targets at the same range. With several targets on different bearings within ten miles, their echoes and side lobes will ring the PPI scope and cause too much confusion for fire-control coaching.

When the primary interest is fire-control coaching, the PPI should be operated on the 20-mile range. The gain should he reduced to an amount just sufficient to keep the targets at the longest ranges appearing on the scope. This will eliminate some side lobes and reduce strength on all side lobes while holding echoes from the main lobe on the screen. This method of operation eliminates any chance of observing planes coming in at ranges greater than 20 miles, but is the most effective method when the primary purpose is fire-control coaching. At GQ, the standby operator can keep the fighter director officer informed of the general situation outside 20 miles by observing the range scope and taking ranges and bearings with continuous antenna rotation.

When the set is operating so as to read true bearings on the PPI, only true bearings are put on a repeater. If relative bearings are desired, the PPI relative-true switch can be thrown to RELATIVE, and the bearing indicator switch from RADAR to PPI. The bug is then adjusted to read the same on the outer dial as it is read on the yoke. Now, all bearings from the PPI will be relative, and the repeaters will read relative.

Composition.

Determination of composition of the target requires more operator experience and closer observation than any other phase of operation. Determination of composition involves use of IFF to determine whether a contact is friendly or not, and observation on both range and PPI scopes to determine number and size of planes in the group.

Large planes will have a low rate of fluctuation in echo amplitude, while small planes will have a high rate of fluctuation. The range scope is a better source of information on composition than the PPI scope. Upon making a contact, the antenna should he stopped on the target, the gain reduced to 1/16-inch grass on the "A" scope, and a thorough examination of the echo made. The number of planes can he estimated from the number of peaks on top of the echo. The range at which the target comes in is not conclusive proof of either its size or altitude, but is a major factor contributing to these estimations. The operator should give his estimate of the composition of every contact and this estimate should he substantiated or corrected by visual means whenever possible. The operator should then be notified of the exact number, size, formation, and altitude. Continuous repetition of this process is the only means of improving the operator's technique in determining composition.

Clouds, rain squalls, and ionized masses of air are readily detected on the "A" scope, and are usually easily disclosed on the PPI. Broad fuzzy pips, that

4-SC/SK-7


move slowly with occasional fading out, are characteristic of these targets, although sharp narrow pips have been observed. If identification is difficult by looking at the pip, a plot should be made to determine the course and speed. This should then be compared with the course and speed of the wind, which is the best check outside of actual observation.

Any operator will learn to recognize land readily. However, most of them, on looking at a group of pips from land, will call the highest pip the highest peak of land as "seen" by the radars. This is wrong. The highest pip will be from that part of the land which has the best reflecting surface. The peak will be hard to identify if there is a range of mountains behind it, or mountains in the near vicinity at about the same range.

Jamming and deception.

There is no doubt that the enemy considers our radar an extremely dangerous weapon, and consequently it is only reasonable to expect him to try every means possible to make it less effective. He may use two tactics to do this: jamming and/or deception. Every operator should learn how to recognize these countermeasures, and expect them when in combat zones.

When the enemy broadcasts radio signals intending that our radar receive them, and they show a confusing pattern on the screen, it is called jamming. Use of dummy targets (tinfoil, kites, balloons, etc.) is called deception. More precise definitions are sometimes given, but these are satisfactory for this discussion.

The SC radar can be jammed, and it will show echoes from the tinfoil the enemy sometimes throws out to confuse the operator. The operator should not become alarmed when either of these things happen.

If you were suddenly confronted with jamming, without previous experience, it would appear impossible to work through. However, it is not really that serious if the following procedure is carried out:

  1. DF on the jamming.
  2. Use available anti-jamming devices on the receiver when provided.
  3. Try moving the gain control up and down.
  4. Try changing the receiver local oscillator tuning.
  5. Keep operating.
  6. Report the type and bearing of jamming to CIC.

The first reason for obtaining a hearing on the jamming is to determine whether or not it could be accidental interference instead. Jamming will not only be directional, but its true hearing will not he changed by any sudden change in your ship's course. Interference originating aboard your own ship will either be non-directional and appear on all bearings, or else it will always be on some certain relative bearing regardless of changes in own ship's course.

Try moving the gain control up and down. This is probably one of the most important countermeasures that can he taken and the one most commonly overlooked because of its simplicity.

In most cases, except when effective noise modulated jamming is being encountered, there is a setting of the gain control with which it is possible to range on a target in the presence of heavy jamming. If there are several echoes on the same bearing, the best setting for each echo is different. Of course it is more difficult to obtain these ranges because of the distortion of the echo produced by jamming, but it is possible to obtain the desired information. The extra effort is worth while because the enemy would not be jamming unless he were trying to conceal something important.

Two general methods of using the gain control, both of which should be tried, are as follows:

  1. Reduce setting; this prevents overload of the radar receiver; echoes are visible "riding on top" of the jamming pattern.

  2. Increase setting; this limits (or clips) jamming; echoes are visible as a break in the base line.

Be sure to return the gain control to its normal setting when no jamming is present, or when the antenna is turned to an unjammed bearing.

Try changing receiver local oscillator tuning. When you change the oscillator tuning, you lose some of the height of the desired echo. However, if the jammer is not exactly on your radar frequency, there is a chance that you will detune the jamming signal more than the echo signal. Considerable improvement can sometimes be obtained this way. Try "swinging" the oscillator tuning dial in both directions to see which direction makes the greatest improvement. Note the correct setting of the oscillator dial so that it can he returned to its normal position when no jam is present, otherwise your radar will not give optimum results.

Even if the jamming is extremely effective, keep operating: do not turn your radar off. Turning your radar off informs the enemy that his jamming is effective, and makes the radar completely worthless. The effectiveness of the jamming may change from

4-SC/SK-8


time to time, and if you are persistent enough some information may be obtainable.

Report the nature and bearing of the jamming to CIC. Recognizing the type may be difficult because non-synchronous patterns sometimes appear blurted beyond recognition. Inasmuch as knowledge of the jamming type* may possibly help identify the jammer in some cases, this information should be reported.

If the equipment is provided with an anti-jamming receiver, the jamming may he reduced sufficiently for reading targets without any detuning of the receiver. Detuning should be a last resort, and then should be done very carefully and cautiously, otherwise all targets may be lost and the equipment made completely ineffective. No set procedure is offered for setting the controls of the AJ receiver, except that they should be varied for maximum readability through jamming, the gain control coming first and then the AVC control followed by Rej 1 and Rej 2. Turn all AJ controls to the OFF or NORMAL position when no jamming is being encountered.

Above all, never turn off the radar.

Even when jamming and/or deception is encountered, full 360° search must be continued. However, the antenna should be stopped for short intervals from time to time in order to try reading through the jamming (using the "A" scope). You also must be prepared for diversionary tactics, for the enemy may or may not use jamming and or deception to divert your attention from the bearing of the main attacking forces. This problem is simplified when similar but separate radars are used for reading through jamming and for searching.

PERFORMANCE

Ranges obtained on planes will vary greatly with the altitude of the plane, because of fade areas and the curvature of the earth. Large, high-flying planes have been observed at 120 miles. Average ranges on medium altitude planes are from 60 to 70 miles, and on low-flying planes from 20 to 40 miles on the SC-1, with better results on SC-2 and SK.

Ranges on surface targets will vary with antenna height, size of target, and weather conditions. In most cases, the ranges will be 6,000 to 10,000 yards shorter than those obtained on the same targets with surface-search gear.

Maximum reliable range.

SC-2 RADAR
Antenna 90 feet

BB, CV, CB, Large auxiliaries   37,800 yards
CA, CL, Medium auxiliaries   25,000 yards
DD, DE, DM, AV, PC, CG   17,000 yards
Submarines   5,900 yards
Large planes, PBM, PB2Y   132,000 yards
Small planes, 6F6, TBF, SB2C   72,500 yards
Land   142 miles

SK RADAR
Antenna 130 feet

BB, CV, CB, Large auxiliaries   51,500 yards
CA, CL, Medium auxiliaries   35,000 yards
DD, DE, DM, AV, PC   226,500 yards
Large planes   250,000 yards
Small planes   150,000 yards
Land   170 miles

Minimum range.

SC-1, SC-2, SK "A" scope   1,500 yards
PPI
      20-mile range   2½ miles
      75-mile range   6 miles

Accuracy.

Reading directly from the PPI, range accuracy is 2,000 yards or better, and bearing accuracy 4°.

Bearing and range accuracies for the different ranges on the "A" scope and PPI, when the antenna is sweeping or stopped, are listed in the table below.

Ranges Sweeping Stopped
  Range Bearing Range Bearing
30,000 yards 1,000 200
20 miles 1/2 mile  
75 miles 1 mile 1/2 mile
200 miles 2 miles  
375 miles 5 miles 1 mile

Resolution.


* See Part 3, Defense Against Jamming and Deception.

4-SC/SK-9


TROUBLES

There are in general, two methods of improper operation. One will result in complete disappearance of all target indications from the screen. This should be observed by the operator instantly, and measures should be taken promptly to remedy the trouble. The other is a general decrease in the ranges obtained. Detection of this type of failure requires much greater alertness on the part of the operator.

The jar of gunfire or surge currents may cause the overload relay in the transmitter to kick out, cutting off the transmitter. The red transmitter pilot light will go out, all targets and the transmitter pulse will disappear from the screen, and the sweeps on the range and PPI scopes will be jittery, because they are not receiving a synchronizing pulse from the transmitter. The operator should turn down the high voltage variac, press the overload relay reset button, and then turn the high voltage variac back to its normal operating position. Should the relay continue to kick out, notify the maintenance man as to what occurred and what has been done.

A gradual decrease in the operating efficiency of a set is harder to detect. The operator must be on the lookout for this at all times. One indication may be the point to which the receiver gain control must be turned to get the normal amount of grass. The best indication is the ranges that are being obtained on objects with which the operator is familiar, such as ships in his group or land in the vicinity. If poor results are being obtained, the operator may try retuning the receiver. If this does not help, the maintenance man should be notified.

The operator can greatly assist the maintenance man by giving a true and accurate description of what happened on the scope when the set went our of operation. This is even more true of intermittent troubles.

4-SC/SK-10


PART 4
MARK 3 AND MARK 4 RADAR
(FC, FD)

CONTROLS   4-Mk. 3/Mk. 4-2
  Main unit   4-Mk. 3/Mk. 4-2
  Control and indicator unit (range scope)   4-Mk. 3/Mk. 4-2
  Range unit   4-Mk. 3/Mk. 4-3
  Train or elevation indicator   4-Mk. 3/Mk. 4-3
   
TURNING ON AND OFF   4-Mk. 3/Mk. 4-4
  Turning on the main unit   4-Mk. 3 Mk. 4-4
  Turning off the main unit   4-Mk. 3 Mk. 4-4
  Turning on the control and indicator (C&I) unit   4-Mk. 3/Mk. 4-4
  Turning off the control and indicator unit   4-Mk. 3/Mk. 4-5
  Turning on the trainers and pointer's scopes   4-Mk. 3/Mk. 4-5
  Turning off the trainer's and pointer's scopes   4-Mk. 3/Mk. 4-5
  Tuning the receiver   4-Mk. 3/Mk. 4-5
   
CALIBRATION   4-Mk. 3/Mk. 4-6
  Range zero set   4-Mk. 3/Mk. 4-6
  Double range echo method of obtaining zero set   4-Mk. 3/Mk. 4-7
  Train and elevation calibration   4-Mk. 3/Mk. 4-7
   
OPERATIONAL TECHNIQUE   4-Mk. 3/Mk. 4-8
  The range operator   4-Mk. 3/Mk. 4-8
  The trainer and the pointer   4-Mk. 3/Mk. 4-8
  Searching with bearings and ranges given   4-Mk. 3/Mk. 4-9
  Searching when no bearings or ranges are given by the search radar   4-Mk. 3/Mk. 4-9
  Tracking   4-Mk. 3/Mk. 4-9
  Spotting   4-Mk. 3/Mk. 4-10
  Determining composition   4-Mk. 3/Mk. 4-11
  Anti-jamming technique   4-Mk. 3/Mk. 4-11
   
PERFORMANCE   4-Mk. 3/Mk. 4-13
  Maximum reliable ranges   4-Mk. 3/Mk. 4-13
  Minimum ranges   4-Mk. 3/Mk. 4-13
  Accuracy characteristics   4-Mk. 3/Mk. 4-13
  Resolution   4-Mk. 3/Mk. 4-13
   
TROUBLES   4-Mk. 3/Mk. 4-14

4-Mk. 3/Mk. 4-1


MARK 3 AND MARK 4 RADAR
(FC, FD)

CONTROLS

Main unit.

  1. Plate current meter of modulation generator: should read about 200.

  2. Plate voltage meter of modulation generator: should read about 500.

  3. Load voltage: should be set to 120 at all times by means of control No. 11. (A recent directive says 115, but do not set it at 115 unless the set has been adjusted for this.)

  4. Magnetron plate current meter: should he set, to read about 30 by controls 13 and 12.

  5. Magnetron plate voltage meter: should be set to 12 (12,000 v.) by means of control No. 12.

  6. Magnetron filament voltage meter: should read 13.5. Can be seen by looking through the wire mesh on the front of the transmitter.

  7. Frequency control of modulation generator: adjusted by technician.

  8. Radio dial light dimmer: controls the brightness of the illuminated dial on the receiver.

  9. Receiver tuning control.

  10. Receiver sensitivity control:

  11. Load voltage control.

  12. Magnetron plate voltage control.

  13. Field control: adjusts plate current to the magnetron.

  14. Remote-local switch: determines whether the receiver sensitivity is controlled from the main unit by control No. 10, or whether the sensitivity is controlled by the receiver sensitivity knob on the range scope.

  15. Main off-on switch or line switch.

  16. Plate off-on switch.

  17. Dim-bright switch: controls brightness of the pilot lights on the face of the main unit.

  18. Mon jack: used in tuning up the receiver.

  19. Audio jack: used to obtain a synchronizing voltage when tuning up the receiver.

  20. Screw lock for 21.

  21. Magnetron filament voltage adjustment.

Control and indicator unit (range scope).

  1. Intensity control: controls the brightness of the picture on the scope.

  2. Image spread control: controls the size of the notch and expanded sweep.

  3. Receiver sensitivity control: controls height of the grass and echoes.

  4. Focus control: focuses the image on the face of the scope.

  5. Sweep gain control: controls the length of the sweep. Should be completely clockwise.

Line drawing of the main unit.
Figure 4 Mk. 3/Mk. 4-1. Main unit.

4-Mk. 3/Mk. 4-2


  1. Lobing on-off switch: turns lobing motor on or off.

  2. Transmitter standby switch: turns the transmitter on or off. Used as a stand-by switch.

  3. Pilot light dim-bright switch: (to be replaced by an A.G.C, switch.) Some sets have an anti-jamming switch above control 2.

Line drawing of control and indicator unit.
Figure 4 Mk. 3/Mk. 4-2. Control and indicator unit.

Range unit.

  1. Inner knurled nut: locks friction drive between the range knob, No. 3, and the electrical system controlling position of pips on the lace of the scope.

  2. Outer knurled nut: moves images across the scope.

  3. Range knob: moves images across the scope.

  4. Pilot light bright-dim switch.

  5. Dial light bright-dim control.

  6. Signal button.

Line drawing of range unit.
Figure 4 Mk. 3/Mk. 4-3. Range unit.

Train or elevation indicator.

  1. Intensity control: controls the brightness of the image.

  2. Image spacer control: move one sweep with relation to the other.

  3. Sweep expansion control: opens or contracts the two steps.

Figure 4 Mk. 3/Mk. 4-4. Train or elevation indicator.
Figure 4 Mk. 3/Mk. 4-4. Train or elevation indicator.

4-Mk. 3/Mk. 4-3


  1. Focus control: focuses the image.

  2. Pilot bright-dim switch.

TURNING ON AND OFF

Turning on the main unit.

  1. Make sure main off-on switch (15) and plate off-on switch (16) are turned OFF and the plate voltage control (12) is turned completely counterclockwise (against the stop).

  2. Turn on line transformer switch (mounted somewhere on the bulkhead).

  3. Check magnetic controller switches (if any).

  4. Turn on stand-by rotary switch near C and I Unit (when installed).

  5. Turn on transmitter stand-by switch (7) on C and I Unit.

  6. Turn on the main off-on switch (15). Before turning on anything else, listen to see if the blower fan cooling the magnetron starts running as soon as the main switch is thrown. The load voltage meter (3) should go to 120 volts. Adjust it to this value by means of the toad voltage control (it) and make sure it stays at this value. The plate voltage meter (2) in the modulation generator will swing to the right of the scale and slowly come down to about 500 volts. The plate current meter (1) on the modulation generator will start at zero and after a few seconds will slowly come up to about 200 milliamperes. When this meter reaches a stable value, the 1,639 c/s note will be heard coming from the modulation generator.

  7. Turn on the plate off-on switch (16). Wait at least 5 minutes before turning up the plate voltage. When the plate switch is turned on, the two tubes located in the front of the high voltage rectifier light up.

  8. After 5 minutes have elapsed, slowly turn up (clockwise) the plate voltage control (12) until the plate voltage meter (5) reads 12 kilovolts. Make sure the plate current meter (4) does not go above 30 milliamperes. Adjust the held control (13) until the plate current meter (4) reads 30 milliamperes (30 milliamperes is an average value, it will he different on some sets). The plate current and plate voltage are not independent. Any change affecting one will affect the other. Thus both plate voltage control (12) and held control (13) must be moved together.

  9. Check filament voltage meter (6) to see if 13.5 volts are applied to the filament of the magnetron. If not, adjust to this value by magnetron filament voltage adjustment (21).

  10. Check to see if the remote-local switch (14) is on REMOTE. The main unit is now turned on and the set is all ready to operate. It is a good policy to tune up the receiver upon turning on the set, and about once every hour thereafter-more frequently if the set is subjected to serious vibration or temperature change.

Turning off the main unit.

  1. Turn the plate voltage control (12) counterclockwise slowly until it hits the stop.

  2. Turn plate on-off switch (16) to OFF.

  3. Turn main off-on switch (15) to OFF.

  4. Turn bulkhead switches off.

    Every time the main unit is turned on from a cold start, the wear on the set is equivalent to three hours steady running of the set. Thus, if the set is to be turned off and on eight times a day it would be more profitable to let the set run continuously.

    Another even more important consideration in this respect is that it requires approximately three hours running before the set is warmed up sufficiently for most accurate operation. If the modulation generator has a red light at the top of the front panel which flashes off and on, it will take a much shorter time to warm up (approximately one hour).

When turning on any of the units in the director, the stand-by bulkhead switch, which turns on the scopes, must be turned ON-reverse procedure, for securing the gear.

Turning on the control and indicator (C&I) unit.

  1. Turn sweep gain control (5) completely clockwise.

  2. Turn intensity control (1) clockwise until an indication is observed on the face of the scope.

  3. Focus the trace by means of the focus control (4). Note: For each setting of the intensity control there is a distinct setting of the focus control. Be careful not to make the trace too bright. The trace should never be so bright that the return trace can be seen over the notch. (This undesirable condition is apparent when the notch is fully expanded. It makes the notch look like a box.)

  4. Turn the image spread control (2) completely counterclockwise.

4-Mk. 3/Mk. 4-4


  1. Turn the receiver sensitivity control (3) clockwise until the grass is about a half-inch high.

  2. Make your "zero set" and continue to check it as frequently as possible while operating the set.

  3. Turn the transmitter switch (7) on. The instant this switch is turned on the set is "on the air." The main frame should never be turned off and the transmitter should be controlled by means of this switch; the switch is designed to do this, If it is found that fuses are blown by doing this, it is an indication that some element is not functioning properly and should be promptly remedied.

  4. The lobing motor should he turned on only when using the set. It should remain on while searching for targets and while tracking. But remember, whenever the set is not actually being used, turn the lobing motor off.

Turning off the control and indicator unit.

  1. Turn off lobing motor (6).

  2. Turn off transmitter (7).

  3. Turn intensity control completely counterclockwise (1).

Turning on the trainer's and pointer's scopes.

  1. Turn the image spacer control (2) completely clockwise.

  2. Turn the sweep expansion control (3) completely clockwise.

  3. Make sure the range scope operator has the lobing motor turned on.

  4. Turn the intensity control (1) clockwise until two horizontal lines appear on the scope. These lines will not be straight, but will be slightly curved.

  5. Focus the traces by means of the focus control (4). It is important that the sweep should be just bright enough to see and no brighter. It should be focused to a fine, sharp line.

  6. The image spacer (2) and the sweep expansion controls (3) should now be turned counterclockwise until the sweeps are about 1/4 inch wide and separated by about 1/8 inch.

Turning off the trainer's and pointer's scopes.

  1. Turn the intensity control (1) completely counterclockwise.

Tuning the receiver.

  1. Connect a patch cord to the vertical input terminals of the test scope. The BLACK side is connected to the grounded side which on RCA scopes is marked with a zero. The RED, or high side is connected to the top of the two vertical terminals which are marked high. Plug this cord into the right hand plug of the four jacks in the radar receiver panel; this is marked mon (18).

  2. Connect another patch cord to the sync terminals. Connect the BLACK to the ground terminal and the RED to the high terminal. Sometimes the red and black markers have become obliterated. They can be readily distinguished, since the BLACK side, or ground side, is the outer conductor of the cable and probably will have no insulation on it. The RED side, or high side, is the inner conductor and will be insulated. This cable is plugged into the audio jack (19) in the modulation generator panel.

  3. Turn the vertical and horizontal centering controls on the test scope to mid-position. Turn vertical amplifier knob off. Turn the horizontal amplifier knob to EXT. Turn the vertical and horizontal gain controls to zero. Turn the range to 550-4,500 (for RCA 155 A or B) or 700-7,000 (for RCA 155 C). Turn the frequency to zero. Turn the sync knob to zero.

  4. Plug in the scope to 110 volts AC and turn the intensity clockwise until a click is heard.

  5. Wait for about one minute and then turn the intensity control clockwise until a spot is observed on the screen. Be careful that this spot does not become bright. Turn the horizontal gain control clockwise until a horizontal line covers the scope with a small margin left over at each side. Focus this line by means of the focus control. Adjust the horizontal and vertical centering controls until one line is centered on the face of the scope.

  6. Turn the vertical amplifier to the ON position. Increase the vertical gain control until the pattern occupies about 10 divisions on the scope.

  7. Turn the frequency control clockwise slowly. It will be noticed that images will be formed on the face of the scope with the pips displaced downward from the horizontal sweep. As the control is advanced, first, four pips will be formed, then three, then two, and finally one. When one image is formed, it will be found that it will be almost impossible to make that pip appear stationary on the scope. Get it as steady as possible, then slightly turn the sync control clockwise, and it will be found that the image on the scope will

4-Mk. 3/Mk. 4-5


    lock in and cease to move, The image thus formed will be the same picture that is on the C and I scope in the director, except there will be no notch and there will be no expanded portion of the sweep. It should be noted here, that the operator might find the actual tuning procedure, which is about to be described, easier if he stops the image on the screen with two pips on it rather than one. This is largely a matter of preference, By adjusting the horizontal gain and the horizontal centering knobs, the operator can make the two pips line up with the divisions on the graduated face of the scope. By counting the number of divisions between the pips, and realizing that this distance corresponds to 100,000 yards, it is possible for him to estimate roughly the distance to any target.

  1. Turn the remote-local switch (14) to LOCAL, and the height of the grass and the echoes may be controlled by the receiver sensitivity control (10), located on the front panel of the receiver. Turn the receiver turning control (9) back and forth until the pips come to a maximum, and decrease on each side of the maximum point. By going back and forth over this point several times, it is possible to find accurately the position of the knob which gives maximum echoes on the test scope. It is best to tune on small echoes and get them as big as possible.

Note. For precise tuning, it is absolutely necessary that no one move the antenna while the receiver is being tuned, either in train or elevation. It is also highly desirable that the echo used to tune the set be a steady pip from a land target. This is the only tuning adjustment the operator need know. Further tuning requires the more extensive knowledge of the maintenance man.

CALIBRATION

Range zero set.

  1. To show accurate ranges, it is necessary that the range dial be accurately calibrated so that zero range on the range dial corresponds to zero range on the scope. Turn the grass to the height usually used in operation (about half an inch), and turn the image spacer knob (2) completely clockwise.

  2. Turn the range dial to the zero set given by the technician. It is a minus value of range, usually about minus 200 yards, at which the range dial is set, (A value of minus 200 yards is the same as a range of 99,800.)

  3. Loosen the inner knurled nut (1) located above the range crank,

  4. Turn the outer knurled nut (2), and move the image across the scope until the left-hand edge of the transmitted pulse coincides with the left-hand edge of the notch. Adjust this nut until the left-hand edge of the notch falls half-way down to the bottom of the notch.

    Transmitter pulse position for correct zero set.
    Figure 4 Mk. 3/Mk. 4-5. Transmitter pulse position for correct zero set.

  5. Check to see if the range dial is at the zero set. and then carefully tighten the smaller knurled nut with the right hand, while holding the larger nut with the left hand to prevent it from turning.

  6. Crank the pulse out of the notch, then crank it back to the position described in step 4 above, and check to see if the zero set has slipped while tightening up the smaller nut. If it has slipped, repeat the above procedure until the correct setting is obtained.

Note: The above procedure should be practiced until an accurate zero set can be made very rapidly. During the first half-hour after the radar has been turned on from completely off, the zero setting should he checked at least as frequently as once every two minutes if accurate ranges are necessary during this time. After this time has elapsed, the zero setting may be checked less frequently. After three hours, the zero setting may be checked about once every half-hour, and always before each firing run in gunnery practice or battle, if practicable.

4-Mk. 3/Mk. 4-6


Double range echo method of obtaining zero set.

(See Part 1. General Radar Principles.)

  1. Train on another ship-the larger the better, on a course parallel to your ship and not more than 2,000 yards from it. (Between large ships, greater distances may be used.)

  2. Start getting ranges on the other ship. It is important that the pointer and trainer remain right on the target during the following procedure.

  3. If the other ship is close enough, two pips will be observed on the range scope. The closest pip will be saturated and the second pip will probably be quite small. The second pip will be at approximately twice the range of the first pip. (See fig. 4 Mk. 3/Mk. 4-6.)

    Double range echo.
    Figure 4 Mk. 3/Mk. 4-6. Double range echo.

  4. The first pip is placed in the notch, and its range is noted. Let us say its range is 1,700 yards. Then the second small pip is placed in the notch, and its range is noted. Let us suppose its range is 3,200 yards. The difference between these two readings gives the accurate range between the two pips. In this case the range would be 1,500 yards. The range to the double echo should be just twice the range to the first echo, since the pulse has had to travel just twice the distance in forming the double echo that it traveled to the first echo. Therefore, the total distance traveled by the pulse in forming the double echo was 3,000 yards, and the distance to the first echo must be half that distance, or equal to the distance between the first and second echoes, namely 1,500 yards.

  5. The first pip is then placed in the notch and the range dial is set to the difference between the ranges of the first and second pips (in this case 1,500 yards), by means of the zero adjustment nuts.

  6. After securing the zero adjustment nuts, the transmitted pulse is cranked back to the notch and placed as though making a zero set. The minus zero set is noted when the transmitted pulse is as shown in figure 4 Mk. 3/Mk. 4-5.

    This zero set should be written down in a conspicuous place near the range unit, as it is the zero set that should be used. Steps 4, 5 and 6 should be executed as quickly as possible and repeated several times until consistent results are obtained. Occasionally, there will be two pips where the double echo should appear, and the range operator may not know which is the true double echo. One of these pips, however, will be clear and the other foggy. The clear one will be the double echo. The reason for this is, that if you are on the target the pip from the target will be clear and not foggy. A foggy target would indicate another ship, sore debris, or another extraneous target which is off the line of sight. Finding the zero set should be done only after the set has been on at least three hours, and is thoroughly warmed up. This is only one method of obtaining your zero set. Other methods are described in BuOrd Pamphlet No. 657.

*Train and elevation calibration.

  1. Alignments of the radar antenna with the optics is an easy matter. The trainer and pointer have merely to look through their telescopes when their pips are matched, to see if their cross-hairs cut the target. During an exercise using full radar control, the control officer can determine if the radar is aligned with the optics, by looking through his telescope when the crew gives the word that they are on the target.

  2. Level and cross level should always he cut in when aligning the antenna.

  3. To align the antenna in train, two men are placed on top of the director with wrenches to loosen the securing bolts, and move the adjusting screws holding the antenna. The trainer and painter


* Note: This is a technician or Navy Yard job.

4-Mk. 3/Mk. 4-7


    stay on a small, distant target with their optics. The maintenance man watches the pips on the trainer's scope, and directs the men adjusting the antenna to move it to the right or left, as indicated by the pips on the trainer's scope. When the pips are even, the antenna is locked in place.

  1. The antenna should never be checked for elevation accuracy at angles less than 15°. If it is found to be off, it is realigned by training optically on a plane flying directly to the ship, and passing over the ship. The maintenance man should adjust the microcoupler on the antenna shaft, while watching the pointer's scope, until the pips on the pointer's scope are equal.

  2. For more details see BuOrd Pamphlet No, 657.

OPERATIONAL TECHNIQUE

The range operator.

The range operator is the keyman of the FD team. Upon his shoulders rests the responsibility of supplying pips of the proper size to the trainer and pointer. It is up to him to select the particular target the gunnery officer may designate. He must also be able to tell what type of target a certain pip indicates, if a ship, the approximate size; if a plane, its size; if a number of planes, the approximate number in the flight. He must be able to distinguish the pip presented by a submarine from the water return which tends to confuse it. He must be ever alert to detect even the weakest echoes, and he prepared to get his team on them before they disappear.

The two greatest responsibilities of the range operator are: (1) to keep the pip in the notch, and (2) never to let it saturate (flatten on top due to too much receiver sensitivity). The pip must be kept in the center of the notch so that the pip appears even on the pointer's and trainer's scopes. If the pip saturates on the range scope, it will saturate on the trainer's and pointer's scopes, thus preventing them from knowing which way to train or elevate.

One of the range operator's hands should always he on the range knob. When he wants to change range quickly, he should turn the range wheel with the small crank on it. For fine adjustment of range, such as keeping the pip in the notch, the operator should grasp the wheel with his hand and not use the crank. Usually this will be the right hand, but in some installations it may require the left.

The opposite hand (usually the left), should always be resting on the top of the range scope. The range operator will find that after once setting up the scope correctly, there are only two knobs that require further adjusting. but those two knobs will have to be adjusted frequently. These are the image spread (2) control, and the receiver sensitivity (3) control. The receiver sensitivity must be readjusted as often as necessary, to prevent saturation of the pips seen on the pointer's and trainer's scopes. He should make all adjustments on the range scope with his left hand (or with his right if his left hand is on the range knob). He must know the position of all controls so well that he can make adjustments to the scope without groping for the knob or taking his eyes from the scope.

Figure 4 Mt. 3/Mk. 4-7. Pips on trainer's or pointer's scope.
Figure 4 Mt. 3/Mk. 4-7. Pips on trainer's or pointer's scope.

The trainer and the pointer.

The trainer trains toward the smaller of the two pips. (fig. 4 Mk. 3/Mk. 4-7, train left.)

The pointer elevates if his left pip is lower. (fig. 4 Mk. 3/Mk. 4-7, elevate.)

A rule to follow is the Three L Rule. For the trainer: left, low, left; meaning if his left pip is low, train to the left. For the pointer: left, low, lift; meaning if his left pip is low, lift or elevate the antenna.

Some pointers think of the left pip on their scope as an indication of the position angle of the antenna. If the left pip is low (in relation to the right pip, of Course), the antenna is pointed below the target. If the left pip is high, the antenna is pointed above the target. This is a good way to tell the position angle of the antenna.

4-Mk. 3/Mk. 4-8


When the pips are of the same height, the pointer and the trainer say. mark," or "on train," or "on point." Occasionally you will notice that the pips will act in reverse, in other words, when you train or point toward the lower pip, it will get lower rather than higher. This indicates that you have a minor lobe contact. The target actually bears 15° to 20° to the left or right of this.

Sometimes the trainer will be able to match up two pips, but no pips will show on the pointer's scope. This can be caused by minor lobes again, and the trainer should train back and forth until the pointer and the trainer both can see two pips. The angle between the minor lobes and the main lobe is 15° to 20°.

Below 12° of elevation, the ED cannot be relied upon to give accurate position angles. With surface targets we know what the position angle is, and so are not concerned about the inability of the ED to give an accurate position angle. In train there is not this inaccuracy.

Searching with bearings and ranges given.

The approximate bearing and range will be given to the operator by CIC. The approximate range is placed on the range dial. When the director is trained to the approximate bearing, the lobing motor should be turned on, and a search begun through a small angle (15°) for the target. The elevation angle should be varied from zero to about 10°. It is most important that the image spread knob (2) be turned completely counterclockwise. The range operator must be extremely alert to see any echo that may appear along the length of the sweep. He should never allow his gaze to concentrate on one portion of the sweep for too long a time. Echoes frequently appear as a small, straight line, no higher than the grass, and the operator must be quick to notice them. Turning the range knob back and forth slightly helps somewhat, because echoes which ordinarily would be hard to distinguish from the grass become more readily discernible, appearing as small, bright lines, moving back and forth in the grass. The selector switch should not be on RADAR RANGE when doing this.

As soon as the range operator sees the target he should call out "mark," or "hold train and point," so that the pointer and trainer will stop searching. Then, opening the notch with one hand, and turning the range knob with the other, he should rapidly bring the target into the notch at no time losing sight of the target. If the target is at a great range, it will probably disappear by the time the operator has it in the notch. To help speed op the process of getting the pip in the notch, the operator should have previously cranked onto his range dial the range given by the search gear. If the target should disappear, close the notch, hold the train and elevation and turn the range knob back and forth. Soon the pip will show up again, and this time the operator will be able to get it into the notch; the pointer and the trainer will also get a fix or an indication of which way to train or elevate before it disappears. This process should be continued patiently. If the pip is clear the range operator knows that the pointer and or trainer are on target. If the pip is cloudy, the trainer and pointer are off the target. On some targets, however, such as a flight of planes, it will be impossible to get a clear pip.

Searching when no bearings or ranges are given by the search-radar.

In searching, when bearing and range are not given by the search radar, practically the same method is used as was described in the preceding section. The only difference is in the range operator's use of the sweep gain control. While searching, when you do not know that there are any targets, the sweep gain control should be turned counterclockwise until the trace occupies only about three inches. Targets can still be seen with ease, and this method possesses the advantage that the operator will be able to keep the whole sweep under his eyes at once. An experienced operator will not have to do this as often as an inexperienced operator, since the experienced man can watch alertly the greater trace as easily as the inexperienced man can watch the shorter sweep.

It seems to be the current practice, to keep the lobing motor turned off at all times, except when actually tracking a target. The only valid reason for this is that it saves the lobing motor from excessive wear. This admittedly is important since the lobing motor and cam assemblies are one of the weakest units of the Mark 3 and Mark 4 radars. They are located in a place where it is difficult to work and repairing them properly is a tedious job.

There are many in the held, however, who feel, that the benefits to be derived from operation of the lobing motor for searching outweigh the disadvantages. The greatest benefit of using lobing while searching is that it causes the beam width to increase from 9°, the normal width of the beam, to 15°, the width of the radiation pattern between half-power points with the lobing on. This increased coverage accompanied by no loss in power, since actually

4-Mk. 3/Mk. 4-9


we are simply waving the same beam back and forth in front of the director. It is easier to spot a target quickly with the increased beam width than it would be if you had only the one 9° beam.

Another reason for keeping the lobing motor on while searching, is that, once a target is picked up, and the trainer and pointer get on it by using optics, the C and I operator will have no need to turn the lobing motor on. He probably could read ranges under this condition, but let us suppose the target was suddenly obscured from view for some reason, as the laying of a smoke screen, or the sudden appearance of a rain squall. The trainer and pointer would immediately turn to their radar to track the target, and it might take some time to determine that their lobing motor was not on, and another period of time to line up their scopes. In the excitement of battle, working under nervous tension, such a delay might easily be prolonged. Any delay, however slight, at such a time, might very well change the outcome of a battle. So if such a delay can be eliminated, even at the expense of giving the maintenance men additional work, it should be done, and the lobing motor should he left on.

When the lobing motor is turned off, the beam, which was being swung in four distinct positions, gradually comes to a stop. It might be pointed up into the air or down into the sea. It might be pointed to the right or left. There is absolutely no accurate method of telling just where the beam is pointing. In any case, it never comes to rest pointing along the line of sight. Thus you might be searching for a ship with the beam pointing up into the air. However, if you turn your lobing motor on when searching your beam will be swung in all four positions, and you can always be sure you will not miss your target because you know your beam is pointed in the right direction.

Tracking.

Gradually the pip will become strong enough that it may he continuously tracked. When this occurs, the computor may be switched in, if full radar control is desired. As soon as the target is close enough to appear in the pointers and trainer's telescopes, the optical rangefinder should notify the control officer, and the trainer and pointer should switch over to their optics. Radar ranges should be used whenever possible, since they are more accurate than optical ranges. Furthermore, radar will give the range to the target continuously, whereas most stereo-rangefinders have to put their reticules back and forth over the target, thus not transmitting ranges continuously. Accordingly, a set-up on the director can be made more quickly by using radar ranges and rate control on the director than by any other means.

After the range operator has picked up the target and told the pointer and trainer to "hold train and point," he cranks the pip into the notch as described above. When it is in the notch, he says loudly, "on target." This indicates to the trainer and pointer that he has a pip in the notch and they accordingly look closely for it. When they have their pips matched up, they each say "mark." They continue saying "mark" whenever their pips are matched, and the range operator continues to say "on target," whenever he has the pip in the notch and the pointer and trainer are still using their radar.

Another good method is for the range operator to say "on range"; the trainer, "on train"; and the pointer, "on point."

The control officer will instruct the range operator as to the procedure and doctrine of pushing the range button. This range button is located in the center of the range knob and, when pushed, signals plot that the range is on at that instant. It also activates the range rate mechanism.

Spotting.

It is possible to see the shells leave the guns of your ship and follow them for quite a distance on the scope. Sometimes they look like "mice running under a carpet." Usually, they appear as distinct pips and move across the scope. You can also see shells from the enemy coming toward you on the screen. That should not prove too disconcerting, since they could miss your ship by quite a distance and still appear to be coming toward it,

The range operator has the additional function of spotting misses. This is done by estimating the distance from the target's pip to the pip produced by the miss. The notch should be completely expanded. The width of the notch and the width of the expanded portion of the sweep should be determined for the operator's set. This can be accomplished by cranking an echo, or the leading edge of the transmitted pulse across the notch or sweep, and noting how much range was covered on the range dial. The notch is generally about 600 yards wide, and the expanded portion of the sweep about 6,000 yards. If the set is in perfect operating condition, the notch should remain in the center of the C and I scope. You can estimate the spot by mentally comparing the distance from the target to the splash with the

4-Mk. 3/Mk. 4-10


width of the notch. Some ships have installed a scotch tape scale on the face of the range scope to aid in spotting.

Determining composition.

Skill in identifying targets by means of their pips is largely developed by experience. Aircraft pips flutter up and down vigorously. Their bearing, range, and elevation change rapidly. Clouds and atmospheric conditions which sometimes give echoes similar to planes are easily distinguished by means of their slow change in bearing, range, and elevation. Sea-return, which also looks like planes, usually appears within 2,000 yards, and it is impossible to obtain a bearing on it. Two planes flying together produce a beating effect, and their pip will bounce up and down with some regularity. A group of planes will produce a large echo which is never clear inside. They can be picked up by a good operator at 90,000 yards if they are high enough, and the set is operating properly.

The range to surface targets is limited by the horizon. Ships produce pips which will fluctuate up and down rather slowly; the larger the ship, the slower the fluctuation of the pip. They change range and bearing (but not elevation) slowly. Land targets are steady and strong. Sometimes land echoes will fluctuate like planes or ships. Good judgment together with experience will enable you to identify such pips as echoes from land. Satisfactory results cannot always be obtained when tracking a sleeve, for the sleeves in current use give echoes too weak to be used properly.

If the radar team must be coached on to the target by means of optics, they are knowingly passing up one of the greatest advantages we possess over the enemy. Radar should always pick up the target when it is far beyond optical ranges. Remember, that your skill as an operator will increase with practice. When you are able to distinguish an SBD from a TBF by the difference in their pips, you have really accomplished something.

Anti-jamming technique.

Oilier radars may produce interference on the range scope. This, as well as electrical faults in the set itself, can produce effects which might be called jamming by the inexperienced operator. If the interference is caused by the transmitted pulse from another radar set, an occasional pip will move across the screen in either direction. Effects which occur on all bearings or on the same relative bearing should also be classified as unintentional interference rather than jamming.

If the range scope seems to be jammed, report the fact immediately to the control officer, and also to the maintenance man. Continue to try to work through the jamming. Turning your lobing off may help. Sometimes the narrower antenna beam resulting when lobing is off will enable the operator to direct the beam on the target alone, and not on the target plus the jammer, as might well happen with lobing on, and double the area being covered. Thus the operator might be able to range on the target, but he would have to turn the lobing on again to get a bearing. Vary your receiver sensitivity control (3) carefully to determine the optimum setting. Return the receiver sensitivity control to its normal setting when the jamming ceases, or when operating on unjammed bearings. This is important, because targets may sometimes be visible at low sensitivity control settings in the presence of jamming, but completely absent at the same sensitivity control setting when the jamming ceases.

It is possible to train on the jamming station by simply matching the height of the jamming in the trainers pips. Remember, that the jamming will probably be much stronger than most echoes, and will tend to produce saturation signals. Therefore, when matching pips in jamming be sure that the gain control is turned down sufficiently, otherwise it will be difficult to pip match. Two ships can thus get a fix on the jammer. The pointer should also match the jamming on his scope. Remember though, minor lobes are much more important when being affected by a jamming signal than they normally are. So be very careful when using this method that you do not get on a minor lobe when matching up the height of the jamming on the two scopes.

Rotate the antenna to determine whether the jammer and the target are on the same bearing. If they are not on the same bearing, a pointing and training error of several degrees or more is to be expected, even if it is apparently possible to match pips. Report this to CIC. When the target and jammer are less than 5° apart in bearing it will be difficult to determine whether the jammer is on or off the target bearing. The accuracy of range information is not seriously affected by jamming on any bearing, but it will, of course, be more difficult to obtain. It will be found that the pip matching scopes are more difficult to interpret than the range scope when jamming is encountered.

The maintenance man can change the frequency of

4-Mk. 3/Mk. 4-11


the transmitter slightly by varying the field control, and the plate voltage of the magnetron, or by varying the duplexer tuning. This method is valuable, but the jammer may shift to your new frequency. Changing the receiver local oscillator tuning at the main frame may also be of some assistance.

As pointed out previously, it is of the greatest importance to keep trying to work through the jamming. The jammer will have to stop operating occasionally to check your frequency. in order to see if it has been changed. The second he stops jamming, obtain ranges and bearings (sometimes position angles), on the target. You must keep alert in order to get on the target almost instantly.

Some sets have an anti-jamming modification installed in the C and I unit. Turning this device on will sometimes improve the C and I scope. Always remember to cut all anti-jamming devices out of the circuit when no jamming is present. The official policy is to keep your transmitter on at all times, attempting to work through the jammer, even though at first glance it may seem impossible to do so. Perseverance and patience will be rewarded many times by your being able to range on the target. Because the echoes increase more rapidly with decreasing range than the jamming signal increases, it may he possible to suddenly see the pip from a closing target. This is another reason for leaving the transmitter on at all times.

Never give up hope. Look for small discontinuities in the jamming, they might well be echoes. The British have shown that good jamming is extremely difficult to carry out successfully. So keep trying to work through the jamming, be patient, and above all do not get excited. A cool head is the best anti-jamming device ever discovered.

RELIABLE RANGES OF MARK 3 RADAR

Type 75' Antenna height 125' Antenna height
Without
preamp.
With
preamp.
Without
preamp.
With
preamp.
Large ships-(BB, CV, Large Aux.) 17,500 20,000 20,500 27,000
Medium ships-(CA, CL, Med. Aux.) 15,000 17,000 18,500 25,500
Small ships-(DD, DM, AD, PC, etc.) 11,500 13,000 13,500 18,000
Submarine (surfaced) 4,500 --- 10,000 7,000
Submarine (periscope) 2,500 --- --- ---
Large planes-(PBM, PBY, PB2Y, etc.) 25,500 20,500 23,000 36,500
Small planes-(SOC, OS2U, SBD, F4F, etc.) 14,000 8,000 15,000 ---

RELIABLE RANGES OF MARK 4 RADAR

Type 75' Antenna height 125' Antenna height
Without
preamp.
With
preamp.
Without
preamp.
With
preamp.
Large ships 16,000 18,500 15,500 26,000
Medium ships 12,000 15,500 16,000 25,000
Small ships 9,000 11,000 11,000 18,000
Submarine (surfaced) 3,500 --- 7,000 ---
Submarine (periscope) --- --- 4,000 ---
Large planes 22,500 16,000 21,000 47,000
Small planes 13,500 13,500 13,000 23,500

4-Mk. 3/Mk. 4-12


PERFORMANCE

Maximum reliable ranges.

The tables on the opposite page show the maximum reliable ranges of the Mark 3 and Mark 4 Radar. The figures given are the averages of many ships reporting. These data are taken from BuShips' publications.

A good crew with well-maintained sets should he aide to get considerably better results than these.

Minimum ranges.

On ship targets the minimum range is 800-1,000 yards. The minimum range on aircraft is 1,100-1,700 yards.

Accuracy characteristics.

The following table is taken from BuOrd Pamphlet No. 657, and shows the accuracy-resolution characteristics of the Mark 3 and Mark 4 Radar, using three different antennas.

Resolution.

The range resolution of the Mark 3 and the Mark 4 is 400 yards. The bearing resolution of the Mark 3 (3' × 12' antenna) is 5°. The bearing resolution of the Mark 4 is 10°.

These are important figures, and they should be kept in mind at all times. If a target is greater than 400 yards offshore, a Mark 3 or Mark 4 will distinguish the target from the land as long as the line of sight to the target is perpendicular to the shore line. In this ease, only the range resolution of the set is being used. If, however, the line of sight is not perpendicular to the shore line, the bearing resolution of the set comes into the problem, and it will be more difficult to pick up the target. The greater the deviation from the perpendicular, the farther out from the beach the target will have to be to be distinguished from the land by the radar. This can be seen in figure 4 Mk. 3/Mk. 4-8.

The same dependency on accurate knowledge of the range and bearing resolution also conies into effect when there are a number of ships steaming in column making a target angle of 90° or 270°. If the ships are close together they will appear as one pip on the range scope. If they made a target angle of 0° or 180° they would have to be separated by 400 yards to be seen as distinct pips.

Many similar applications of these principles will he obvious to the thoughtful operator. For example, suppose that a ship is stationed off the mouth of a harbor or large river waiting for the enemy to come out. Assume the target to be midway in the mouth of the passage. So long as the shores did not intercept the two lobes (as they would if the channel were narrow or the target close to one side), land at the same range as the target would appear on the range scope, and it would be difficult to range on the target itself. Let us also suppose that two planes are coming toward your ship, both at the same range and close together. If they are not too far apart (subtending an angle of less than 10°) the radar, unable to distinguish each individual plane, would train at a point midway between them. The same would be true of two ships.

Characteristic FC long ant.
(3' × 12')
FC Short ant.
(6' × 6')
FC Antenna
(6' × 7')
Maximum range by direct indication (nominal range) 100,000 yds. 100,000 yds. 100,000 yds.
Minimum range (approx.) 1,000 yds. 1,000 yds. 1,000 yds.
Horizontal beam width (lobing off) 4.6° 9.0° 9.0°
Vertical beam width (lobing off) 30.0° 11.0° 19.0°
Horizontal beam width (lobing on) 7.2° 15.0° 15.0°
Vertical beam width (lobing on) 30.0° 11.0° 15.0°
Range accuracy ±40 yds. ±40 yds. ±40 yds.
Bearing accuracy ±2 mils ±4 mils ±4 mils
Elevation accuracy* --- --- ±4 mils
Range resolution ±400 yds. ±400 yds. ±400 yds.
Bearing resolution ±5° ±10° ±10°
Elevation resolution* --- --- ±10°
* Elevation data applies only when antenna is elevated above 10°.

4-Mk. 3/Mk. 4-13


What has previously been said regarding the horizontal plane, also applies to the vertical plane. The elevation resolution is 10°.

Target can be ranged on, since it is off shore a distance in excess of the range resolution of the Mk.3 and Mk.4; Land at same range obscures target; Target clear of land echo, and can be ranged upon. The spread of land due to beam width distortion is shown.
Figure 4 Mk. 3/Mk. 4-8.

TROUBLES

When the scope will not light up, or there is no transmitted pulse, it is obvious at once that something is wrong with the set. However, there are many minor malfunctions which only the experienced operator will notice. For example, when the image spread knob on the range scope is varied, that is, if tile position of the notch (not the width) moves across the face of the scope, and does not remain in the exact center of the sweep, the set is not functioning properly. (In this ease, the 29.5 KC and the 1.64 KC gears in the range unit may need realigning.)

Sometimes a false echo is seen at about 50,000 Yards on the range-scope. This can readily be detected as a "ghost," since it is present for all angles of train. (In this case, the fault may be caused by parasitic oscillations in the 807 tubes in the modulation generator. It can be removed by changing tubes or by soldering a small piece of wire to the cathode connection of one of the tube's sockets.) Double humps in the pips can be caused by faulty receiver tuning. Often the pips will saturate too soon on the trainers and pointer's scopes. In other words, the pip will only seem F-3 on the range scope, yet will be saturated on the other scopes. (This can be remedied by changing R88 in the C and I scope from 2K ohm to 1,200 ohms.)

All these are minor faults, yet for peak operating efficiency they must be eliminated. An operator should consider it an important part of his job to see to it that the set is kept in the best condition at all times.

4-Mk. 3/Mk. 4-14


PART 4
SA RADAR

CONTROLS   4-SA-2
  Power control   4-SA-2
  Selection switches   4-SA-3
  Operating controls and indicators   4-SA-4
  Adjustments   4-SA-4
  Alarms   4-SA-5
   
TURNING ON AND OFF   4-SA-5
  Turning on   4-SA-5
  Turning off   4-SA-5
   
CALIBRATION   4-SA-5
   
OPERATIONAL TECHNIQUE   4-SA-6
  Tuning the receiver   4-SA-6
  Miscellaneous adjustments   4-SA-6
  Long-range search   4-SA-6
  Searching over land   4-SA-7
  Reading hearings on the fly   4-SA-7
  Tracking   4-SA-7
  Fire-control liaison   4-SA-8
  Jamming and deception   4-SA-8
   
PERFORMANCE   4-SA-9
  Maximum reliable range   4-SA-9
  Minimum range   4-SA-10
  Range accuracy   4-SA-10
  Bearing accuracy   4-SA-10
   
TROUBLES   4-SA-10

4-SA-1


SA RADAR

CONTROLS

Like all other radars, the SA is a complex instrument, requiring careful and precise adjustment and operation. Many of the adjustments should be made by the operator, and the controls are conveniently placed so that this may be done.

The controls with which the operator must concern himself may be divided into five main classifications: power controls and indicators, selector switches, operating controls and indicators, adjustments, and alarms. The majority of these controls arc found on the receiver-indicator panels, which are located at the operating position. A few of these controls are mounted on the transmitter unit which is usually installed elsewhere in the ship. One control (on-off switch) is mounted on the train control amplifier cabinet.

The various controls and associated meters and dial lights are listed and explained below. Their arrangement is shown in the accompanying drawings.

Power controls.

P-1. Main power switch (labeled main power emergency): controls all power to the set except that to the heaters. Power is applied to the set when this switch is in the UP position.

P-2. Line voltage meter.

P-3. Line voltage variac: controls the voltage applied to the set. It should be adjusted so that the line voltage meter (P-2) reads 115 volts continually.

P-4. Transmitter power switch (labeled plate voltage): applies the high-voltage to the plate voltage variac when in the UP position.

P-5. Plate current meter: indicates the DC current flowing through the transmitter tubes.

P-6. Plate voltage variac: controls the voltage applied to the transmitter tubes. (The numbers around this knob indicate only relative voltages, and not actual amounts.)

P-7. Fuses (labeled "5 amp. fuses") : these fuses are in the power line to the lobing and slewing motors. If either or both should blow, the antenna must be rotated by manual control or by the emergency train motor (control S-2). Lobe switching is impossible when fuses are open.

P-8. Fuse (beside dimmer control) : protects the indicator circuits. When it opens, no trace appears on the screen and no dial lights come on.

P-9. Emergency off (on transmitter) : this switch opens the high voltage circuits in the transmitter.

P-10. Plate current meter (on transmitter): indicates the same thing as P-5 on control-indicator panel.

P-11 Fil. primary voltage variac (on transmitter) an adjustment of the filament voltage applied to the transmitter tubes.

Drawing of transmitter unit.
Figure 4 SA-1. Transmitter unit.

4-SA-2


P-12. Fil. voltage meter (on transmitter): indicates voltage on the primary of the filament transformer that supplies voltage to the filaments of the oscillator tubes. Control P-11, should be adjusted until the meter reads the same voltage as that marked on the small card above it.

P-13. Hours operation meter: records the total time the filament voltage has been applied to the transmitter tubes.

Selection switches.

S-1. Antenna train-relative, true: when in relative position, the antenna will stay on the same relative bearing when the ship changes heading. When in true position, the antenna stays on the same true bearing as the ship changes course.

S-2. Emergency train-CCW, auto. CW: the setting of this switch determines what unit will govern rotation of the antenna. When in auto position, the antenna may be rotated by hand, or controlled by the Mewing motor (control S-3). In either case, power passes through the train control amplifier (TCA). When the switch is in the CCW or CW position, the antenna is turned either counterclockwise or clockwise (respectively) by a motor which does not depend on the TCA for power. If the TCA should fail, this switch permits a continuation of the search.

S-3. Slewing motor-low, off, high: when switch S-2 is in auto position, this slewing motor switch permits automatic rotation of the antenna at either of two speeds (1 rpm or 4 rpm), or manual rotation of the antenna.

S-4. Range sel (range selector): setting of this switch determines the range scale being used: 30,000 yard scale when in position A, 75 miles when in position B, and 375 miles in position C.

S-5. Cal-fid IFF: the setting of this switch selects the picture seen on the screen. When in cal position (extreme CCW), range markers appear. When in the No. 2 position, the usual "A" scope picture appears, but maximum strength of the pips is limited so that the PPI scope (if any) will not be damaged by too much echo intensity. Position No. 3 is the same as position No. 2, except that maximum pip height is greater. Position No. 4 is used only when challenging a target for IFF response. It operates the interrogator (at present, the BL), and removes the range step.

S-6. Cal synch (calibrate, synchronizing switch): this switch, with switch S-5 controls the picture on

Figure 4 SA-2. Receiver indicator unit.
Figure 4 SA-2. Receiver indicator unit.

4-SA-3


the screen, and on the "osc. adj. scope" (2-inch CRT). When in position 1, any strong signal occurring at a rate of about 60 cycles per second will "synchronize the sweep" so that a strong pulse will appear fairly steady on the sweep. This is called internal synchronization. In position 2, the sweep on the scope is started by the transmitter pulse.

S-7. L.R. motor-on, off, on: this switch controls the lobing motor. The lobing motor is turned on by switching to either the left (CCW) or right (CW) position. The lobing motor (left-right motor) is off when the switch is in the OFF (center) position.

S-8. L.R. off: this switch makes normal search possible even while the lobing motor is on. When lobe switching (L.R. motor is on), two traces from each target normally appear on the screen. However, when searching, too pips would be confusing, so this switch is used to permit blanking of the right-hand trace when thrown to position 1. When in position 2, both pips appear.

Operating controls and indicators.

Op-1. Range oscilloscope (the scope) : the cathode-ray tube used to indicate presence of the echoes and to permit ranging on these echoes.

Op-2. Yards range counter: indicates the range in yards, corresponding to the step position on the scope when control S-4 (range selector switch) is in position "A" (when set for a 30,000-yard nominal range).

Op-3. "B" miles range counter: dials indicate the range, in nautical miles, corresponding to the step position on the scope, when control S-4 is in position B (for a 75-mile nominal range).

Op-4. "C" miles range counter: indicates the range corresponding to step position on the scope when control S-4 is in position C (or for a 375-mile nominal range).

Op-5. Range step control: this knob controls the position of the step on the range scope, and the corresponding reading of the numbers on the range counters.

Op-6. Bearing indicator: indicates the direction of antenna train, with the outer dial indicating the relative hearing, and the inner dial the true bearing (if control S-1 is in TRUE position and gyro compass is operating properly). Two diamonds, or bugs rotate with the antenna; the orange bug should he read when adjusting for the maximum pip, and the white bug used when lobe switching and matching pips.

Op-7. Manual antenna-train knob: this knob makes it possible to rotate the antenna manually to any bearing desired, so long as control S-2 is in the AUTO position. When control S-3 is in either the LOW or HIGH position, the antenna rotation may he stopped or reversed by operating this handle.

Adjustments.

Ad-1. Focus: controls the sharpness of the picture on the screen of the range scope (Op-1).

Ad-2. Astig (Astigmatism control): no single setting of the focus control (Ad-1) can bring all parts of the sweep into correct focus. This control permits the operator to bring any desired part of the sweep into a sharper focus. The astigmatism control may he considered as a fine adjustment of the focusing.

Ad-3. Intensity: controls the brilliance (or intensity) of the trace on the screen of the range scope.

Ad-4. Horiz (Horizontal centering control): the complete trace on the range scope (Op-1) may be moved horizontally by adjustment of this control.

Ad-5. Vertical (Vertical centering control): the complete picture on the range scope may be raised or lowered as the operator desires, by means of this control.

Ad-6. Oscillator adjustment oscilloscope (the 2inch oscilloscope): the scope used to indicate when the calibrating oscillator is adjusted to the right frequency (so that the range marks will have the proper time interval). Control S-6 must be in position 3 for any picture to appear on this scope.

Ad-7. Oscillator ad just meet oscilloscope focus: permits focusing the picture on the osc. adj. screen.

Ad-8. Cal. osc.: controls the time interval between the range marks (by controlling the frequency of the calibrating oscillator). This, of course, changes the picture on the osc. adj. (Ad-6).

Ad-9. Cal max.: controls the speed of the sweep (travel of the spot of light across the screen) on the range scope. Changing this speed gives the appearance of crowding the range marks closer together, or spreading them farther apart.

Ad-10. Cal min.: permits moving the range step along the time base without moving the range counters, so that the range counters will indicate the correct range.

Ad-11. Dimmer: adjusts the brightness of the dial lights.

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Ad-12. First R.F.: receiver tuning adjustment.

Ad-13. Second R.F.: another adjustment of the receiver tuning.

Ad-14. Osc.: tuning control of the "local oscillator." Another receiver tuning control.

Ad-15. Ant.: adjustment to tune the input circuit to the receiver.

Ad-16. Calibration chart: lists settings which are approximately correct for controls Ad-12, Ad-13, Ad-14, Ad-15. These four tuning controls should he adjusted for the greatest echo strength. (There are four sets of settings-only one will be correct for a particular radar set. The technician decides which set of readings to use.)

Ad-17. IFF gain: the "volume control" of the IFF receiver, since it adjusts the size of the IFF pips on the range scope screen as the operator desires.

Ad-18. L.R. amp: controls separation of the two blips from a target when using lobe-switching. To he effective, control S-7 should he ON, and L-R off in the ON position.

Ad-19. Duplexer adjustment (on transmitter) tunes the duplexer (a part of the antenna connections).

Alarms.

Al-1. Bearing mark: a push-button which rings a buzzer on the bridge when the operator wishes to call attention to the remote bearing repeater.

Al-2. Range mark: sounds alarm at the remote range repeater to call attention to the range indicated.

TURNING ON AND OFF

Turning on.

  1. See that these controls are in the proper position.

    1. Transmitter power OFF.
    2. Slewing motor OFF.
    3. L-R motor OFF.
    4. Emergency train-AUTO.
    5. Antenna train-TRUE (if ship's gyro compass is operating properly).
    6. Plate voltage control fully counterclockwise.
    7. Receiver gain down (fully CCW).
    8. Intensity down (fully CCW).
  2. Snap on the main power-emergency switch. The dial light on the line voltage meter will come on. Adjust line voltage control so that this meter reads 115 volts, The blower motor in the transmitter will start, and the red lights on the TCA and the transmitter will go on.

  3. Alter about 30 seconds, a relay will snap in the TCA.

  4. Now snap transmitter power switch ON (up). The plate current meter should light up.

  5. While watching the plate current meter, turn the plate voltage knob clockwise until the meter shows a sharp dip. Continue raising the plate voltage until the 5-7 milliamperes is read on this meter, or until the present stop is reached. If the overload relay trips while doing this, it may he necessary to lower the plate voltage, reset the relay in the transmitter (click emergency switch on the transmitter off, then on again), and continue operation, using a lower plate current.

Turning off.

  1. Turn plate voltage variac fully counterclockwise.

  2. Snap transmitter power switch to OFF position.

  3. Turn off main power switch.

CALIBRATION

  1. If the cal-synch switch is in position 2 and cal-fid-IFF is in position 2, 3 or 4, the transmitter pulse will be visible on the scope when gain is increased.

  2. Snap cal-fid-IFF switch to cal (No. 1) position and cal-synch switch to position 3. The trace will disappear from the range scope. Adjust focus (No. Ad-7) control until some indication appears on the 2-inch scope.

  3. Now adjust cal-osc control until a stationary pattern appears on the 2-inch scope. Either a figure eight pattern or a horizontal V is satisfactory.

  4. Then turn focus (No. Ad-7) control so that this picture disappears and snap cal-synch to position 2. Range marks should again he visible on the range scope. Snap range selector switch to the A position (30,000 yards).

  5. Set the range counters to read precisely 6,000

Figure 4 SA-3. Pattern for calibrating minimum range on 15,000-yard scale.
Figure 4 SA-3. Pattern for calibrating minimum range on 15,000-yard scale.

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    yards; next adjust cal-min so the step is accurately aligned with the beginning of the second range mark. This adjustment is correct when the little peak just beyond the right-hand end of the first range mark is leveled up with the end of that mark (at the beginning of the second range mark). (see fig. 4 SA-3.)

  1. Adjust cal-max until the counter reads 26,000 yards when the step is lined up with the beginning of the seventh range mark. (see fig. 4 SA-4.)

  2. Repeat steps 5 and 6 until no further adjustment is necessary to make the step read correctly at either end, then snap cal-fid-IFF switch to position No. 2.

Display showing 6 peaks.
Figure 4 SA-4. Pattern far calibrating maximum range an 15,000-yard scale.

OPERATIONAL TECHNIQUE

Tuning the receiver.

Increase the receiver gain until some grass appears. If any targets are present, adjust OSC., 2nd R.F., and 1st R.F. controls until the pip appears largest. Unless some target is present to tune on, this step should not be attempted. Sea-return is a "target," if visible, and you can tune on it-using the short range scale. If no targets are available, and set is known to be out of tune, set controls as listed on the calibration chart (Ad-16).

Move the step until the range counters read 40 miles. If the step is not accurately lined up with the 40-mile mark on the transparent-tape scale, adjust horizontal centering control until it is. (Operate vertical control until the trace appears directly above the scale.)

Now begin to search by starting the antenna rotating either automatically or manually.

Miscellaneous adjustments.

If lobe switching is to be used, turn plate voltage control completely down (counterclockwise), snap L.R. motor on (either to right or left), and wait one complete minute before again raising the plate voltage, except in emergencies; the voltage may be raised after about 30 seconds. Snap L.R.-off switch to ON position (No. 1) and adjust L.R. amp. control until the traces are separated suitably. While matching pips, read the white bug.

If IFF equipment is used with this set, turn the IFF equipment on, snap cal-fid-IFF switch to position 4, and adjust IFF gain until a reasonable amount of grass appears below the time base, then set cal-fid-1FF back to either position 2 or 3 until ready to challenge a target. Snap cal-fid-IFF switch to position A to challenge a target.

Long-range search.

The SA radar was designed primarily for long range air search-an early warning of approaching aircraft. Its effectiveness depends not only on the materiel condition of the equipment, but also on the efficiency of the operator. The following search procedure permits the set to be used efficiently and effectively.

Search first on the 75-mile scale, using low speed automatic antenna rotation. Keep the gain fairly high (at least one-sixteenth of an inch of grass), and watch for very weak pips. The lobing motor (L.R. motor) should be kept off. Continue searching on this scale and in this manner for about four minutes, then make one or two complete rotations of the antenna using the manual antenna control, studying the trace very carefully.

Next switch to the A-scale (30,000 yards), and search for two complete antenna rotations, looking especially for small pips which may not have been on the B-scale. Use manual rotation of the antenna for the second turn of the antenna. Readjust the gain and astigmatism controls slightly, if a clearer, sharper trace is desired. Low flying planes may be detected first on this scale.

Again search on the B-scale for about five minutes, as outlined above.

Then use the C-scale (375 miles) for two rotations of the antenna, using manual control. Pay particular

4-SA-6


attention to the left-hand portion of the time base. Again readjust gain, astigmatism, and intensity controls slightly, if necessary. Repeat in order, the steps outlined above.

The procedure described above must be used when operating independently. A somewhat different procedure is required when serving as radar guard ship. In this case, the O.T.C, will state whether search should be made using only the 75-mile scale or only the 30,000-yard scale. The antenna should not be stopped on a target except for a few seconds (while challenging for IFF, etc.), without specific instructions from the O.T.C.

Searching over land.

If search must he made over land, target pips will be mixed with the land pips. However, planes will give echoes which bob up and down more rapidly and irregularly than the land pips. Also, the plane pips will move with respect to the land pips. When faced with the problem of searching over land, the antenna may be stopped for a few seconds to determine whether the pip is actually behaving as a plane echo or as a land echo. Bearings cannot be obtained very accurately, but the bearing of maximum swing of the pip should be reported. Land masses may cause the pip to be higher on a bearing a few degrees to one side of the actual target bearing, and so maximum pip height may not give the correct indication-it is the maximum bounce that counts. The approximate bearings secured are well worth the effort expended to get them.

The operator must remember to keep searching. He should not find one target and "camp on it" from then on.

Reading bearings on the fly.

With practice, almost any operator can read the bearing of an object with considerable accuracy even though he does not stop the antenna. This speeds up tracking and makes the SA radar much more effective.

Any experienced operator can tell when the pip on the scope first begins to drop off as the antenna scans past the bearing of the target. If he then glanced at the bearing indicator and read the bearing indicated, he would be reading a bearing somewhat large (for CW rotation of the antenna), because of the delay before reading the bearing. The size of the error involved would depend upon the time required by that particular operator to realize that the pip height had begun to drop off and then to look at the bug. For each individual, this time is practically constant; in other words, the bearing error will be practically constant. When an operator determines the magnitude of his individual "error" he can read the bug, correct for his "error" and report the corrected reading. An example will serve to make this clear.

Assume that the operator has the antenna set for low speed automatic rotation, clockwise, and knows that the antenna rotates nine degrees after the pip first begins to drop off in height, and before he can read the bug. He watches the pip increase in size, and then begin to drop off, he immediately reads the bug, silently. If he read "one-nine-seven," he would subtract nine degrees (his "personal error") and call off "one-eight-eight."

When the pip first appears, the range can be read immediately and remembered. As soon as the bearing has been reported, the operator can call off the range without hesitation and with no need of again looking at that pip until the antenna gain approaches the bearing of that target. With practice, this reporting procedure becomes almost automatic.

Operators must make every effort to learn this method of reading bearings. They must practice until the delay in reading is unchanged each time they report. (In other words they must not slow down or speed up glancing from the scope to the bug.) To find their own lag, they should first watch the pip grow in height, read the bug, and then use lobe switching to find the accuracy bearing. Comparing these two readings will indicate the amount of correction to be applied each time. This must be repeated over and over again, until the operator gets the same correction (within a degree or so) each time.

This is not as difficult as it sounds. It does take practice, but results are well worth the effort involved.

Tracking.

Targets probably will be contacted first on the 75mile range scale; hence, this is the scale most often used for tracking. The addition of a transparent tape range scale to the scope, makes accurate tracking of several targets relatively quick and simple. Tracking while using this 75-mile scale will he discussed first.

When a pip appears, stop the antenna approximately on the target, but do not waste time getting an accurate bearing. Read the bearing indicated by the orange bug, and note the range indicated on the

4-SA-7


scale marked on the front of the scope. (Do not use the range step.) If the plane is close on initial contact, you can save valuable time by reporting it as a bogey without interrogating first. The next time around, interrogate, estimate composition, get accurate bearing and range, and see whether they are opening or closing range, or crossing. Report. Snap cal-fide-IFF switch to position 4 to check for IFF-response.

When the contact is identified as friendly or bogey, start the antenna rotation at slow speed, automatic, and continue searching for other targets. When the pip from the first target reappears, note the range immediately from the scale on the scope, and read the bearing "on the fly." This report should be made every time the pip appears, reporting the bearing first and then the range.

Keep in mind the number of targets present, and if one fails to appear when the antenna scans past its previous bearing, report it as being "in a fade."

Generally speaking, there is no reason for changing from the 75-mile scale while tracking. Even after a plane, or group of planes, has closed well within 30,000 yards, the 75-mile scale is still sufficiently accurate and much more easily read than the 30,000-yard scale,

If a target is first discovered at a range greater than 75 miles, tracking must be conducted using the 375-mile scale. This requires stopping the antenna on the bearing of the target and using the range step, then starting the antenna once more. When the target closes to within 75 miles, use the 75-mile scale, as explained above.

If a plane is discovered while searching on the 30,000-yard scale, give the initial contact report and continue searching. If the pip can be seen clearly on the 75-mile scale, that scale should be used in tracking. Search must be continued while tracking air targets.

Fire-control liaison.

Use of the SA radar for antiaircraft fire-control is limited to warning of the approach and tracking the targets (getting course and speed). However, this radar is useful in surface fire-control work, for it gives ranges and bearings which may be used in an emergency for this task. In any event, it gives information sufficiently accurate for star shell illumination of surface vessels.

When the SA radar is used for this work, lobe switching should be employed and ranges read from the 30,000-yard range counter. Also the antenna must be kept bearing on the target. The operator does this by keeping the two pips from the target matched in height; it may be necessary to reduce the gain to keep these pips below saturation. He keeps the two steps lined up with the two pips, and reads the ranges indicated on the counters.

The actual tracking procedure would be for the plotter to call "stand by" every 25 and 55 seconds after the minute, followed by "mark!" on the minute and half-minute. The operator should read true bearings as indicated on the inner scale by the white bug during the tracking. When directed, to do so by the CIC evaluator, he should report ranges, relative bearings, and read the enter dial, to the gunnery officer. He should read these ranges and bearings continuously.

Jamming and deception.

There is no doubt that the enemy considers our radar an extremely dangerous weapon, and consequently it is only reasonable to expect him to try every means possible to make it less effective. He may use two tactics to do this: jamming and or deception. Every operator should learn how to recognize these countermeasures, and expect them when in combat zones.

When the enemy broadcasts radio signals intending that our radar receive them, and they show a confusing pattern on the screen, it is called jamming. Use of dummy targets (tinfoil, kites, balloons, etc.) is called deception. Of course, more precise definitions are sometimes given, but these are satisfactory for this discussion.

The SA radar can be jammed, and it will show echoes from the tinfoil the enemy sometimes throws out to confuse the operator. The operator should not become alarmed when either of these things happen.

If you were suddenly confronted with jamming, without previous experience, it would appear impossible to work through. However, it is not really that serious if the following procedure is carried out:

  1. DF on the jamming.
  2. Use available anti-jamming devices on receiver when provided.
  3. Try moving gain control up and down.
  4. Try changing receiver local oscillator toning.
  5. Keep operating.
  6. Report type and bearing of jamming to CIC.

The first reason for obtaining a bearing on the jamming is to determine whether or not it could be accidental interference. Jamming will not only be

4-SA-8


directional, but its true bearing will not be changed by any sudden change in your ships course. Interference originating aboard your own ship will either be non-directional and appear on all bearings, or else it will always be on some certain relative bearing regardless of your own ships course changes.

Try moving the gain control up and down. This is probably one of the most important countermeasures that can be taken, and the one most commonly overlooked because of its simplicity.

In most cases, except when effective noise modulated jamming is being encountered, there is a setting of the gain control with which it is possible to range on a target in the presence of heavy jamming. If there are several echoes on the same bearing, the best setting for each echo is different. Of course it is more difficult to obtain these ranges because of the distortion of the echo produced by jamming, but it is, after all, possible to obtain the desired information. However, the extra effort is worth while because the enemy would not be jamming unless he were trying to conceal something important.

The two general methods of using the gain control, both of which should be tried, are as follows:

  1. Reduce setting; this prevents overload of the radar receiver; echoes are visible "riding on top" of the jamming pattern.

  2. Increase setting; this limits (or clips) jamming; echoes are visible as a break in the base line.

Be sure to return the gain control to its normal setting when no jamming is present, or when the antenna is turned to an unjammed bearing.

Try changing receiver local oscillator tuning. When you change the oscillator tuning, you lose some of the height of the desired echo. However, if the jammer is not exactly on your radar frequency, there is a chance that you will detune the jamming signal more than the echo signal. Considerable improvement can sometimes be obtained this way. Try "swinging" the oscillator tuning dial in both directions, to see which direction makes the greatest improvement. Note the correct setting of the oscillator dial so that it can be returned to its normal position when no jam is present, or if detuning does not help, otherwise the radar will not give optimum performance.

Even if the jamming is extremely effective keep operating. Don't turn your radar off. Turning your radar off informs the enemy that his jamming is effective, and certainly makes the radar completely worthless. The effectiveness of the jamming may change from time to time, so if you are persistent enough some information may be obtainable.

Report nature and bearing of jamming to CIC. Recognizing the type may be difficult because nonsynchronous patterns sometimes appear blurred beyond recognition. Inasmuch as knowledge of jamming types* may possibly help identify the jammer in some cases, this information should he reported.

If the equipment is provided with an anti-jamming receiver, the jamming may he reduced sufficiently for reading targets without any detuning of the receiver. Detuning should be a last resort, and then should he done very carefully and cautiously, otherwise all targets may be lost and the equipment made completely ineffective. No set procedure is offered for setting the controls of the AJ receiver, except that they should be varied for maximum readability through jamming, the gain control coming first, and then the AVC control followed by Rej 1 and Rej 2.

Above all, never off the radar.

When jamming/and or deception is encountered, full 360° search must be continued. However, the antenna should be stopped for short intervals from time to time in order to try reading through the jamming (using the "A" scope). You also must be prepared for any diversionary tactics, for the enemy may or may not use jamming and or deception to divert your attention from the bearing of the main attacking forces. This problem is simplified somewhat when similar but separate radars are used for reading through jamming and for searching.

PERFORMANCE

Maximum reliable range.

Antenna 89 feet


          Target                      
BB, CV. CB, Large auxiliary   43,900 yards
CA, CL, Medium auxiliary   24,900 yards
DD, DM, AU, PC, CG, etc   15,600 yards
Submarines (surfaced)   4,500 yards
Large planes-PBM, PB2Y, PBY   40 miles
Small planes-SOC, SBD, F6F   20 miles
Groups of planes   60-80 miles
Land (1,500 feet or higher)
      depending on atmospheric condition
  90-200 miles
Low flying planes   10-15 miles


* See Part 3, Defense Against Jamming and Deception.

4-SA-9


Minimum range.
Ships-depends on sea-return                     750-2,000
Planes                     1.0 mile

Range accuracy.

When using the step and the 30,000-yard scale, the accuracy is about ± 100 yards. When using the 75-mile scale and reading ranges from the transparent tape, the accuracy is about ± 1.0 mile.

Bearing accuracy.

With lobing ± 1°
Without lobing ± 3° - 5°

TROUBLES

Probably the most frequent failure of SA equipment, is the failure of the oscillator tubes in the transmitter. The operator can easily recognize this because the plate current meter does not show a dip when the high voltage control is turned up. One, or both tubes must be replaced when this happens. Usually, failure will be gradual. The operator should notice when the plate current rises more rapidly than it does normally as the high voltage is increased, since this indicates that the tubes are going bad. The small white spot on the high voltage knob (No. P-6), indicates how high the high voltage has been raised. Another common fault is called multiple pulsing. The trace appears to flicker and jump, especially when using the 375-mile scale. Sub-multiple pulsing is indicated when the normal opening below the pip is closed by a bright line.

When signals appear very weak, or when no targets appear, even though land or other objects are in the vicinity, a receiver tube may not be working. The transmitter pulse may appear at its "normal" strength, even though one of these tubes is not functioning, but echoes will not appear.

If the antenna fails to rotate when either the manual control knob is turned or when the automatic control is on, the train control amplifier probably is not operating properly.

Sometimes one or both of the 5 amp. fuses (No. P-7) will open. When this happens, no power can be applied to the lobing motor (L-R motor), or to the automatic antenna train motor. The ten amp. fuse (No. P-8), near the dimmer control carries power to the indicator unit. If the trace should suddenly disappear from the indicator screen, and the dial lights go out, this fuse has probably blown.

If the ship's gyro compass should fail, immediately throw antenna train-relative, true switch to relative position.

If the bug fails to move when either the manual or automatic antenna rotation controls are used, snap emergency train switch to either CCW or CW position.

4-SA-10


Part 4.
SA-1, SA-2 RADAR

CONTROLS
  Power controls
  Selection switches
OPERATING CONTROLS AND INDICATORS
TURNING ON AND OFF
  Turning on
  Turning off
CALIBRATION
  Tuning the receiver
  Final adjustments on "A" scope
  Turning on PPI scope
  Miscellaneous adjustments
OPERATIONAL TECHNIQUES
  Search procedures
  "Anti-jam" receiver
    Unmodulated CW interference
                    Modulated interference
    Railings (or pulsed) interference
    Non-intentional interference
PERFORMANCE
TROUBLES

SA-1, SA-2 RADAR

The SA and SA-2 radars employ almost identical operating procedures. Therefore, the discussion of SA-2 radar will only supplement and enlarge upon the information already presented on the SA radar.

The SA-1 radar is obsolete and practically nonexistent on ships of the fleet, and accordingly merits very little discussion.

Model SA-1 is a small, general-purpose detection radar. It does not incorporate the master PPI unit and accessory components furnished with the models SA and SA-2, and hence further falls by the wayside as an important air-search radar.

Model SA-2 is a medium-range aircraft search radar intended for use on certain small combatant vessels and auxiliaries. All the latest models of SA-2 have included a master PPI unit and its associated components, the Bearing Amplifier Converter, and the new Anti-Jam Receiver, and will be substantially equivalent to the latest model SA-2 equipments. The following discussion will therefore treat the PPI, Bearing Amplifier Converter, and Anti-Jam Receiver as being integral parts of the SA radar system.

CONTROLS

The controls the operator may come in contact with may be divided into five main classifications: operating controls and indicators, selector switches, power controls and indicators, adjustments, and alarms. The majority of the controls are found on the receiver-indicator panels. A few of these controls are mounted on the transmitter unit, which usually is installed elsewhere in the ship. In addition, once control (on-off switch) is mounted on the Bearing Amplifier Converter cabinet.

It should be emphasized that the most important operating controls are located on the receiver-indicator panel. Under normal operating conditions, this is the only unit upon which the radar operator must focus his attention.

The various controls will be explained by accompanying drawings and by frequent cross references to page 4-SA-2 through page 4-SA-10.

Power Controls

Controls P-1 to P-13, inclusive, are identically located in the SA and SA-2 radars and have the same functions in the sets. However, meter P-13 is called "tube hours" in the SA radar and "elapsed time" in the SA-2 radar.

If the fuse (P-8) opens, there will be no trace on the "A" scope, and no dial lights will appear on the receiver-indicator unit. In addition, there will be no receiver output fed to the PPI unit, and the set will be inoperative.

Due to the addition of the master PPI unit to the original model SA radar, two more power controls have been added.

P-14. PPI main power switch: Controls all power applied to the PPI unit. Power is applied to the PPI unit when the switch is in the ON position.

P-15. Fuse (labeled "heater"): this 3 amp fuse is in serries with a heater unit, the purpose of which is to prevent moisture from condensing inside the

4-SA-11


Figure 4 SA-5. Transmitter unit.

equipment. If P-15 should open, there would be no immediate visible indication.

P-16. Fuse (labeled "H.V."): This 5 amp fuse is in series with the primary of the high voltage transformer, T1202. If it opens, the PPI unit becomes inoperative.

P-17. Filament tuning: This control regulates the amplitude of oscillation (output) of the transmitter tubes. It is primarily a technician's and not an operator's control.

Selection Switches

Selection switches S-1 through S-8, inclusive, have the same general functions in the SA-2 radar as they do in the SA radar. However, the following minor differences exist:

S-2. Emergency train, CCW, normal, CW (called "emergency train, CCW, auto, CW," in the SA).

S-4. Range sel: The setting of this switch determines the range scale being used--40,000-yard scales when in position A, 80 miles when in B, and 400 miles when in position C.

S-5. Cal-oper IFF (called "cal-fid IFF" in the SA). S-6. Cal synch (calibrate, synchronizing) switch: With the cal-oper IFF switch (S-5) in position 3 and the cal synch switch (S-6) in position 2, it can be observed on the two-inch cathode ray tube (Ad-6) whether or not the transmitter is pulsing normally. In the SA radar there is no corresponding visual indication to show if the pulse repetition frequency is correct at 60 cycles. Typical keying indicator patterns are shown in figure 4 SA-7.

S-8. Lobing off (called "L.R. off" in the SA). Modification of SA equipments and early model SA-2 equipments to include the master PPI unit and "Anti-Jam" receiver makes necessary a discussion of several additional selection switches:

S-9. AVC bal (automatic volume control balance): This three-position switch adjusts the speed with which the AVC action takes place. Fast AVC action occurs with the switch in position 3 (switch turned clockwise all the way), position 2 of S-9 corresponds to medium AVC action, and position 1 (all the way counterclockwise) corresponds to slow AVC.

S-10. Range: Setting of this switch determines the range scale being used on the PPI. The range scales available are 20, 80, or 200 miles.

S-11. True bearing-relative bearing switch: With the switch in the relative bearing position, the antenna will stay on the same relative bearing when the ship changes heading, the PPI will indicate relative bearings, and relative bearings only are indicated on the bearing indicator. A green pilot lamp in the PPI unit will light with the switch in relative bearing. When the switch is in the true bearing position, the antenna stays on the same true bearing as the ship changes course, true bearings are read from the PPI, and both true and relative bearings may be read from the bearing indicator.

S-12. Sector sweep off: With the sector sweep in the up (or on) position, and the emergency train switch (S-2) in the CW position, the antenna will

4-SA-12


Figure 4 SA-6. Receiver indicator and PPI unit.
Figure 4 SA-6. Receiver indicator and PPI unit.

4-SA-13


train back and forth through approximately a 90° arc. The sweep on the PPI scope is synchronized with the antenna rotation and hence rotates back and forth over the same sector that the antenna is searching.

S-13. Sector train selector switch: This switch has eight positions, which enable the operator to choose any of the eight sectors that he may desire to have around a true bearing coinciding with any one of the four cardinal directions of the compass, or 45° off from any of these, or else around the corresponding fixed relative bearing. In other words, the center bearing line of any two adjacent sectors are separated by 45°. Turning the emergency train switch to the CCW position causes the antenna to sweep an arc of approximately 300°.

S-14. Operation switch: This is a five-position selector switch. The IFF & cal. (extreme CCW) and IFF positions of this switch (S-14) permit the PPI equipment to be used for recognition operation, respectively, with and without range calibration markers appearing on the screen of the indicator tube. In the normal Position (middle), the radar video output signal of the SA receiver is applied to the PPI unit. This constitutes normal radar operating conditions. Electronic calibration markers can be made to appear on the master PPI by putting the Operation switch on the cal-mas (calibrate markers) position. In the cal. rem. (calibrate remote) position of this switch, calibration markers appear on the remote equipments connected with the main radar.

S-15. PPI bearing repeat: Closing this switch enables either true or relative antenna bearing indications to be transmitted to remote positions. Whether true or relative bearing is transmitted depends on the mod of operation selected from the panel controls on the SA-2 radar.

OPERATING CONTROLS AND INDICATORS

Operating controls (Op-1) to (Op-7) inclusive, have the same general functions in the SA-2 radar, Op-2 (A-yards range counters) indicates the range in yards for a 40,000-yard nominal range, Op-3 (B-miles range counter) the rang in miles for an 80-mile nominal range, and Op-4 (C-miles range counter) the range in miles for a 400-mile nominal range.

Figure 4 SA-7. Keying indicator patterns.
Figure 4 SA-7. Keying indicator patterns.

4-SA-14


In addition to the operating controls mentioned above, inclusion of the PPI unit and the "Anti-Jam" Receiver in the SA-2 radar system makes necessary a discussion of several more operating controls.

Op-8. Gain control: This control is on the "Anti-Jam" Receiver, and is perhaps one of the most important controls that the operator has to manipulate. As its name implies, this control makes it possible to control the over-all amplification of the "Anti-Jam" Receiver, and hence regulate the size of the echo indication presented on the cathode ray tube.

Op-9. Cursor dial: Field change 31 added this improvement to the master PPI unit, the purpose being to enable the operator to get faster and more accurate bearings. The cursor dial consists of a transparent shield which covers the PPI screen. This screen is covered with range calibration circles but has only one single radial line on it from the center outward. Furthermore, this shield is mechanically connected to a hand crank located on the lower right hand side of the indicator screen window. To determine the bearing of a target, turn the hand crank until the radial line (cursor pointer) bisects the circular arc formed by the echo indication on the fluorescent screen. The bearing of the target can then be read off the azimuth scale to which the cursor is pointing.

Op-10. PPI tube: This is a cathode ray tube used in conjunction with the "A" scope (Op-1) in getting ranges and bearings.

Op-11. Bearing markers off: Throwing this switch on, turns lights illuminating the azimuth scale around the PPI scope.

Adjustments

Adjustments Ad-1 through Ad-19, inclusive, have the same general functions in the SA-2 radar as in the SA radar. However, several of these controls are named differently in the SA-2 radar. In particular, Ad-9 (cal max on the SA radar) is called max set; and Ad-18 (L.R. amp on the SA radar) is called lobe sep.

The new "Anti-Jam" Receiver contains two RF stages, just as did the original SA receiver. However, condensers for both RF stages have been ganged together and are controlled by one RF control (Ad-23). Hence, in tuning the "Anti-Jam" Receiver, the operator is making the same adjustments when he turns Ad-3 that he made on the original receiver when he turned both Ad-12 and Ad-13.

Ad-22 [sic: "Ad-19"?]. Duplexer adjustment: Is not used if an external duplexer is incorporated in the transmitter.

Ad-22. Video balance: This is an "Antijam" control designed chiefly to eliminate railings or to at least keep them of no larger amplitude than the echo. Under normal operating conditions (no jamming present), the Video balance control should be in the CCW position.

Ad-23. R.F. (Radio Frequency): This is a receiver tuning adjustment.

Ad-24. Rej. (rejection control), and Ad-25 Rej. bal. (rejection balance control): The rejection control and the rejection balance control are "Antijam" controls designed to work together to prevent an undesired signal from being passed through the receiver. If adjusted correctly, they constitute a wave trap for a particular undesired signal. These controls are designed to be used chiefly against an interfering continuous wave signal.

Ad-26. Video gain: This control is on the PPI unit. It is used to adjust the strength of the echo signals received at the PPI independently of the main gain control. Under normal operating conditions this control is not of much importance.

Ad-27. Focus: Controls the sharpness of the picture on the screen of the PPI (Op-20).

Ad-28. Intensity: Controls the brilliance (or intensity) of the trance on the screen of the PPI.

In addition to the above adjustments on the receiver-indicator, there are two adjustments on the SA-2 transmitter unit.

Ad-20. Grid tuning: This transmitter control will be manipulated by the technician and not by the operator. The SA-2 transmitter is designed to operate at the rate of 60 pulses per second. Any departure from this pulse repetition frequency (as evidenced by the picture on the 2-inch scope) can be offset by proper adjustment of the grid tuning control.

Ad-21. Locking voltage: This control is a fine adjustment of the pulse repetition frequency. In general, coarse adjustment of the pulsing rate is obtained by means of the grid tuning control (Ad-20), and find adjustment by means of the locking voltage control (Ad-21).

Alarms

A1-1 and A1-2: These alarms are the same on the SA-2 radar as on the SA radar. (Actually they are seldom used on either radar system.)

4-SA-15


Nomenclature

In line with Navy standard nomenclature, some of the controls mentioned above will be renamed. Consequently, it may be noted on some SA-2 radar systems that the name plates of the controls bear revised designations of the controls affected as listed below:

Original designation:           New Designation:
Range.   Range sel.
Operation:    
      IFF & Cal.   Markers and IFF
      Normal.   Operate.
      Cal Mas.   Markers.
      Cal. Rem.   Markers remote.
Bearing Markers Off.   Indicator lights off.
Sector Seep-Off.   Sector train--normal.
AVC Balance   Time constant.
Video Balance.   Balance.

TURNING ON AND OFF

Almost identical operational technique is required for the SA and SA-2 Radars. Thus the section below on operation of the SA-2 Radar can be applied equally well to the SA radar. It should be noted, however, that the method of turning on and off given below for the SA-2 radar differs somewhat from that given for the SA radar on page 4-SA-5.

Turning on

1. See that the following controls are in the proper position before turning on:

  1. Gain down (fully CCW).
  2. Intensity down (fully CCW).
  3. Slewing motor OFF.
  4. L.R. motor OFF.
  5. Plate voltage variac down (fully CCW).
  6. Transmitter power switch OFF.
  7. Emergency train in center position.
  8. PPI intensity down (fully CCW).
  9. PPI video gain down (cully CCW).
  10. Sector sweep switch OFF.
  11. True--relative switch on TRUE if ship's gyro system is operating properly, otherwise both should be on RELATIVE.

2. Snap on the main power switch, and adjust the line voltage control to read 115 voltes on the line voltage meter (P-4). Immediately turn on the PPI power, and leave it on until ready to work on this unit. Then snap on the transmitter power switch (P-4), and when light appears in the plate current meter, it is ready to be adjusted as follows. While watching the plate current meter, turn the plate voltage variac clockwise until the needle on the plate current meter makes one sharp dip, and then continue to move it clockwise until the meter reads from 5 to 7 milliamperes, or until a stop is reached. If the overload relay should trip while doing this, it may be necessary to lower the plate voltage, reset the relay in the transmitter (turn the emergency control switch on the transmitter OFF and then ON again), and continue operation using a slightly lower plate current. As a final check, make sure the line voltage still reads 115 volts.

Turning Off

1. Turn the PPI intensity and the video gain fully CCW.

2. Snap the sector sweep switch OFF.

3. Snap the PPI main power switch OFF.

4. Turn down the gain and the intensity on the "A" scope (fully CCW).

5. Turn the plate voltage variac down and the transmitter power switch off.

6. Turn off the main power switch.

CALIBRATION

1. Turn the Cal-oper IFF switch to position 1, and the Cal synch switch to position 3. This allows the marker oscillater to be calibrated as follows: Vary the focus control (Ad-7) until a sharp trace appears on the 2-inch scope. Then adjust the cal-osc control until a clearly defined, stationary pattern appears on the 2-inch scope. (Either a figure eight or a horizontal "V" is satisfactory.) This will insure that the markers are exactly 4,000 yards apart in range.

2. Next, turn the cal synch switch to position 2 and place the range selector switch in the position A. Set the range counter to read exactly 6,000 yards, and adjust cal min so the step is accurately aligned with the beginning of the second range marker. This adjustment is correct when the little peak just beyond the right hand end of the range mark is leveled up with the end of that (at the beginning of the second marker). See figure 4SA-3.

3. Adjust the range counters to read exactly 34,000 yards, and adjust cal max so that the range step is accurately aligned with the beginning of the ninth marker or the trailing edge of the eight marker.

4. Repeat steps 2 and 3 as many times as necessary until the stop reads correctly at both ends.

4-SA-16


In other words, make sure that when the range dial reads 6,000 yards, the range step is lined up with the 6,000-yard range marker; and when the range dial reads 34,000 yards, the range step is lined up with the 34,000-yard marker. When calibration is completed, switch the Cal-oper IFF switch to position 3.

Tuning the receiver

1. First set the antenna, osc., and R.F. controls to approximately correct setting by use of the technicians calibrate chart (Ad-16). Then increase the receiver gain until grass appears on the "A" scope. Pick a steady pip to tune on, and readjust the tuning controls for maximum height of pips. Repeat each adjustment at least twice. While working with the receiver unit, check to see that the "Anti-Jam" controls are secured properly: rej. control CW, rej. Bal. control CCW, vid. bal. CCW, and AVC bal. CW.

Final adjustments for the "A" scope

Turn the cal-oper IFF switch to position 4, and adjust the IFF gain until approximately one-eight inch of grass appears below the "A" scope time base. Throw the cal-oper IFF switch to position 3, switch to the "B" range scale, and adjust the range step as follows. Move the step in until the range counters read 40 miles, and adjust the horizontal centering control until this step falls exactly on the 4-mile range mark of the transparent range scale. Recheck to make sure there is a clear picture on the "A" scope.

If the screen of the "A" scope has no transparent range scale, adjust the horizontal centering control so that the time base falls at a convenient position on the scope.

Turning on PPI Scope

Snap the emergency train switch from the normal position to CW. Turn up the intensity control until there is a faint time base. Increase the video gain for a brighter picture, and adjust the focus control. Select any range desired for the PPI. If sector sweep is wanted, select the area desired and energize the sector sweep power by throwing the sector sweep switch (S-12) to the up position.

Miscellaneous adjustments

If lobe switching is to be used, turn the plate voltage control completely down (counterclockwise), turn the L.R. motor ON (either right or left), and wait one complete minute before again increasing the plate voltage. (This procedure should be followed except in emergencies when the plate voltage may be increased again after about 30 seconds delay.) Turn the lobing off switch to position 1 and adjust the lobe sep. control until the traces are separated suitably. While matching pips, read the bearing given by the white bug.

To make IFF adjustments, first turn on the IFF unit, and then switch the cal-oper-IFF switch to position 4. Adjust the IFF gain until a reasonable amount of grass appears below the time base, and then turn the cal-oper IFF switch back to position 3. Turn the cal-oper IFF switch to position 4 to challenge a target.

On the SA-2 a check on the pulsing rate can be made by putting the cal-oper IFF switch (S-5) in position 3 and the cal-synch switch (S-6) in position 2 and observing the picture on the 2-inch cathode ray tube. If the circle is broken, and a small neck protruding upward, the set is pulsing correctly. (Refer to fig. 4 SA-7.)

OPERATIONAL TECHNIQUES

Search procedures

The SA radars were designed primarily for long-range air search--an early warning of approaching aircraft. Its effectiveness depends not only on the material condition of the set, but also on the efficiency of the operator. The following search procedures are recommended for utilizing the SA radars to their maximum efficiency.

For normal tracking and search, the 80-mile range scales should be used. The operator should adjust the "A" scope for one half [inch] of grass so that echo signals of sufficient amplitude will reach the PPI scope. Watch the PPI for targets with an occasional search on the "A" scope. When a target first appears, report its presence in the following manner. On the first sweep, for example, report "contact 180, 45 miles." On the next sweep, throw the emergency antenna train switch to normal approximately 30° ahead of the reported bearing. This will allow the antenna to coast up to the correct bearing, and with a minimum of time, the operator can go to the "A" scope, challenge for IFF, and get the approximate composition of the contact. The operator should start the antenna rotating again and then finish his report. Example: "Contact is few bogeys, estimate 3 to 5 planes, closing." This procedure has been used very effectively. It enables the operator to search and also

4-SA-17


track many raids at once, with a minimum of time lost in challenging the various raids. Occasionally the operator can switch to the longer and shorter ranges on both scopes as a double check on any possible new contact that might appear. It is felt the above described system of operation should be the SA operator's basic search and tracking procedure.

In the event that the PPI unit fails, the following "A" scope search procedure is recommended. Adjust the "A" scope for one-fourth inch of grass, and use low-speed antenna rotation. When a signal is noticed,immediately stop the antenna and rotate it by hand until the echo pip is at is maximum height. Report the bearing from the orange bug, and read the range from the transparent scale on the scope, also challenging for IFF. Start the antenna rotating again and finish the report.

If a track on a reported plane is needed, the following procedure can be used. As the pip reaches a maximum height on the "A" scope, glance over quickly at the bearing dial and report the bearing indicated. This procedure, of course, will probably develop a bearing error, but with some practice, the operator's own time lag can be measured in degrees and deducted by him in his report. This system is known as reading target information "on the fly," and with practice can be developed efficiently. It should be remembered that it is desirable to keep the antenna rotating as much of the time as possible.

If there is reason to believe long range search of an area is needed, the "A" scope can be adjusted and the area searched manually by turning the antenna train knob. If continual long range search is desired, operate on low-speed antenna rotation. Bearings and ranges can be called in by using the "on the fly" method.

In searching over land it must be emphasized that target pips will be mixed with land pips. However, plane pips will bob up and down more rapidly than land pips; also the plane pips will move with respect to the land. The antenna should be operated manually, and a close watch kept on the receiver gain, so that when echoes from land masses become saturated, the gain can be reduced in order that the plane pip can be followed. The operator must remember to keep searching, taking only a minimum of time to check the planes over land. Use of the "Anti-Jam" controls facilitates, to some extent, tracking over land.

"Anti-Jam" Receiver

Essentially the "Anti-Jam" receiver provided for the SA and SA-2 radars is a superheterodyne receiver which contains special circuits to allow for its operation through various types of jamming or intentional interference.

The A-J receiver contains four controls designed expressly for the purpose of eliminating, or at least reducing, jamming. These four control are:

  1. Rej bal control.
  2. Rej control.
  3. Time const control
  4. Bal control.

Originally, the time const. control was called the AVC bal control, and the bal control was called vid bal control. In line with standard Navy nomenclature, the four controls will be discussed as named in the list above.

For normal operation the bal control should be in a clockwise position, the rej bal control counterclockwise, the rej control clockwise, and the time const. counterclockwise.

Briefly, the rej bal control and the rej control work together to eliminate an undesired signal from being passed through the receiver. They constitute a wave trap for a particular undesired signal if they are adjusted correctly. They are designed to be used chiefly against an interfering continuous wave signal.

The time const. control varies the speed of the automatic volume control of the receiver. This control acts so as to automatically cut down the strength of a large signal more than it cuts down a small signal coming into the receiver. The faster its action, the greater is its differentiation between strong and weak signals. Position three is fast AVC action, position two is medium AVC action, and position one is slow AVC action.

The bal control is designed chiefly to eliminate railings, or at least to keep them at no larger amplitude than the echo.

To use the A-J controls intelligently, it is first necessary to decide what type of signal is causing the jamming. This is done by interpreting the form of the pattern appearing on the "A" scope screen, which then serves as a guide for choosing a possible adjustment procedure for the interference eliminating controls. Supposedly the A-J controls are most effective against interference due

4-SA-18


to CW (Continuous wave) signals, frequency modulated signals, amplitude modulated signals, and pulse modulated signals (railings). However, irrespective of the type of interference, it will be impossible to obtain as good a pattern as during normal operation. The echo may be difficult to distinguish, but will probably appear as a stationary line or break through the more confused and generally moving interference background. Even with optimum setting of the anti-jam controls the pattern is seldom fully restored to its normal appearance, but it will be cleared up enough to permit effective echo observations to be made. The antijam controls are to be operated in the manner set forth below. It should be noted that the rej control, which is normally in the clockwise position, and rej bal control, which is in the "zero" position for normal reception, should be operated only if all other controls fail to reduce interference satisfactorily.

Indication of corrective adjustments for various types of interference is given below. It should be emphasized that in almost all cases, only practice will teach the operator how to best cope with the various cases encountered.

A. Unmodulated CW interferences.--This type of interference produces a more or less complete shrinkage of the height of the pattern, which may go so far as to reduce the entire pattern to a single horizontal trace when the gain control is set for normal operation. In order to counteract this effect, it is best to readjust the gain control and leave all other controls in their respective normal positions. Then adjust the rej and rej bal controls alternately and in small steps until improvement of the signal is noted. The three positions of the time const. switch should also be tried, and the best one selected.

B. Modulated interference.--Depending on the setting of the range sel switch, frequency or amplitude modulated interference causes the entire pattern either to wobble bodily or flutter up and down, or to assume the shape of a wavy line moving from right to left or left to right across the screen. Since the effectiveness of the various anti-jam controls will depend oto some extent on the modulation frequency of the interfering signal, these controls should be operated in a logical sequence, as described below:

1. With all controls in their normal positions, readjust the gain control until the signal is improved or restored.

2. If the adjustment of the gain control is not effective, place this control in its usual position for normal reception. Then adjust the rej and rej bal controls alternately and in small steps until improvement of the signal is obtained.

3. The next step is to see if adjustment of the gain control will improve the signal.

4. Finally, try the three positions of the time const. switch and select the one giving the most readable pattern. During the entire procedure, the bal control should be kept in its maximum counterclockwise position.

C. Railings (or pulsed) interference.--This type of interference generally causes a number of vertical lines to appear on the screen, superimposed on the normal pattern and extending high above the radar echo pip. To combat this type of interference, the operator should first try the procedure outlined under Modulated Interference. If this fails, he should proceed as follows:

  1. Set the time const. switch to position 3 (fast AVC).

  2. Turn the bal control clockwise to a point where the railings will be displaced toward the horizontal base line or even below this, while leaving the echo pips above this line.

  3. Vary the gain control to obtain optimum operation.

  4. Repeat steps (2) and (3) with the time const. switch in positions 2 and in position 1, and select the best setting combination.

D. Nonintentional interference.--In case of nonintentional interference, such as may be caused by communication or electrical equipment or by other radars, the [procedure described in varying the gain and time const. controls in the section on Unmodulated CW Interference will generally be found satisfactory.

4-SA-19


If the type of jamming cannot be determined, the operator's problem will still be one of intelligently experimenting with the controls so as to counteract the jamming most effectively. Experience is the best guarantee to success!

PERFORMANCE

Maximum reliable range (Antenna 89 feet):           Miles
      Large surface craft           20
  Medium surface craft   10
  Large planes   40
  Small planes   20
  Low-flying planes   10-15
  Land (1,500 feet or higher)   90-200
  Yards
Minimum range: Ships and Planes   1,600
Range accuracy:    
  40,000 yard scale   ±150
  Miles
  80-mile scale   ±1
  400-mile scale   ±2
Bearing accuracy:   Degrees
  with lobing   ±1
  Regular search   ±3-5

TROUBLES

Troubles in the SA-2 system are essentially the same as those listed for the SA on page 4 SA-10.

Another frequent source of trouble is found in reduced sensitivity of the receiver tubes. Those which are the worst offenders are the first RF amplifier, V201, and the converter, V203.

4-SA-20


Part 4.
SL RADAR

CONTROLS 4-SL-2
  Power controls 4-SL-2
  Selector switches 4-SL-2
  Adjustment controls 4-SL-3
   
TURNING ON AND OFF 4-SL-3
  Turning on 4-SL-3
  Turning off 4-SL-4
   
CALIBRATION 4-SL-4
   
OPERATIONAL TECHNIQUE 4-SL-4
  Preliminary operational adjustments 4-SL-4
  Tuning the receiver 4-SL-4
  Recommended operation 4-SL-4
        Normal operation

        Station keeping

        Submarine contact

        Surface contact

  Clouds jamming 4-SL-5
   
PERFORMANCE 4-SL-5
  Maximum reliable range 4-SL-5
  Minimum range 4-SL-6
  Range accuracy 4-SL-6
  Bearing accuracy 4-SL-6
   
TROUBLES 4-SL-6

4-SL-1


CONTROLS

Power controls.

P-1. Power: controls all power to the set (except heater power) . Power is off when this switch is snapped to the left (or to the right on some models).

P-2. Load voltage meter: indicates the voltage applied to the set.

P-3. Line voltage adjustment; an adjustment of the load voltage (the transtat). (Adjustment governs reading of load voltage meter.)

P-4. High voltage: this switch turns the high voltage on or off: ON to the right. OFF to the left.

P-5. Mag. or conv. current: current: this meter indicates either the magnetron current or the converter current, depending on position of the ammeter-mag. conv. switch.

P-6. High voltage adjustment: this controls the amount of voltage applied to the transmitter. (It is called the variac. Setting of this control governs reading of the ammeter when in mag. position.)

P-7. Drive motor: this switch controls power to the antenna drive motor and to the indicator motor rotating the sweep (in synchronism with the antenna) When the switch is snapped to the right, the antenna and the deflection coil (around the PPI) rotate et 18 rpm.

Selector switches.

S-1. Range: a three-position switch, permitting use of one of the three range scales provided: 5 miles, 25 miles, or 60 miles.

S-2. Ammeter-mag. conv.: a switch which permits use of the same meter to indicate either magnetron current or converter current.

S-3. Warning: a switch used to operate a warning bell or buzzer at some remote location, to attract attention to the remote PPI scope.

S-4. IFF-off, on: this switch applies power to the interrogator (if one is attached).

S-5. Compass-on, off: (Under indicator panel -below cony, current meter) in the ON position, this switch permits connecting the gyro compass to the radar so that true bearings will be indicated, regardless of the changes in ship's heading. If relative bearings are desired (or necessary, due to failure of the gyro compass), this switch can be turned to the OFF position, disconnecting the gyro compass.

Plan view drawing of indicator panel.
Figure 4 SL-1. Indicator panel.

4-SL-2


Adjustment controls.

A-2. Brightness: a screwdriver adjustment of the over-all brilliance of the trace on the screen.

A-3. Focus: a screwdriver adjustment to bring the sweep into a sharp, clear, and even line.

A-4. Horizontal centering: a screwdriver adjustment shifting the complete picture on the scope to the right or left.

A-5. Vertical centering: a screwdriver adjustment shifting the complete picture on the scope up or down.

Line drawing of indicator modulator assembly.
Figure 4 SL-2. Indicator modulator assembly.

A-6. Receiver gain: this is the volume control of the receiver, and as such, it controls the brightness of the echoes on the scope, and in addition, the brightness of the time base.

A-7. Receiver tune: this permits accurate tuning of the receiver to the transmitter frequency so that echoes may be received.

A-8. Scale light: permits the adjustment of the brightness of the dial lights on the meters and behind the amber shield over the scope.

A-9. Azimuth mark, increase: controls the brightness of the azimuth mark (indicates relative bearing of the antenna at 000°. when properly adjusted).

A-10. Range mark: controls the brightness of the range mark which should appear at the outer edge of the scope.

A-11. Retard: indicator, antenna: these push button controls permit setting the azimuth mark to any desired direction on the screen (to 000° when relative bearings are to be read, and to the ships heading when reading true bearing).

The indicator button stops the indicator while the antenna continues rotating, and consequently makes the azimuth mark move counterclockwise.

The antenna button retards the antenna without stopping the indicator, and this makes the azimuth mark move clockwise.

A-12. IFF gain: controls the strength of IFF response applied to the SL screen.

TURNING ON AND OFF

Turning on.

Check controls for normal positions:

  1. Rec. gain-CCW.
  2. Azimuth mark-CCW.
  3. Drive motor-off.
  4. High voltage switch-off.
  5. High voltage adjustment-full CCW.

Power adjustments:

  1. Turn power switch ON. The dial lights should come on and a motor should begin whirring inside the modulator unit. The scale light control should be adjusted to suit the operator.

  2. Adjust the line voltage adjustment until load voltage meter reads 115 volts.

  3. Snap the high voltage switch ON and wait for a loud whistling tone (the 800-cycle note). A time delay relay, requiring about one minute to operate, must close before the 800-cycle note will start. As soon as the whistling starts, check the ammeter reading with the ammeter switch in mag. position. if reading is less than 10 milliamperes, turn off the set and call the technician; if above 10 milliamperes, readjust line voltage control until load voltage meter reads 115 volts. Adjust high voltage control until the magnetron current is 15 to 19 milliamperes.

  4. Turn drive motor on and listen for grinding of gears.

4-SL-3


Turning off.

  1. Turn rec. gain fully CCW.
  2. Turn azimuth mark fully CW.
  3. Turn high voltage adjustment CCW.
  4. Turn off high voltage switch.
  5. Turn off drive motor.
  6. Turn power switch off.

CALIBRATION

Calibration should he checked by turning the range mark control fully clockwise. A bright spot will then rotate at the end of the trace line, around the edge of the PPI screen. If the circle drawn by this spot lies below the outer circle on the plastic scale, the calibration is correct. If the calibration is off, adjust the screwdriver adjustment, sweep length, which is underneath the indicator cover, until it conforms with the correct calibration.

OPERATIONAL TECHNIQUE

Preliminary operational adjustments.

Turn the azimuth mark increase clockwise, and set the position of the azimuth mark by operating the retard- indicator, antenna. If relative bearings are wanted, set the azimuth mark to 000°; if true bearings are desired, set it to indicate the ship's heading at that moment. (Compass switch must be in compass position if true bearings are to be read.) Turn the azimuth mark low, but visible.

With the rec. gain turned completely CCW, adjust the screwdriver control on brilliance until trace barely appears. Increase rec. gain slightly until trace appears clearly, then adjust focus control until the trace is a sharp, distinct line. Then adjust the horizontal and vertical centering controls until the trace starts directly beneath the center of the amber shield over the screen.

Tuning the receiver.

Set the range selector switch as follows:

  1. If at sea, with no objects in the vicinity, or with objects within five miles, set on 5-mile scale.

  2. If at sea, and the nearest object is beyond 5-mile range, but still within radar range, set on 25-mile scale.

  3. When within 25 miles of land, use 25-mile scale.

Tune the receiver, adjusting for maximum brightness of the targets. The receiver gain should be adjusted while doing this to keep the brightness low. If no targets are visible, tuning may be done by adjusting rec. tune for maximum sea-return. In case the sea is very calm, and you can not even get a satisfactory echo from your own ship's wake, it is possible to tune the receiver approximately by watching the converter current. This method is to be used as a last resort when no echoes of any kind can be seen.

Set the mag.-conv. switch in the cony. position and adjust rec. tune control for maximum meter reading, from .4 to .8 milliamperes. Be sure to switch mag.-conv. back to mag., the proper position during operation. (Do not attempt to tune the receiver during the 15- to 30-minute warm-up period after turning on the equipment.)

Adjust receiver gain until "snow" appears in the background of the screen. This should be adjusted for the best target indications on tile PPI scope. If no targets are in the vicinity, adjust for noticeable amount of "snow."

Recommended operation.

The operator should check the tuning of the SL on taking over the watch. Tuning should not be attempted unless targets are available, or sea-return is present. Tuning is done by adjusting receiver tune control for maximum intensity.

Normal operation: use 25-mile scale primarily, with gain set so that background noise ("snow") is visible, but not bright enough to obscure indications. Search on the 25-mile scale for about four minutes, then search for about 30 seconds on the 60-mile scale, readjusting receiver gain slightly, if necessary, and paying particular attention to the longer ranges. After about 30 seconds on the 60-mile scale, switch to the 5-mile scale, and readjust the receiver gain if necessary. This is the scale on which the operator will detect small objects, close aboard, such as submarines awash. Report all contacts.

Station keeping: if radar information is needed for station keeping, the receiver gain should be reduced sufficiently to show ships in formation clearly. Do this immediately after completing the 30-second search on the 5-mile scale, then switch to the 25-mile scale, and repeat the cycle.

Submarine contact: after sound contact has been made with a submarine, or when such contact is probable, you should operate primarily on the 5-mile scale, with the gain sufficient to bring out some background noise. (Remember, unless the gain is up, small targets will not be seen.) Look for a short,

4-SL-4


faint arc or spot, which recurs at the same spot for two or more successive rotations of the antenna. (Snow splotches will not repeatedly appear in the same place, while indications from targets will.) Every three minutes, reduce the gain and search for pips near the center. These might have been masked by the sea-return while the gain was high. Search in this way for about 30 seconds.

Surface contact: operation after contact with the surface target is made, including surfaced submarines or submarines awash.

The recorder shall call "stand by" five seconds before "mark" is called. If a single target is being tracked, "mark" should be called every minute (unless the 60-mile scale is being used, then "marks" are given every two minutes). If two targets are being tracked, one should be called on the minute, and the other on the half-minute, thus each target is "marked" at one minute intervals. Operators will call off bearing and range of target when "mark" is called.

If target is beyond the 5-mire range, but nearer than 25 miles, normal search routine should be followed, except for the reporting of targets every minute. A "mark" might be missed while searching on the 5-mile scale, but this is not serious, If "mark" is called while on the 60-mile scale, the operator may call the bearing and ranges from that scale. This point however, should not be used in determining course or speed.

If the target is within a range of 5 miles, search should be continued on the 5-mile scale primarily, switching to the 25-mile and 60-mile scales for 30 seconds each after 4 minutes on the 5-mile scale. Possibility of contact with other units must not be overlooked.

If the target is first detected at a range greater than 25 miles, the 60-mile scale should be used primarily, until the target has closed to within 25 miles, Search for four minutes on the 60-mile scale, then switch to the 25-mile scale, for about 30 seconds, and the 5-mile scale for about 30 seconds. Recorder should call "stand by," followed by "mark," every too minutes while reading from the 60-mile scale.

Clouds: echoes from clouds are often seen on the radar screen. Operators usually can recognize these as such, because of their distinctive appearance. Occasionally, however, this distinction cannot he made, and the cloud echo will resemble a ship echo closely. The operator should report them in either case, giving all information he can.

Jamming.

Jamming is deliberate interference, caused by the enemy, which limits the effectiveness of your radar; or it is interference produced by our ships to limit the effectiveness of enemy radars. There are several types of jamming, but all are characterized by some strong form of interference pattern on the indicator. These interfering signals are directional in nature, and the bearing or bearings from which they come, can be easily found by looking down the center of the lamming pattern. The jammer does make it difficult or impossible to read range, but effective jamming is not easy for the enemy to accomplish, and it is apt to disappear momentarily from time to time. Learn to expect it, and be prepared to follow the best course of action when the time comes. Do not mistake interference created aboard your own ship, or trouble in the radar set for jamming, the real thing will be directional, and its true bearing will not change immediately when your own ship changes course.

As you approach the jammer, the radar echoes from the jamming ship (if it is sea-borne) will increase in strength more rapidly than the jamming signal, and you stand a good chance of being able to read range through the interference. See part 3, Defense Against Jamming and Deception.

When jamming occurs:

  1. Get the bearing and report it.

  2. Keep operating the set and try to read the ranges through the interference. Try various settings of gain control. There is a chance the jamming will stop long enough for you to get range.

  3. Keep reporting its bearing periodically.

  4. Be ready to turn on a radar which operates on a different frequency band if ordered, provided that you have one,

  5. Draw a picture of the jamming pattern while it is fresh in your memory, and send it to the Bureau of Ships without delay.

PERFORMANCE

Maximum reliable range.

The higher the antenna, the greater the maximum range; for this reason, performance figures are given on the following page for several antenna heights.

4-SL-5


Target                     Maximum Reliable Range in Miles
    53 feet 69 feet 85 feet
BC, CV, Large auxiliary   13-15 19-21 21-23
CA, CL, Medium auxiliary   12-14 16-18 17-19
DD, DE, DM, AV, CG, etc   10-12 11-13 13-15
Submarine on surface   3-5 9-11 6-8
Submarine periscope   2 2 ?
Buoys   ? 3-4 3-4
Large aircraft below 3,000 feet   14-20 14-20 14-20
Small aircraft below 3,000 feet   9-13 9-13 9-13

Minimum range.

The average minimum range for ship targets is about 500 yards (1/4 mile), and on aircraft targets about 700-1,000 yards. These figures will be somewhat higher when sea-return is strong.

Range accuracy.

The figures for the possible error of the set, plus the probable error of estimation are approximately:
5-mile scale ± 500 yards or ± 1/4 mile  
25-mile scale ± 1,000 yards or ± 1/2 mile  
60-mile scale ± 2,500 yards or ± 1¼ miles

Bearing accuracy.

Approximately ± 2° - 3°

TROUBLES

Inferior performance of the SL radar can be recognized by the operator paying close attention to the indicator screen, the mag., cony. current meter, and by listening to the 800-cycle note of the spark gap keyer.

If the set is not tuned properly, targets will not appear on the screen with their usual intensity. Consequently, targets may approach your Ship considerably nearer than usual before they are first detected. Sea-return may he dimmer, and more reduced in area than you would expect, considering the condition of the sea. In general, echoes look normal except that they appear weaker than usual or reduced in size. You should try retuning the receiver whenever you observe this condition, but if that does not help, you should notify the technician.

Sometimes, echoes will look scalloped, and the "snow" will appear in fan-like streaks radiating straight out from the center of the screen. When this occurs, it is an indication that the set is being keyed improperly; the technician should cheek the spark wheel electrodes. This trouble will also he revealed by a spitting noise, or an unsteady whistling from the modulator unit.

If the modulator whistles normally and the converter current is normal, but the magnetron current reads zero, either the pulse cable or the pulse transformer is faulty, and the technician should be notified immediately. No echoes will appear on the scope until the failure is corrected. When the bright spot of the transmitted pulse appears on the scope along with some "snow," but no echoes appear, check both magnetron current and converter current for normal readings. If they are working properly, a receiver rube is probably faulty; ask the technician to replace it.

If the equipment is set to indicate true bearings, and the azimuth mark does not change bearing when the ship changes course, the gyro compass may not be functioning. This fault may also be indicated by drifting of the azimuth mark and target indications on the screen. If the fault is not with the gyro, the trouble may arise from a slipping clutch. If the gyro compass is not functioning, you should request permission to switch to relative bearing, and do so by snapping the control switch (compass on-off), beneath the indicator panel, to OFF, and by setting the azimuth mark to 000°.

4-SL-6


Part 4.
SL-1 RADAR

CONTROLS
  Power controls
  Adjustment controls
TURNING ON AND OFF
  Preliminary checks
  Turning on
  Initial adjustments
  Synchronizing the antenna and deflection coils
  Turning off
CALIBRATION
OPERATIONAL TECHNIQUES
  Tuning the receiver
  Recommended operation
    Search procedure
    Station keeping
    Submarine contacts
    Surface contacts
    Clouds
TROUBLES
PERFORMANCE
  Maximum reliable range
  Characteristics

Figure 4 SL-3. Indicator panel and range unit.
Figure 4 SL-3. Indicator panel and range unit.

CONTROLS

Power controls

P-1. Main power switch: Controls all power to the set (except heater power). The power is off when switch is snapped to the left.

P-2. Load voltage, set to 115-volt meter: Indicates the voltage applied to the set.

P-3. Load voltage control: Adjusts the voltage applied to the set. It should be adjusted so that load voltage meter (P-2) reads 115 volts.

P-4. High voltage: wait 60 sec: Switches on and off the high voltage. The right-hand switch is used to apply the high voltage; the left-hand switch to remove it. High voltage should not be applied to gear until 60 seconds after turning on main power switch (P-1).

P-5. Magnetron-Converter current meter: Indicates either the magnetron current or the converter current, depending on the position of magnetron-converter current switch (S-2).

P-6. Tube hours meter: An electric clock indicating the total number of hours the set has been in operation.

P-7. Drive motors switch: Controls power to the antenna drive motor and to the indicator motor which rotates the sweep synchronism with the antenna. When the switch is snapped to the

4-SL-7


right, the antenna and the deflection coils around the PPI rotate at 18 rpm.

Figure 4 SL-4. Indicator modulator assembly with range unit.
Figure 4 SL-4. Indicator modulator assembly with range unit.

Selector Switches

S-1. Range select switch: A three position switch permitting use of one of the three range scales provided--4 miles, 20 miles, or 60 miles. In the 4-mile position, a 2 mile sweep is available when switch S-5 is in ON position.

S-2. Magnetron-converter current switch: Permits use of the same meter (P-5) to indicate either magnetron current or converter current.

S-3. IFF switch: Turns on the IFF interrogator.

S-4. Bearing switch: In TRU position, connects the gyro compass to the radar so that true bearings will be indicated, regardless of the changes in ship's heading. If relative bearings are desired (or necessary, due to failure of the gyro compass), this switch can be turned to REL position, disconnecting gyro compass.

S-5. This switch makes a 2 mile sweep available when range select switch (S-1) is in the 4 mile position.

S-6. Dial light switch (on range unit): Turns on and off the lamp which illuminates the range dial.

S-7. AFC switch: Controls AFC (automatic frequency control) circuit. In the ON position, the AFC circuit automatically keeps the receiver in tune, while in the OFF position the receiver must be tuned manually using the rec tune control (A-6).

S-8. Tell tale switch: Throws on and off the telltale mark on the PPI. With the bearing switch (S-4) in the TRU position, the mark shows own ship's course. With the bearing switch in REL position, the mark will be at 000 degrees.

S-9. Measure-calibrate switch: Determines whether the electronic range ring or the calibrating ring used in calibrating the Range Unit will appear on the PPI.

S-10. Remote bearing switch: Should be in the TRU position if true bearings are desired at a remote repeater, and in REL if relative bearings are desired.

Adjustment Controls

A-1. Intensity: A screwdriver adjustment controlling the overall brilliance of the trace on the PPI screen.

A-2. Focus control: A screwdriver adjustment used to bring the sweep into a sharp, clear line.

A-3 and A-4. H--centering--V: Screwdriver centering adjustments used to shift the complete picture to the right or left, up or down, respectively.

A-5. Rec gain; The volume control of the receiver. It controls the brightness of the echoes on the scope.

A-6. Rec tune: Permits manual tuning of the local oscillator in the receiver.

A-7. Dial light control: Permits adjustment of the brightness of the dial lights on the meters and behind the PPI cursor.

A-8. Bearing mark: Controls the brightness of the azimuth mark which flashes at 000 degrees relative when the antenna and the PPI sweep are synchronized.

A-9. Retard: indicator, antenna; Push button controls which permit setting the azimuth mark to any desired bearing on the screen (to 000 degrees when relative bearings are to be read, and to the ship's heading when reading true bearings). The indicator button stops the indicator trace while the antenna continues to rotate and, consequently, makes the azimuth mark move counterclockwise. The antenna button retards the antenna without stopping the indicator, and, hence, the azimuth mark moves clockwise.

A-10. IFF gain: Controls the strength of the IFF responses applied to the SL-1 scope.

4-SL-8


A-11. A screwdriver adjustment which controls calibration of the 2 miles sweep.

A-12. Range yards crank: Moves the range dial on the Range Unit as well as the electronic rang ring appearing on the PPI.

A-13. Range-calibrate control: Permits calibration of the Range Unit.

A-14. Intensity control: Varies the intensity of the electronic range ring on the PPI.

A-15. Bearing cursor: rotates the cursor mounted above the PPI scope.

TURNING ON AND OFF

Preliminary Checks

Before applying power, check the following:

1. Turn the rec. gain (A-5) counterclockwise.

2. Turn the drive motors switch (P-7) to OFF position.

3. See that the bearing switch(S-4) is in the proper position (TRU if gyro power is available).

4. Turn the switch (S-5) to OFF.

5. Turn the dial light (S-6) to ON.

6. Turn the AFC switch (S-7) to ON.

7. Turn the telltale switch (S-8) to ON.

Turning On

1. Turn the main power switch (P-1) to ON position.

2. Wait one minute after turning the main power (P-1) to ON before operating the high voltage switch (P-4) momentarily and releasing it.

3. During the one minute wait:

  1. Switch the range select (S-1) to the proper setting for initial adjustment (20-mile scale at sea, 4-mile scale in port).

  2. Adjust the load voltage control (P-3) so that load voltage meter (P-2) reads 115 volts.

    Rotate the bearing cursor (A-15) handwheel until the range of the first inscribed range circle on the cursor is read on the range dial (in preparation for centering).

4. After the one minute delay, turn the high voltage switch (P-4) to the ON position momentarily. A relay will operate and high voltage will be applied to the modulator. A 800-cycle tone will be heard.

5. Check the reading of the magnetron-converter current meter (P-5). If the magnetron current does not show between 16 and 21 ma., notify the technician.

6. Again adjust the load voltage control (P-3) for 1155 voltes on meter (P-2).

7. Turn the drive motors switch (P-7) to the ON position.

Initial Adjustment

1. Adjust the intensity screwdriver control (A-1) so that sweep is just visible on the PPI.

2. Adjust the range ring intensity and the focus (screwdriver controls A-14 and A-2) to give best appearance of the electronic range ring on scope.

3. Turn the H and V center control (A-3 and A-4) until the sweep is accurately centered by making the range ring coincide with the first inscribed range circle on the cursor, or by placing the small circle at the inner end of the sweep in the center of the screen.

Adjust the rec. gain (A-5) until some "snow": appears on the scope.

5. Turn the IFF gain (A-10) full clockwise. this can later be adjusted to suit the operator.

Synchronizing the Antenna and Deflection Coil Motors

1. Turn the bearing mark control (A-8) toward INCREASE until the azimuth and telltale marks are visible on the PPI. The telltale switch (S-8) should be in the ON position.

2. With the bearing switch (S-4) in the TRU position, check to see that the telltale mark on the scope indicates own ship's course.

3. Operate the retard: indicator, antenna push buttons (A-9) as required until the azimuth mark and telltale mark coincide to form a single radial line.

4. Adjust the bearing mark control (A-8) until the coincident telltale and azimuth marks are just visible.

Turning Off

1. Turn the rec. gain (A-5) counterclockwise.

2. Throw the drive motors switch (P-7) to the OFF position.

3. Operate the left-hand high voltage switch (P-4) momentarily and then release it. This will remove the high voltage from the modulator.

4. Turn the main power switch (P-1) to the OFF position.

CALIBRATION

The following procedure is used to adjust the zero setting of the range unit. The sweep speed will not be adjusted by the operator.

4-SL-9


1. Operate the range select switch (S-1) to the 4-mile scale.

2. Turn the range yards crank (A-12) until the range dial reads 400 yards (unless the notice on the range dial window reads "CALIBRATE AT 500 YARDS", in which case adjust the crank for 500 yards).

3. Operate the measure-calibrate switch (S-9) alternately to the MEASURE and CALIBRATE positions. If there is no change in the radius of the electronic range ring, the zero setting of the range unit is correct.

4. If a change in radius of the ring is noted, loosing the locking nut under the range-calibrate control (A-13), and adjust this control until no change of radius is obtained when measure-calibrate (S-9) is switched from one position to the other.

5. Lock the rang-calibrate control (A-13) by tightening the locking nut under the knob. The range unit has now been calibrated.

6. Throw switch (S-5) to the ON position.

7. Turn the range yards cranks (A-12) until the range dial reads 2,000 yards.

8. Adjust the screwdriver control (A-11) until the electronic range ring lies directly under the second inscribed marker on the cursor. The 2-mile sweep is now calibrated.

OPERATIONAL TECHNIQUES

Tuning the Receiver

1. Set the range select switch (S-1) as follows:

  1. If at sea, with no targets in the vicinity, or with targets within 4 miles, set on the 4-mile scale.

  2. If at sea, and the nearest target is beyond 4 miles, but within radar range, set on the 20-mile scale.

  3. When within 20 miles of land, use the 20-miles scale.

2. Turn the AFC switch (S-7) to the OFF position.

3. Adjust the rec. tune control (A-6) for maximum brilliance of targets. The rec. gain (A-5) should then be adjusted while doing this to keep the intensity low in order to prevent the screen from becoming damaged by too bright a spot. If no targets are available, tune for maximum sea return. If the sea return is not strong enough, operate the magnetron-converter current switch (S-2) to the converter position and adjust the rec. tune (A-6) for maximum current reading on the megnetron-converter meter (P-5). This last method will only give fair results, and should be used as a last resort.

4. Observe the scope with the AFC switch (S-7) turned to its OFF and ON positions alternately. (This should be done only after the gear has been in operation for over 15 minutes to allow time for the AFC circuit to warm up sufficiently.)

5. If echoes are stronger with the AFC switch (S-7) turned OFF, the AFC circuit requires readjustment by the technician, and the switch should be left in the OFF position. If there is no change in strength of echoes as the switch is thrown from one position to the other, operate with the AFC switch (S-7) in ON position.

6. Operate the magnetron-converter switch (S-2) to the Converter position and check the reading of magnetron-converter current meter (P-5). If should read between 5 and 10 scale divisions (0.5 to 1.0 ma.).

7. Adjust the rec. gain (A-5) for noticeable "snow" on scope. Note that the tuning of the SL-1 should be checked once every watch regardless of whether the AFC switch (S-7) is in the ON or OFF position.

Recommended Operation

When relieving the watch, the operator should check the following: Intensity, focus, centering of trace, azimuth and telltale mark alignment, calibration, tuning, and meter readings. Tuning should not be attempted unless targets are available or sea return is present. Check to see if the AFC circuit is operating properly by comparing echoes on the scope with the AFC switch in the ON and OFF positions.

Search Procedure: Use the 20-mile scale primarily, with a normal amount of gain--not too bright to obscure indications nor too low to prevent small echoes from appearing on the scope. Search for 3 minutes on the 20-mile scale, 1 minute on the 60-mile scale, and 1 minute on the 4-mile scale. During the 4-mile search, check the 2-mile sweep for three or four revolutions of the antenna. The gain setting must be changed slightly when switching from one scale to another; it should always be lowered when switching to the 4-mile scale. It is possible to detect such small contacts as PT boats and submarines on the 2- and 4-mile sweeps.

4-SL-10


Station Keeping: IF radar information is needed for station keeping, the 4-mile scale should be used unless operating with a large convoy where the guide ship is more than 4 miles distant. When using the 4-mile scale, the gain should be reduced sufficiently to show ships in formation clearly and to cut out the effect of side lobes.

Clouds: Echoes from clouds are very common on the radar screen. Operators can usually recognize clouds by their hazy and distorted appearance. However, on the 60-mile scale especially, clouds may appear as sharp and well-defined echoes and can be mistaken for ship contacts. The operator should report all contacts, even if he is sure that they are clouds, giving all the information he can.

Jamming

See page 4-SL-5.

TROUBLES

See page 4-SL-6.

PERFORMANCE

Maximum Reliable Ranges

The higher the antenna, the greater the maximum range; for this reason, performance figures are given below for several antenna heights.

Submarine Contacts: See pages 4-SL-4 and 4-SL-5.

Surface Contacts: When a surface contact is first detected, it should be challenged for IFF and reported as either "skunk" or "friendly" together with information as to bearing, range, and composition. Composition is determined by the size and number of indications, and by the range at which the contact si first picked up. After the initial contact report is made, the recorder will give a 5-second "stand-by" and "mark" every minute (unless the 60-mile scale is being used when "marks" will be given every 2 minutes). Ranges will be determined by aligning thew electronic range ring with the inner edge of the indication, unless ranges are greater than 20 miles, in which case they must be estimated using the inscribed circles on the cursor as a guide. If two or more targets are being tracked, they should be reported in order after each "mark." In each report, the operator will give the destination of the contact, the bearing, range, and additional information on target movement (opening, closing, crossing, holding).

If the target is beyond 4 miles but inside 20 miles, normal search routine should be followed. If the operator is searching on a different scale when the "stand-by" is called, he must switch scales and report the contact as soon as possible after the "mark."

If the target is within a range of 4 miles, search should be performed primarily on the 4-mile scale, switching to the 20-mile and 60-mile scales for 30 seconds each, every 3 minutes. Possibility of the appearance of other contacts must not be overlooked.

If the target is first detected at a range greater than 20 miles, the 60-mile scale should be used primarily until the target has closed to within 20 miles. Search fo 3 minutes on the 60-mile scale, then switch to the 20-mile and 4-mile scales for 30 seconds each. The recorder should call "stand-by" followed by "mark" every 2 minutes while the 60-mile scale is in use.

Target Maximum reliable range
in miles
53 feet 69 feet 85 feet
BB, CV, large auxiliary 13-15 19-21 21-23
CA, CL, medium auxiliary 12-14 16-18 17-19
DD, DE, DM, AV, CG, etc. 10-12 11-13 13-15
Surfaced submarine 3-5 6-8 9-11
Submarine periscope 2 2 ---
Buoys --- 3-4 3-4
Large aircraft below 3,000 feet 14-20 14-20 14-20
Small aircraft below 3,000 feet 9-13 9-13 9-13

Characteristics

4-SL-11


Part 4.
SO RADAR

CONTROLS 4-SO-2
 
TURNING ON AND OFF 4-SO-3
  Turning on 4-SO-3
  Turning off 4-SO-3
  Adjusting the echo box 4-SO-3
 
OPERATIONAL TECHNIQUE 4-SO-4
  Reading ranges 4-SO-4
  Reading bearings 4-SO-4
  Long and short range search 4-SO-4
  False contacts and how they look PPI interpretation 4-SO-5
  Special use of SO Radar by PT's 4-SO-6
  Piloting by radar 4-SO-6
  Jamming 4-SO-7
 
PERFORMANCE 4-SO-7
  Maximum reliable rang 4-SO-7
  Minimum range 4-SO-7
  Range accuracy 4-SO-7
  Bearing accuracy 4-SO-7
 
TROUBLES 4-SO-7

4-SO-1


CONTROLS
  1. Off-on: this switch controls line voltage to the motor starting relays, blower, protective solenoid, and synchro phasing relay circuit. This switch is not used on the SO-1 and SO-2 radars. A separate bulkhead switch (18) is mounted near the plan position indicator to be used instead of 1.

  2. N E: this is a normal-emergency switch which will be in the N or normal position during ordinary operation. There is a protective thermostat in the transmitter unit, which will turn the transmitter off if its temperature gets high enough to cause possible damage. If this should happen at a time when the radar must be used in spite of possible damage to the equipment, it can be started again by keeping the start button (4) pressed while turning the N E switch (2) to E, the emergency position. If the stop button (4) or the off-on switch (1) or the bulkhead stop button (18 used with SO-1, SO-2, SO-8) should be operated, the set will be turned off and high voltage can not be applied again until the N E switch (2) is returned to N, and the procedure for emergency operation described above is repeated.

  3. Pilot: adjusts the illumination of the bearing scale around the PPI tube (9).

  4. Start stop: controls the application of high voltage to the transmitter. (Do not confuse this with the bulkhead start stop switch used with SO-1, SO-2, SO-8.)

  5. Humidity indicator: when this becomes pink, the technician knows that the dehydrators are saturated with moisture.

  6. S W L: a screw driver control of sweep length. Sweep length may be varied to show a minimum of three range circles, and a maximum of six range circles.

  7. Range selector switch: the scales are 5, 20, and 75 nautical miles on the SO and SO-A, with 1, 4, and 15-mile intervals between range circles on the respective scales, The SO-1, SO-2, SO-7, and SO-8 have range scales of 4, 20 and 80 nautical miles, with 1 mile between the circles on the 4-mile range, 5 miles between the circles on the 20-mile range, and 20 miles between the circles on the 80-mile range.

  8. INT: this is the PPT intensity control for adjusting the brightness of the sweep and the range circles.

  9. The PPI (plan position indicator) tube.

  10. The Cursor: by means of this the relative bearings of contacts are read.

  11. CCW off CW: this is the antenna rotation toggle switch. When in the CCW position the antenna goes counterclockwise automatically at 12 rpm. In the CW position it goes clockwise at 12 rpm. There is no provision for manual rotation.

  12. Focus: used to focus the PPI tube for maximum definition.

  13. Center: this control positions the start of the sweep. The sweep can be made to start from

Drawing of plan position indicator unit.
Figure 4 SO-1. Plan position indicator unit.

4-SO-2


    the center of the PPI, or may be offset from the center as much as a half-inch. This leaves a dark circle in the PPI center which indicates our own ship's position. All contacts move out from the center when the sweep is offset, and it is easier to get bearings of near-by targets. The, calibration of the set is not changed in any way by this control. Normally, there will be a small dark circle about 1/16-inch in diameter at the PPI center.

  1. Tune: this is the fine tuning adjustment. When it is adjusted for maximum echo brightness, the receiver will be tuned to the transmitter.

  2. Marks: controls the intensity of the range marking circles on the PPI.

  3. Gain: corresponds to the volume control on any radio receiver, it controls the sensitivity of the receiver.

  4. Tune set: a rough tuning adjustment. It tunes the receiver approximately to the transmitter. It is adjusted for maximum echo, while the tune control (14) is in the mid-position. This is a semi-permanent adjustment.

  5. Bulkhead stop start switch, used with SO-1, SO-2, SO-8.

TURNING ON AND OFF

Turning on.

  1. Operate NE switch (2) to N. marks counterclockwise, pilot counterclockwise.

  2. Be sure INT (8) is turned full counterclockwise; this is done to prevent burning on PPI.

  3. Turn off-on switch (1) to ON if an SO. Press start button (18) on SO-1; dial light will come on when turned up.

  4. The blower in the transmitter will be heard to start.

  5. After two or three minutes, press start button (4), a relay will be heard to click, and the 400-cycle hum will be distinguished.

  6. Turn INT (8) clockwise until the trace on the PPI can be seen with moderate intensity. It is possible to burn the PPI if the trace intensity is too high.

  7. Adjust focus (12) for sharpness of sweep trace on PPT.

  8. Operate CCW off CW switch (ii) to either CCW or CW, and the trace will rotate on the PPI at 12 rpm automatically.

  9. Set the range switch (7) to the range on which contacts are most likely to be seen. If there are no ship or land targets within radar range, set this switch to short range so that sea-echoes or sea-return may be used for tuning.

  10. Turn gain (16) completely clockwise.

  11. Adjust tune (14) until contacts or sea-return (echoes from waves nearing your ship) can be seen on the PPI indicator.

  12. Stop the antenna on the best contact and adjust tune (1-1) for maximum brightness. If it fails to respond, set tune (14) to mid-position and adjust tune set (17) for maximum brightness; then make final adjustment with tune control (14). Tune set (17) is the rough tuning control, and tune (14) is the fine tuning control.

  13. With switch 11, start the antenna in automatic rotation again in either direction.

  14. Using center control (13) adjust the sweep trace so that the origin is almost in the center of the PPI scope. A small, dark circle, about 1/16-inch in diameter, should be seen at the center of the PPI to assure us that the sweep is not overlapping the center point.

  15. Turn marks clockwise until range-mark circles appear on the PPI, and adjust SW-L (16) until 5 range circles show on the SO, or 4 range circles on the SO-1.

  16. Note that no calibration is necessary. The set is permanently calibrated at the factory.

Turning off.

  1. Operate CCW off CW switch to OFF.

  2. Turn INT (PPI intensity control, 8) completely counterclockwise.

  3. Turn marks (15) completely counterclockwise.

  4. Turn pilot (3) completely counterclockwise.

  5. Push stop switch (4).

  6. Turn off-on switch (1) to OFF if set is an SO; push bulkhead stop button (18) if set is an SO-1, SO-2, or SO-8, and hold it down several seconds.

Adjusting the echo box.

The echo box furnishes an artificial echo or contact on the PPI indicator, to be used in tuning the receiver when no other radar targets can be found. It can also be used to determine if the transmitter is functioning. Adjustment is made as follows:

  1. Put the operate lever in a horizontal position. (See illustration of echo box, fig. 4 SO-1.)

  2. With the radar operating, stop the antenna on the bearing of the echo box pick-up antenna; this will be either 000°, or 180°,

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    depending upon the type of set you have. Adjust the echo box for the brightest indication from the neon bulb. The glowing of the light indicates that the transmitter is functioning.

  1. Put the range switch (7) in short range position. The artificial echo should be seen extending out a mile or two when the receiver is tuned. You may use this echo to tune on, just as you would tune on any echo. Any decrease in sensitivity of the radar will be indicated by a decrease in the range extent of the false echo. On some sets, the echo extends in all directions.

  2. To detune the echo box when not in use, pull the operate lever into a vertical position.

OPERATIONAL TECHNIQUE

Reading ranges.

Ranges are read by turning marks control (15) clockwise, until the range mark circles arc dimly visible on the PPI. The range circles are to he interpreted according to instructions already given in the section on Controls (7). Ranges must be read by estimation unless the contact happens to lie on a circle. Estimation of range is easiest and most accurate when using the short range scale, becoming more approximate as the length of scale increases. When the contact can be read on short scale, its range can be determined to within about 500 yards or a quarter of a mile. The medium range scale can be read with practice to a half-mile, and the long range scale to within about 1½ miles. When not reading ranges, keep the range mark circles off the PPI since they may obscure weak contacts.

Reading bearings.

The bearings blade or cursor should be rotated by turning the bearing crank until it bisects the arc formed by the contact. Unless the operator's eye is in the plane of the blade-shaped cursor, a parallax error will result. His eye should therefore see the cursor as a fine line, which is adjusted carefully to the center of the contact. Proper use of the cursor will result in superior bearing accuracy.

When the cursor has been set, turn pilot control (3) clockwise until the relative bearing scale is illuminated sufficiently so that the bearing can be read. When not reading bearings, keep the pilot (dial light control) secured in a counterclockwise position, since the light from the bearing scale destroys the contrast between a contact and its background, and the weakest contacts are seen best in complete darkness.

If you are yawing considerably on your course (as will often be the case on a PT boat), the relative bearing of contacts will be continually increasing and decreasing. For the same reason, contacts on the PPI will broaden into an ill-defined smear when yawing is excessive. If your own ship is steady on its course, bearing accuracy can be as good as ±2° or ±3°.

When taking bearings of close in targets which appear near the center of the PPI even on short range scale, and with SW-L (6) set for full expansion, it will be found helpful to use center control (13) to de-center the sweep trace, and move the contact out to a more convenient position on the scope.

If the contact is weak, and intensifies only once in several sweeps of the antenna, or if the bearing rate of change is high, it will be found helpful to operate CCW off OW switch (11), so that the antenna moves back and forth over the target instead of making full revolutions. Do not make this sector sweep less than approximately 90°.

Long and short range search.

When long range detection is desired, put the range switch (7) in this position, use full receiver gain (gain full clockwise), and be certain that the receiver tuning control (14) is precisely adjusted. The maximum range at which targets can he detected increases with the size of the target and its presentment. For large ships, the maximum range will be about the same as the line-of-sight distance from the antenna, and can be approximated by the formula d = 1.2 (square root(HA) +square root(HT)); where d is distance in nautical miles, HA is your antenna or eye height in feet above water, and HT is the greatest height of the target above the sea.

If you did not expect to detect even the largest ship beyond 20 miles because your own antenna is low, you should use your medium range scale for long range search and adjust it to show 6 range-mark circles, using SW-L control (6). Under these conditions, you would be able to read ranges much more accurately, and therefore could get a course and speed solution more quickly (from your plot), than if you used long range scale. The formula above will not hold true for small ships or wooden ships since such craft do not reflect enough echo to be detected at maximum line-of-sight distance.

Short range search may he used to detect nearby submarines (if partly or completely surfaced), navigation buoys, small objects in general, and for station

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keeping. The range selector switch (7) will be on short scale, and the gain control (16) will be turned down (counterclockwise) just enough to rid the PPI of excessive sea-return. Sea-return means echoes from waves near your ship, which causes interference from 3/4 miles to one mile in all directions, in even a moderate sea. With gain reduced, close range detection is now possible down to 200 yards, although the detection sensitivity at longer ranges will be lessened. If a contact is made at close range, it will be seen so close to the center of the PPI that it may be hard to get its bearing with normal accuracy. To facilitate getting a bearing on such a target, de-center the PPI trace by turning center (13) clockwise. The origin of the trace has now moved away from the PPI center, and the contact has moved out a corresponding distance. Its bearing can now be read more accurately. To facilitate station keeping, a dot may be put on the PPI where the guide should be, then when you get off station, the guide's contact will move out from under the spot.

If ships in your convoy or task force, are on stations inside your normal sea-return area, make periodic short range sweeps with the low gain, to see that they are not dangerously close or possibly on a collision course. A ship on a collision course will move down a radial line on the PPI. If a ship is going to execute a maneuver which will bring him close to you, put your cursor on him, if he moves straight down the cursor toward the center of the PPI, something has gone wrong and he is on a collision course with your ship.

False contacts and how they look.

Rain clouds: wide in bearing, deep in range, not sharply defined, with course and speed same as wind.

Ionized clouds: not visible to the eye, not easy to identify, often in groups, the course and speed same as wind, upper air will not always move with surface wind.

Floating objects (barrels, cans, etc.) small contact considering the short range, no course or speed.

Double range echoes: caused when returning echo is reflected from own ship, and makes a second round trip to the target, usually seen only when a large ship is close and on a parallel course. Will appear on the same bearing as a large ship, and at twice the range, its range rate will be twice the range rate of the large ship.

Reflection contacts: caused by your own radiated waves being deflected by some object aboard your ship, or another ship, in such a way as to cause a legitimate target to be seen on a wrong bearing; rarely visible, except when many ships are traveling together. These contacts are often distorted, and not as well defined as the usual contact. Their appearance and disappearance is usually related to course changes.

Wakes: always appear as a small contact astern of some nearby ship; they vary in size, becoming largest when the target ship is in a turn.

Whitecaps to windward: sometimes, a contact will he seen just beyond the sea-return area in the direction from which the wind is coming. It will keep the same relative position regardless of course and speed of your ship.

Side lobe contacts: rarely give trouble, but may be seen when good radar targets are at close range. They appear at the same range as some target that is giving a good contact, and come in pairs, one on each side of the true target contact. They are smaller than the true contact, and smaller than might be expected at that range. Operating the set near high mountains may give side lobe contacts, which will be large smudgy contacts on the PPI scope.

Second sweep echoes: you may hear of these, but you will never see one on the SO radar, because their repetition rate is low enough to preclude this possibility.

PPI interpretation.

The radar beam is projected into space in much the same manner as light from a searchlight, and there are radar shadows similar to ordinary shadows. Radar can not "see" through mountains, or behind them, or through any other large obstruction; it cannot see around corners, whether they be formed by headlands or the horizon. For this reason, radar shadows show as dark areas behind high points of land, and in the position of low lying land. Visualize the light and shadow detail presented to an observer looking down from a high position in the sky just at sunset. The lighted areas would be light areas on the PPI scope of a radar, bearing in the direction of the sun from the island, and the shadow areas would be dark as you visualize them, You can now see why topographical details of a region help you recognize land features as they appear on the radar. Without these details you cannot fully interpret the picture.

Because of beam width distortion, all targets give pips which spread to the left and right of their correct bearing. Thus all targets seem wider than they actually are. A good finite target, for example, will cause a contact 15° or more in width in a typical

4-SO-5


case (SO-1 radar). If two targets have the same range, but differ in bearing by no more than 15°, they will merge into one contact on the scope.

Distortion of the beam width affects radar's portrayal of a coast line. If your beam strikes the coast at right angles, there will be no coast line distortion at that point, but the smaller the angle between the coast line and the radar beam (in horizontal plane, of course), the more the land seems to come out to meet you. This spread tends to reach a maximum at the points of left and right tangency established from the radar observers position. In other words, if you were off a coast line as straight as a ruler, your radar would show it as a slightly crescent-shaped shore line.

Since all targets spread considerably in bearing, and incidentally to some extent in range, ships may succeed in concealing themselves from radar by getting as close to shore as possible. Their contacts will then either be obliterated by the land contacts, or they will merge and appear as part of the land mass. Chances of escaping detection will be maximum alongside a high island, and at points of tangency established from the radar observer's probable position.

Special use of SO radar by PT's.

Due to yawing of the PT boat on its course, the relative bearing of all contacts will vary somewhat from one instant to the next. When a torpedo attack is made by full radar control, the accuracy of radar bearings will depend not only on the radar operator, but also on the helmsman's ability to keep the boat on a steady course.

Some PT's draw relative movement lines on the face of their PPI's, and maneuver during the approach so that the target contact comes down one of the lines to one of the range circles. This is done to establish the course of the target without having to plot it, and to reach a definite optimum position for firing torpedoes. When using a relative movement line on the PPI for target course determination, adjust center control (13) so that the sweep origin is at the center of the PPI. De-centering the sweep, while useful in getting bearings of nearby objects, introduces distortion, so that the picture is no longer a true plan position view, and ships on a straight course will not move in a straight line on the scope. In the final stage of this approach, the relative bearing of the target may be changing as much as two degrees per revolution of the antenna. When the bearing is changing fast use CCW off CW switch, as described previously in the section titled "Reading Bearings."

Piloting by radar.

This type of radar navigation may give fixes that are approximate, and fixes that are as accurate as the set itself (plus or minus 2* and plus or minus 500 yards), depending on the features of land. If prominent, finite radar targets, such as peninsulas, river mouths, buoys, large rocks offshore, buildings, lighthouses, and radio towers can be identified on the PPI scope, the best type of radar fix is possible. Under these conditions it is possible to determine set and drift due to current, by comparing dead reckoning with successive radar fixes. Otherwise, the position must be approximated by cutting in on mountain peaks, using left and right land tangents, using "range off" lines of position, and by plotting ranges to shore for about every 10° on a transparent overlay, and fitting it to shore-line contours of a chart. These data can be used to good advantage in conjunction with those secured by use of the pelorus and fathometer. If the position must be approximated, it should be estimated by all possible methods and agreements looked for.

Tangents on land are not reliable because of two sources of error. In the first place, beam width distortion makes the land appear wider to the radar; therefore, left tangents tend to be small, and right tangents large. In the second place, radar often ignores low lying or sloping land, so that there may be doubt as to whether the radar is showing the land tangent or some other point inland. This introduces a tendency to carry tangent bearings inland, making the left one too large and the right one too small. These two sources of error offset one another to some extent varying with different types of terrain. Use every opportunity to compare radar tangents with pelorus tangents, so that you know the magnitude and direction of its error on various types of land.

Beware of radar's range off shore, because here again, it may ignore low lying land and indicate that you are farther off shore than you actually are. If the land is precipitous, radar will give your range off shore within the limits of the set's accuracy.

Do not rely on radar to pick up reefs or shoal water. These constitute low lying, poor radar targets, and will be detected at dangerously close range or else not at all.

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When you are approaching an unfamiliar shore, it is well to study charts and topographical data, and try to predict the way it will appear on the PPI, keeping in mind your approach course. This will facilitate an early radar fix and confusion will he avoided.

When close to shore or entering a harbor, it will be found that land details can often be found by reducing receiver gain (turn gain control 16 counterclockwise). This tends to minimize beam-width distortion and sea-return. Remember, when studying details of land or entering a harbor, use low gain.

Jamming.

Jamming is deliberate interference, caused by the enemy, which limits the effectiveness of your radar, or interference produced by our ships to limit the effectiveness of enemy radars. There are several types of jamming, but all are characterized by some form of strong interference pattern in a given sector on the indicator. These interfering signals are directional in nature, and the bearing or bearings from which they come can be easily found by adjusting the cursor to the center of the jamming pattern. The jammer does make it difficult or impossible to read range, but effective jamming is not easy for the enemy to accomplish, and it is apt to disappear momentarily from time to time. Learn to expect it, and he prepared to follow the best course of action when the time comes. Do not mistake interference created aboard your own ship or trouble in the radar set for jamming, the real thing will be directional, and its true bearing will not change immediately when your own ship changes course.

As you approach the jammer, the radar echoes from the jamming ship (if it is sea-borne) will increase in strength more rapidly than the jamming signal, and you stand a good chance of being able to read range through the interference. See Part 3, Defense Against Jamming and Deception.

When jamming occurs:

  1. Get the bearing and report it.

  2. Keep operating the set and trying to read ranges through the interference. Try various settings of gain control (16). There is a chance the jamming will stop long enough for you to get range.

  3. Keep reporting its bearing periodically.

  4. Be ready to turn on a radar which operates on a different frequency band if ordered, providing you have one.

  5. Draw a picture of the jamming pattern while it is fresh in your memory, and send it to the Bureau of Ships without delay.

PERFORMANCE

Maximum reliable range.

The maximum reliable range depends mainly upon the antenna height. The higher the antenna, the greater the range of detection of ships, due to the line-of-sight nature of the radiation. The figures given below are for an antenna height of 17 feet. Insufficient data is available at present for performance at higher antenna heights, but comparisons indicate that maximum range performance is roughly comparable to that of the SG radar.

Antenna 17 feet
Target Maximum Reliable
Range in Miles

BB, CV, Large auxiliaries 14-16
CA, CL, Medium auxiliaries 10-12
DD, DE, DM, AV, PC, CG, etc. 6-8
Large planes 10-14
Small planes 6-10
Submarines (surfaced) 4-5

Minimum range.

Target           Minimum
Range in Yards

Ship           300-500
Plane           about 1,000

Range accuracy.

The possible errors of the set may add to the probable errors of estimation, so that the following figures result for contacts that are not exactly on a range circle.

Short scale           ± 500 yards or 1/4 mile
Medium scale           ± 1/2 mile
Long scale           ± 1½ mile

Bearing accuracy.

± 2° for SO, SO-A, SO-1, SO-2, SO-8, provided your own ship is not yawing on its course.

TROUBLES

Reports from forces afloat indicate operational difficulties caused by moisture getting into the equipment. The transmitter-receiver, and PPI unit of the SO series radars are mounted in watertight cases, and sylica

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gel dehydrators (protek plugs) are provided to keep the units dry inside. A few reports have stated that condensation appeared on the scope after the equipment had operated for a few hours, but disappeared after the unit was shut down and allowed to cool. This is an indication that the heat generated by the equipment has driven the moisture out of the dehydrator plugs.

The instruction hook requests that the dehydrator plugs he changed when they have turned from deep blue when dry, to light pink after they have absorbed moisture, and are near saturation. Replacement plugs are sealed at the perforated end to prevent saturation; be sure to remove the seals before inserting in the units.

Abnormally high temperature in the transmitter-receiver unit, due to blower failure or some other cause, will turn off the high voltage automatically. It cannot be turned on again by the usual method. If it is necessary to operate the set in spite of probable damage to it, proceed as described under N E control in the section on Controls.

4-SO-8


Part 4
SF RADAR

CONTROLS 4-SF-2
 
TURNING ON AND OFF 4-SF-3
  Turning on 4-SF-3
  Turning off 4-SF-3
 
CALIBRATION 4-SF-3
  16.000-yard scale 4-SF-3
  18,000-yard scale 4-SF-3
 
OPERATIONAL TECHNIQUE 4-SF-4
  Receiver-indicator adjustments 4-SF-4
  Reading hearings 4-SF-5
  Reading ranges 4-SF-5
  Special situations 4-SF-6
            General search

            False contacts

            Reporting

            Fire-control

            Navigation

  Jamming and deception 4-SF-6
 
PERFORMANCE 4-SF-8
  Maximum reliable range 4-SF-8
  Minimum range 4-SF-8
  Range accuracy 4-SF-8
  Bearing accuracy 4-SF-8
 
TROUBLES 4-SF-8

4-SF-1


CONTROLS
  1. "A" indicator: used to identify targets at extreme ranges, for studying composition of echoes, and for accurate ranges.

  2. Range scale: read the one that is illuminated.

  3. PPI indicator: used to show tactical situations, for station keeping, and the most watched "scope" during general search. It is surrounded by a relative bearing scale.

  4. Range knob: moves the range step on the "A" scope, and the range circle on the PPI scope when getting range.

  5. Cal synch: a semi-permanent adjustment made by the technician.

  6. "A" scope intensity: controls the brightness of the picture.

  7. "A" scope focus: controls the clarity or sharpness of definition of the "A" scope picture.

  8. 16,000-yard set: used in calibrating 16,000-yard range, and to put the first range mark on the step; the first range mark represents 2,000 yards.

  9. 16,000-yard range set: used in calibrating the 16,000-yard range, and to put the seventh range mark on the step.

  10. 48,000-yard range set: used in calibrating the 48,000-yard range, and to put the 20th range mark on the step.

  11. 48,000-yard zero set: used in calibrating the 48,000-yard range, and to put the first range mark on the step; first range mark represents 2,000 yards.

  12. PPI focus: controls the clarity or sharpness of definition of the PPI scope picture.

  13. PPI intensity: controls the brightness of the picture on the PPI indicator.

  14. Calibrate-operate switch: when in calibrate position, range marks appear on the two scopes for

Line drawing of indicator unit.
Figure 4 SF-1. Indicator unit.

4-SF-2


    use in calibration. When in operate position, grass and target echoes appear on the two scopes. 15. Dial light control: illuminates the PPI bearing scale. This is to be used only when a bearing is being read.

  1. Green tuning eye: intended to be a tuning aid, but its use is not recommended.

  2. Rec-gain control: adjusts the sensitivity of the receiver; it controls the height of the echoes and the grass.

  3. Stop-start buttons: for turning set off and on.

  4. Range switch: selects either the 16,000-yard or 48,000-yard scale,

    Line drawing of transmitter unit.
    Figure 4 SF-2. Transmitter unit.

  5. Lo-tunning: this tunes the receiver to the transmitter; it is adjusted to give maximum pip height. This is an extremely critical adjustment, and the one on which the ability of the set to detect targets chiefly depends.

  6. IFF gain: to be turned clockwise when interrogating with identification equipment. This is inoperative unless BL or its equivalent is used in conjunction with the SF radar.

  7. Warning-training error: a light which indicates that the antenna (and consequently the target) is not on the indicated bearing. When lighted, it tells us that the antenna training equipment is out of commission and bearings will be wrong until repairs are made.

  8. Antenna train control: when pushed in, the antenna can be trained by hand; when pulled out, the antenna will rotate automatically.

  9. IFF on-off switch: when BL or its equivalent is connected to the SF radar, this switch is used to interrogate a desired contact.

TURNING ON AND OFF

Turning on.

Assuming ship's power is on and adjusted to 115 volts DC:

  1. Press the black start button (18), on the receiver-indicator. In about 30 seconds, the pilot lamps will illuminate the range scale (2). See that PPI intensity (13) is counterclockwise.

  2. Be sure the training control (23) is pushed in for manual operation.

  3. After two and one-half to three minutes, the transmitter will automatically go into operation. If you are close to it you can hear the blower motors go on at this time.

  4. Look at the meter on the transmitter unit. Set the toggle switch near the meter to MAG and the current should be five to six milliamperes.

  5. Set the same toggle on CRYSTAL, and the meter should read between 0.2 and 0.6 milliamperes, if not, the lo-tuning (20) is probably off adjustment. (This is to be discussed later.) Full scale deflection represents 1.0 milliampere.

Turning off.

  1. Push the red button marked stop (18 on the receiver-indicator unit).

  2. Turn PPI intensity (13) down (counterclockwise).

  3. Push in the training control (23) to manual the operation position.

CALIBRATION

16,000-yard scale (at the receiver-indicator unit)

  1. Throw calibrate-operate (14) toggle on the receiver-indicator unit to CALIBRATE position.

  2. Turn PPI (plan position indicator) intensity control (13) located near the right-hand indicator down to secure PPI during calibration. This prevents burning of its florescent screen during a prolonged period of calibration.

  3. Adjust intensity of the "A" scope trace with the "A" scope intensity control (6), located under the left-hand indicator. Do not make it unnecessarily bright.

  4. Adjust the focus knob, located under the left-hand indicator, until the "A" scope trace is sharp and clear.

  5. Set the 16,000-48,000-yard range selector switch (19), located on the lower left side of the center to the 16,000-yard scale.

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  1. Set range dial (2), upper center, carefully to 1.75 on the bottom scale (1,750 yards).

  2. Adjust 16,000-yard zero set (8), located on the lower left side of the range knob, with a screwdriver until the trace looks like figure 4 SF-3. That is, until the first range mark is on the edge of the step as illustrated. The right side of the first range mark, makes an almost straight line from its peak to the bottom of the step.

    Figure 4 SF-3. Pattern for calibrating 2,000-yard range an 16,000-yard scale.
    Figure 4 SF-3. Pattern for calibrating 2,000-yard range an 16,000-yard scale.

  3. Now set the range dial to read 13.75 on the lower scale (13,750 yards).

  4. Adjust the 16,000-yard range set (9), with a screw driver, so that the seventh range mark is on the upper edge of the step, as in figure 4 SF-4. Note, that the range marks represent 2,000-yard intervals on the scope. They may be regarded as artificially created pips at ranges of 1,750 yards (first), 3,750 yards (second), etc., the seventh being 13,750. Naturally, you want the seventh one to be on the range step when the range dial reads 13.75.

    Pattern for calibrating 14,000-yard range an 16,000-yard scale.
    Figure 4 SF-4. Pattern for calibrating 14,000-yard range an 16,000-yard scale.

  5. Again set the range dial to 1.75 and repeat step seven. Since adjustment of zero set and range set are interdependent, you must alternately repeat step seven and step nine until both adjustments are simultaneously correct.

48,000-yard scale.

  1. Set the 16,000-48,000-yard selector switch (19) to the 48,000-yard range. You now see more range marks than before, since they appear closer together. They still represent 2,000-yard intervals.

    Pattern far calibrating 2,000-yard range an 48,000-yard scale.
    Figure 4 SF-5. Pattern far calibrating 2,000-yard range an 48,000-yard scale.

  2. Set the range knob (4) to read 1.75 (1,750 yards) on the upper scale (2). Adjust the 48,000-yard zero set (11) to put the first range mark on the edge of the step. See figure 4 SF-5.

  3. Set the range dial (2) to read 39.75 (39,750 yards). Adjust the 48,000-yard range set (10) to put the 20th range marks exactly on the step, since the 20th 2.000-yard range mark represents 39,750 yards. See figure 4 SF-6.

    Figure 4 SF-6. Pattern far calibrating 40,000-yard range on 48,000-yard scale.
    Figure 4 SF-6. Pattern far calibrating 40,000-yard range on 48,000-yard scale.

  4. Now alternately repeat steps two and three until adjustments are simultaneously correct. The 48,000-yard range is now calibrated. It has been found that SF and SF-1 radars will have a constant range error of about 250 yards (low) if calibrated on 2,000 yards and 14,000 yards, or 2,000 yards and 40,000 yards rather than as shown above.

OPERATIONAL TECHNIQUE

Receiver-indicator adjustments.

  1. Throw the calibrate-operate toggle (14) to OPERATE.

  2. Turn up rec-gain (17), located in the lower-left-hand corner, until grass appearing on the sweep (25) is about 1/8-to-1/4-inch high. It will look like figure 4 SF-7.

    Normal grass height.
    Figure 4 SF-7. Normal grass height.

  3. Push in the 10-tuning (20) knob to engage clutch drive and turn it slowly back and forth, at the same time watching for a cluster of pips to rise up at the left end of the sweep. These pips are echoes from waves near the ship, and are known as sea-return (see fig. 4 SF-8). Adjust the lo-tuning (20) until they rise to maximum height. If there are two or more settings

4-SF-4


    of lo-tuning (20) which make echoes peak up. use the setting which makes them the highest. Do not try to tune by the green tuning eye (16).

    Tuning for maximum echo.
    Figure 4 SF-8. Tuning for maximum echo.

  1. Targets may be found now by training antenna with the train wheel (23), (located under the right-hand PPI indicator). Train on a ship or land target if possible.

  2. Make the final adjustment of lo-tuning (20), by tuning for maximum height of the target pip.

  3. Adjust the PPI intensity knob (13), located under the PPI indicator, so that the trace is just visible on the PPI with rec-gain (17) at minimum, turn completely counterclockwise.

  4. Adjust the focus knob (12), located under the PPI indicator, for a clearly defined sweep.

  5. Pull out on the antenna training knob (23), and the antenna will rotate automatically.

  6. Adjust the rec-gain (17) for the best picture while watching the PPI. About 4-inch of grass is best if the PPI is to be watched. The PPI is now in operation.

Reading bearings.

As the antenna rotates, a pointer (bug) revolves around the PPI indicator (3) in synchronization with it. The pointer indicates the direction, relative to the ship's head, in which the antenna points. Consequently, it also indicates the relative bearing of the target. New targets cause arc-shaped marks to appear on the PPI (see fig. 4 SF-9). Where they appear depends on their relative bearing and their range. Your own ship is always at the center of the indicator: the farther a target is from you, the more distant it will be from the center of the indicator.

To get the relative bearing of a target, stop the sweep and bug near it by pushing in the antenna training wheel, and then train by hand until the sweep passes through the estimated center of the target echo. It may help to train back and forth on the target until the echo is well defined on the indicator screen, before trying to stop on the center of it. Having done this, read the relative bearing on the scale opposite the bug. It should be noted, that due to non-uniform magnetic fields always being present, the trace will not line up with the bug (pointer) at all points around the dial. Therefore, bearing readings should always be made from the bug rather than the trace. If true bearings are desired, it will be necessary to install a gyro-repeater near the operator, unless the true bearing modification has been made on your set. Always read bearing in three figures, zero zero five instead of 5 degrees. To read bearings in the dark turn tip the dial light intensity knob in the center of the panel.

Correct bearing setting.
Figure 4 SF-9. Correct bearing setting.

Reading ranges.

The range of an object may be found by ether of two methods; the range circle method, or the step method.

The range circle method is quickest and most commonly used. Notice that a circle of light appears on the PPI. It can be made larger or smaller by turning the range knob. If the circle is made to pass through the target echo, the range of the target may then be read on the illuminated range scale. Notice also, that the upper range scale is illuminated automatically when the 16,000-48,000 switch is on 48,000 yards; the lower range scale is illuminated when on short range (16,000 yards), so there is little chance of reading the wrong scale.

The step method of getting range is more accurate; the "step" can be seen to move back and forth on the "A" type (left-hand) indicator as the range knob is turned. When the target pip is just at the upper edge of the step, as in figure 4 SF-10, the range of the target can be read on the illuminated range scale. Of course, it is necessary to stop the antenna on the target to get the range by this method.

4-SF-5


Notice that the range circle on the PPI, and the range step in the "A" scope move in unison and always indicate the same range, which may be read on the illuminated range dial.

Position of step for correct ranging.
Figure 4 SF-10. Position of step for correct ranging.

Special situations.

The operator should check calibration of both range scales, and the adjustment of the lo-tuning when he comes on watch.

General search. If he is standing a general search watch, the operator will spend most of his time on long range, using PPI and automatic antenna rotation, but making an occasional sweep at 1 rpm on manual control, watching the "A" indicator, Every five minutes it is a wise precaution to switch to 16,000 range scale and search in the sea-return area by reducing rec-gain (17).

Less gain will be required when using the "A" scope than when using the PPI. The gain is carried high when searching for targets at the maximum range of the set, i.e., enough gain to cause a snowy background on the PPI when it is being watched, or about 3/16-inch of grass on the "A" scope when using it. However, it will be turned lower when observing nearby objects.

False contacts. From time to time, false radar contacts will be made. Even with experience it is not always possible to tell with certainty when one has a false contact, so the operator should not fail to report a contact merely because he thinks it is false. These phonies may he caused by invisible ionized clouds, rain squalls, birds, white-caps to windward, small floating objects, and less common items. For further information, see the section on Pipology, Part 3.

Reporting. The operator should keep careful track of all visible contacts and watch especially for the sudden appearance or disappearance of echoes (strong indications of subs). He should also report all ships when they first become visible, report ships which may pass dangerously close, watch for ships on collision course (those whose bearing remains constant as the range closes), and make a routine report on first picking up land or losing it. Furthermore, it is a good policy to have the operator make some sort of routine report every five or ten minutes to the OOD, or evaluator, as the case may be, to give assurance that lie is alert, and that he can be relied upon at night for instance, when the watch officer can see nothing, and the operator is likely to become drowsy. If a report is made to the OOD by way of a bridge talker, the latter should give his report in such a way that the radar operator may listen and sing out if an error is made,

Fire-control. It is conceivable that SF radar may have to he used from time to time for fire-control. When this is done, train on the target, and stop the antenna there; get ranges by the range step method using the "A" indicator. Radar bearings should not be used unless there is no alternative, since the error may be + or - 2° to 3°, It is also possible to pick up the shell, splash and estimate the range error; to spot in range, stop on the target and watch the "A" scope. The shell pip looks like a mouse running under a sheet.

Navigation. Radar is a handy navigational aid when within range of land. It is important, though, to know when you can depend upon it and when you can not. Radar is apt to ignore low-lying land so that any attempt to get the range of a long sloping shore, or the tangent bearing on a section of land that rises gradually, would be unwise. Where land or buildings rise abruptly from the sea, the range to shore or a tangent bearing is easy to get. Mountain peaks and other prominent radar targets, are often identified by reducing rec-gain, since they will be the last targets seen as the gain is cut down. All targets on the PPI appear wider than they really are, due to the width of the beam of energy from the antenna. For this reason, tangent bearings may have to be taken inland a few degrees, the exact amount depending on the strength of the echo. Experience will improve this technique.

Since ranges are relatively accurate, range fixes on two positively identified, small, finite targets, are dependable.

When entering waters in which the PH picture is complicated by many strong land echoes (as in a harbor), it is necessary to reduce rec-gain to see the land-sea boundary, because of the blurring effect of the beam width distortion, and the obliterating effect of sea-return at close range.

Jamming and deception.

There is no doubt that the enemy considers our radar an extremely dangerous weapon, and consequently it is only reasonable to expect him to try every means possible to make it less effective. He may use two tactics to do this: jamming and/or deception. Every

4-SF-6


operator should learn how to recognize these countermeasures, and to expect them when in combat zones.

When the enemy broadcasts radio signals, intending that our radar receive them, and they show a confusing pattern on the screen, it is called jamming. Use of dummy targets (tinfoil, kites, balloons, etc.) is called deception. Of course, more precise definitions are sometimes given, but these are satisfactory for this discussion.

The SF radar can he jammed, and it will show echoes from the tinfoil the enemy sometimes throws out to confuse the operator. The operator should no! become alarmed when either of these things happens.

If you were suddenly confronted with jamming, without previous experience, it would appear impossible to work through. However, it is not really that serious if the following procedure is carried out:

  1. DF on the jamming.

  2. Use available anti-jamming devices on the receiver when provided.

  3. Try moving the gain control up and down.

  4. Try changing the receiver local oscillator tuning.

  5. Keep operating.

  6. Report type and bearing of the jamming to CIC.

The first reason for obtaining a bearing on the jamming is to determine whether or not it could be accidental interference instead. Jamming will not only be directional, but its true bearing will not be changed by any sudden change in your ship's course. Interference originating aboard your own ship will either he non-directional and appear on all bearings, or else it will always be on some certain relative bearing regardless of your own ship's course.

Try moving the gain control up and down. This is probably one of the most important countermeasures than can be taken, and the one most commonly overlooked because of its simplicity.

In most cases, except when effective noise modulated jamming is being encountered, there is a setting of the gain control where it is possible to range on a target in the presence of heavy jamming. If there are several echoes on the same bearing, the best setting for each echo is different. Of course, it is more difficult to obtain these ranges because of the distortion of the echo produced by jamming, but it is possible to obtain the desired information. However, the extra effort is worth while, because the enemy would not he jamming unless he were trying to conceal something important. The two general methods of using the gain control are:

  1. Reduce the setting; this prevents overload of the radar receiver; echoes are visible "riding on top" of the jamming pattern.

  2. Increase the setting; this limits (or clips) jamming; echoes are visible as a break in the base line. Be sure to return the gain control to its normal setting when no jamming is present, or when the antenna is turned to an unjammed bearing. Both of these methods should be tried.

Try changing the receiver local oscillator tuning. When you change the lo-tuning, you lose some of the height of the desired echo. However, if the jammer is not exactly on your radar frequency, there is a chance that you will detune the jamming signal more than the echo signal. Considerable improvement can sometimes be obtained this way. Try swinging the lo-tuning dial in both directions to see which direction makes the greatest improvement. Note the correct setting of the lo-dial, so that it can be returned to its normal position when no jamming is present, or if detuning does not help, otherwise the radar will not give optimum performance.

Even if the jamming is extremely effective, keep operating and do not turn your radar off. Turning your radar off informs the enemy that his jamming is effective, and certainly makes the radar completely worthless. The effectiveness of the jamming may change from time to time, so if you are persistent enough some information may be obtainable.

Report the nature and bearing of the jamming to CIC. Recognizing the type may be difficult because non-synchronous patterns sometimes appear blurred beyond recognition. Inasmuch as knowledge of jamming type* may possibly help identify the jammer in some cases, this information should be reported if possible. Above all, never turn off the radar.

When jamming and/or deception is encountered, full 360° search must be continued. However, the antenna should be stopped from time to time for short intervals, in order to try reading through the jamming, using the "A" scope. You also must be prepared for any diversionary tactics, for the enemy may or may not use jamming and 'or deception to divert your attention from the bearing of the main attacking forces. This problem is simplified somewhat when similar but separate radars are used for reading through jamming and for searching.


* See part 3, Defense Against Jamming and Deception.

4-SF-7


PERFORMANCE

Maximum reliable range.

The maximum reliable range on various types of targets depends on the height of the antenna. The higher it is, the greater will be the maximum range of detection. This is especially true for large ship targets. The performance data below shows approximately what you can expect if your antenna is between 50 and 70 feet above the sea.
Type of Target           Approximate
Maximum Reliable
Range in Yards

BB, CV, Large auxiliary   33,000
CA, CL, Medium auxiliary   28,000
DD, DM, AV, PC, CG, etc.   19,600
Submarines surfaced   9,000-15,000
Submarine periscopes   2,700
Buoys   7,000
PBM, PMY, PB2Y at 1,000 to 3,000 feet altitude   27,500
SOC, OS2U, SBD, F4F, F6F, etc., at 1,000 to 3,000 feet altitude   14,000

Minimum range.

The minimum range with all controls adjusted for shortest range detection will vary somewhat, depending on the roughness of the sea. A rough sea, means more sea-return interference and greater minimum range, especially on smaller targets. The figures below show approximately what to expect:

Minimum range.

The minimum range with all controls adjusted for shortest range detection will vary somewhat, depending on the roughness of the sea. A rough sea, means more sea-return interference and greater minimum range, especially on smaller targets. The figures below show approximately what to expect:

Type of Target           Minimum
Range in Yards

Ship           600
Planes           1,000 to 1,600
Range accuracy.

The range accuracy of this radar will be best when the ranges are read from the "A" scope using the step. The accuracy under these conditions is about ±200 yards, + 1.0% of the range. In other words, even when you calibrate correctly and read the range indicated by the range dial properly, your radar range may be off 400 yards on a target 20,000 yards away, or 600 yards on one 40,000 yards away, but only 220 yards on one 2,000 yards away.

Bearing accuracy.

Bearing accuracy will he best when the contact is strong and steady. By using manual antenna train, that is, stopping the sweep in the center of the contact seen on the PPI, a good operator will usually be within ±2° of the correct bearing of such a target. If the contact is E-1*, and visible only periodically the error may rise to 3 degrees or 4 degrees.

TROUBLES

If for any reason the bug should fail to give the correct relative bearing of the antenna, the light near the train wheel, marked warning training error, will glow. The technician should be called if this light continues to glow, but an occasional intermittent flash will be of no consequence.

Gunfire or depth charging might possibly jar open relay K 201, which is located behind the front panel of the transmitter unit. If this happens, the transmitter will become inoperative for about 2 minutes, but will come on of its own accord at the end of that time.


* See Part 1, How Does Radar Determine Bearing--E Units.

4-SF-8


Part 4. SJ-a, SJ-1 Radar

CONTROLS 4-SJ-2
  Main control unit 4-SJ-2
  Transmitter-receiver unit 4-SJ-2
  Range-indicator unit 4-SJ-2
  PPI-indicator unit 4-SJ-3
  Range unit 4-SJ-3
   
  TURNING ON AND OFF 4-SJ-4
  Turning on 4-SJ-4
  Turning off 4-SJ-4
   
CALIBRATION 4-SJ-4
  Zero setting 4-SJ-4
  Zero set procedure 4-SJ-4
   
OPERATIONAL TECHNIQUES 4-SJ-5
  Tuning the receiver 4-SJ-5
    Adjusting PPI intensity
            Drift in tuning during warm-up
  Reading bearing and range 4-SJ-5
  Operation at short range 4-SJ-6
  Pipology 4-SJ-7
            Clouds and rain squalls

            Birds

            Ships

            Aircraft

            Minor lobes

  Jamming 4-SJ-8
  Mechanical jamming 4-SJ-9
  Diving procedure 4-SJ-9
   
PERFORMANCE
  Maximum reliable range 4-SJ-9
  Minimum range 4-SJ-9
  Accuracy 4-SJ-10
  Resolution 4-SJ-10
   
TROUBLES 4-SJ-10

4-SJ-1


CONTROLS

Main control unit.

  1. Main off and on switch: applies AC voltage to the SJ radar set.

  2. Green light: when illuminated this indicates the main switch is on.

  3. Load voltage meter: indicates the voltage applied to the radar set.

  4. Load autotransformer: controls the voltage reading of 3.

  5. Regulated rectifier voltage meter: indicates the DC voltage output of the regulated rectifiers.

  6. Meter switch: positions 1 and 2, determines which regulated rectifier voltage is indicated on 5.

  7. High voltage rectifier off-on switch.

  8. Red light: indicates when the AC power is applied to the high voltage variac.

    Line drawing of main control unit.
    Figure 4 SJ-1. Main control unit.

  9. High voltage variac: controls the DC output of the high voltage rectifier.

  10. High voltage rectifier voltmeter: indicates the DC voltage applied to the transmitter-receiver unit.

  11. High voltage rectifier current meter: indicates the current in the rectifier circuit.

  12. Antenna control on-off switch: controls the applied to the automatic training device.

  13. Heater switch on-off: controls the AC plied to the heating elements in the range and transmitter-receiver unit.

  14. Pilot lights: bright-dim switch.

Transmitter-receiver unit.

Line drawing of transmitter-receiver unit.
Figure 4 SJ-2. Transmitter-receiver unit.

  1. Crystal current meter: reads 0.5 to 0.7 milliamperes when the equipment is properly tuned (this, however, is not the maximum crystal current reading obtainable).

  2. Fine pulse rate control: will vary the pulse repetition rate from 1,300 to 1,700 pulses per second.

  3. A.F.C. on-off switch: the automatic frequency control (automatic tuning circuit) will tune the receiver when ON, however, this circuit drifts and should be used only to check manual tuning.

  4. Wave-guide transmission line to antenna.

Range-indicator unit.

  1. Horizontal centering control: controls the position of the sweep or picture on the scope.

4-SJ-2


  1. Lobe separation on-off: allows separation of pip, on the scope for lobe switching.

  2. Lobe separation: determines the amount of separation of the pips when 2 is on.

  3. Sweep control: determines the length of sweep on the scope.

    1. Main sweep: 0 to 60,000 yards.
    2. Expanded sweep: 0 to 20,000 yards.
    3. Precision sweep: 3,000 yards (1,500 yards each side of the range step).

    Figure 4 SJ-3. Range-indicator unit.
    Figure 4 SJ-3. Range-indicator unit.

  4. IF gain: controls output of the receiver (determines height of grass and pips).

  5. Focus control.

  6. Lobe motor on-off switch: applies power to the lobing motor.

  7. Intensity control: screwdriver adjustment, to be set by the technician.

  8. Range zero knob: used to zero the sweep.

  9. Receiver-tuning: tunes the receiver to the transmitter frequency.

  10. Noise suppression: screwdriver adjustment, to be set by the technician.

  11. Scope: cathode-ray tube.

PPI-indicator unit.

  1. PPI cathode-ray tube.

  2. Sweep selector switch: (8,000, 40,000, 80,000 yards range).

  3. Scale light: azimuth circle.

  4. Driving cable.

  5. Video gain: screwdriver adjustment.

  6. Focus: screwdriver adjustment.

  7. Horizontal centering: screwdriver adjustment.

  8. Vertical centering: screwdriver adjustment.

  9. Range circle: adjusts intensity of the range dot.

  10. Intensity: adjusts brilliance of the scope.

Illustration of SJ-4. PPI unit.
Figure 4 SJ-4. PPI unit.

Range unit.

  1. Dial light dimming switch.

  2. Heating circuit indicator lamp.

  3. Range counter dial.

  4. Zero adjustment: to be adjusted by the technician.

  5. Counter adjustment: to he adjusted by the technician.

  6. Clutch adjustment: to be adjusted by the technician.

  7. Range crank.

Range unit.
Figure 4 SJ-5. Range unit.

4-SJ-3


TURNING ON AND OFF

Turning on.

Open antenna wave guide valve and perform the following operations from the main control unit:

  1. Turn on heater switch (13) 30 minutes before attempting to operate, if at sea, leave heater switch on at all times.

  2. Turn on main switch (1), a green light will glow if set is operating correctly.

  3. Check to see if blower motors can be heard in the transmitter-receiver unit, If not, turn the main switch off and call the technician.

  4. Check the load voltage meter (3) for 120 volt reading. If this is not indicated, make adjustment of load variac control (4) for 120 volts.

  5. Check regulated rectifier voltage meter (5) for 300 volts, check both positions of switch 6. If either one is off more than 15 volts, call the technician.

  6. Turn on high voltage switch (7) 55 seconds after line switch was operated, a red lamp will light (8) if the high voltage switch is on. The high voltage should immediately jump to 0.9 and to 1.2 K.V.; providing the H.V. variac has been left at its proper setting when set was last secured.

  7. The high voltage rectifier current meter (11) should read between 140 and 160 milliamperes.

  8. Check the load voltage meter (3) again, for a value of 120 volts.

  9. Turn on antenna control switch (12).

Turning off.

  1. Turn off antenna control switch (12).

  2. Turn off high voltage switch (7), do not reduce high voltage variac (9).

  3. Turn off load voltage switch (1).

  4. Do not turn off the heater switch (13) unless the set is to be worked on. Other units need not be touched.

CALIBRATION

Zero setting.

There has existed sonic uncertainty as to the proper zero set adjustment. In most cases there is no reference target available, whose range is known precisely enough to enable a satisfactory determination of zero set correction. Scribing ranges from charts is not generally satisfactory, because of shrinkage of the paper and because the scale of the chart is too small. The range of a reference target, to be used for calibrating purposes, should be known within 5 yards.

Where such a known range is not available, all SJ-1 equipment should use the counter setting of 99,940 for zero set. This number has been established by repeated observations over accurately surveyed ranges, and while it is subject to a possibly 10 yards variation among equipment, it should be used in preference to any but positively known local reference ranges.

One way of accurately determining a range, is by the use of double range echoes, (see Part 1, External Calibration). To do this, maneuver alongside a large ship at a range of 500 to 1,500 yards. When you train your antenna on this ship, two echoes should be seen; one at approximately the correct range, and a small double-range echo at approximately twice the correct range. Read these two ranges carefully and subtract the smaller from the larger-the difference is the actual range of the ship, regardless of whether your radar has been properly zeroed or not. Assuming this range is 800 yards, to find the exact zero set figure for your radar, you would proceed as follows: crank the range counter to exactly 800 yards and use the zero adj. knob to line up the target pip and step (use precision sweep during this operation). Now crank the range knob until the left edge of the transmitted pulse lines up with the step, and then read the range counter. It will probably read somewhere between 99,940 and 99,960 yards. Record the reading for future use in making the zero set adjustment. It is wise to avail yourself of every opportunity to check the zero set by means of double range echoes. If the double range echo appears at exactly twice the range of the true echo, you can be sure that the zero set adjustment is correct.

Under no circumstances should zero set be made with the counter at 00,000. This would increase all range readings by about 60 yards, and would go far toward defeating one of the main contributions of radar-accurate ranges.

The correction is required due to two factors: distance traveled from the transmitter to and from the antenna, and certain transmission delay and other effects within the equipment, such as build-up time in interstage filters.

Zero set procedure.

  1. Turn on the set and tune properly.

4-SJ-4


  1. At range unit, turn range crank counter-clockwise until range dials read exactly 99,940 yards, or a more accurately determined figure found by double range echoes.

  2. Turn IF gain fully clockwise (5 on range indicator unit).

  3. Set sweep selector switch on precision sweep (4 on range indicator unit).

  4. By adjusting the set range zero knob, move the step to the right until the leading edge of the transmitter pulse meets the downward portion of the step, as shown in figure 4 SJ-6.

Transmitter pulse for proper zero set.
Figure 4 SJ-6. Transmitter pulse for proper zero set.

OPERATIONAL TECHNIQUES

Tuning the receiver (at range-indicator unit).

  1. Check sweep switch (4) on all three positions to see if a sweep and step are present on the scope for each position. If any are missing, notify the technician.

  2. Turn IF gain (5) fully counterclockwise; and adjust focus (6) for narrowest sweep or line possible.

  3. With sweep switch (4) on expanded, rotate IF gain fully clockwise.

  4. Adjust receiver tuning control (10) for maximum pip height on scope if pip is present. AFC switch (3) on transmitter-receiver unit must be off during this adjustment.

  5. If pip height is saturated (pip has a flat top and not a sharp point), reduce IF gain (5) until pip is pointed, and make further adjustment of receiver tuning control (10) for maximum pip height.

  6. Should no echo be present for use in tuning, put the sweep switch (4) on precision and the range dial at about zero. Tune for maximum indication of the wave echoes. If no wave echoes or other indications are available, the experienced operator can tune the set by noting: appearance of transmitter pulse on precision sweep, and reading of the crystal current meter on the transmitter unit. If an echo box is available, it can he used to put a false echo on the scope. The receiver can he reliably tuned on such an echo, as soon as the antenna is above the water.

  7. If targets are available, train on one, and turn on the AFC switch on the transmitter (3). If the automatic tuning circuit is working properly, and if manual tuning is correct, no change in echo height should occur. In any case, if echo height increases, the manual tuning is not correct.

    Note: The AFC circuit should be used only to check manual tuning.

  8. Adjust wave guide valve for maximum tuning or echo height.

  9. Never use receiver tuning control (10) to decrease pip height. Always use IF gain control (5).

Adjusting PPI intensity. It is to be noted, that this control must he set precisely, and not varied to suit personal preferences and lighting conditions. Adjust intensity (10 PPI unit) until the sweep trace is just visible on the scope, when the IF gain (5 on range indicator) is set at minimum.

Any light which shows, with no signals or noise present, will impair the usefulness of the indicator by reducing the contrast of the pattern, that is, echoes will not stand out clearly nor be distinguishable from noise.

The intensity should not be turned too low, because then, unless special care is taken, weak signals will not be able to excite the screen sufficiently to be detectable.

Drift in tuning during warm-up. When the system is turned on, after a considerable period of shut-down, at least 5 to 10 minutes is required for the beat-oscillator in the receiver to reach final, stable, operating temperature. This period can be reduced to about two minutes by applying line voltage to the SJ-1 at least 10 minutes before surfacing, and by opening the antenna wave-guide valve. High voltage maybe applied before the antenna breaks surface and tuning checked approximately, by the appearance of the transmitted pulse on the precision sweep, with the range crank at about 99,940 yards. Zero setting of the range step is also checked at this time. Use hand train of the antenna, and report to the Captain when the antenna is free of water. Immediately check tuning on sea-return (wave pips), and make two complete 360° searches, reporting the results of each search. These searches should he made on expanded sweep. Continue to search with hand train of the antenna until surfacing is complete.

Reading bearing and range.

  1. To obtain approximate bearing of the target, rotate the antenna crank back and forth (lobing

4-SJ-5


    off), until maximum height of the pip is found. Read the bearing on the bearing indicator and subtract 2½° from this reading. The result will be an approximate or non-lobing bearing.

  1. When an accurate bearing of the target is desired:

    1. Turn the lobe motor switch (7) on the range indicator unit on.

    2. Turn on the lobe separation knob (2) on the range indicator.

    3. Rotate lobe separation knob (3) clockwise, until two pips and two steps are present, as illustrated in figure 4 SJ-7.

      Scope with and without lobing.
      Figure 4 SJ-7. Scope with and without lobing.

    4. Rotate antenna crank back and forth until the two echoes are at the same height.

    5. Read bearing dial for correct bearing of the target with respect to own ship-relative bearing.

  2. To measure the range, first turn lobing switch (7) off; then rotate the range crank, which moves the step on the scope, until the step is approximately at the pip being measured.

  3. Turn sweep switch to precision sweep.

  4. Advance the step until the beginning of the pip sets exactly in the corner of the step as in figure 4 SJ-8.

    Position for correct ranging.
    Figure 4 SJ-8. Position for correct ranging.

  5. When the pip is in the step correctly, the range of the target can be read from the range dial on the range unit.

It is suggested, that after adjusting trace separation correctly, that the lobe separation switch be left on at all times, and that the trace separation knob not be touched. Minimum time will then he required for obtaining lobe bearings.

Due to increased power output of SJ-a and SJ-1 radars, minor lobes present considerable trouble at close ranges; they can be easily located and avoided by use of the PPI scope. Echoes from minor lobes (side lobes) will disappear as receiver gain is decreased.

Bearings and ranges may he read approximately from the PPI scope without stopping the antenna. It is possible to obtain target course within 5°, and target speed within 3 knots from this data. The following suggestions will speed the obtaining of data from the PPI and increase the accuracy:

  1. Add inked circles on the face of the PH tube for estimating range (four solid circles, interspaced by four dotted circles). Care must he taken not to scratch the tube in any way.

  2. Improvise a more accurate 360° bearing circle over which rides a cursor, or thread stretched across the screen. Targets may then he split by this thread and hearing read on the circle.

Operation at short range.

Any radar antenna projects a small amount of energy in every direction. This can be visualized by comparison with a searchlight. There is a certain amount of illumination, even directly behind the light. In the case of SJ-1, the distribution is known, and is such that a very small amount is projected to the rear of the antenna. This is obviously extremely low, but since the sensitivity of the receiver is such that a signal will begin to show when the received energy is infinitesimally weak, it is not surprising that when the IF gain is set high, an echo will be received in practically a full circle, from a large target, at ranges of less than 2,000 yards. The only recourse in such a ease is to reduce the IF gain sufficiently to remove all but the main echo.

In a situation where this is done, it is well to use the time between taking data to turn up the gain, and to observe any other targets which may not be seen with the low gain setting required to resolve the short-range contact. It is stressed, that the IF gain must continually be adjusted to suit circumstances during any operation, except long-range search.

It will be found, that as range is closed, the arc subtended by an echo will increase. This is particularly evident on the PPI. There are two reasons for this: the angle subtended by the target will increase; and the echo will begin to show well before the antenna bears full on the target. Reducing the IF gain will

4-SJ-6


make the latter effect negligible, but at the same time reduce long range sensitivity.

The following search routine is suggested for SJ-a and SJ-1 equipment: 360° searches are to be made at all times; suggested antenna speeds are 6 rpm, or less, for PPI search, and 1/2 rpm for "A" scope search.

  1. Use the PPI 80,000-yard scale (high gain) for 2 minutes.

  2. Use the PPI 40,000-yard scale (high gain) for 5 minutes.

  3. Use the PPI 8,000-yard sweep (low gain) for 2 minutes. (or "A" scope expanded sweep in hand train).

High gain indicates the most efficient receiver gain setting for long-range search. Low gain refers to the receiver gain sufficiently reduced to enable targets to be detected inside the sea-return area. Care must be taken not to reduce gain too much. It has been found that alternate PPI and A scope searching provides diversion for operators, thus relieving strain.

The following suggestions pertain to the tracking of targets:

  1. Designate multiple targets on the PPI as Able, Baker, Charlie, etc.; escorts as escort one, escort two, etc.

  2. Have the plotting officer look at the disposition of the targets on the PPI when approach begins. He may assign designations.

  3. Keep the antenna in hand training while obtaining bearings for TDC.

  4. Obtain data for the TDC by use of the "A" scope only.

  5. Use a second operator to aid in reading "A" scope data, and ranges on escorts and secondary targets.

If necessary, shift the antenna to power training for a 30-second interval every two or three minutes, to secure this auxiliary data. Complete search must be made at least every three minutes.

  1. The best estimates possible of target size and type must be passed to the plotting officer and to TDC, as well as apparent changes in the course of target. These generally become widest due to changes in the echo strength on the PPI and "A" scope.

If provisions are not available for operation of IFF with SJ-a or SJ-1 radar, all questionable targets should be challenged by means of the SD radar's IFF system. Simply look for IFF response at the range of the surface target on the SD screen. See Part 2. General IFF Principles. It suggested that operation of the SJ-a underway, be carried on with half-hour watches, if possible. In no ease, should the watches be for more than one hour. Radar watches may be combined with sound, radio, or both, but should under no circumstance be combined with lookout watches. When relieving the watch, all meters should be checked for proper readings, and the three indicator sweeps checked for proper operation. Tuning and zero-set should be checked, and special information, such as maximum range on wave pips, interference present, etc., should be obtained from the operator. Any indication of trouble should be reported to the radar technician or radar officer. In case trouble occurs in the set during the watch, immediately turn off the high voltage in the transmitter' and secure the set, reporting the sequence of events which occurred when operation failed. Location of trouble may be greatly speeded in this way.

Pipology.

Clouds and rain squalls. These can frequently be detected at great ranges, and are not always easily identified. Usually, they will show on the PPI as being several degrees wider than normal ship echoes, depending on the extent of the cloud. They will frequently tend to look like landfalls, but can be distinguished from such, where certainty as to ship's location is lacking, by tracking to determine whether the target has course and speed as clouds have when driven by wind. Fluctuation of the echo is not necessarily an identification, because at long ranges land echoes sometimes fluctuate abnormally. Echoes from clouds are usually mushy, due to the absence of definite, reflecting planes.

Birds. Echoes from birds constitute a source of confusion to radar personnel. Birds in flight can usually be identified by their random courses and speeds, as well as by the fact, that, being so small, they will only show echoes at ranges within 2,000 yards. There should be no confusion between birds and aircraft, because the latter will show stronger echoes and will be seen at far greater ranges than the birds.

Ships. The approximate size of ships can be estimated by the maximum range of detection, the rapidity of the bobbing motion, and in some cases the speed. The first two factors will be affected by the following:

  1. Target size.
  2. Sea condition.

4-SJ-7


  1. Target type (amount of freeboard, lines, superstructures, etc.)
  2. Target course (presentment).
  3. Target speed (variation of reflecting surfaces).
  4. Own speed (variation of our antenna pattern).

Aircraft. The beam of the SJ-1 antenna, is directed toward the horizon, but low flying aircraft will frequently produce echoes. To recognize them, set the range mark on the echo, and watch for noticeably fast target motion. The PPI can also be used. The course of the aircraft might be such that range changes slowly, in which case, the PPI will indicate rapid change of bearing. It is important to realize, that echoes from aircraft will never zip across the screen, because so much range is compressed and displayed in the few inches of the screen. Even projectiles can be followed with ease. An airplane traveling at 200 mph, either directly toward, or away from the antenna, will require about 40 seconds to traverse the prec. sweep.

Minor lobes. It is characteristic of radar antennas, that some energy is projected in minor lobes or beams of energy, at some divergence from the main beam. In the case of SJ-1, the required small size of the antenna, as well as the necessarily massive construction of the projector head, accentuate the minor lobes. These are greatly reduced in power from the main lobe, but echoes will be received in response to minor lobes when the target is large, close, ad the IF gain is high. When present, minor lobe echoes will show at roughly 15° divergence from the main echo, and at the same range as the main echo.

The presence of minor lobe echoes is easily observed on the PH. Since they are weak, compared to the main echo, they will not show on small or distant targets. Roughly, with the IF gain well up, minor lobe echoes may be expected from a destroyer at 3,000 to 6,000 yards. The nominal divergence of 15° will vary among installations, and the minor lobes will seldom be alike in strength.

Where a group of targets, such as a convoy, is being viewed, echoes from minor lobes are confusing. The first recourse is to study the PPI pattern, for main and side echoes in characteristic groups, and to reduce the IF gain to where only the main echo from each group remains. Where the range is short, and the convoy is widely spread, this must be done judiciously in order not to lose real echoes from small targets, such as wooden escort vessels. Where uncertainty exists, as to whether a particular signal is real or a minor lobe echo, positive check can be made by attempting to lobe-switch on the echo in question. It will be found, that the two pips from a minor lobe echo will tend to rise and fall together, instead of sea-sawing, as a main echo does when the antenna is trained through the bearing of the target.

Jamming.

Since local interference or trouble may resemble jamming, an operator, after first reporting it, should perform these cheeks to see if the signals are from an outside source. Check whether the strength of interference varies as the antenna bearing is changed; or whether interference disappears when the antenna wave-guide valve is closed.

If interference is external and from another radar, it will consist of a definite series of equally strong pulses, consistent in width and spacing. These pips may move to the right or left on the screen (pulse spacing remaining constant), depending upon the pulse repetition rate of your radar and that of the interferer. Their speed of travel along the time base may be varied as your own pulse rate is varied. The interference will disappear when the wave-guide valve is closed. They are definitely effected by a variation of receiver tuning, and vary in strength as the antenna is rotated.

Note: All of the above points will appear on the PPI scope as bright spots, moving along the sweep (or as spirals from the center to the outer edge, if the antenna is rotating).

If the interference is external, and from an intentional jammer, it will generally conform to a known type of jamming signal, and may not be effective enough to prevent an operator from seeing targets in the jammed sector. It will also disappear when the wave-guide valve is closed. It will definitely vary as antenna bearing is changed, and due to the strength of the signal, it may burn a definite, brilliant sector on the PPI scope.

To read through jamming, concentrate on the "A" scope in the jammed sector; an experienced operator can spot a target on it most of the time. Do not neglect searching completely around 360°. The effectiveness of a jammer, which is covering a target you are tracking, may be decreased by very slightly changing receiver tuning without losing your echo. Training the antenna slightly off the target, to one side or the other, may reduce the jamming more than the echo. Changing pulse repetition rate, or changing the high

4-SJ-8


voltage applied to the transmitter, and retuning the receiver may help.

A jammer must continually transmit at the radar frequency of your radar. You can slightly vary the frequency by varying high voltage, as described above. The corresponding correction on the part of the jammer, may allow a free operating interval.

Do not give up trying to read through a jamming signal, because as the range of a jammer closes (and the range of any accompanying target), the target echo will increase much faster in strength than the jamming signal. The higher the frequency of transmission, the harder the job of jamming, hence, the easier the task of evading or reading through. Enemy use of radar jamming in the Pacific has not been pronounced, but can be expected as soon as they can produce equipment which will do the job.

Mechanical jamming.

The Japs and the Germans have been known to use several types of radar deception. Window has been used in an attempt to hide aircraft. It consists of concentrations of reflecting material, which can be spread by dropping it from aircraft, or by firing it from a gun. It may also be used to mask ships. This material presents a numerous collection of pips, which may cover a wide sector; all pips fluctuate at a very rapid speed, and may appear quite similar to a cloud, though much stronger.

Echoes emanating from balloon bourne reflectors have been used to draw radars off of true targets. If you track these, their course will he that of the wind and one-half to two-thirds of the wind speed.

Diving procedure.

When the word "standby to dive" is passed, remove high voltage from the transmitter, and close the antenna wave-guide valve. Secure the rest of the set in a routine manner. The antenna should be secured on a 180° bearing when not in use, especially while running on the surface.

PERFORMANCE

Maximum reliable range.

The range capability of a given installation is effected mainly by the following conditions:

  1. General condition of the radar.

  2. Accuracy of the tuning, particularly the rec-tuning control.

  3. Height of the antenna above the water.

  4. Size and height of the target, also, material of the target.

  5. Atmospheric conditions.

Of these, the first three are entirely obvious. Concerning item (4), a slight degree of confusion is possible when attempting to judge the size of a target by the strength of an echo, because a large wooden ship will usually not produce an echo larger than a considerably smaller steel ship.

The effects of atmospheric conditions are comparatively obscure, but a few generalizations may be made. Fog causes occasional slight reduction in range. Heavy rain causes some reduction, but no cases are known of serious reduction due to rain. It seems well established, that in the North Temperate zone there is some daily cycle, whereby range capability of SJ-1 radar equipment, increases above normal in the late afternoon and early evening.

Antenna 33 Feet

Target           Maximum Reliable Range
in Yards

BB, CV, Large auxiliaries           25,000 to 30,000
CA, CL, Medium auxiliaries           20,000 to 25,000
DD, DE, DM, AV, PC, CG, etc.           15,000 to 18,000

Mountainous landfalls and freak conditions, can produce echoes under conditions which may lead to considerable confusion, if not fully understood. The maximum range displayed on the indicators is nominally 80,000 yards (PPI). However, echoes have been received many times from ranges so great, that the received echo does not arrive until the next succeeding sweep, or cycle of operation. Such second-sweep echoes, usually appear on the indicators at relatively short ranges, and can he misinterpreted as nearby targets. In the SJ-1, provided with variable pulse (recurrence) rate control, this type of false signal can quickly be identified by shifting the pulse rate control on the transmitter back and forth. This will cause any second-sweep echoes to move back and forth in range across the screen. Since this condition cannot be called rare, remember, the best protection against it is to understand the possibility, and the method of checking.

Minimum range.

Target           Minimum Range
in Yards

Ship           350-400

4-SJ-9


Accuracy.

The main source of bearing error, assuming accurate alignment of the bearing indicator, is play in the training gear. This is beyond the control of the ship's personnel, but operators can do much to overcome this play, by lobe-switching to match the pips carefully, and by then feeling for the ends of the backlash motion, and by holding the handwheel as near as possible to the middle of the free motion to read bearings. By this practice, bearings may be read very consistently with a maximum error of 1/4° on large steady pips. Range approximately, ± 25 yards, + .1% of the indicated range.

Resolution.

TROUBLES

There are two factors which can cause had bearing readings (other than minor lobe and extended close-in echoes as described previously). These are changes in the transmitter frequency and obstruction, or distortion, of the antenna pattern by periscopes or the SD radar mast. The bearing indicator alignment can be thrown off up to 2 degrees by changes in the frequency, due to shifted tuning of the antenna or internal transmitter adjustments, or by replacement of the magnetron. Whenever any of these troubles occur, bearings should he checked against one or both periscopes. During this check care should be taken that the antenna is not pointing within 30 degrees of the periscope to avoid distortion of the pattern. Presence of a periscope or the SD mast within 30 degrees of the antenna beam can cause varying hearing errors up to some 5 degrees.

It is recommended that each submarine make calibration runs, to provide tables or charts showing the bearing indicator corrections, for conditions of either or both periscopes raised, SD mast raised, and combinations of periscopes and SD mast. It is probable that the charts or tables for some combinations of SD mast and periscopes will he identical. Such information, posted at the operating position, will enable full accuracy to be obtained under all circumstances.

4-SJ-10


Part 4
SD RADAR

CONTROLS 4-SD-2
  Receiver-indicator 4-SD-2
  Transmitter 4-SD-2
  Diplexer 4-SD-3
   
TURNING ON AND OFF 4-SD-3
  Turning on 4-SD-3
  Turning off 4-SD-4
  Abbreviated procedure 4-SD-4
  Use of the SD radar before surfacing 4-SD-4
   
CALIBRATION 4-SD-4
  Use of markers for range measurement 4-SD-4
   
OPERATIONAL TECHNIQUE 4-SD-4
  Tuning the equipment 4-SD-4
  Air-search during surface cruising 4-SD-5
  Diving procedure 4-SD-5
  Care of equipment during long dives 4-SD-5
   
PERFORMANCE 4-SD-5
  Maximum reliable range 4-SD-5
  Minimum range 4-SD-6
   
TROUBLES 4-SD-6

4-SD-1


CONTROLS

Receiver-indicator.

  1. Focus control: controls focus of the sweep.

  2. Intensity control: controls brightness of the sweep.

  3. Markers: allow markers to be put on the scope. Used for obtaining ranges of targets; use of IFF in extreme right position.

  4. Centering: controls position of the sweep on scope-horizontal positioning.

  5. Stand-by light: when illuminated indicates power switch is on.

  6. Power switch on-off: controls AC power applied to the set.

  7. Transmitter plate light (red): when illuminated indicates switch, No. 14, is on.

  8. Oscillator control: tunes the receiver to the transmitter frequency.

  9. Sensitivity control: volume control of the receiver, controls height of the grass and pips.

  10. Fuse F-202-Fuse F-201: protection for the AC supply.

  11. Scope: cathode-ray tube.

  12. Transmitter plate current meter: reading determines setting of the high-voltage variac, No. 15. 13. Transmitter plate power off-on switch: controls AC power applied to the high voltage variac, No. 15.

  13. Transmitter plate variac: controls the amount of DC voltage applied to plates of the transmitting tubes.

  14. IFF gain control: varies amplitude of IFF signals appearing below the time base.

Transmitter.

  1. Red pilot light: when illuminated, indicates that the power switch is on at the receiver-indicator unit.

  2. Transmitter plate current meter: reads the same as meter No. 13 on the receiver-indicator unit.

  3. Filament primary voltage meter: indicates voltage applied to the primary of the filament transformer, which supplies AC power to filaments of the transmitting tubes.

  4. Filament control variac: controls the amount of voltage applied to the filament transformer.

  5. Operation hour meter: registers the total number of hours the set has operated.

  6. Emergency switch off-on: is in series with main power switch, to be used only in case of emergency.

Illustration of range indicator unit.
Figure 4 SD-1. Range indicator unit.

4-SD-2


  1. Diplexer tuning dial: indicates position of the tuning condenser in the diplexer.

  2. Diplexer tuning control: varies the position of the condenser in the diplexer: to he set by radar technician.

  3. Exhaust of blower: maintains cooling for the transmitter.

Transmitter unit.
Figure 4 SD-2. Transmitter unit.

Diplexer.

(Diplexer unit is to be adjusted by the radar technician only.)

Antenna mast and diplexer, with most raised.
Figure 4 SD-3. Antenna mast and diplexer, with most raised.

TURNING ON AND OFF

Turning an.

  1. Check to see that the transmitter plate high voltage switch is off.

  2. Turn on the power switch at the receiver-indicator.

  3. Red pilot light on the transmitter should illuminate.

  4. Check to see that the blower motor in the transmitter is operating.

  5. Rotate the primary filament variac slowly clockwise, white watching the filament primary voltage meter increase to a value determined by the radar technician (110 to 120 volts).

  6. At the receiver-indicator unit, check to see that the transmitter plate variac and the intensity control are fully counterclockwise.

  7. Raise the antenna mast until the top insulators on the mast shoes are even with the top insulators of the diplexer shoes (see fig. 4 SD-3.)

  8. Turn on the transmitter high voltage switch on the receiver-indicator unit. Check to see that the red pilot light on the receiver-indicator unit is illuminated.

  9. If the line switch has been on for at least 30 seconds, proceed to turn transmitter plate variac clockwise until the plate current meter reads 8 milliamperes (or value specified by technician).

4-SD-3


Turning off.

  1. Turn the transmitter plate variac to zero.

  2. Turn off the transmitter plate switch.

  3. Turn off the power switch.

  4. Do not touch other controls.

  5. Lower the antenna mast.

Abbreviated procedure.

It is suggested that the following controls he left at the proper settings at all times, thus decreasing to a minimum the time required for tune-up:

  1. Filament control variac on the transmitter unit.

  2. Intensity, focus, tuning, sensitivity, and horizontal centering controls on the receiver-indicator unit.

Turning on is then reduced to the following procedure:

  1. Turn on the power switch on the receiver-indicator unit.

  2. Check the green pilot light on the receiver-indicator unit; blower motor in the transmitter, and the filament primary voltage meter on the transmitter.

  3. Raise the antenna mast as described above.

  4. Check to see that the transmitter plate variac on the receiver-indicator unit is at zero.

  5. Turn on the transmitter plate high voltage switch and increase the transmitter plate variac (if line switch has been on at least 30 seconds), until the plate current meter on the receiver-indicator unit reads 8 milliamperes (or as specified).

Use of the SD radar before surfacing.

  1. The power switch should he on for 10 minutes before using the set.

  2. Raise the antenna mast while at periscope depth.

  3. When depth decreases to a point at which the antenna is clear of the water (7 to 10 feet), turn on the transmitter plate high voltage switch.

CALIBRATION

Use of markers for range measurement.

With the set properly on and tuned, turn the sensitivity control counterclockwise. Then turn the markers switch to the left, markers should appear on the screen. (Their appearance is illustrated in fig. 4 SD-4.) Place a strip of scotch tape across the screen, just below the sweep line; carefully indicate, in ink. each 2-mile point on the tape (the first marker represents a 2-mile point on the sweep, and each marker thereafter is a 2-mile point).

Range markers.
Figure 4 SD-4. Range markers.

Return the marker switch to its normal position, and increase the sensitivity control to read target ranges from the tape. If this arrangement is used, care must be taken to switch markers on and check horizontal centering of sweep each time the set is turned on.

Range markers may he used directly for range measurement if desired.

OPERATIONAL TECHNIQUE

Tuning the equipment.

  1. Increase the intensity control until the sweep is visible on the scope.

  2. Adjust the, focus control for clearness.

  3. With the sensitivity control near minimum (counterclockwise), rotate the oscillator control until a point of maximum response is noted on the scope (increase sensitivity control if necessary).

  4. Adjust the sensitivity until the flag at the top of the transmitter pulse (left end of the sweep on the scope) is about 1-inch above the base line.

  5. Adjust the oscillator control for maximum height of the flag. Now rotate the oscillator control through 360°, checking for another tuning point which may increase the altitude of the flag. Leave the oscillator control on the best tuning point.

  6. Increase the sensitivity control until grass appears on the screen. If a steady echo is present, cheek the oscillator tuning for the maximum echo

4-SD-4


    height. This check should he made with the sensitivity control adjusted so the echo tuned on is just visible above the grass.

  1. Re-check focus.

Typical appearance of FLAG when properly tuned (sensitivity low).
Figure 4 SD-5. Typical appearance of FLAG when properly tuned (sensitivity low).

The appearance of the flag at the top of the pulse (left end of the screen) will vary in different sets. Become familiar with the appearance of this flag when properly tuned, and tune for maximum height as well as proper appearance.

If the sweep does not appear immediately on the scope, turn the variac back to zero, and make successive attempts to increase it until a sweep is obtained. The sweep may jump and appear unsteady until water has drained from the antenna, this will cause no damage.

If the depth of the submarine increases to a point where waves may strike the antenna, arcing will occur at the antenna and possibly in the transmitter. Turn the transmitter plate variac to zero if there is a possibility that the antenna will become submerged, and then wait until the proper depth is reached. Quickly check the tuning and range markers, and make reports to the Captain.

It is important in this connection that controls and adjustments on the receiver-indicator unit be left untouched while submerged. A check of over-all tuning must be made as quickly as possible during the surfacing procedure.

Air search during surface cruising.

Watches of a half-hour duration should be adopted whenever possible. Only those men who have had previous SD radar experience, if available, should be used as operators. When an operator is standing an SD search watch, he must stay within three feet of the equipment, keeping a continual watch on the screen.

Report all targets and IFF signals, giving their ranges. Identify the composition of targets, using the following characteristics as a guide to your interpretation of target pips.

  1. Land (sharp, fairly steady pip).

  2. Single plane (narrow pip, fuzzy at the top, fading and bouncing rapidly).

  3. More than one plane (wide pip, fuzzy at the top, melting off occasionally on either side from the top, and fading at a slower and more even rate than the single plane pip).

Report any unfamiliar signal or disturbance appearing on the screen. The OOD will immediately call the radar officer or technician to check this interference. Internal interference may come from any AC equipment aboard. External interference may represent jamming or other radar signals.

Caution: When jamming, or other radar interference is encountered, it is likely that your position, or approximate position is already known.

Diving procedure.

When the word "stand by to dive" is passed, the operator will perform the following operations:

  1. Turn the transmitter plate variac to zero and turn the transmitter plate voltage switch off.

  2. Lower the antenna mast.

  3. Turn the power switch off.

Care of equipment during long dives.

To minimize troubles or possible damage, due to condensation and moisture, keep the canvas covers on all units; remove and dry these covers frequently if condensation is heavy. Also turn the power switch on (keep the transmitter plate high voltage switch off) for ten minutes every three hours. The controls in the transmitter unit and the receiver-indicator unit should not be touched.

PERFORMANCE

Maximum reliable range.
Target           Range in Miles

Land 3,000 feet or higher           35
Land 1,000 feet           20
Large planes above 1,000 feet           12-20
Small planes above 1,000 feet           8-15
Low planes           Not detected

4-SD-5


Due to the fact that low flying planes will usually not be detected, lookouts must be alert for aircraft flying at low elevations during daylight hours.

Minimum range.

The minimum range on aircraft is about 2,500 to 3,000 yards.

TROUBLES

Trouble is indicated in the SD radar by the following operational difficulties:

  1. From 1/4 to 1½ inches of grass are not present at all times when the sensitivity is turned to maximum. 2. Sweep position, intensity, and focus do not remain constant when untouched by the operator.

  2. Appearance of the transmitter flag does not remain substantially the same.

  3. Internal interference is heavy and persistent.

  4. Arcing is audible in the antenna during normal operation.

  5. Bi-directional, or a non-uniform pattern of transmission is suspected.

  6. Echoes and ranges on known land and friendly planes, appear to be below normal.

    Typical screen interference.
    Figure 4 SD-6. Typical screen interference.

4-SD-6


Part 4.
SU RADAR

CONTROLS
  Controls and range unit
  Modulator unit
TURNING ON AND OFF
  Preliminary checks
  Turning on
  Turning off
CALIBRATION
OPERATIONAL TECHNIQUES
  Tuning the SU
    Tuning with echoes
    Tuning with sea return
    Tuning using the echo box
  Normal search
  Short range search
  Long range search
  General operation
  Station keeping
  Auxiliary fire control and navigation
  Composition
    Type and number of ships
    Aircraft
    Land
    False and misleading echoes
  Antijamming operation
TROUBLES
CHARACTERISTICS AND PERFORMANCE

CONTROLS

The operator of the SU radar is concerned primarily with the Control and Range Unit, although inspection of the Modulator and Bearing and Gyro Switch Units will occasionally be necessary. A line drawing of the Control and Range Unit is shown in figure 1 and of the Modulator and Bearing and Gyro Switch Units in figures 2 and 3. The operator will be called on to make adjustments on these other units of the radar: Transmitter-Receiver; Control Rectifier; Antenna Motor-Generator; and Antenna Assembly.

Identification and Function

All of the controls are plainly labeled on the SU radar. A brief summary of the functions follows: Identifying letters and numbers refer to line drawings in figures 1, 2, and 3.

Figure 4SU-1. Control and range unit.
Figure 4 SU-1. Control and range unit.

Control and Range Unit

A. Line Voltage meter: Reads the AC voltage input to the unit from the ship's line after the power switch (W) has been pressed. The reading should be within the red lines marked on the scale, 105 and 125 volts, and preferably above 112. volts.

B. Operate-stand-by switch: Controls the operation of the transmitter. When in STAND-BY position, the transmitter does not operate, but the filament supplies are kept on. Operation may be resumed immediately by throwing to the OPERATE position.

C. Stand-by lamp: Lights when the operate-stand-by switch (B) is in the STAND-BY position.

D. Battle short on lamp; Lights when the battle short switch (7) is in the ON position, indicating that safety interlocks are shorted out.

E. Range dimmer knob: Controls the intensity of the range scale dial lights.

F. Range handwheel: Controls the position of the step on the A-scope trace, the position of the ranger marker spot on the PPI, and the reading of the range counters.

G. Stabilization correction meter: Shows the angle between the (vertical) position of the stabilized antenna and a line normal to the deck of the ship. This meter should read zero when the Stow-stabilized switch (H) is in the STOW position.

H. Stow-stabilized switch: Normally in the STABILIZED position. In this case, the antenna stabilizing system operates to keep the reflector

4-SU-1


vertical. In the STOW position, the reflector locks in a position normal to the deck of the ship.

I. Danger R.F. unit overheating lamp: Lights if the temperature of the Transmitter-Receiver Unit becomes too high. This is an indication of trouble in this unit.

J. Bearing dimmer: Controls the intensity of the dial lights on the PPI bearing scale.

K. For manual train, push in: The training control. When pushed in, the rotation of the antenna and of the PPI trace is controlled manually by the handwheel. When pulled out, the antenna and trace rotate automatically at 6 r.p.m.

L. Receiver gain: Controls the amplitude of the echo signals and "grass" on the A-scope and brilliance of echoes and amount of "snow" on the PPI.

M. Intensity: Controls the intensity of the trace on the A-scope.

N. Echo box tuning knob: Used to tune the echo box cavity to resonate at the frequency of the transmitter. It controls a motor which, in turn, moves a plunger either in or out of the cavity resonator, depending upon the direction in which the Echo Box Tuning knob is turned.

O. Echo box amplifier switch: When in the ON position, applies the echo box crystal output to the IFF trace. This switch must be in the ON position for tuning when using the echo box method, and in the OFF position for reception of IFF signals. Normally this control is left in the OFF position.

P. Focus: Controls the focus of the image appearing on the A-scope trace.

Q. Intensity: Controls the intensity of the PPI trace.

R. IFF Gain: Varies the amplitude of IFF signals appearing on the A-scope and the PPI.

S. Focus: Controls the focus of the image appearing on the PPI.

T. IFF ON-OFF Switch: produces the IFF trace on the A-scope when in the ON Position. Note that the Echo box amplifier switch (O) must be OFF to allow IFF signals to appear on the IFF trace.

U. L.O. Tuning: Adjust the frequency of the local oscillator in the Transmitter-Receiver unit provided the Manual-afc switch (V) is in the MANUAL position.

V. Manual-afc: Switches in or out the automatic frequency control circuit in the Transmitter-Receiver unit. In MANUAL position, the L.O. Tuning control (U) may be used as a fine adjustment of the local oscillator frequency. In AFC position, the local oscillator frequency is controlled by the AFC circuit.

W. Power (PUSH ON, PUSH OFF): A button used to apply line voltage to, or disconnect line voltage from, the various units.

X. Range Selector switch: Allows the operator to select one of the following scales for the A-scope and PPI. 8,000 yards, 40,000 yards, or 80 miles. The appropriate set of range counters will be illuminated.

Y. Power-on lamp: Lights when power is supplied to the equipment.

Z. Marker intensity potentiometer: Varies intensity of the calibration pips on the PPI scope only. Markers on-off switch (1) must be in the ON position.

1. Markers on-off switch: Controls the markers circuit. When this switch is in the ON position, calibration pips appear on both scopes. The number of pips appearing depends on the setting of the Range selector (X).

2. Relative bearing only lamp: Lights when the SHIP'S GYRO-REL. BEARING ONLY switch located on Bearing and Gyro Switch Unit is thrown to REL. BEARING ONLY position. When lamp is lighted, only relative bearings can be read on the bearing indicator on the PPI. When the lamp is not lighted, both true and relative bearings may be read.

3. Warning Training error lamp: Lights if the antenna and PPI trace fall out of synchronism to an excessive degree.

4, 5, 6. Min. set knobs: Adjust the zero set of the 8,000-yard, 40,000-yard, and 80-mile scales, respectively.

7. Battle short switch: In the ON position, shorts out all interlocks in the Control and Range Unit so that the power remains on even if the chassis is pulled out and the cover is raised. It may be necessary to place this switch in the ON position if gun fire or other vibration opens the interlocks.

8. IFF Delay: Controls the timing of the IFF trace in relation to the transmitted radar pulse. This is adjusted as follows: Rotate Range Selector (X) to 8,000-yard scale and Range crank (F) to the 0-yard position. IFF on-off (T) must be in the oN position. Then turn the IFF Delay control (8) until the trailing edge of the upward pulse

4-SU-2


on the IFF trace (the image of the IFF transmitted pulse) coincides with the leading edge of the range notch.

9. Range step on-off switch: Controls the range step on the A-scope. In the OFF position, the step will no longer appear on the A-scope trace.

10. PPI Bias: Controls the intensity of PPI trace.

11, 12, 13. Max set knobs: Adjust the sweep speeds of the 8,000-yard, 40,000-yard, and 80-mile scales, respectively.

14. PPI-IFF switch: Permits IFF signals to appear ln the PPI when the switch is in the ON position.

Figure 4 SU-2. Modulator unit.
Figure 4 SU-2. Modulator unit.

Modulator Unit

15. Magnetron current meter: normally reads magnetron current, but if the switch marked Push to read modulator current (16) is pressed, it reads modulator current. When the gear is properly adjusted, modulator current should read between 7.5 and 10 ma. when the magnetron current is adjusted to 5.0 ma.

17. AC Line voltage meter: measures the voltage applied to the input of the unit from the ship's line, whether the main power switch in the Control and Range Unit is on or off.

18. All safety switches inoperative lamp: When lighted, indicates that interlocks in the unit have been shorted out by the Battle short switch located behind the lower front panel.

19. High voltage supply on lamp: Lights when the gear is in operation.

20. Accumulative hours meter: Indicates the total length of time the gear has been in operation.

21. AC Power on lamp; Lights when power is applied to the gear.

22. Magnetron current control variac: Should not be adjusted by the operator. The technician will set this control so that the megnetron current will read 5 ma. with power on.

Figure 4 SU-3. Bearing and gyro switch.
Figure 4 SU-3. Bearing and gyro switch.

Bearing and Gyro Switch Unit

23. Ship's gyro-rel, bearing only switch: Normally should be set to SHIP'S GYRO position. In this position, relative and true bearings are indicated on the outer and inner PPI bearing scales, respectively. When the switch is in the REL. BEARING ONLY position, the movable outer scale swings around and locks in at the position where its readings agree with those of the stationary inner scale, and both scales give identical relative bearing readings.

TURNING ON AND OFF

Preliminary Checks

These checks should be made before power is applied to gear:

1. Turn ship's gyro-rel. bearing only switch (23) to SHIP'S GYRO position unless gyro power is unavailable. In this case, turn to REL. BEARING ONLY position.

2. Stow-stabilized switch (H) in STOW position.

3. For manual train-push in (K) crank should be pushed in.

4. IFF gain control (R) should be fully counterclockwise.

5. Echo box amplifier switch (O) should be in the OFF position.

4-SU-3


6. PPI intensity control (Q) fully counterclockwise.

7. PPI bias (10) fully counterclockwise.

8. A-scope intensity control (M) fully counterclockwise.

9. Receiver gain control (L) should be fully counterclockwise.

10. Operate-stand-by switch (B) should be in STAND-BY position.

Turning on

1. Press power (push on-push off) button (W) applying power to the set. Stand-by lamp (C), power on lamp (Y), and C power on lamp (21) should light and the fan motor in the Control and Range Unit will be heard.

2. Check reading of line voltage meter (A). If it does not read between 105 and 125 volts, call a technician.

3. Approximately 1 minute after applying power as above, a clicking noise will be heard indicating that an internal relay has closed. If the intensity controls are then turned up, sweeps will be visible on the scopes.

4. Stow-stabilized switch (H) is thrown to STABILIZED position. It will take 15 minutes or so for the stabilizing circuit to warm up sufficiently to operate satisfactorily.

5. As soon as step number 2 in this procedure has been accomplished, Operate-stand-by switch (b) should be thrown to OPERATE position. Stand-by lamp (C) will go out.

6. Turn on IFF gear.

7. About 3 minutes after the Operate-stand-by switch has been turned to OPERATE, the modulator time delay mechanism will operate, and a click will be heard. High voltage supply on lamp (19) will light. Plate voltage is now supplied to modulator tubes and the gear is transmitting.

8. Check magnetron current by reading meter (15) in the Modulator Unit. If this does not read 5 ma., call a technician.

9. Push switch marked Push to read modulator current (16). If modulator current does not show between 7.5 and 10 ma., call a technician.

10. Turn up A-scope Intensity (M) until the trace is of sufficient brilliance.

11. Focus the trace using Focus control (P).

12. Start the antenna on automatic rotation, and switch to 40,000 yards range scale.

13. Adjust PPI Bias control (10) until the PPI trace is just visible.

14. Turn the Receiver gain control (L) until about three-eights inches of grass is visible.

15. Adjust PPI Intensity (Q) for a faint indication of snow.

16. Throw IFF on-off switch (T) to the ON position. A second sweep will now appear on the A-scope.

17. Adjust the IFF Gain (R) for grass on the IFF trace.

18. Throw the IFF on-off (T) switch to the OFF position.

To place the gear in stand-by condition, merely throw the Operate-stand-by switch (B) to STAND-BY. Stand-by lamp (C) will then light indicating that no radiation is leaving the transmitter.

Turning Off

In order to shut down the gear, the above procedure should be reversed:

1. Push the antenna crank into the manual position. The antenna may be left at any bearing since it is covered from view by a dome.

2. Throw the Stow-stabilized switch (H) to STOW. This will remove power from the stabilizing circuit.

3. Turn PPI Intensity control (Q) fully counterclockwise.

4. Turn A-scope Intensity control (M) fully counterclockwise.

5. Receiver gain (L) counterclockwise.

6. IFF Gain (R) counterclockwise.

7. Throw switch Operate-stand-by control (B) to STAND-BY.

8. Turn off IFF gear.

9. Press Power on-off (W) removing power from the SU gear.

Figure 4 SU-4. How to calibrate.
Figure 4 SU-4. How to calibrate.

4-SU-4


CALIBRATION

To make sure that the SU gear will give accurate range readings, the operator should check the calibration of the ranging unit every half hour for the first hour of operation and every hour thereafter. Each of the three range scales must be calibrated independently. Adjustment of one range scale will not affect the calibration of the other scales. In lining up the range step with the calibration pip, it is suggested that the steps be brought to the left-hand edge of the pip. It is important that the same method of positioning the range step used during calibration be used when ranging on echoes. The preferred method is shown in figure 4-SU-1.

1. Turn the Markers on-off switch (1) to the ON position.

2. Set the Range selector switch (X) on the 8,000-yard scale.

3. Rotate the Range handwheel (F) until the counters read 0 yards.

4. Adjust the Min. set knob (4), aligning the FIRST calibration pip with the range step.

5. Rotate Range handwheel until the range counters read 8,000 yards.

6. Adjust the Max. set knob (11), aligning the FIFTH calibration pip with the range step.

7. Repeat steps 3 through 6 until no further adjustment of Min. set or Max. set is necessary.

8. Set the Range selector switch on the 40,000-yard scale.

9. Calibrate this scale as indicated above, aligning the SECOND calibration pip with the range step at 2,000 yards, and the TWENTY-FIRST pip with the range step at 40,000 yards. Vary Min. set (5) and the Max. set (12).

10. Set the Range selector switch on the 80-mile scale.

11. Calibrate this scale as above, aligning the SECOND calibration pip with the range step at 4 miles and the SIXTEENTH pip with the range step at 79 miles. Use Min. set (6) and Max. set (13).

Note that on the 8,000-yard scale and the 40,000-yard scale, calibration pips appear 2,000 yards apart. On the 80-mile scale, the pips are 5 miles apart, with the exception that the first and second pips are 4 miles apart.

The technician can check the calibration markers circuit of the SU with a double range echo or by knowing the exact range to a given target. The range markers can be moved left or right (before or after in time) with respect to the transmitted pulse to get them lined up correctly. This should be done periodically when such targets are available, but only after the SU is thoroughly warmed up.

OPERATIONAL TECHNIQUES

Tuning the SU

Tuning the SU may be accomplished using echoes from land, surface targets, clouds, or sea return. If none of these is available, the SU may be tuned using the echo box gear with which the radar has bee equipped. Under normal conditions, the AFC (Automatic Frequency Control) circuit will hold the receiver in proper tune. However, the tuning should be checked each watch to determine whether the AFC circuit is operating properly.

(A) Tuning With Echoes.--

1. Stop the antenna on the best target available.

2. Throw the Manual-AFC switch (V) to MANUAL position.

3. Turn the Receiver gain down until the echo is not saturated. (Until it is considerably below maximum height.)

4. Push in the L.O. Tuning control (U) and turn it through its entire range, about three-quarters of a turn. One or more points where the echo will appear on the scope may be found.

5. Select the point at which the echo comes in the strongest, and carefully adjust the L.O. Tuning until the echo pip is at maximum height.

6. Throw the Manual-AFC switch to the AFC position and compare the height of the echo pip with the height when the switch is in the MANUAL position.

7. Normally an echo will appear to be of the same height or slightly higher with the switch in the AFC position. If it is smaller, the AFC circuit is not operating properly, and the switch should be left in the MANUAL position. Tuning should be checked each watch.

(B) Tuning with Sea Return.--The same method is used as described above, except that the sea return should be maximized in range rather than in height. By this, it is meant that the L.O. Tuning control should be adjusted until the sea return extends out to the greatest range possible.

(C) Tuning using Echo Box.--

1. Set the Range selector switch (X) on the 8,000-yard range scale.

4-SU-5


2. Stop the antenna at the desired bearing. Any bearing may be used, but the same relative bearing should be used whenever the echo box is used for tuning.

3. Turn the IFF on-off switch (T) to ON.

4. Turn Receiver gain (L) fully counterclockwise.

5. Throw the Manual-AFC switch (V) to MANUAL.

6. Throw the Echo box amplifier switch (O) to the ON position. No IFF indications will now appear.

7. Turn the Echo Box Tuning knob (N) customarily clockwise and hold it until a negative pulse appears at the left end of the IFF trace. Carefully turn the knob back and forth, maximizing this negative pulse. Now the echo box is tuned to the frequency of the transmitter.

8. Adjust the L.O. Tuning control (U) for maximum ringing time (positive pulse) on the upper trace. The receiver is now tuned to the frequency of the echo box and, hence, to the frequency of the transmitter. This ringing time should be measured in yards by aligning the step with the point where the lagging end of the pulse reaches the base line. This measurement gives a method for determining the efficiency of the gear. If the transmitter decreases in power or the receiver in sensitivity, the ringing time will be decreased.

9. Check the AFC circuit as in the ordinary tuning procedure. If the AFC gives the same or a longer ringing time, as it should, leave the Manual-AFC switch (V) in the AFC position.

10. Detune the echo box by turning the Echo box tuning knob (N) clockwise and holding it until the negative pulse disappears. If the echo box is not detuned, the minimum range of the g ear will equal the ringing time in yards.

11. Throw the Echo box amplifier switch (O) to the OFF position so that IFF responses may appear on the IFF trace.

12. Set the range selector switch (X) on the 4,000-yard scale, and adjust the Receiver gain (L) for the desired grass.

Normal Search

Normally, the 40,000-yard scale will be used for search. Both the A-scope and the PPI should be watched, though echoes will usually appear on the PPI as soon as they are visible on the A-scope. It will be necessary to stop the antenna to obtain accurate evaluation of the composition of targets. Since it is imperative that the antenna be stopped for as short a time as possible, the operator should check for IFF at the same time that he is estimating composition. The antenna need rarely be stopped for over 12 to 15 seconds. If it is impossible to stop the antenna because of orders from the bridge, during complicated maneuvers or other emergencies, it is possible to obtain ranges form the PPI by aligning the range spot, appearing on the PPI trace, with the target. When obtaining ranges, either using the step on the A-scope or the PPI range spot, it is suggested that the step, or spot, be aligned with the leading edge of the target, rather than with the center.

Short Range Search

Short range search is primarily used when submarines, PT boats, or other small targets are anticipated, as well as for station keeping. For this type of search the 8,000-yard scale is used. Attention should be directed principally to the PPI and the antenna should be rotated automatically.

A different gain setting than that used for search on the 40,000-yard scale must be employed unless the gear is equipped with an STC (Sensitivity Time Control) circuit. The operator can discover whether this circuit has been added to the gear by questioning a technician. If this circuit has not been installed, the gain control must be set at a lower value so that the sea return will not make the detection of small targets close to the searching ship impossible. Because of the extremely high frequency of the SU (considerably higher than that of most surface search gears such as the SG and the SL), sea return will be of greater magnitude and will extend to greater ranges.

Long Range Search

This type of search is conducted using the 80-mile range scale. The antenna is rotated manually with the bearing crank. The A-scope should be watched closely, although targets will usually appear on the PPI as soon as on the A-scope. The determination of ranges and bearings is accomplished in the same manner as in the Normal Search procedure.

General Operation

Each ship will have its own search procedure, and it is important that every operator become familiar with the methods used. Ordinarily,

4-SU-6


normal search will be conducted on the 40,000-yard scale, with a 360° long range (80-mile scale) hand sweep every 5 minutes. Ranges and, possibly, bearings to the guide ship will be requested occasionally. Thus it is very necessary that the operator be capable of switching rapidly from one scale to another, making adjustments of gain, focus, intensity to give the best obtainable picture for each scale. A good operator will make these small adjustments instinctively each time he changes from one scale to another.

Station Keeping

If radar is used to supplement regular station keeping methods, it is preferable that a remote indicator such as the VD or VF be employed rather than obtaining information from the SU itself. It should be remembered that the primary function of this gear is surface search, and that any stoppage of the antenna or change in range scale cuts down on the time available for search. All OOD's should realize that while radar give more accurate ranges than the stadimeter, bearing information from optical gear is more reliable. If the SU is used for station keeping, the 8,000-yard range scale should be employed and, if possible, ranges should be taken using the range spot on the PPI without stopping the antenna.

Auxiliary Fire Control and Navigation

(See pages 4-SG-8 and 4-SG-9 of RADTHREE.)

Composition

It is impossible to do more than state a few generalities on the subject of composition. The ability to make intelligent estimates as to the composition of a contact comes only with experience at sea. However, the following may prove to be of some aid to the inexperienced operator.

Type and Number of Ships.--Large ships will be detected at greater ranges than smaller craft. For normal installations aboard DE's, carriers, and battleships will appear at 42,000 yards, cruisers at 38,000 yards, destroyers at 30,000 yards, surface submarines at 20,000 yards, and periscopes at 5,000 yards. These ranges, of course, are only approximate and are dependent upon the exact height of the antenna, weather conditions, and the condition of the gear. The echoes from larger ships will appear to be steadier; fluctuations will be slower than those from small vessels.

The number of ship in a group may be estimated more accurately if the gain is turned down to a lower value than that used for search. Count the peaks on large pips rather than expecting a separate pip for each ship. If ships are closer together than 300 yards in range or 4° in bearing, separate pips will not appear.

Aircraft.--The SU will detect bombers flying close to the water (300 feet) at about 30,000 yards. An aircraft echo will bob, or fluctuate, and will change range and/or bearing much more rapidly than that of a ship.

Land.--Land masses give wider and steadier echoes than ships. Of course, they have no course or speed.

False or Misleading Echoes.--Second-sweep echoes can appear from targets whose range is greater than 1387 miles. These will rarely be observed, and then only from very high land masses.

A more common phenomenon, experienced when operating close to other ships, is the multiple-range (or double-range) echo. If other ships are near by, within 3,000 or 4,000 yards, the returning echo from one of these ships can reflect off the searching ship, strike the target ship again, and finally return to the antenna of the searching ship. The double-range echo may be recognized easily since (1) it will always be on the same bearing as one of the larger targets and (2) it will always be at exactly twice the range of that target. The double-range echo will be very weak under most conditions.

Mast reflections are caused by energy from the radar striking a mast or superstructure, reflecting from this interfering structure, hitting the target, and returning over the same route. The false echo will appear at the same range as the real target and at the bearing of the interfering structure.

Anti-jamming Operation

Although the SU is an X-Band radar, and no practical transmitter has yet been developed to jam such high frequencies, there is every reason to suppose that such a transmitter can be designed in the near future. Therefore, the operator should learn to expect jamming or deceptive measures and know best how to combat them. Deception by the use of dummy targets such as "window," "kites," corner reflectors, and so on will not be covered here. The reader should refer to the section on deceptive countermeasures on RadThree.

It is necessary that the operator know the procedure to be followed in case he finds himself

4-SU-7


jammed. The following is a brief list of rules that should be remembered:

1. Keep Operating. This is most important, since the enemy has no way of knowing whether his jamming is effective and, if operation continues, he may conclude that his efforts are a failure and may secure the jammer. Also, a close watch should be kept of the unjammed sectors to prevent sneak attacks from coming in undetected.

2. Try to get a bearing on the jamming. If two ships can take bearings on a jammer, the approximate position of the jammer may be plotted and positive action can be taken.

3. Report the type and bearing of the jamming to the CIC watch officer. Recognition of the type of jamming may be difficult if not impossible. The operator should refer to Part 3 of RADTHREE for the more common types and their appearance on the A-scope and PPI.

4. Attempt to read through the jamming.

The most important anti-jam device on the SU is the gain control. There is always an optimum setting for any particular type of jamming and this setting will usually be different from that used for search. The proper amount of gain to be used in a particular case must be found by trial and error. When jammed, rotate the gain control back and forth to find this best setting.

Sometimes, some relief may be experienced by changing the receiver local oscillator tuning. This will be true if the jamming is not exactly on the same frequency as the radar, since detuning may detune the jamming signal more than the echo. This measure has a very bad disadvantage, however, which makes it ordinarily inadvisable. The receiver may be detuned and, if no known targets are in the vicinity, the operator will not be able to bring it back into tune quickly. Thus there is considerable chance of missing targets that may be within radar range. Once the receiver is detuned and there is a lack of known targets, the echo box must be used to retune.

Stopping the antenna on the jamming in hopes of reading through with the A-scope is often effective since pips can be detected Through jamming on the A-scope more readily than on the PPI. However, stopping the antenna will inform the enemy that his jamming is, at least, troublesome. Also, of the antenna is stopped, there is more chance of enemy raids coming in undetected on unjammed sectors. The decision of whether to stop the antenna or not, will depend upon the tactical situation.

TROUBLES

Although most troubles will be handled by the technician, the operator should recognize the symptoms of some of the more common failures.

If, when the gear is first turned on, the power-on lamp (Y), the AC power-on lamp (21), and the fan motor in the Control and Range Unit do not operate, the fuses in the power line should be checked by a technician.

If no echoes, sea return, or transmitted pulse appear on the scopes and the high voltage supply on lamp (19) does not light when the operate-standby switch (B) has been in the OPERATE position for over 3 minutes, the fuses in the modulator plate voltage supply should be checked as well as the modulator time delay mechanism.

The danger r.f. unit overheating lamp (I) will light if some trouble in the Transmitter-Receiver Unit on the mast causes dangerous overheating. This may be due to faulty circuit components or shorts in this unit.

Trouble in the antenna drive system may be indicated by the warning training error lamp (3) lighting. When this lamp is lighted, the "bug" on the bearing indicator no longer indicates the direction in which the antenna is pointing. If the antenna has stopped rotating and the "bug" and the PPI trace continue to rotate, the picture on the PPI will appear as a series of markers described through the full 360°. If there are no targets in the vicinity, or if the antenna has stopped on a bearing where no targets are located, nothing will appear on either screen except sea return. The trouble will not be so apparent, but the sea return on the A-scope will not change as the "bug" rotates. If the antenna system does not appear to be operating properly, the operator should try turning the ship's gyro-rel, bearing only switch (23) to the REL. BEARING ONLY position. In this position, only relative bearings can be read off the bearing indicator. If this measure fails, a technician should be notified.

4-SU-8


CHARACTERISTICS AND PERFORMANCE

Antenna-Reflector: Type, dishpan with radome; shape, paraboloid; size, 24 inches diameter.

Feed: Dipole feed from waveguide.

Beam width: Horizontal, 3.8°; vertical, 3.8°.

Rotation speed: Manual train or automatic at 6 r.p.m.

Pulse width, 1 microsecond.

Pulse repetition frequency, 600 pps.

Minimum range, 200 yards.

Range accuracy, 8,000-yard scale: plus or minus 200 yards; 40,000-yard scale; plus or minus 500 yards; 80-mile scale: plus or minus 1,000 yards.

Bearing accuracy, plus or minus 1°.

Range resolution, 300 yards.

Bearing resolution, 3°.

Performance--Maximum Reliable Range:

4-SU-9


ST RADAR (AS USED WITH SJ)

CONTROLS
      Selector control unit
Transmitter-receiver unit
TURNING ON AND OFF
  Turning on
Turning off
CALIBRATION
OPERATIONAL TECHNIQUES
  Tuning
Reading bearing and range
PERFORMANCE
ACCURACY
RESOLUTION

CONTROLS

The ST radar is used in conjunction with the SJ to provide a search radar to be used by submarines while submerged at periscope depth. It can also be used as an emergency search while surfaced. The ST and the SJ both use the same units with the exception of the transmitter-receiver, wave guide, antenna, and the adapter switch box, which is used to switch from SJ to ST. All units except those noted above are fully explained in the SJ section pages 4-SJ-2 and 4-SJ-3.

Selector control unit (for the ST as used with the SJ)
Figure 4 ST-1. Selector control unit (for the ST as used with the SJ).

Selector Control Unit

A. ST antenna switch: selects the ST antenna in the up or ON position or the dummy antenna in the down position.

B. Red lamp which lights when the ST antenna is in use.

C. ST-SJ switch: determines which radar is to be used.

D. Red lamp which lights when the ST radar is selected.

E. Red lamp which lights when the SJ radar is selected.

F. ST echo box switch: turns on the echo box when in the up or ON position for normal operation this is left in the down position.

G. ST rep rate control: varies the pulse repetition rate. The PRF is 1500 ± 10 percent (when the ST is used with the SJ).

Transmitter-receiver Unit

A. Crystal current meter: reads 0.5 to 0.9 milli-amperes when the equipment is properly tuned.

B. Wave-guide transmission line to antenna.


Figure 4 ST-2. Transmitter-receiver unit.

TURNING ON AND OFF

In general the procedure for turning on and off is similar to that outlined in the section on the SJ page 4-SJ-4. The asterisks marks (*) are used to indicate the operations which differ from those where the SJ alone is used. These operations are performed from the main control unit and the selector control unit. (NOTE. --The antenna wave guide valve should be left in the open position at all times.)

Turning On

1. Turn ON heater switch (13) 30 minutes before operating. If at sea, leave heater switch ON at all times.

2. Flip ST-SJ switch (C) to ST position.

3. Put ST antenna switch in the down position (selecting the dummy antenna).

4-ST-1


4. Turn ON main switch (1). A green light will glow if the set is operating correctly.

5. Check to see if the blower motors can be heard in the transmitter-receiver unit. If not, turn the main switch OFF and call the technician.

6. Check the load voltage meter (3) for 120-volt reading. If this is not indicated, adjust the load autotransformer control (4) for 120 volts.

7. Check the regulated rectifier voltage meter (5) for 300 volts. Check this in both positions of the meter switch (6). If either one is off more than 15 volts, call the technician.

8. After a time of approximately 1 minute (sufficient to allow the time delay to act), turn on the high voltage switch (7). If the time delay has operated, the red lamp (8) will light, and the high voltage should be on. The needle on the high voltage rectifier meter (10) should immediately jump to between 0.9 and 1.2 kv. providing the high voltage variac (9) has been left at its proper setting when the set was last secured.

9. The high voltage rectifier current meter (11) should read between 140 and 160 milliamperes.

10. Check the load voltage meter (3) again, for a value of 120 volts.

11. When the ST antenna breaks surface, flip the ST antenna switch (A) to the ON position.

Turning Off

1. Turn off the high voltage switch (7). Do not turn down the high voltage variac (9).

2. Turn off the main switch (1).

3. Do NOT turn off the heater switch (13) unless the set is to be worked on. Other units need not be touched.

4. Put the ST antenna switch (A) in the down (or dummy) position.

5. Flip the ST-SJ switch (C) to the SJ position.

CALIBRATION

Calibrate using the procedure outlined for the SJ on page 4-SJ-4. The ST must be calibrated each time after switching from SJ to ST.

OPERATIONAL TECHNIQUES

In general the operational techniques for the SJ and the ST are the same. Tuning

The ST must be tuned each time after switching from the SJ to the ST. Follow the outline for the SJ on page 4-SJ-5, for tuning.

NOTE.--The ST does not have AFC (automatic frequency control); therefore tuning should be done with the echo box before surfacing and checked when surfaced with available targets or sea return.

The PPI is not used with the ST.

Reading Bearing and Range

Bearings are obtained visually through the periscope. Radar bearings may be obtained by rotating the periscope across the target, stopping when the pip is at maximum height. The ST does not use lobing.

Ranges are obtained in the same manner as that used with the SJ. There is one thing that the operator should remember; in the event there are more than two targets on the scope he must check with the periscope operator to be sure that they are both on the same target. Due to the 40° beam width, it is quite possible to give range readings on the wrong target. Practice and cooperation between the two operators will help correct this trouble.

The ST is not generally used while surfaced. The ST may be used to the best advantage for submerged approaches or obtaining navigational fixes where it is impossible to surface.

NOTE.--AJ operations are the same as those discussed for the SJ on page 4-SJ-8.

PERFORMANCE

The same general conditions affecting SJ ranges are also true with the ST.

Maximum reliable ranges while submerged to 52 feet:

  Yards
BB, CV, large auxiliaries 16,000 to 20,000
CA, CL, medium auxiliaries 13,000 to 16,000
DD, DE, DM, AV, PC, CG, etc. 10,000 to 12,000

Surfaced, the ranges are about two-thirds for those obtained with the SJ.

ACCURACY

The bearing accuracy of the ST is that of the periscope optics. Radar bearing accuracy is about ±5° due to the 40° beam width.

The ST range accuracy is the same as that of the SJ.

RESOLUTION

Bearing: Very poor due to the wide beam. It is about 20°.

Range: 40 yards.

4-ST-2


SR RADAR

INTRODUCTION
CONTROLS
  Panel No. 1:
    Receiver unit
    Control unit
    IFF coordinator
  Panel No. 2: PPI unit
  Panel No. 3:
    Range scope unit
    Bearing indicator unit
  Panel No. 4: Rotation control unit
TURNING ON AND OFF
  Turning on
  Setting up the PPI
  Turning off
CALIBRATION
  Calibrating the "A" scope
  Calibrating the PPI
OPERATIONAL TECHNIQUE
  Tuning the receiver
  Assuming the watch
  Initial contact reports
  Long range search
  Searching over land
  Multiple target tracking
  Fire control liaison
  Composition
  Jamming and deception
PERFORMANCE
TROUBLES

SR RADAR

The SR is the first of a series designed to standardize air search radars. More complete standardization has been achieved in the subsequent SR-1, SR-2, and SR-3. The SR-2 and SR-3 operate on different frequency bands. Thus, with SR, SR-2, and SR-3 in a task force, three different frequency radars would be available. The SR-1 and SR-4 are developmental models.

The SR-6 is a junior version of the SR-3 and on the same frequency band. It is designed to exploit the possibilities of the current practice of using search radars in conjunction with remote scopes. Planned for destroyer installations, it will have slightly lower power output than the SR-3, a 500-pound antenna and no Servo-Antenna control. The SR-3 characteristics make it suitable for heavier ships. The SR-2 is designed for destroyers and cruisers.

The SR is the only one of the series which has reached the fleet in any great quantities.

The antenna is normally rotated clockwise or counterclockwise by a drive motor which revolves the antenna at two speeds, 1¼ and 2½ r.p.m., or 1¼ and 5 r.p.m., depending on the particular installation. An emergency source of power is provided for the antenna drive motor which can be cut in immediately should something occur to the normal system. This emergency system rotates the antenna at 6 r.p.m. clockwise with no servo-control.

An echo box is provided to permit tuning the set when no targets are available and to enable comparative readings to be made which, over a period of time, give an indication of dropping off in performance. The echo box antenna is mounted at the antenna pedestal. In order to tune or take an echo box reading, the operator trains the SR antenna toward the pick-up antenna on the echo box, energizes the echo box by turning on switch (C) of Panel 1, (1-C), and tunes on the echo which will appear on the 4-mile range scale. Over a period of time a "par" range reading may be determined. Deviation from this "par" will indicate the condition of the set.

The SR radars are composed of two major consoles as follows:

The operator is concerned principally with the indicator console. Complete control is ordinarily accomplished from the indicator console. This is done by placing the remote--local switch on the transceiver console in the REMOTE position. All other controls on the transceiver console are the concern of the technician.

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Indicator console
Figure 4 SR-1. Indicator console.

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The SR Indicator Console is composed of four sections, each of which contains one or more standard units as follows:

Identification and Function.--Panel No. 1

Receiver Unit.--A. Receiver band-pass pulse-length selector switch: This switch performs two functions. It selects any desired pulse length with its corresponding pulse repetition frequency from the three combinations available--1, 4, and 20 microseconds; and it also adjusts the receiver band pass characteristic to give best results for each pulse length. The switch positions are labeled according to the sharpness of the band pass characteristic desired, thus the " sharp" position is used when the 20-microsecond pulse is desired, the "medium" position is used when the 4-microsecond pulse is desired, and the "broad" position is used when the 1-microsecond pulse is desired. Note that this labeling is just the opposite of what it would be if pulse lengths rather than band pass characteristics were used as a basis for the labels.

B. PPI Markers: This toggle switch introduces the A-scope range markers into the video input of the PPI Unit. This enables the operator to check the calibration of the PPI against the A-scope and thus insure that ranges to the same contact read on the two indicators will agree.

C. Echo box: switch: This switch energizes the echo box when it is desired to tune the receiver and no steady echoes are available.

D. IF Gain control: This controls the amplification of the receiver and hence affects both the amount of "grass" on the A-scope and the amount of' 'snow'' on the PPI scope. Since there is another gain control (video gain) (2-C) provided which affects only the "snow" on the PPI, the IF gain control should be adjusted for the proper amount of "grass" on the A-scope; and after this adjustment is made the video gain control should be set to give the proper amount of "snow" on the PPI. If any change in the amount of "grass" on the A-scope is subsequently desired, it will be necessary to readjust both the IF gain control and the video gain control.

The following five controls are located inside the door on the Receiver Unit and are marked A-J (anti-jamming) controls on the outside of the door.

E. Balance control: This control is used only when attempting to read through jamming. It is normally left fully counterclockwise.

F. IF tune control: This is the only control the operator will use in tuning the receiver. It is operative only when the 4- or 20-microsecond pulse lengths are being used. Tuning from the indicator console is not possible during use of the 1-microsecond pulse.

G. Time constant switch: Position one is used for normal operation of the set. The other two positions provide two different fast-time constants for use as an aid in reading through jamming and as an echo separator when tracking over land.

H. Rejection filter 1: An anti-jamming control.

I. Rejection filter 2: An anti-jamming control.

J. Jamming indicator: The meter normally reads 0.1 to 0.2 milliamperes. During jamming, the reading increases. The A-J controls are used to minimize the reading of this meter.

Control Unit.--K. Local control indicator light: When lit, this indicates that the operator may take control of the transmitter from the console by use of the controls on the control unit. If this light is not on, it will be necessary to turn the control switch on the transceiver to the REMOTE position before the console controls will be effective.

L. Transmitter on indicator light: When lit, this indicates that the set is in a stand-by condition.

M. Radiation switch: This switch controls the generation of high frequency energy in the transmitter. When the switch is in the counterclockwise position no energy is being generated.

N. Power-on button: This button energizes the plate voltage circuits in the transmitter as well as making power available to the console.

O. Power off button: This button removes plate voltage from the transmitter and power from the console.

P. Plate voltage raise button: This button allows the operator to raise the plate voltage applied to the transmitting tubes.

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Q. Plate voltage lower button: This button allows the operator to lower the plate voltage applied to the transmitting tubes.

R. Indicator console power switch: This switch applies power to the PPI Unit and Range Scope Unit.

IFF Coordinator Unit.--

S. IFF challenge switch: This puts the IFF system into operation from a stand-by condition.

T. IFF overload relay reset button: This will reset the overload relay of the interrogator connected with it. It is not found on all SR's.

U. Echo suppressor switch: This is used to suppress echoes appearing on the IFF time base at ranges less than 10 miles when tracking over land.

V. IFF receiver gain control: This controls the gain of the IFF receiver.

Panel #2

PPI Unit.--

A. Bearing marker dimmer:

B. Miles--The range scale indicator window.

C. Video gain control: This controls the amount of "snow" on the PPI, the strength of the echoes applied to the PPI, and the strength of the markers that may be brought from the range scope by means of switch (1-B).

D. Fine intensity control: This controls the intensity of the trace on the PPI and hence affects the sensitivity of the PPI.

E. Range selector switch: This switch selects one of the four operating ranges, 4, 20, 80, or 200 nautical miles. The range scale selected appears in the window (2-B).

F. Focus control: This adjusts the sharpness of the trace on the PPI.

G. Center expand switch: This throws the inner end of the time base outward about three-eighths of an inch from the center of the tube to allow bearings to be read easier on nearby contacts.

H. Markers control: This controls the intensity of the markers produced in the PPI unit. There are four such markers on each range scale.

I. Relative bearing indicator: This light glows when bearings on the PPI are relative and is out when they are true bearings.

J. Power switch for PPI unit:

K. AC: 115-volt outlet for maintenance purposes.

Panel #3

Range Scope Unit.--A. A-scope intensity control: This controls the brightness of the trace on the scope.

B. Vertical centering control: This controls the up and down position of the trace on the scope.

C. Markers switch for A-scope: This turns on the four range markers which appear as downward pips on each range scale.

D. Miles: This is the range scale indicator window.

E. Focus control: This adjusts the sharpness of the trace on the A-scope.

F. Horizontal centering control: This is used to align the zero range marker with the zero range mark printed on the glass over the scope face.

G. Sweep length control: This should be used to align the remaining three markers with the corresponding marks on the scale printed on the glass over the scope face.

H. Range switch: This switch selects one of the four operating ranges available. The four range scales are 4, 20, 80, 400 nautical miles.

I. Range step control: When this knob is pulled out, an offset appears on the A-scope trace coincident in range with the reading of the range counters. There is no range step on the 80- and 400-mile scales.

Bearing Indicator Unit.--

J. True bearing indicator light: This green light glows when true bearings appear on the left hand dial in the window on this unit.

K. Relative bearing indicator light: This red light glows when the left hand dial in the window is indicating relative bearing.

L. Slewing motor or antenna speed control: The middle position of this switch is OFF. Other positions of this switch rotate the antenna at l}i and iy2 or 5 r.p.m. clockwise or counterclockwise.

M. Emergency antenna rotation control: In case of a casualty to the servo-generator or associated devices this switch can be thrown from the NORMAL to the PPI or EMERGENCY position, and the antenna will rotate clockwise at about 6 r.p.m.

N. Hand slew control: This control allows the operator to rotate the antenna manually.

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Panel No. 4

Rotation Control Unit.--

A. Remote indicators switch: This must be in the ON position for remote indicators to be operative.

B. Synchro system--true relative bearing switch: On some SR's this switch is labelled OSC-AC. With the switch in the OSC or TRUE position, true bearings may be read from the bearing indicator and from the PPL If the gyro compass is out, the antenna will stall and remain still until this switch is thrown into the AC or RELATIVE position. In this position all bearings from the bearing indicator and PPI will be relative bearings.

C. Circuit breaker for antenna train motor: In case of a temporary or permanent overload of the antenna train motor, this breaker will cut off its power.

D. Circuit breaker for servo-generator motor: This breaker will protect the servo system from damage during a temporary or permanent overload.

E. Power light.

F. Power switch for Rotation Control Unit: When this switch is on, power is furnished the Rotation Control Unit and (E) is lighted.

TURNING ON AND OFF

Turning ON

Preliminary Checks

1. Synchro system switch (4-B) to OSC or TRUE.

2. Remote indicators (4-A) to ON.

3. Rotation Control Unit power switch (4-F) to ON.

4. Rotation switch (3-M) to NORMAL.

5. Slewing motor (3-L) to OFF.

6. A-scope intensity control (3-A) counterclockwise.

7. PPI video gain control (2-C) counterclockwise.

8. Fine intensity control (2-D) counterclockwise.

9. Center expand switch (2-G) to the LEFT.

10. Markers control (2-H) counterclockwise.

11. PPI Unit Power switch (2-J) to ON.

12. IF gain control (1-D) counterclockwise.

13. Echo box switch (1-C) to OFF.

14. PPI markers switch (1-B) to OFF.

15. Radiation switch (1-M) to OFF.

Applying Power

1. Press power ON button (1-N). If remote--local switch at the transceiver is in remote position, the plate volts indicator light will glow and the plate volts meter will read minimum voltages.

2. Check all fuse lights. No fuse alarm should be lighted. If any is lighted, replace the fuse with one from spares, making certain one of the same size is used in the replacement.

3. Throw radiation switch (1-M) to ON or LOCK.

4. Press the RAISE button on the raise--lower switch until the plate volts meter reads 11 kilo-volts.

Setting up the A-Scope

1. Turn up intensity control (3-A) until the line on the A-scope is about the same brilliance as the dot which appears at the beginning of the sweep and adjust the focus control (3-E) until the line is fine and clean. It may be necessary to readjust the intensity and focus controls together until the fine, clean line appears on the scope face.

2. Adjust the horizontal centering control (3-F) until the sweep or line starts at the zero figure on the glass over the tube face and adjust the vertical centering control (3-B) until the sweep is slightly above the zero figure.

3. Set the range switch (3-H) so that the numeral 20 appears through the small window indicated as miles (3-D) on the panel. This places the A-scope on the 20-mile range.

4. Turn the markers switch (3-C) to ON. Four markers should appear as vertical depressions in the sweep.

5. Adjust the sweep-length control (3-G) until each of the four markers falls behind a figure on the glass over the tube face.

6. Turn the range switch (3-H) to the 4-mile, 80-mile, and 400-mile ranges and make certain that the markers appear on all the range scales. They will not necessarily fall behind the numbers on the other ranges. Therefore it will be necessary to repeat step (5) above each time the range scale is changed during operation.

7. Pull out the range step control (3-1). A vertical break, or step, should now appear on the sweep if the range switch (3-H) is in the 4-mile or the 20-mile position. There will be no range step present when this switch is in the 80-mile or 400-mile position.

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8. Push the challenge switch (1-S) to the MOMENTARY position and hold it there a moment. A second trace should appear about three-eighths of an inch below the sweep on the A-scope face. If this second trace does not appear or is out of proper position, a technician should be called to adjust the IFF coordinator.

Setting Up the PPI

1. Set the slewing motor control (3-L) to the 1¼ position in either direction.

2. Set the range selector switch (2-E) to the 200-mile range scale as indicated by the numeral which appears through the small window directly above the switch labeled miles (2-B).

3. Turn up the fine intensity control (2-D) until a fine trace is barely visible on the scope face.

4. Adjust the fine intensity (2-D) and focus (2-F) controls alternately until the trace appears sharp and clear and just barely visible.

5. Turn up the markers control (2-H) slowly until four bright dots appear along the sweep on the face of the tube. These should be approximately equally spaced.

6. Throw the range selector switch (2-E) to the other three positions and check to see if the dots appear as above.

7. Leave the range selector switch (2-E) set on the range scale to be used and adjust fine intensity (2-D) focus (2-F) and markers (2-H) until the sweep is sharp and clear and the concentric circles traced by the markers are as narrow and clear as possible.

Turning off

1. Stop the antenna rotation about 3-5° away from 000° relative. At 000° relative bearing the PPI sweep is intensified to act as a ship's head marker. If the antenna is secured at that bearing the bright trace may do damage to the PPI tube face when the set is turned on and before the antenna is put into motion.

2. Turn down the A-scope intensity (3-A).

3. Turn down the PPI video gain (2-C) and fine intensity (2-D).

4. Turn down the IF gain (1-D).

5. Press the plate voltage lower button (1-Q) until the meter reads zero.

6. Press the power OFF button (1-O).

CALIBRATION

Calibrating the A-scope

1. Turn markers switch (3-C) to ON.

2. Set the range switch (3-H) so that the numeral 4 appears through the small window indicated as miles (3-D) on the panel. This places the range scope on the 4-mile range.

3. Adjust the horizontal centering control (3-F) until the sweep starts at the zero figure on the glass over the tube face and adjust the vertical centering control (3-B) until the sweep is slightly above the zero figure.

4. Adjust the sweep length control (3-G) so that each of the four markers falls behind a figure on the glass over the tube face.

5. Pull out the range step control (3-I) and rotate the range step handle until the break or range step just touches the left-hand side of the first marker. The range yards counters should now read 2,000 yards. Repeat this operation with the other markers. The counters should read 4,000, 6,000, and 8,000 respectively for these markers. All range counters should read correctly to within 100 yards on all marker points. If the range counters do not indicate to the required accuracy, a technician should be called to adjust the circuit.

6. Repeat the above steps for the 20-mile scale as selected by the range switch (3-H).

Calibrating the PPI

1. Turn the slewing motor control (3-L) to 1¼.

2. Turn the PPI markers switch (1-B) to ON.

3- Switch to the 20-mile scale on both scopes (2-E) (3-H).

4. Turn up the video gain (2-C) until four bright dots appear along the sweep on the face of the tube. These four dots will draw 4 concentric circles on the PPI and should be approximately equally spaced.

5. Turn up the markers (2-H) until four more bright dots appear along the sweep on the face of the tube. This second set of markers should produce concentric circles coincident with the others to within a mile.

6. Switch to the 80-mile scale on both scope (2-E) (3-H) and repeat steps 4 and 5 above. If the two sets of markers are found not to be coincident within the tolerance of 1 mile, a technician should be called to make the necessary adjustments. Under no circumstances should the operator attempt to make these adjustments.

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OPERATIONAL TECHNIQUE

Tuning the Receiver

The technician will have the transmitter tuned for maximum power output and it should not be touched by the operators. The duplexer, R. F. lines, pre-amplifier, and mixer are also tuned by the technician. The adjustments necessary for the operator to make are few and are outlined below:

1. Turn up IF Gain (1-D) until echoes appear or until there is some grass on the A-scope.

2. Switch to the 20-mile scale (3-H).

3. Operate IF tune control (1-F) for maximum echoes on the A-scope adjusting IF Gain (1-D) as necessary to keep the target from becoming saturated. Tune for maximum echo height by going a little over and then a little under maximum. Jockey back and forth rapidly stopping between the two points, a little over and a little under, for optimum tuning. When available, land echoes should always be used for tuning.

Assuming the Watch

When taking over the watch, the SR operator should make the following checks as soon as possible:

1. Check search procedure set-up.
2. Check the tuning of the receiver.
3. Check A-scope calibration.

Initial Contact Reports

Since the primary function of an air-search radar is served only when the antenna is in motion, operational technique should be such that the antenna is kept moving a maximum amount of time. The importance of this is generally under estimated, except by fighter director officers who have their own obvious reasons and by anyone else getting information from a remote PPL

Since most of the time lost is in reporting a new contact, a quick, efficient, and standard method of submitting an initial contact report is required. This should include:

1. Bearing.
2. Range.
3. Identification.
4. Composition.
5. Apparent relative movement (opening, closing, crossing) is possible.

On the SR the quickest way to obtain this information is to read the bearing and range from the PPI as soon as the target appears, without the use of the range step. With a little practice, almost anyone can read ranges from the PPI with facility and accuracy to within 1 mile using only the 20-mile markers as indicators. This is sufficient accuracy for an air-search radar. The bearing is obtained by merely splitting the target on the PP with the cursor. After the bearing and range are reported, the operator should stop the sweep under the cursor, adjust the IF gain (1-D) so that he can check composition on the A-scope, and check identification. Before reporting this information, he should put the set back into operation by adjusting the gain and starting the antenna rotating. He should then report. The total time the antenna is stopped normally should not exceed 20 seconds. The information will come to CIC in a manner similar to the following:

Combat, SR. I have a contact zero zero three, fifty-two. (Pause while interrogating, noting composition and relative movement.)

Bogie, three to five, crossing.

Thereafter, the good operator should obtain fixes from the PPI only, never stopping his antenna on that same target again unless it must be tracked over land.

When a contact has disappeared or is starting to disappear, the fade should be reported immediately and reappearance of a raid from a fade should be reported with the same promptness since this information can be a means of determining the approximate altitude of the raid.

Long Range Search

Searching for initial contacts at any range while striving for optimum performance of the radar to obtain these contacts at maximum range is the meaning of long-range search. It is conducted with or without indications being present on the scopes.

The range scale used on the scopes will depend on the tactical situation. In a carrier task force, initial contact at long range is highly desirable. Two methods of search are possible:

1. PPI on 80-mile range scale, and A-scope on 400-mile range scale, or

2. PPI on 200-mile range scale and A-scope on 80-mile range scale. Check the calibration when changing range scales on the A-scope.

When using the first method, most careful watch is made on the A-scope with an occasional search on the PPI.

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Method No. 2 indicates that the most careful watch will be maintained on the PPI with an occasional search using the A-scope.

Except when tracking over land, the PPI is used almost exclusively in giving target ranges and bearings to the plotter. Thus the advantage lies with method No. 1 since most tracking will be done within 80 miles. This can be done immediately since no change of scale on the PPI is necessary.

If the task force has no air support, 80-mile warning of approaching aircraft is sufficient, and both scopes may be operated on the 80-mile range.

The IF Gain or receiver gain (1-D) setting should be such as to give about one-fourth to three-eighths of an inch of grass on the A-scope at all times. The Video Gain control (2-C) should be turned up until there is considerable "snow" on the PPI, but not so high that a target which appears as a "cucumber," will be obliterated.

The 20-microsecond pulse width is the best to use on long-range search since targets will appear in greater thickness and can be detected at greater distance.

The antenna should be rotated at its slow rate--1¼ r.p.m. A plot should be started on the first indication no matter how weak the signal. Stop the antenna on the next sweep, study the blip on the A-scope for composition, and challenge the plane with IFF equipment. This pause in searching should consume as little time as possible.

Searching Over Land

When the radar is used for searching over land, target pips will be mixed with land pips and in many cases obliterated. Since planes give less steady echoes than land on the A-scope, these bobbing echoes can be followed through the land clutter somewhat readily. The PPI, of course, is almost valueless while tracking over land and should be used only as an auxiliary scope on a different range scale than the A-scope. Bearings cannot be obtained very accurately, but the bearing of maximum fluctuation of the pip on the A-scope should be reported.

It will be well to use the 20-mile range scale of the A-scope, leaving the PPI on the 80-mile scale. Use manual control of the antenna rotation; and since better definition is obtained with a shorter pulse, use the 4- or 1-microsecond pulse widths. The gain setting will be shifted as needed to reduce land echoes from saturation. When the Time Constant switch (1-G) is in one or the other of the two fast time constant positions available, echoes from land masses can be broken up to further enable the operator to see the bobbing moving pip produced by the plane.

The operator must remember to keep searching. He must not find one target and stay there from that time on.

Multiple-target Tracking

Multiple-target tracking must be done on the PPI. The 80-mile range scale will be found to be most suitable in most cases. When tracking targets over 40 miles in range, better performance will be obtained using the 20-microsecond pulse. In tracking targets closer than 40 miles, the advantage of better range definition makes the 4-microsecond pulse most useful. The antenna rotation speed should be increased to 2½ or 5 r.p.m. Report half the targets on each revolution of the antenna if the 2½ r.p.m. speed is the one available. Report half the targets for each two revolutions of the antenna if the 5 r.p.m. speed is available. The IF Gain (1-D) setting should be high--from one-fourth to three-eighths inches of grass on the A-scope. The Video Gain (2-C) should be high enough for plenty of "snow" on the PPI. All bearings are obtained by rotating the ring around the PPI until the cursor splits the target and then reading the bearing from the illuminated dial. All ranges are estimated from the PPI using the markers as guide. An experienced operator can estimate these ranges to within 1 mile.

Fire Control Liaison

Fire control liaison may be conducted on the 80-mile range with normal gain setting at about 10 miles, provided there are not many targets at the same range. When there are several targets on different bearings within 10 miles, their echoes and side lobes will ring the PPI and cause too much confusion for fire-control coaching.

When the primary interest is fire-control coaching, the PPI should be operated on the 20-mile range. The gain should be reduced to an amount just sufficient to keep the targets at the longest ranges appearing on the scope. This will eliminate some side lobes and reduce strength on all side lobes while holding echoes from the main lobe on the screen. This method of operation eliminates any chance of observing planes coming in at ranges

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greater than 20 miles, but is the most effective method when the primary purpose is fire-control coaching. At GQ, the stand-by operator can keep the fighter director officer informed of the general situation outside 20 miles by observing the range scope and taking ranges and bearings with continuous antenna rotation.

Composition

Determination of composition of the target requires more operator experience and closer observation than any other phase of operation. Determination of composition involves use of IFF to determine whether or not a contact is friendly, and observation on both range scope and PPI to determine number and size of planes in the group.

Large planes will have a low rate of fluctuation in echo amplitude, while small planes will have a high rate of fluctuation. The range scope is a better source of information on composition than the PPI. When a contact is made, the antenna should be stopped on the target, the gain reduced to one-sixteenth inch of grass on the A-scope, and a thorough examination of the echo made. The echo received from one plane will always be sharply pointed, and its shape will remain essentially the same. This is true of all types of planes. The echo from two or three planes will give a slightly rounded point with the top of the pip filled in so that it is brighter than the remainder of the pip and a somewhat wider base. Five to eight planes will have an echo pip with its peak showing two or more points. The top will be filled in and the base will be fairly wide. In all cases, the point is the telltale feature of the pip. Remember that the larger the flight, the larger the echo pip will be. Ten or more planes cause the top of the pip to become quite jagged. The pip may be filled in halfway down. Watch also for indication of a tendency for the echo pip to pull apart in several places. For large groups of planes, watch the break in the base line. This will tell the operator if the group is stacked (at various altitudes) or spread out at the same altitude. Remember to turn down the gain to see. The range at which the target comes in is not conclusive proof of either its size or altitude, but is a major factor contributing to these estimations. The operator should give his estimate of the composition of every contact and this estimate should be substantiated or corrected by visual means whenever possible. The operator should then be notified of the exact number, size, formation, and altitude. Continuous repetition of this process is the only means of improving the operator's technique in determining composition.

With the 20-microsecond pulse, all echoes will be larger than with the 4- or 1-microsecond pulses. Therefore, at first the tendency will be to overestimate when interpreting during use of the 20-microsecond pulse and to underestimate during use of the 4- and the 1-microsecond pulses.

Clouds, rain squalls, and ionized masses of air are readily detected on the A-scope, and are usually easily identified on the PPI. Broad fuzzy pips, that move slowly with occasional fading out, are characteristic of these targets, although sharp narrow pips have been observed. If identification is difficult by looking at the pip, a plot should be made to determine course and speed. This should then be compared with the course and speed of the wind, which is the best check outside of actual observation.

Any operator will learn to recognize land readily. However, most of them, on looking at a group of pips from land, will call the highest pip the highest peak of land as "seen" by the radars. This is wrong. The highest pip will be from that part of the land which has the best reflecting surface. The peak will be hard to identify if there is a range of mountains behind it, or mountains in the near vicinity at about the same range.

Jamming and Deception

There is no doubt that the enemy considers our radar an extremely dangerous weapon, and consequently it is only reasonable to expect him to try every means possible to make it less effective. He may use two tactics to do this: jamming and/or deception. Every operator should learn how to recognize these countermeasures, and expect them when in combat zones.

The broadcast of radio signals with the intent that our radar receive them, and that they show a confusing pattern on the screen, is called jamming. Use of dummy targets (tinfoil, kites, balloons, etc.) is called deception. More precise definitions are sometimes given, but these are satisfactory for this discussion.

The SR radar can be jammed, and it will show echoes from the tinfoil "window" which the enemy sometimes throws out to confuse the operator. The operator should not become alarmed when either of these things happen.

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The anti-jamming features of the SR receiver include two rejection filters rej 1 (1-H) and rej 2 (1-H), a receiver balanced video control--bal video (1-E) a fast time constant switch (I-G), and a jamming indicator (I-J). During normal operation the above controls should be to the left or all the way counterclockwise. The jamming indicator will read 0.1 to 0.2 milliamperes. In addition to these special controls the IF gain (1-D), IF tune (1-F) and the receiver band pass selector switch (1-A) (pulse length selector and therefore PRF selector) are extremely helpful in antijam technique.

To the uninitiated, sudden appearance of jamming on the scopes appears impossible to combat. It is not that serious if the following procedures are adhered to:

When jamming is first noted, the operator should not stop the antenna on the bearing from which the jamming appears to come. This would immediately reveal to the jammer that he was right on frequency and therefore effective. Instead, take the following steps:

1. Report the presence, intensity, bearing and any other information available while the antenna is rotating.

2. Request permission to attempt to "read through" the jamming. From this step on, the IF gain control (1-D) should be turned to various positions for the different tests tried.

3. Using the jamming indicator (1-J), operate the first and second rejection filters--rej 1 and rej 2 (1-H) (1-1) until the jamming indicator reads a minimum value, relative to one setting of the gain control.

Note: It should not be expected that a normal A-scope picture will be obtained. With close observation, the merest break or hook in the time base will be enough to reveal the bearing, range, and perhaps even composition of a target. The PPI is valueless when attempting to read through jamming of any appreciable intensity.

4. Try first one of the time constant switch (1-G) positions and then the other.

5. Operate the receiver Balance control (1-E) through its entire range using different settings of the rejection filter controls as well as the gain control.

6. Shift PRF.

7. Detune the receiver, first noting the original setting of IF tune (1-F), in order to reset it, should detuning prove ineffective.

8. If none of the above steps is effective, request permission to secure the transmitter by turning off the radiation switch (1-M) for a period of 2 to 4 minutes. Turning the set off informs the enemy that his jamming is effective and this should never be done unless there is sufficient reason to believe the enemy already knows he is effective. Turning off the transmitter might also lead the enemy to believe that your set is secured and that you have given up. At the end of the silent period^ with the antenna trained on the last known bearing of the jamming, turn the radiation switch (1-M) back on in the attempt to pick up the source of the jamming before the enemy realizes the transmitter is back on the air. Under no circumstances should the operator secure the radar for more than the 2 to 4 minutes prescribed.

The reason for obtaining a bearing on the jamming is to determine whether or not it could be accidental interference instead of jamming. Jamming will not only be directional, but its true bearing will not be changed by any sudden change in your ship's course. Interference originating aboard your own ship will either be nondirectional and appear on all bearings, or else it will always be on some certain relative bearing regardless of changes in own ships' course.

Moving the gain control up and down is probably one of the most important countermeasures to be taken and the most commonly overlooked because of its simplicity.

In most cases, except when effective noise modulated jamming is being encountered, there is a setting of the gain control with which it is possible to range on a target in the presence of heavy jamming. If there are several echoes on the same bearing, the best setting for each echo is different. Of course, it is more difficult to obtain these ranges because of the distortion of the echo produced by the jamming but it is possible to obtain the desired information. The extra effort is worthwhile because the enemy would not be jamming unless he were trying to conceal something important".

Two general methods of using the gain control, both of which should be tried, are as follows:

(a) Reduce the gain: This prevents overload of the radar receiver; echoes are visible "riding on top" of the jamming pattern.

(b) Increase the gain: This limits (or clips) jamming; echoes are visible as a break in the base line.

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Be sure to return all controls to their normal setting when no jamming is present. The gain control must be returned to normal every time the antenna is turned to an unjammed bearing.

Perseverance is a particularly valuable quality in operational technique when attempting to "read through" jamming. The effectiveness of the jamming may change from time to time, and if you persevere some of the information may be obtainable. The necessary information may be presented on the scope for only a few seconds. Alertness and close observation will make these few seconds valuable. A point to keep in mind is that the echo signal strength of the jamming ship or aircraft increases faster as it closes than does the strength of the jamming signal.

PERFORMANCE

Maximum ranges obtained on planes will vary greatly with the altitude of the plane, because of fade areas and the curvature of the earth. Large, high-flying planes have been observed at 130 miles. Average ranges on medium altitude planes are from 70 to 90 miles, and on low-flying planes, from 25 to 40 miles.

Maximum ranges on surface targets will vary with antenna height, size of the target, and weather conditions. In most cases, the maximum ranges will be 6,000 to 10,000 yards less than those obtained on the same targets with surface-search gear.

Maximum Reliable Range

BB, CV, CB Large AuxiliariesCA, CL Medium AuxiliariesDD, DE, DM, AV, PCLarge planes at 10,000 feetLarge planes at 500 feetSmall planes at 10,000 feet
        Miles
  20
  20
  15
  90
  25
  75

Minimum Range

A-scope:
1 microsecond pulse yards 300   
4 microsecond pulse " 1,200   
20 microsecond pulse miles

Accuracy

Reading directly from the PPI, range accuracy is ±2,000 yards or better, and bearing accuracy ±2°.

Range accuracy is dependent on the pulse length chosen. Listed in the table below are range accuracies, for the A-scope for the three possible pulse lengths:

Pulse
length
(micro-
second)
Range scale
4-mile 20-mile 80-mile 400-mile
1 ±100 yds. ±300 yds. ±1,200 yds.    ±1 mile  
4 ±150 yds. ±500 yds. ±1 mile   ±3 miles
20   ±1,000 yds. ±2 miles ±5 miles

Resolution

Bearing degrees 10
Range:
          1 microsecond pulse yards 200
  4 microsecond pulse " 800
  20 microsecond pulse miles 2

TROUBLES

1. Transmitter kicking out: This may occur due to jar of gunfire or surge currents. Sweep traces will disappear from both scopes, the transmitter plate voltage meter will read zero and the transmitter ON indicator light (1-L) will go out. After some time, the light (1-L) will go back on. When this occurs, press the plate voltage Raise button (1-P) until the meter reads 11 kilovolts.

2. IFF interrogator kicks out: This trouble is recognized by lack of the IFF transmitter pulse and grass on the IFF time base. Press the relay reset button (1-T) which is installed in the IFF panel on some SR's. On gear not having this control, it is necessary to go to the interrogator itself.

3. Servo-generator motor circuit breaker (4-D) operates automatically to OFF: When this trouble occurs, the antenna, the sweep on the PPI, and the bearing dials will stop. Operate rotation switch (3-M) to the PPI on EMERGENCY position.

This will give an antenna rotation of 6 r.p.m. clockwise with no speed control and no manual train control. Notify the technician.

4. Antenna train motor circuit breaker (4-C) operates automatically to OFF:

When this trouble occurs, the antenna, the PPI sweep and the bearing dials will stop. Notify the technician immediately. There is now no way of training the antenna until the trouble is corrected.

A second type of trouble, that producing a gradual decrease in the operating efficiency of the set, is much harder to detect. The operator must be on the lookout for this second type of trouble at all times. One indication can be the point to which the IF gain control and video gain control must be

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turned to get the normal amount of grass. A knowledge of the "par" range reading of the echo box will aid in detecting a gradual decrease in operating efficiency. The best indication is the ranges that are being obtained on objects with which the operator is familiar, such as ships in his group or land in the vicinity. If poor results are being obtained, the operator may try retuning. If this does not help, the maintenance man should be notified.

On all troubles, the operator can greatly assist the technician by giving a true and accurate description of what happened on the scope when the set went out of operation. This is especially true of intermittent troubles.

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SP RADAR

 
UNITS OF THE CONSOLE
IFF Coordination Unit
  Power Control
  Indicator
  Plan Position Indicator
  Range Unit
  Radar Receiver Unit
  Main Power Unit
  Precision Alignment Unit
  Auxiliary Power
  H. V. Power Unit
TURNING ON AND OFF
  Turning On
  Placing the Gear in Ready Stand-by Position
  Placing the Gear in Complete Off Position
  Emergency Off
CALIBRATION
  Checking the Calibration
    Fine Range "R" Scope
    Coarse Range "R" Scope
    PPI Scope
OPERATIONAL TECHNIQUE
  Tuning the Receiver
    Controls
    Tuning--Using the Land Echo
       Using the Ship Echo
       Using Sea Return
       No Echo or Sea Return
  Operating the Set
    General
    Detecting the Target
    Special Tasks Composition
    Double or Triple Trip Echoes
    Second Sweep Echoes
    Cloud Echoes
    Jamming and Deception
THE DUAL IFF SYSTEM
TROUBLES
PERFORMANCE

SP RADAR

UNITS OF THE CONSOLE (Fig. 4 SP. 1)

IDENTIFICATION AND DESCRIPTION OF CONTROLS AND INDICATORS ON THE CONSOLE

1. IFF Coordination Unit

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Schematic SP console
Figure 4 SP-1. Schematic SP console.

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2. Power Control Unit

3. Indicator Unit

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4. Plan Position Indicator Unit

5. Range Unit

6. Radar Receiver Unit

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7. Main Power Unit

8. Precision Alignment Unit

9. Auxiliary Power Unit

10. High Voltage Power Unit

TURNING ON AND OFF

The antenna unit, mounted on the mast, has three mechanical "stow" controls, (1) elevation, (2) azimuth, and (3) cross level. The antenna must be stowed and unstowed only by an experienced person. The operator must ascertain that the antenna unit is ready for remote control from his console before turning the set on. Azimuth, Elevation, and Cross Level Telltale Indicators (2R, 2S, 2T) will flash on if controls are turned away from true position of antenna.

Turning on SP RADAR

1. Throw bulkhead switches admitting ship's power to entire set. Usually the stable element is energized from the same switches.

2. Determine whether you are to use the "A," CG-35ABD (serial 1) 600 cycle, 1-microsecond or the "B" CG-35ABE (serial 2) 60 cycle, 5-micro-second modulator.

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3. On the console turn Pulse Length (4D) to "1" for modulator "A" or "5" if using modulator "B."

On transmitter unit close transmitter "ON-OFF."

On modulator close modulator" ON-OFF."

On console hold "STOP-START" switch (2U) on "START" for three seconds.

The following events will occur.

4. On console turn Console Power Switch (7H) "ON." White Lamp (7G) "on."

Close Plate Power Switch (7D). Red Lamp (7E) "on."

Close Local Oscillator Switch (9G). Red Lamp (9H) "on."

Close Scop Plate Power Switch (10B). Red Lamp (10A) "on."

Heater Switch (10F) is left "ON" at all times. Energizes automatically when set is secured.

Meters (9C) and (9D) must be set accurately at 200 volts and 300 volts respectively.

5. Throw Radiate Stand-By (2W) to "RADIATE." Red Lamp (2P) "on." Identical indicators on modulator and transmitter units.

6. Operate Raise-Lower (2V) to obtain correct reading on Oscillator Current Meter (2F). Modulator Primary Voltage Meter (2D) indicates rise or fall. Identical controls on modulator and transmitter units.

IFF Gear

at the "A" Band Interrogator

1. Main Power Switch on outside panel is turned "ON."

2. Power Switch on inside panel is turned "ON."

3. Sync Switch is turned to "EXTERNAL." High Voltage Toggle Switch turned "ON."

R. F. output should be turned to maximum (control at console will vary output). Other controls left as technician has set them.

4. Main door on gear must be closed.

At the "G" Band Interrogator

1. Steps to turn on exactly the same as above for "A" band interrogator.

At the Console, "A" band Interrogator

1. " A" Band Power Toggle (1L) to " ON."

2. Selector Switch (1Q) to the " BM-A Scope" position.

3. "A" Band Challenge Switch (IP) set to "lock on" or "key" as desired will start the IFF to challenge. Yellow Lamp (1A) "ON." NOTE: If yellow lamp does not flash on during challenge, turn "A" Band Power Control(1C) extreme counterclockwise. Press Reset Switch (IB) and turn 1C clockwise to desired output level. Call technician if this reset procedure will not work.

4. Adjust Receiver Gain (1M) clockwise to desired IFF return level. NOTE: The IFF Time Trace should appear about ¼ inch below the range time base. This can be adjusted by the technician from an inside control.

At the Console, "G" Band Interrogator

1. A similar set of control is available on the unit for "G" band control and are labeled correspondingly.

Placing the Gear in Ready Stand-by Position

SP RADAR

1. Throw Radiate Stand-By (2W) to "STANDBY."

2. Throw Scop Plate Power (7D) to "OFF."

3. Secure antenna at usual bearing (dead ahead). Do this by throwing Relative-True Bearing Switch (2B) to "RELATIVE" and rotating antenna to 000 on Relative Bearing Dial (1G). Red Lamp (2A) will be "on" as long as antenna is cut into Relative Bearing.

IFF Gear

1. Throw Challenge Switch (IP) and (1R) to "OFF."

2. Throw Power Toggle (1L) and (1U) to " OFF."

Placing the Gear in Complete Off Position SP RADAR

1. Reverse steps 5, 4, 3, and 1 in order. See Turning On SP Radar. IFF Gear

1. Throw Power Toggle (1L) and (1U) to "OFF" on console.

2. Throw Height Voltage Toggle and Main Power Toggle on inside panel of "A" and "G" band interrogators to " OFF.

3. Throw Main Power Switch on outside panel of "A" and "G" band interrogators to "OFF."

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Emergency Off

1. Push SP Radar Stop-Start Switch (2U) to "OFF." This will shut down console, modulator and transmitter units.

CALIBRATION

Calibration of the SP Radar scopes must be done by an experienced and qualified person. This person will be, except under unusual circumstances, a technician. The operator, however, should know how to check the calibration and do so each time the watch is relieved.

Checking the Calibration.--fine Range "R" Scope

1. Throw Calibrate-Operate Switch (5L) to" CALIBRATE" and Selector Switch (3M) to position 3. (Be sure Stand-By Radiate Switch (2W) is at "STAND-BY"). Marker pips will appear on "A" and "R" scopes. "R" scope will have 7 pips at one mile intervals, the first pip being at zero range.

2. Rotating Fine Range Dial (5G) each pip should coincide with leading edge of ditch as "whole" miles are brought to Fine Range Indicator. (If the pips are more than 0.1 mile off a balance of adjustments must be made between 5M and 5N, fine range adjusters. A technician should do this).

Coarse Range "A" Scope

1. The "A" scope will have pips at 1 mile intervals on its 100 mile range. To check, start Coarse Range Dial (5E) at zero and watch the strobe (bright dot) jump 5 pips (about ¼inch) on the time trace each time the dial is moved one "5-mile" click. Go through entire range. (If strobe light on trace fails to jump at any time or if the trace on the " R" scope disappears on one of the Coarse Range settings, a balance of adjusters 5J and 5K is necessary).

2. To secure calibration circuit return Calibrate-Operate Switch (5L) to "OPERATE" and Selector Switch (3M) to position 1.

PPI Scope

Coarse and fine range calibrations must be checked first as above.

1. Throw Markers Switch (4T) "ON" and PPI Pattern Selector Switch (4Q) to position 1--Range Mark. The markers will appear every 1, 5, 10, 20, 50 miles on the PPI sweep for its ranges of 4, 20, 50, 100, and 200 miles respectively. The range mark or strobe will appear at the range indicated by the sum of the Fine and Coarse Range Dials.

2. Set PPI Range Selector Range Switch (4R) to "50." Set strobe to 10 miles and rotate antenna. Marker and strobe should coincide and trace coincident circles. Check 20-, 30-, 40-, and 50-mile markers the same way. (If trace must be adjusted, the technician will have to do this with adjustments located behind the panel).

OPERATIONAL TECHNIQUE

Tuning the Receiver.--Controls

The operator has two controls to perfect his picture on the scope after proper brilliance, focus and centering have been set. These are Main Gain Control (6C) and L. O. Tuning (4A). If echoes will not appear on adjustment of these controls, the technician will have to make adjustment at the transmitter itself. The AFC Switch (4M) must be set to "MANUAL" (down) when using 4A.

Tuning

Using the Land Echo.--Turn to bearing of land and set Main Gain (6C) so grass is at least one-eighth inch high but not more than one-fourth inch. Then tune L. 0. Tuning (4A) for a compromise between maximum echo height and maximum width of echo on the time base.

Using the Ship Echo.--Tune as normally on any moving target. Attempt to get a maximum echo return watching the pip over a period of a minute or so.*

Using Sea Return.--Tune on the "R" Scope with Coarse Range Dial at zero range. Tune L. O. Tuning (4A) for maximum width of sea return as well as maximum height.*

No Echo or Sea Return.--Have technician tune the built-in echo box at.the transmitter for proper setting leaving the echo probe in the "IN" position. Elevate antenna so that no sea return appears at zero range. Tune L. O. Tuning (4A) for maximum width of no grass at the zero range. See figure 4SP-2. The Echo Box, tuned to the transmitter, gives a negative echo of transmitter frequency to the receiver. Thus, the receiver can be tuned to the transmitter by using this echo which is generated each time the transmitter pulse excites the Echo Box.* Set probe in "out" position.**


* Note on operating with Automatic Frequency Control: If radar has modification for automatic frequency control circuit always return AFC switch to "Automatic." If not, leave on "Manual" position. Sets installed after Jan. 1, 1945, have this modification.

** The Echo Box probe should be left in the "Out" position to insure the best minimum range the set is capable of getting. (See Performance.)

4-SP-7


Operating the Set.--General

Two operators are required at the console. The PPI and the "A" operators.

The principal duties of the PPI operator are to observe the PPI pattern, to control the antenna in elevation and bearing by means of the Elevation and Bearing Handwheel, and to observe the Precision or Target Alignment Scope when aligning the antenna on a target.

The principal duties of the "A" operator are to control the position of the ranging notch or ditch on the "R" scope, and consequently the strobe on the "A" scope by means of the Coarse and Fine Range Handwheels, to read the height meter, and to operate the IFF units.

SP will detect a target through two general types of operation: (a) detection by continuous search of aircraft at low angles from the horizon, and ships, depending upon antenna height above the water, weather conditions, size of target and the limiting factor-power of the set; and (b) detection of aircraft at high angles from the horizon depending upon adequate "coaching" by information from other detectors designed for such search and, again, weather conditions, size of target, and power of the set.

Detecting the target is the first part of the process. Obtaining a "fix" is the second step, which in the case of the SP is complicated by the attempt to fix in three dimensions: bearing, range, and elevation.

The ultimate performance depends upon the operators' sensible analysis and use of the controls at their disposal for presenting the target information for correct interpretation. The necessity for team work will be at once apparent when the operators attempt to do this together.

The third step is a matter of policy depending upon the situation: The tracking of the target to the exclusion of other radar duties; or the periodic fix of the target between searches for new information at low angles and on the surface. The first choice is an extremely dangerous practice and the operators should never take it upon themselves to make this choice. The second choice should be taken automatically unless given specific instructions otherwise.

Special tasks will arise. Operation for the more important of these are discussed below.

Echo Box
Figure 4 SP-2.

Detecting the Target--Continuous Low Angle and Surface Search

Adjustment of the Radar.

Antenna Elevation.--Zero to -30 minutes. The beam should clear the horizon at the surface of the sea and thus beam its energy out into space providing coverage of low angle and surface at a maximum possible distance. Experience with the radar aboard your own ship will find the best antenna position.

Antenna Sweep.--360 degrees to provide complete coverage of the area about the ship. The low angle attack by plane or approach by fast force may be launched from any azimuth depending upon such factors as enemy speed, strength, location of base, sun, weather, cloud coverage, etc.

Antenna Speed.--About two to three revolutions per minute. The sweep must be fast enough not to allow the approach of high speed targets over a large distance between sweeps of the approach area. It must be fast enough to keep a pattern on all azimuths of the PPI and, yet, slow enough to get readability from the "A" and "R" scopes. Too much speed combined with the narrow beam will cause the targets to "flash" on and off the "A" and "R" scopes so rapidly as to be missed.

Gain Used.--Optimum gain level is obtained with between one-eighth inch to one-fourth inch grass on the "A" and "R" scopes. (Main Gain Control

4-SP-8


6C.) Adjustment of the PPI Intensity (4K) and Video Gain (4L) is made to obtain a clearly defined sweep that seems "jeweled" as it rotates. Focus, brightness, and position of the time traces on the "A" and "R" scopes should be adjusted with controls 3H, J, K, L, and N, P, Q, and R.

Range Scale.--The 100 mile range is used in general search. The SP is provided with a 200 mile sweep on the PPI (the "A" scope has only one sweep length, 100 miles) but cannot be used unless the "B" type modulator is provided and cut into operation. The repetition rate of the "A" modulator allows only a little over 100 miles between transmitter pulses. Refer RADTHREE-Continuous and Discontinuous sweeps, page 1-36.

Watching the Scope.--The "A" and PPI operators must assume a conscious alertness to searching the time trace with their eyes. Don't get into the habit of starting at one spot on the scope. The strobe mark should be carried on the "A" scope at zero range if there is any tendency for the operator to find himself staring at the strobe.

High Angle Search

The narrow beam of the SP precludes the use of any general air search technique. Covering the entire vertical area on all azimuths about the ship will take too long and never give adequate protection. In addition, the power of the SP radar is not sufficient to guarantee protection at the great distances demanded in the combat task force. The long range air search sets must take care of this function.

High Angle Search with Coaching

Information of range and bearing and a rough altitude guess will come from the air search gear. To detect the target, rotate antenna to bearing and move the range notch to range. (The height meter used to estimate the altitude of your beam at a given range is useless unless the range notch is set at that range.) Elevate antenna using meter to indicate the altitude of your beam, at the range of the notch, and make at 15° to 20° bearing spread.

If you fail to pick up the target, a search in elevation must be made as well as in bearing. The design of the antenna allows this to be done quickly and systematically. The antenna throws a small cone of energy the vertical width of which is enough to cause the energy to be spread over a substantial altitude at any distance from the set. Remember this rule: At ranges greater than 25 miles the antenna can search in elevation in jumps or levels of 5,000 feet; at ranges less than 25 miles the antenna can search in elevation in jumps of 2,500 feet. --With the one requirement, that the range strobe on the "A" scope is set at the expected range of the target. If the set is operating normally, this procedure will provide plenty of overlap in vertical search. (See fig. 4SP-3.)

An experienced operator can make a bearing search at a given altitude and range in 5 seconds. Thus, a target at 040-35, say, and with no altitude information would be detected at any altitude up to 30,000 feet in 6 sweeps or 30 seconds.

Changes of the average bearing and range must be made constantly as new air search data comes in. The constant adjustment plus the coordination of bearing and elevation change to accomplish a through search require practice and teamwork.

Having detected a target the second step, obtaining the fix, is begun.

Obtaining the Fix

Several additional controls come into use at this time. The function and adjustment of these controls is described here.

The Scanner.--The energy of the set is piped to the parabolic reflector on the mast and much like the light in a car headlight focused and projected into space as a cone. The nozzle which projects this energy to the parabola is mounted on an eccentric rotating device which will cause the nozzle to make a very small looping motion about the center line, the perpendicular to the antenna face. The energy is thus slightly" cocked" off the center line. Where before the maximum energy of the cone was straight down the center line, it is now making a tiny loop about this line.

It will occur to the operator that this cone of energy might detect a target more quickly, since it is larger, than the straight shooting cone. Practically this is not so as the increase is too small to have that effect. The scanner operates at high speed and should be used only when the precision fix is desired. This is a common sense rule designed to save undue wear of the mechanical parts of the scanner system.

4-SP-9



Figure 4 SP-3. "Overlap of radar cone searching in elevation in 5,000 feet jumps at 25 miles.

Precision Scope.--When the scanner is turned on, the precision scope and the circuit feeding it are also energized. This circuit compares the echo strength received from a target when the cone of energy is in four positions in relation to the center line: "UP," "RIGHT," "DOWN," "LEFT." See figure 4. Realize that no signal goes to the precision scope at any other time although the cone does make a complete loop.

The "UP" and "DOWN" echo strengths are compared and a net signal applied to the vertical deflection plates of the precision scope. The "RIGHT" and "LEFT" signals are compared and the net signal applied to the horizontal deflection plates. If the "UP" is equal to the "DOWN" and the "RIGHT" is equal to the "LEFT," the dot will stay in the exact center. If one signal is bigger than its mate, the dot will be deflected. Refer RADTHREE--Structure of the Electrostatic Cathode Ray Tube, page 1-30. It is important to realize that the circuit is connected so that if the dot moves to the right and up, you turn the antenna to the left and down--the same way the dot must move to return to Center. The antenna center line is pointed precisely at the target whenever the dot returns to the exact center of the scope.

The Wings.--In order that the operator will know that he has a target on his precision scope a further restriction is placed on the circuit which feeds the precision scope. The "A" operator must place the detected target in his notch, or ditch, on the "R" scope. As long as the target remains in the notch the precision circuit has a


Figure 4 SP-4. 1. Precision circuit receives target only in four positions of cone. 2. Precision scope gets "net" signal from "up-down" and "right-left."

4-SP-10


target to work on. Further the operators will know which target is being aligned. In order to provide an instant and constant warning to the PPI operator that he does or does not have a target on the precision scope, "wings" are caused to appear on the dot when a target is in the notch. Before using the precision circuit the main gain of the receiver (6C) must be set at the proper level and the Wings Level Control (6B) adjusted so that the grass or noise will not cause the wings to appear on the dot when the "R" scope notch is empty. See figure 5.


Figure 4 SP-5 Wings level and main gain adjusted properly.

The Height Computing Meter.--See figure 6. The Height Meter is a computer which solves for the leg of the triangle, altitude, knowing the one leg, range and the angle between the radar beam and zero elevation. In addition most SP radars have a circuit which adds a figure corresponding to the error due to the curvature of the earth at the range of computation. If your meter does not have this feature a table or graph will be necessary to add this correction. See figure 7. Figures 8 and 9 are tables which can be used to check your meter. Use the appropriate table. These tables check the meter for various angles at a given range and at various ranges for a given angle. If the meter checks both ways, you may assume the meter will compute all range and elevation combinations. The meter is built to withstand a current greater than any combination you can achieve on the set so off-scale readings will not harm it. Always, however, secure at zero elevation so that sudden power application will not surge the current through the meter when starting the set.


Figure 4 SP-6. Height meter reading.

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Altitude Range 30--
Angle
Angle
2°30'--
Range-Miles
500 -- 2.0
1,000 0°8' 3.8
5,000 1°25' 19.0
10,000 3°0' 35.5
20,000 6°12' 66.0
30,000 9°25' 93.5

For height meter with earth curvature correction built in.

Altitude Range 30--
Angle
Angle
2°30'--
Range-Miles
500 -- 2.1
1,000 0°19' 4.2
5,000 1°41' 20.8
10,000 3°11' 41.7
20,000 6°23' 83.3
30,000 9°35' 125.0

For height meter without earth curvature correction.

A final precaution must be observed. The Height Meter is used in other ways by the technician to make certain necessary checks on the set. The Height Meter will give height solutions only if Switch 5C is in the "Height" position.

Obtaining the Precision Fix.--When either the "A" or PPI operator detects an echo, the PPI operator stops the antenna and rotates it by the Bearing Handwheel to the bearing of the target while the "A" operator advances the strobe with the Coarse Range Handwheel until the target appears on the "R" scope and then places the target in the notch with the Fine Range Handwheel. Usually the PPI operator will spot the target first and should call out an approximate range to the "A" operator while returning to the target's bearing.

As the target drops into the notch, "A" operator calls out "in the ditch" and the PPI operator starts the scanner and focuses his attention to the precision scope. The "A" operator continues to keep the target just next to the leading edge of the ditch and in the ditch. The PPI operator will see his winged dot moving rapidly about the face of his precision scope. Sometimes the dot will be off the scope but its general position can be noticed by the green glow off to one side or the other. He then moves his bearing and altitude handwheels

in the direction the dot should move to approach center. Once the winged dot is on the scope do not attempt to respond to every small movement it makes. Get the knack of determining which way the dot tends to drift and how fast, and smoothly compensating for the movement. If the dot persists, say, in moving into the first quadrant, think "down and left." Sudden surges of power or variation in echo amplitude will kick the dot off or across the scope but it will return quickly to its general movement. (If the dot is extremely erratic and the slightest movement of elevation and bearing handwheel throws it about the scope, the scope is not properly balanced and the technician should be called to make adjustments with 8A, B, C, D, and 6E.) Call out "ditch" if the wings disappear to warn the "A" operator to get the target back into the ditch. The "A" operator should say "off target" if the echo disappears.

The instant the target is brought smoothly to coincide with the cross hairs etched on the scope, the PPI operator calls "mark." Do not move the Elevation and Bearing Handwheels until the following is completed. If an evaluator or talker is not present, the PPI operator calls out the bearing immediately and the "A" operator, warned by "mark," is ready to call out the range and elevation. If there is a talker, the talker calls out the bearing, range, and elevation warned by the "mark" that the information is ready.

The "A" operator will continue to keep the target in the ditch if further fixes will be called as his change of range will not materially affect the elevation reading. The PPI operator must not move the elevation dial, as this will greatly affect the Height Meter. As he becomes more experienced, the Bearing Handwheel can be used during the readings to help stay on.

If the search is to be resumed, the PPI operator resets the elevation to zero as soon as he hears the elevation called out, starts the antenna rotating and turns off the scanner.

Special Tasks

Fighter Direction.--In combination with high-power air-search gear such as the SK, the SP lends itself to the Fighter Director's work through supplying the third dimension, elevation, of his target. In a combat task force the SP will be engaged routinely as the preferred long-distance surface search set, but upon the contact of enemy aircraft by the air-search gear, will be called upon for fixes

4-SP-12



Figure 4 SP-7. Curvature of the earth correction.

by the FDO. Unless specifically ordered, do not assume the responsibility for tracking an aircraft after a fix. The FDO may request a track for, say, three minutes. Do so, but get the habit of dropping back immediately to general search.

If called upon to track a target, the plot will usually use the "Stand-by-Mark" method of obtaining fixes for greater accuracy of speed solutions. The evaluator or talker is necessary for this at the set. The operators will keep aligned on the target and attempt to have a "mark" set when the evaluator follows his "stand-by" with "mark." This takes a great deal of practice, and during exercises and maneuvers a large portion of the time should be spent on this type of operation.

Night Fighter Direction is greatly dependent upon this type of tracking because of the necessity of directing the fighter to an exact preferred position with respect to the target. Here it is important for the operators to understand the value of relative altitude fixes. You will recall, as the Fighter Director watches the friendly and enemy echoes on his PPI scope, he becomes more and more interested in their relative motion as they draw closer together. On initial contacts and vectors he was demanding course, speed, and altitude but now things are happening too fast for plot solutions and he relies upon the fast-moving relative picture. At night the relative elevation is vital, but the FDO has no way of sensing that part of the problem on the PPI.

The SP Radar comes into valuable use here. It may be that the altitude readings you are getting might be 500, 1,000, or even 2,000 feet off the true altitude due to the set's imperfections. You will, if a good operator, get the altitude between two close targets, making rapid alternate fixes. For example, X may be at 17,500 and O at 18,000, and your reading for X, 16,500 and for O, 17,000. The difference or relative altitude is the same and the FDO can use the information to solve his problem.

The Delayed Sweep.--A special feature is incorporated in the PPI as an aid to increased accuracy in interpreting relative movement and composition of the PPI picture which is suitable for use in fighter direction--the Delayed Sweep. PPI Pattern Selector (4Q) when turned to "DELAYED" activates the circuit. When using delayed sweep, a "hole" is left in the center of the screen to indicate delayed sweep is on.

Delayed PPI sweep produces an expanded view of an annular area so that it cannot be used to appreciate true course but only relative movement and composition. For example, if the range ditch is set at 37 miles and the PPI range switch to "50," the PPI picture will be a ring whose inside diameter

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Figure 4 S-8. Delayed SP Sweep for PPI.

is 37 miles and outside diameter 87 miles, See figure 10.

It must be borne in mind that the start of the sweep on the PPI will always be the range at which the ditch is set when using delayed, so ranging to a target will spoil the current picture and bring the target to the center of the PPI.

Operators will find this feature useful in general search for examining the formation and composition of an approaching task force or group of planes. Remember, ranging cannot be done when using Delayed Sweep.

Navigation.--The SP, like the SG, is extremely useful to the navigator, particularly when operating in close waters. The navigator who is always cognizant of the ship's position will be able to give the operator the approximate bearing, distance, and expected time of contact with land. From his chart he will be able to tell if the land rises abruptly out of the water, or, in case the land is low lying near the beach, whether or not it rises farther inland.

Land, that rises at the water's edge to considerable height is excellent for radar purposes since the closest land appearing on the PPI in this case is usually the beach. The chart should always be checked for the possibility of inland mountains appearing; first, by checking the altitude of mountain peaks against the altitude of the shore line, and second, by checking the outline of the shore from the chart against the outline from the PPI. In cases of this type of land, the outlines will be almost identical, and comparison with the chart may be used to fix the ship's position. Almost all the islands in the Aleutians are of this type.

Another type of situation involves a low-lying shore line and inland mountains. When contact is first made, only the mountains will appear on the PPI, since the low shore will be below the horizon. With this type of land it would be a dangerous mistake to assume that the beach is the closest contact. Failure to remember this may result in the ship's grounding. For this same reason, unless your knowledge of the contour of the land justifies it, never depend on bearing tangents for fixing your position.

The best fixes are not necessarily obtained from a large group of random ranges and bearings, or from the closest land. The best method is to obtain a few accurate ranges and bearings of small prominent objects. Isolated rocks, small distinct islands, and isolated mountain peaks are excellent


Figure 4 SP-9.

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for obtaining fixes. The prominent points may be chosen from the chart. If the ranges and bearings obtained on two or three of them plot in at the same point, it is safe to assume that that point is your position.

Always remember to make use of the contours of the land when employing radar for navigation. By closely examining the echo of the "A" scope for multiple peaks and other peculiarities, the echo may be more definitely fixed to some position on the chart.

Islands in the mid-Pacific are very flat, and rise only a few feet above sea level. These islands are usually bounded by coral reefs and shoals, so extreme caution must be observed while using radar navigational fixtures taken close to them. Lack of small prominent points on these islands makes it difficult to obtain reliable fixes.

Sometimes it is possible to detect shoals on the radar screens, if the shoals are close enough to the surface to cause a disturbance in the water. The signal appearing on the radar screen would be much the same as a "wake" signal obtained from another ship. However, shoals are very treacherous and ships should not rely upon radar to detect them.

Auxiliary Fire Control.--Special destroyers have the SG, SC, Mark 12 and 22, and SP radar systems. The SP may be called upon for torpedo fire control as is the SG, especially for targets beyond the SG's range. The SP will also be used as a substitute for the Mark 12 and 22 for accurate tracking for antiaircraft fire as well as surface bombardment. It will also be used for fixing distant aircraft approaching your area but still out of range of the fire control gear. Experience has shown that the operators on the Mark 12 and 22 radars can pick up targets much further than usual when coached to exact target position.

Large carrier classes have the SG, SC, SK, Mark IV and 22, and SP (or SM) and smaller carrier classes have the SG, SK, and SP radar systems. Large carriers will find the same useful advantages for the SP as the destroyer class except of course for torpedo control. The smaller carriers usually have only small caliber antiaircraft weapons and no fire control radar, but the Fire Control Officer can use the advance warning of the SP's low altitude search to good advantage.

Station Keeping.--The SG radar should always have the station keeping duties. The SP is a capable set for this duty in an emergency, particularly because of a good minimum range. For details of procedure refer RADTHREE--Station Keeping, page 4-SG-8.

Composition of the Target (in addition to identification).--Surface or airborne? Speed and altitude, of course, are the quickest means of classifying the target as surface or airborne. The expanded "R" sweep allows the operator to see clearly the approximate speed of his target; the elevation control and precision circuit give the fact of whether or not the target is off the surface. Certain targets such as the carrier with several planes in the landing circle, or a 30-knot cloud at a substantial altitude are exceptions. However, the operator will quickly learn these.

The operator, usually, then must concentrate mostly upon guessing the strength of the target, both as to numbers and size. The "R" scope with a range resolution of 0.1 mile is the scope used to study the details of the echo's behavior. The PPI scope on delayed sweep is used to good advantage to study the number of individual targets making up the group and their disposition.

The basic fundamentals of pipology are well outlined in RADTHREE--Pipology, page 3-10, and must be mastered as a part of good operation. The very narrow beam of the set, the unusual range resolution of the "R" scope and the clear definition of the PPI pattern should make the SP the best set for composition data of any current radar.

A word about false echo characteristics on the SP radar.

Double or Triple Trip Echoes.--The radar beam can return to the source and be reflected from the source to return to the target and back again. The picture resulting from this is an echo at the range of the target and one at twice the range. The high power of the SP makes even triple trip echoes possible. The operator can expect these however, at close true ranges of the order of 1 to 3 miles.

Second Sweep Echoes.--The ranging distance between two transmitter pulses with modulator A" is about 131 miles. This means that large mass targets, which will return enough energy for the set to detect them from more than 131 miles, will return energy the second sweep from the time the energy left the set. A target 145 miles away might appear at 14 miles. Barring a visual check, a set with a different repetition rate

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would be necessary to check this distance. Modulator "B" has such a low repetition rate as to make second sweep echoes impossible on the set and the 200-mile sweep can be used as well.

Cloud Echoes.--Of all the false echoes received on the SP radar the cloud echo is seen the most. This includes cloud banks, small rain squalls, and ionized layers invisible to the eye. The great advantage of this is the ability to keep the air operations informed of suddenly appearing bad weather spots thus enabling the carrier to maneuver to a favorable section for launching and retrieving aircraft. For a description of these and other false contacts refer RADTHREE--False Contacts, page 3-18.

A special Cloud Suppressor Switch (6A) has been provided on the receiver which attenuates targets having a large range width as clouds almost invariably will. The usual ship or plane echo will not be affected by the circuit this switch controls. These echoes can be seen "going thru" the cloud echo. Do not expect too much of this feature.

Jamming and Deception.--The operator must know the practical aspects of jamming and deception and the logical means for preventing the success of its mission--to spoil the SP's ability to get the information it is capable of getting.

RADTHREE--Defense Against Jamming and Deception, page 3-25, gives the information clearly and completely. Pay particular attention to the section "What the Operator Should Do," page 3-28.

In addition, make sure you have been informed when in the combat force of known and expected measures the enemy might take, what his latest wrinkle is for fooling you, from where or what points you can expect the trouble and what reports the CIC will want made. We would know more about jamming if all the fleet's operators had taken this precaution in previous operations.

THE DUAL IFF SYSTEM

The SP radar is fitted to operate two separate IFF systems. One system, is the Mark III "A" band system which is standard throughout the fleet. Refer to RADTHREE, part 2, General IFF Principals. This system the operator will recall is based on a combination of pulses returned from the target at regular intervals, a total of six combinations or codes appearing as a downward echo at the range of the target responding to the challenge. The SP uses the BM or BN interrogator.

There are two differences about the SP radar's MarkIII "A" band IFF as compared to the SC, SK Mark III systems: (1) The challenger or interrogator uses a nondirectional antenna and (2) the IFF time trace is separate from the regular range trace on the scope and directly below it. You will recall that the SG uses Mark III with a nondirectional antenna and a new series of air search radars, the SR's, are using a separate time trace for IFF.

Selector Switch (1Q) places Mark III either on the "A" or the PPI scope. Selector Switch (3M) will place on the "R" scope whichever IFF is on the "A" scope. The usual controls are all explained in the section describing the IFF Coordination Unit.

Refer to RADTHREE pages 2-9, -10, -11, for a complete description of the appearance of Mark III IFF, remembering that the SP will present the IFF on a separate trace.

The second system, for which the SP uses a BO interrogator or equivalent is a special recognition system used by carriers to recognize their own fighter planes. This system is not coded but sends a rapidly repeated challenge pulse and receives a rapidly repeated response pulse on a private frequency. A certain carrier can then ask a plane to turn his special transpondor on and can tell quickly whether or not the plane is one of its own fighters, The Mark III IFF of course can determine originally whether or not the plane is friend of foe.

The second system is known as the Mark III G/R system ("G" band or George IFF for short), and uses a directional antenna and separate IFF time trace. You will notice the antenna for this system mounted as a vertical array of dipoles on the face of the SP parabolic antenna reflector.

Switch 1Q and 3M perform the necessary control for presentation on the scopes for this as well as the Mark III system. Note that both IFFs cannot be presented at the same time on the same scope.

The plane fitted for using both systems has a special dual transpondor. Normally, only "A" band is being answered by the plane's transpondor. Whenever a carrier wishes to determine which of the many friendly targets is its own group, the carrier informs his group to flash "George," and starts challenging with his "G" band IFF. The pilot turns the "G" band section of his transpondor "on." A special time-sharing device alternates

4-SP-16


the "A" and "G" band transpondors in operation, the "A" "on" for three-twentieths and the "G" "on" for one-twentieth of a second--5 times a second. This means that the "A" response continues as usual (the short "off" time 5 times a second does not spoil the transpondor's response or your IFF picture). The "G" band response comes 5 times a second, just rapid enough to appear as a steady but flickering response much like an old time movie with the frames flashing on the screen too slowly.

The pilot cuts the G" band "off" as soon as the carrier has completed the special challenge and the operators cut "off" the "G" band interrogator. The carrier's interrogator, remember, is on a private frequency and should get response only from its own fighter planes.

Comparatively, the "G" response is about the same strength as the "A" response and will show about the same width as the wide pulse of the "A" band codes. Remember that the two bands are set in different ranges of frequencies, thus do not interfere on each other's time traces.

TROUBLES

Major troubles are handled by the technicians, but experience has shown that a great percentage of the troubles are caused by the operators failing to recognize minor break-downs which can be corrected by anyone. In addition much of the misinformation given by the radar is due to the operators failing to know when something is amiss and getting the technician to correct it immediately.

Calibration.--Misadjustment of Coarse Range Calibration will cause the "R" scope trace to disappear at certain settings of the Coarse Range Handwheel. Have technician adjust at once controls 5J and 5K on the range unit.

Tune.--Ultrahigh frequency transmitters drift constantly. Check amount of sea return and known target amplitudes to be sure the receiver is tuned to the transmitter whenever you relieve the set. Don't continue the preceding operator's bad job. Remember to return AFC Switch (4M) to "AUTOMATIC."

Azimuth Elevation or Cross Level Errors.--If antenna fails to respond to console signals the telltale lights 2R, S, T, on the Power Control Unit will flash. Get in the habit of watching for this warning. If these lights persist in flashing for nominal rates of rotation or manual rotation, the servo-mechanisms controlling the antenna need adjustment. Usually the lights will go out if you stop movement for a few seconds, but if any telltale stays on secure the antenna and investigate.

There is an important exception to the telltale system. If a target appears on 360° azimuth, the antenna is not rotating with the sweep. Usually the telltale azimuth light would indicate this. However, if the stable element is not operating the telltale lights will not give warning. You should be able to check this by noticing if the Stable Element Green Indicator (2K) is "on." Secure antenna if this light is out.

Harmful Overloads in Motors and Generators.--A yellow Overload Light (2H) will come on if harmful overloads are present in any of the various motors and generators used to control the antenna. This system will work only if the Selector Switch (2Y) is left in "NORMAL" position. When the light goes on, stop antenna movement and turn Selector off the "NORMAL" position and the light will go out. Then turn Selector until light comes "on" again. The overload exists in the unit indicated by the selector at this point.

Precision Scope Unbalance or Erratic Dot.--The Precision Scope dot will rest at the cross hairs with the scanner motor off. If not, it is out of DC balance. Adjustments 8A and 8B must be used as described in the section on Precision Alignment Unit. The dot should also drift or orbit very closely to the center of the scope with the scanner "on" and no targets present in the "R" scope ditch. If not, it is out of AC balance. Refer to section on Precision Alignment Unit. A technician should do this adjustment. Extremely erratic movement of the dot is adjusted by the AGC Level Control (6E) which controls sensitivity of the precision circuit.

Meters.--There are 6 meters on the console-Learn the. correct position of each pointer on the meter dials (a red line on the meter face will help). They are:

Modulator Primary Voltage Meter (2D)       Range 90 to 110 volts.1
Oscillator Current Meter (2F) Range 25 to 30 mas.
Line Voltage Meter (2G) Range 110 to 120 volts.
Main Rectifier Current Meter (7A) Range 0.6 to 0.7 amp.
Auxiliary Power Meter (9D) Exactly 200 volts.
Auxiliary Power Meter (9E) Exactly 300 volts.

1 Adjust so Oscillator Current Meter reads correctly.

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Constant Altitude Regardless of Range and Elevation.--The Crystal Check Switch (5C) is provided for the technician to make certain checks on the radars. Always make certain this switch has been returned to "Height" position so that the meter will compute height and not stay at a constant level.

Fuse Failures.--If any fuse on the auxiliary power unit fails, a neon telltale should light above it. Always suspect a fuse failure if scopes or units suddenly cease to function or refuse to turn on. All fuses on the console have spares located adjacently.

Refusal of Scopes To Focus.--If focus controls on the scopes will not give a clean, clear trace, the power tubes are usually failing even though they have not burnt out. Have technicians check and try a replacement. Don't waste time with poor focus as these controls will respond readily if properly powered.

Interference on Carrier.--Some sets on carriers experience "hashing" of the time traces when large numbers of planes are warming up on deck (ignition hash). Homing devices occasionally cause similar trouble, though these more likely will interfere with the IFF time trace.

Veracity of the Stable Element.--Even though the height meter is giving correct solutions, errors in altitude will arise if the Stable Element is faulty. Checking the SP altitude against friendly aircraft at known altitudes must be a regular check because of the possibility of this error. In addition to the foregoing check, the use of the SC or the SK estimates of altitude will help. Carriers in the combat zone have found again and again that the air-search gear, properly calibrated, will give excellent height results.

General.--Learn the function of all the telltale and overload indicators and become used to noticing any warning signs of danger to the set. Your set will give consistent service if not allowed to operate in a danger condition.

PERFORMANCE

Maximum Reliable Range

Ranges on surface craft are dependent upon the antenna height. Ranges on low flying aircraft are dependent on both antenna height and aircraft height. Expected ranges with a typical antenna height are listed below as a guide to performance The results listed are considered maximum reliable ranges for an antenna 90 feet above the surface of the water.

Type of target Range
in miles
BB, CV, Large Auxiliaries 25-30
CA, CL, Medium Auxiliaries 22-27
DD, DM, AV, PC 20-25
Submarines 8-10
Submarine Periscope 2-4
Aircraft:
  Altitude:
                    100 feet 18-22
    200 feet 22-25
    500 feet 30-34
    1,000 feet 40-45
    4,000-10,000 feet 55-60
Land:
  Low Lying Islands 10-30
  Volcanic Peaks or Mountainous Masses 75-100

Accuracy

Range accuracy is ±0.1 mile.

Bearing accuracy is ±¼° with scanner unit on. ±1° with scanner unit off.

Elevation accuracy is ±700 feet. This accuracy is dependent not only upon the precision circuit but also upon the ability of the Height Meter to compute the information it receives.

Resolution

Range Resolution-of two targets on the same bearing.

Range scale "A" scope "R" scope PPI scope
4 or 5 XXX 0.1 mile 0.1 mile
20 XXX XXX 0.2 mile
50 XXX XXX ½ mile
100 ½ mile XXX 1 mile
200 XXX XXX 2 miles

Bearing Resolution of two targets at the same range is 6° on the PPI scope and 4° on the "A" scope.

Minimum Range

Minimum range with the Echo Box tuned and probe "IN," 2 miles.

Minimum range with probe "OUT," 0.1 mile.

Planes in the landing circle of the carrier can be seen easily on the PPI scope using the 4-mile range. Escort destroyers close aboard or ships in the task force can be accurately spotted.

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VD, VD-1-2 CONSOLE

UNITS OF THE REPEATER
  PPI scope and control circuit unit
          Power supply and servo assembly
  Selector switch
TURNING ON AND OFF
CALIBRATION
OPERATIONAL TECHNIQUES
  General
  Specific tasks
  Communications
TROUBLES
PERFORMANCE

Units of the Repeater (figure 1)

1. Remote PPI Scope and Control Circuit Assembly.

2. Power Supply and Servo Assembly.

3. Selector Switch.

Identification and description of the Controls and Indicators on the Console.

1. PPI Scope and Control Circuit Unit

2. Power Supply and Servo Assembly

No operator controls.

3. Selector Switch


Figure 4 VD-1. VD-2 console.

4-VD-1


TURNING ON AND OFF

Turning On

1. Turn the Range Marks Control (IE) and Intensity Control (IF) completely counterclockwise.

2. Throw Off-On Switch (ID) to "ON." Pilot Lamp (1C) comes "on."

3. Wait one (1) minute, turn Intensity Control (IF) until trace appears and adjust brightness.

4. Using Focus Control (1G) focus and put Range Selector (ID) to desired range.

5. Turn Range Mark Control (IE) until range marks appear and using Centering Control (1J) and Sweep Length Control (IK) place the first marker at the center of the PPI and the fifth marker at the outer edge.

6. Turn Selector Switch (3A) to desired master radar.

7. Check Sweep by having master radar rotate its PPI sweep and noting that the first marker scribes a dot or very small circle and the fifth marker travels the outside edge of the VD PPI scope.

Turning Off

1. Throw Selector Switch (3A) to "OFF."

2. Turn Range Marks Control (IE) and Intensity Control (IF) completely counterclockwise.

3. Throw On-Off Switch (ID) to "OFF."

CALIBRATION

It should be obvious that placing the range marks on the PPI trace as described in the Turn On procedure does not necessarily mean that the ranges will be correct. The Range Marks are developed by a circuit which sends a mark to the trace at steadily repeated constant intervals. If, say, for the 20-mile sweep they are separated by a time equivalent to 4.5 miles, the fifth marker, placed at the end of the sweep, will be at 18 not 20 miles.

The adjustment of the marker circuit for each range is done from screw driver controls inside the Control Assembly Unit and should be done by a technician. This calibration will take several minutes and a master radar must be available to send calibrated range marks or a target of known distance to the VD PPL

The operator can, however, check the calibration and should always do so for the range he will be using.

Checking the Calibration

1. Set the Range Selector Switch (1B) to the desired range, say, 80 miles and adjust the sweep length, sweep center and markers as described in the Turn On procedure.

2. If the master radar has a range marker for its PPI, set the marker at, say, 20 miles and rotate the PPI sweep. Your VD 20-mile marker should trace a coincident circle with the marker piped from the master set. Check the 60-mile range. If a set of range markers is available from the master compare the master range circles with the VD's range circles as the sweep rotates.

3. If the master radar has a target of known range, check VD range against that given by the master. If possible check with fire control radar ranges.

OPERATIONAL TECHNIQUE General

The remote PPI is used chiefly in the CIC, pilot house, and gunnery Control. The CIC has it available for the Radar Watch Officer, the Evaluator, Gunnery and Torpedo Liaison, and Fighter Director. The pilot house has it available for the Officer of the Deck and the Navigator, and Control on larger ships for the Gunnery Officer himself.

The VD series, then, is used primarily by the officer rather than the enlisted operator. The officer must take it upon himself not to "hog" the radar from which he is getting information unless circumstances demand his exclusive use. The most important single item to remember is that you cannot range a target, get tangents to islands, sweep sectors, and still have the master radar perform a genuine search job. New series remotes (VF) are coming into the fleet to correct this fault.

"Operating" the VD is first the adjustment of the controls and a check on the calibration as described above. The Radar Officer should insist upon a daily calibration and adjustment of gain by the technician. The gain is also a screwdriver inside adjustment and needs daily attention even as the gain on the master radar does. The gain must be set so that it gives a good picture when the master radar is doing the job you will be asking it to perform for your VD. Naturally, if the operator at the master set changes gain to study target composition or "ranges" on an island your picture will be unsatisfactory for the moment. The VD operator will find usually that his picture is much clearer than the master radar itself due to the improved video circuits.

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The only control that the operator will use then, with a properly adjusted VD, is the Mechanical Cursor Dial which rotates the Cursor line. The bearing is obtained quickly by bisecting the target arc with the Cursor line. The Range Marks allow an estimation by eye of the range, but since they are part of the picture, parallax is eliminated (such as was present on older types of remotes--VC series).

Specific Tasks

The main uses of the remote are listed here with references to RADTHREE which explain in detail the handling of the master radar which, in effect, is the way in which the problem must be met with the VD.

1. Station Keeping (Summary Plot). RADTHREE, page 4-SG-8; 4-SL-4.

2. Navigation. RADTHREE, page 4-SG-9.

3. Auxiliary Fire Control. RADTHREE, page 4-SG-8; 4-Mk3/Mk4-9; 4-SC/SK-7; 4-SA-8.

4. Fighter Direction. RADTHREE, page 4-SC/SK-7.

5- Tracking Air Targets. RADTHREE, page 4-SC/SK-7; 4-SA-7.

Communications

The officer using the VD must be in direct contact with the master set and know how to direct the radar operator for best results. He may either use a sound power phone himself or a talker circuit which will leave him free to move about. The MC circuits are not satisfactory during GQ because of the need to minimize the noise level in CIC.

TROUBLES

Aside from miscalibration and improper gain adjustment the VD should not give more than occasional operating trouble. Often after severe gun fire shock, the trace will refuse to start from the physical center of the PPL This is due to the focusing coil being "out of line." The adjustment is inside near the base of the PPI tube.

PERFORMANCE

Maximum and Minimum Range

Performance is dependent upon the master set. Refer RADTHREE, section 4, for individual set performance.

Accuracy

  Miles Range of sweep
Range Accuracy ±5
±3
±1
±½
±¼
  200
80
20
10
4
   
Bearing Accuracy ±4°
±1°
with SC and
with SG.

Resolution

Range resolution of two targets on the same bearing is about 2 miles on the 200-mile sweep with increased discrimination to ¼ mile on the 4-mile sweep.

Bearing resolution of two targets at the same range is about 10° with the SC/SK series and 4° with the SG series.

4-VD-3


VF--PRECISION PPI REPEATER

GENERAL DESCRIPTION
ADVANTAGES
CONTROLS
TURNING ON AND OFF
OPERATION
REMARKS
LIMITATIONS

MODEL VF--PRECISION PPI REPEATER

Navy Model VF is designed for use with various types of search radar equipment. Experience has shown that it is most valuable when used with surface search radars. Its function is to repeat and retransmit the target bearing provided by any selected search radar, and to measure and transmit the accurate range of a target.

General Description

Usually located in CIC, the VF set is equipped with two 5-inch scopes for both PPI and B-scope presentation. As with Model VD gear, the PPI has four range scales of 4, 20, 80, and 200 miles. Similarly range marks consistent with the scale chosen appear at 1, 5, 20, and 50 miles. The bearing accuracy of the PPI tube is within 1° of the master radar, limited only by the ability of the operator to center the cursor on the target. The range accuracy is slightly less than that of the master radar.

The B-scope repeats a selected sector of the PPI screen in a greatly enlarged rectangular coordinate view. That is, the portion of the PPI sector representing close ranges is enlarged more in azimuth than the portion representing more distant ranges. Altered presentation is clarified, however, by suitably intensifying the sweeps to produce azimuth lines at 10° intervals and range lines at 1,000-yard intervals, thus forming a geometric reference grid on the B-scope screen. The vertical sweep represents range; the horizontal sweep represents bearing. The B-scope horizontal sweep occurs once each revolution of the PPI sweep, but the duration of this horizontal sweep is only approximately one-eighth of that of one PPI revolution.

When viewed from the operating position, the bottom of the B-scope screen always represents closer range and the top represents more distant range. The center of the screen corresponds to the range counter reading and to azimuth cursor position on the PPI tube. Positions at the left-hand


Figure 4 VF-1. PPI screen, showing target presentation, range marks, and segment selected for enlargement.


Figure 4 VF-2. B-scope, showing enlarged presentation of targets seen in selected segment on PPI screen.

4-VF-1


side of the B-scope are smaller azimuth angles than the cursor position; and positions at the right-hand side are larger azimuth angles. When the PPI sweep is rotating clockwise, the B-scope is scanned from left to right; when the sweep is rotating counterclockwise, the B-scope is scanned from right to left.

The bearing accuracy of the B-scope is essentially the same as that of the PPI, but the ability of the operator to read information on the B-scope is far greater. Ranges, however, can be read with an accuracy approaching the basic accuracy of B-scope (±100 yards between 600 and 4,000 yards, and ±25 yards between 4,000 and 40,000 yards).

Advantages

(1) An accurate track on one or more targets may be obtained without interrupting the normal search procedure of the master radar.

(2) A range and bearing on the guide or on any ship in the formation is readily available without stopping the sweep on the surface search radar. This is a considerable advantage for ships with only one surface search radar.

(3) The feature of having the VF connected to the target bearing and range designation system affords a quick and accurate method of sending the target bearings and ranges to important stations in the ship.

(4) The ability to spot the fall of shot within about one hundred yards.

(5) Target discrimination with the B-scope of the VF is better than with the SG or Mark 12 radars.

(6) With the operator behind the VF, CIC officers have a clear view of the general and detailed picture without interfering with radar operation.

Controls

Before using the equipment for the first time, the operator should learn the locations and functions of the operating controls. Controls actually used in determining range and bearing are located on the Top Control Panels on the top surface of the unit. Controls for preliminary adjustments (such as Focus and Intensity) are mounted on the exposed front panel of the Control Chassis. Controls for calibration, etc., which are used only occasionally are mounted on the recessed front panel of the Control Chassis, and are normally concealed by a hinged cover.

Dial Lights

A. Dial Lights.--Dial lights for PPI scope.

B. Power.--Standby-On Switch.


Figure 4 VF-3. Controls on top control panel.

4-VF-2


C. PPI Video Gain.--To make signals appear at the desired strength on PPI scope.

D. B Video Gain.--To make signals appear at the desired strength on B-scope.

E. Range.--Range selector switch for 4-, 20-, 80-, 200-mile scales.

F. Dimmer.--Dial light control on range counter and relative bearing vernier dial.

G. Remote Bearing Switch.--To indicate to remote stations that bearings are being transmitted.

H. Bearing Crank.--To rotate the mechanical cursor on the PPI scope.

I. Range Crank.--Coupled to the range counter to read B-scope ranges.

J. Remote Range Switch.--To indicate to remote stations that ranges are being transmitted.

K. Range Counter.--Indicates B-scope ranges in yards.

L. PPI Scope.--Five-inch scope with both true and relative bearing dials.

M. B-Scope.--Five-inch scope with electronic range and bearing marks.

N. Bearing Vernier Dial.--Vernier scale for relative bearings only.

1. Focus.--PPI focus adjustment.

2. Range Marks.--Controls intensity of PPI range marks.

3. Range Ring.--Controls brilliance of illuminated range ring on PPI screen.

4. Intensity.--Adjustment for desired intensity of PPI trace.

5. Center Expand.--Adjustment to correctly center first mark on PPI screen.

6. Intensity.--Adjustment for desired intensity of B-scope trace.

7. Spot.--Controls intensity of B-scope tracking spot.

8. Range Marks.--Controls intensity of B-scope range marks.

9. Focus.--B-scope focus adjustment.


Figure 4 VF-4. Front panel controls on control chassis.

Turning ON end OFF

1. Starting the Equipment.

(a) Check to see if Main Line Switch is on.

(b) Turn POWER switch B to "on."

(c) Set externally mounted Selector Switch to desired master radar.

2. Adjusting the PPI Scope.

(a) Turn up INTENSITY Control 4 until a light trace appears on the PPI screen.

(b) Adjust FOCUS Control 1 for optimum sharpness of PPI trace.

(c) Adjust RANGE MARKS Control 2 for desired intensity.

(d) Adjust RANGE RING Control 3 for desired brilliance of the illuminated range ring.

(e) Set RANGE SWITCH E to the desired range.

(f) Advance PPI VIDEO GAIN Control C until signals of the desired contrast are obtained.

(g) Adjust CENTER EXPAND Control 5 until first mark makes a small circle or dot at the center of the PPI screen.

(h) Adjust DIAL LIGHTS Control A for desired illumination of the PPI Bearing Dial.

3. Adjusting the B-Scope.

(a) Turn up INTENSITY Control 6 until a faint trace appears on the B-scope.

(b) Adjust FOCUS Control 9 for optimum sharpness of center bearing mark.

(c) Adjust RANGE MARKS Control 8 for desired brilliance of marks.

(d) Adjust SPOT Control 7 for desired brilliance of the tracking spot.

(e) Advance B VIDEO GAIN Control D until signals of the desired contrast are obtained.

(f) Adjust DIMMER Control F for desired illumination of Range Counter and Relative Bearing Vernier Dial.

4. Securing the Set.

(a) Turn all intensity, range marks, range ring, and spot controls fully counter clockwise.

(b) Turn down dial light controls and PPI and B-scope gain controls.

(c) Set POWER Switch B to "STANDBY" position.

(d) Set the externally mounted Selector Switch to "OFF" position.

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Operation

1. Interpreting PPI Targets.

Targets appearing on the VF PPI will be similar to those on the master PPI. However, the VF picture will be clearer than the master PPI picture due to the sharper focus obtainable on the former.

2. Determining Range and Bearing on the PPI Scope.

(a) Determining Range.--Estimate the range of the target by reference to the range marks, bearing in mind the value of these marks as determined by the setting of RANGE Switch E.

(b) Determining Bearing.--Rotate Bearing Crank H until the rotating cursor bisects the signal trace on the screen, then read the bearing (true or relative) on the Bearing Dials surrounding the screen.

3. Reading Accurate Range and Bearing on the B-Scope.

(a) Accurate range is read from the RANGE COUNTER K. Accurate bearing (azimuth) is read from the two PPI Bearing Dials in conjunction with the Relative Bearing Vernier Dial at the front of the top panel.

(b) Procedure.

(1) Observe PPI scope and select a target on which accurate range and bearing are desired.

(2) Rotate the Bearing Crank until the white end of the cursor bisects the chosen target.

(3) Rotate the Range Crank until the illuminated range ring on the PPI appears at the range of the target. The desired target will now lie in the approximate center of an intensified sector on the PPI which is 4,000 yards long and 50°-60° wide. The target will also appear near the center of the B-scope the next time the horizontal sweep occurs on that tube.

(4) As soon as the horizontal sweep ends on the B-scope, adjust the vertical line that crosses the tracking spot until it exactly bisects the target.

(5) Simultaneously adjust the Range Crank until the tracking spot rests on the edge of the target trace nearest the front of the set. The next time the sweep occurs the target will appear in the exact center of the screen in the horizontal plane, and the front edge of the target will be on the middle range mark.

(6) Read the bearing from the PPI Bearing Dials and the range directly from the Range Counter.

(7) If range and bearing to remote stations are desired, press the Remote Range and Bearing Switches indicating that information on the selected target is being transmitted.

Remarks

1. A great deal of practice is required before an operator can get a good track from the VF. Poor operating produces a very poor track, much poorer than proportionately substandard operation of the SG would produce. Try to anticipate the movement of the target by placing the spot where the pip will appear on the next sweep. Never read a range and bearing unless the lower edge of the target is just touching the middle range mark and is perfectly bisected by the vertical line.

2. When not tracking it is advisable to keep the VF trained on the guide, allowing information for station keeping to be quickly obtained.

3. When possible VF ranges should be checked against fire-control radar ranges to insure the accuracy of calibration.

4. Operation of the target designation system is very simple and effective. First, set the selector switches on the desired remote indicators. Second, place spot on leading edge of the target. Third, press the Remote Alarm Switch; one blast indicates action to starboard, two blasts action to port.

5. Precision in spotting depends on the bearing and range discrimination of the radar used. The gain must be set sufficiently high to observe the splashes. An ordinary radar sled target at 5,000 yards produces a pip on the VF oval in shape, 400 yards long and 8° wide when % inch of grass on the SG "A" scope is used. The width of the pip depends on the beam width while the length depends on the pulse width. Spots within 100 yards of the target will be very difficult to make since the splash-pip will merge with the target. Also it must be remembered that when the antenna is rotating, the master radar is not continuously looking at the target. Splashes may possibly rise and fall between sweeps. The best solution probably is to rotate the antenna at its fastest automatic speed. VF spotting is practicable and with a little practice should be a very valuable aid.

6. The possibilities of operation with air search radar are very limited by the relatively short range (40,000-45,000 yards) of the B-scope. Long-range air tracking with the VF is not practical. Tracking within the range of the B-scope is made difficult by

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the slow rotation of the air search antenna combined with the swift movement of the target. Getting on in range requires a very good guess at where the pip will be on the next sweep. The wide beam width of air search radars causes most echoes to extend all the way across the screen. Bearings must then be read from the PPI scope.

Limitations

1. When measuring ranges below 2,375 yards on the B-scope, the spot will not return to the center after the tube has been scanned. The bearing and range may be read from their associated dials, however, when the spot is centered on the desired target. Azimuth centering will still occur but range centering is locked out on low range. The LOW RANGE Pilot Lamp on the top panel is lighted when measuring ranges below 2,375 yards. Do not attempt to read ranges under 500 yards on the B-scope.

2. Bearing accuracy is no better than the bearing accuracy of the master radar, being limited only by the ability of the operator to center the cursor on the vertical bearing mark on the target.

3. The user should remember that the shape of the targets as viewed on the B-scope is not the true enlarged plan view of a section of the PPI screen, but rather a portion of the selected PPI section 4,000 yards long and 40° wide, having the sides of the angle opened out to form parallel lines. This picture is then enlarged to the limits of the 5-inch B-scope. In effect, it is really a Mercator Chart conversion.

4. The VF is a precision instrument both electrically and mechanically and hence should be operated only by competent personnel. All adjustments on controls located inside the recessed front panel of the Control Chassis should be made by technicians. The Battle Switch, which shorts out the interlocks, should be used only in the event of an emergency and then only by a qualified technician.

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VG, VG-1 PROJECTION PPI

MAIN CONTROL PANEL
TURNING ON, ERASING, TURNING OFF
OPERATING TECHNIQUE
          General Precautions
  Techniques of Use
  Use as a Summary Plot
  Use as an Air Plot
  Use for Navigation
PERFORMANCE
TROUBLES

CONTROLS

Main Control Panel

Main Power Switch.--In the "on" position, this switch supplies power to the unit, and in "off" position it supplies power to the heaters. With all other switches "off" it will put into operation only the projection lamp and the blower motor.

Operate Switch.--This switch admits power to all electronic components of the unit with the exception of the high voltage circuit.

High Voltage Switch.--This switch energizes the high voltage circuit.

Dial Light Switch.--The True and Relative Bearing Dials are projected on the viewing screen when the O. S. C. projector lamp is turned on by this switch.

C.R.T. Bias.--This control is analogous to the intensity control on the usual Cathode Ray Tube. In the maximum counter-clockwise position only the strongest signals under the maximum video gain will show on the viewing screen. As the control is rotated in a clockwise direction, less and less gain is required to permit signals to pass through to the viewing screen.

Video Gain.--This control varies the strength of the signals received from the radar. It has the effect of changing the intensity of the pattern appearing on the viewing screen. Together with the C.R.T. Bias it should be adjusted to the point of maximum contrast.

Focus.--This control is used to focus the electron beam until the clearest pattern appears on the viewing screen.

Range Selector Switch.--This control is used to select the range scale desired. Five ranges: 4, 10, 20, 80, and 200 miles are available.

Range Mark Intensity.--This control is used to vary the intensity of the four (4) range mark circles. These range marks always appear at quarter range intervals of whatever range scale is selected. Thus for the 4-mile range, the four (4) concentric rings represent 1, 2, 3, and 4 miles; for the 10-mile range, they represent 2½, 5, 7½ and 10 miles; for the 20-mile range, they represent 5, 10, 15, and 20 miles; for the 80-mile range, they represent 20, 40, 60, and 80 miles; and for the 200-mile range, they represent 50, 100, 150, and 200 miles.

Center Expand Switch.--This switch can be used to move the start of the sweep out from the center of the screen. Its purpose is to give better bearing resolution. The screen will no longer be a true map but the marker circles will still give accurate ranges. If used at all, this switch must be turned "on" only momentarily to avoid harming an extremely persistent circle into the face of the scope.

Centering North-South Control.--This is a screwdriver adjustment used to center the projected pattern on the viewing screen in a north-south direction.

Centering East-West Control.--This is a screwdriver adjustment used to center the projected pattern on the viewing screen in an east-west direction.

Miscellaneous Controls

Dial Light Dimmer.--This control is used to vary the intensity of illumination of the bearing dials on the viewing screen.

Selector Switch.--Located on the selector box, this switch selects the master radar from which signals will be taken for the VG.

Picture Erase Control.--This control is used to vary the persistence of the pattern appearing on the screen. In "operate" position a heat absorbing "aklo" glass is inserted in the path of the projection lamp beam which decreases the heating of the tube face. This results in greater persistence. In the "erase" position, the heat filter is removed, allowing more heating of the tube face and less persistence of the pattern.

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Figure 4 VG-1.

Picture Fade-Out Control.--This control also varies the persistence of the pattern appearing on the screen. It actuates a butterfly valve controlling the flow of air from the blower to the optical unit housing. In "fast" position it cuts off the circulation of air allowing the tube face to heat up and decreasing persistence of the pattern. In "slow" position full flow of air is permitted giving maximum persistence to the pattern. Intermediate settings of the control will frequently be found desirable.

Battle Short Switch.--Normally this switch is "off." When directed it can be used to short out all interlocks in the unit. When the switch is

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"on," the red warning light at the right top forward corner of the unit, and the warning lights on either side of the base of the optical unit housing, will light.

Caution:This Battle Short Switch should be used only during such times that the danger to which the operator and service personnel are exposed, thereby, is warranted and justified. It is intended to be used during time of battle only.

TURNING ON, ERASING, AND TURNING OFF

Turning on--Check Controls for Normal Positions:

1. Video Gain.--Counterclockwise.

2. C.R.T. Bias.--Counterclockwise.

3. Range Mark Intensity.--Counterclockwise.

4. High Voltage.--Off.

5. Center Expand- Off'.

6. Operate.--Off.

7. Picture Erase.--" Operate." 8. Battle Short.--Off.

To Place in Operation

1. Turn Main Power Switch "on". The blower motor will start and the viewing screen will be illuminated.

2. Turn the Operate Switch "on."

3. Turn the High Voltage Switch "on."

4. Set the Selector Switch to the desired master radar.

5. Place the antenna of the selected radar in rotation.

6. Set the Range Selector Switch to the desired range.

7. Turn C.R.T. Bias clockwise until the trace appears.

8. Adjust Focus to optimum.

9. Turn C.R.T. Bias counterclockwise until the trace just disappears.

10. Turn Video Gain clockwise until maximum contrast is obtained on the viewing screen--NOT BEYOND.

11. Readjust Focus to optimum.

Further Adjustments Will be Made as Necessary

1. Range Mark Intensity should not be advanced beyond the point where the range circles are faintly visible. Frequently the range circles will not be used at all.

2. The Dial Light Switch will be turned on and the Dial Light Dimmer advanced whenever desired.

3. Picture Erase Control will normally be placed in "Operate" position though it may be placed in "Erase" position for brief periods if minimum persistence is desired.

4. Fade Out Control will be positioned according to the degree of persistence required.

To Erase Pattern

1. Turn Video Gain fully counterclockwise.

2. Turn Range Selector Switch to 200-mile range.

3- Turn Range Mark Intensity fully counterclockwise.

4. Adjust Focus for most diffuse beam.

5. Turn C.R.T. Bias fully clockwise.

6. Set Picture Erase at "Erase."

7. Set Picture Fade Out at "Fast."

8. Keep antenna of selected radar rotating until pattern is fully erased. A surface search radar is most satisfactory for this purpose since the antenna rotates at a higher speed than does the air search radar.

To Turn Off

1. Erase pattern until viewing screen is clear except for black spot in center.

2. Turn Video Gain fully counterclockwise.

3- Turn C.R.T. Bias fully counterclockwise.

4. Turn Range Mark Intensity fully counterclockwise.

5. Turn High Voltage "off."

6. Delay five (5) seconds.

7. Turn Operate "off."

8. Turn Main Power "off."

9. Turn Picture Erase to "Operate."

10. Turn Selector Switch "off."

OPERATING TECHNIQUE

General Precautions

Care must be taken at all times to avoid burning the pattern too deeply into the scope face. Land echoes are a problem particularly on the higher ranges. Ships in formation also burn targets into the scope. In some cases a compromise must be made between the point of maximum contrast and extreme burning in of targets. Where land is concerned it is good to use a shorter scale not covering the land whenever feasible. Burning in is most serious when using SP-SM radar and least serious on poor definition radars such as SC-SK. When ships in formation change disposition, their burned in image will remain. With practice it is

4-VG-3


possible to differentiate a new and an old target by the shade of the image. Still, confusion may result from several images of ships in the formation, if the old one is not erased or marked in a distinguishing manner.

The Center Expand Switch can cause most serious burning in. When it is turned "on," the transmitted pulse will describe a circle about the center of the screen. This device must be used with great care. Its purpose is to obtain better bearing resolution at the inner portion of the sweep. Unless necessary, it should not be used. When used, it should be turned on for the briefest possible period.

Care must also be taken to guard against momentary flare-ups of the sweep. Such flare-ups are likely to occur when the antenna is suddenly stopped, when ranges are changed, and when the gear is switched to a different radar. The intensity is automatically decreased when the antenna stops rotating but the action is not instantaneous. If the antenna is slowly brought to a stop, no flare-up will result. However, it is desirable for the radar operator to give the VG operator the word whenever the antenna is stopped. The VG operator can then reduce Video Gain until the antenna is again put in operation. The VG operator should also turn down the gain when he switches to a different radar or to a higher range.

When a different range is selected not merely the Video Gain should be readjusted but also the C.R.T. Bias. Again the point of maximum contrast should be attained.

Techniques of Use

Provided with the VG are three different types of viewing screens. One is a clear glass screen covered by plotting paper, two are ground-glass screens, one of which is plain while the other is calibrated with bearing lines and range circles. The plotting paper will not be used unless a record of the plot is desired. The calibrated screen will be used in instances where it may be desired to plot information from sources other than radar. Plotting on all three surfaces is most successful with a soft lead pencil. A damp cloth can be used to erase the ground-glass screens.

Accurately calibrated distance scales should be prepared for each of the five (5) ranges. For use with air plot speed triangles may also be prepared. Some ships have found it helpful to mount a Vard or Craig computer on the VG. In any case, a paralleled motion plotting arm will be found useful for maneuvering board problems as well as for plotting.

Plotting technique depends somewhat on the radar in use. Used with SP-SM or SC-SK the correct plot calls for splitting the target arc and placing a small dot on the inner edge of the indication. Used with SG, the dot is placed in the center of the indication rather than on its leading edge. Plots will be made as the antenna rotates past the bearing of the target, completely eliminating dead time. Time is recorded to the closest quarter minute at appropriate intervals.

The long persistence of the scope is a limitation that must be considered at all times. It is not good practice to change ranges frequently or to switch in different radars very often. The scope should be erased each time before such a change, and thus a time delay is inevitable. Long persistence also contributes to a poor target definition already noticeably worse than the master radar.

Use of VG as a Summary Plot

Summary Plot is a relative plot on which is displayed the present position of all surface contacts. It is used to keep track of all friendly forces and thus is invaluable for purposes of identification. By picturing the fleet disposition it is also useful in station keeping.

The 20-mile range will usually be found to be the most satisfactory. Only when used primarily for station keeping will a lower range scale be preferable. Notation of more distant contacts can be kept on the periphery of the plot. Use of the polar coordinate plotting surface will simplify this process of plotting other information.

With respect to the fleet disposition, all assigned positions should be plotted on the screen with our ship at the center. The guide should be designated as such. Names of ships in the formation can be printed in with their voice call also indicated. When the disposition has been plotted in this manner it will become instantly apparent when any of the ships get out of position. It will be equally apparent when we are out of position. Furthermore, new contacts in or near the formation will be easy to discover.

When a change in the fleet disposition is made there is danger of confusing the old burned in image. The best practice is to erase the old disposition, but if time will not allow this procedure,

4-VG-4


the old images should be marked in a distinguishing manner.

When any contacts have relative motion, the use of maximum persistence will result in the target plotting itself. It leaves behind it a "tail" which gradually fades out with time. This process provides a rough indication of the relative course of the target for the "tail" will extend toward the reciprocal bearing of the target's relative course. A rough indication of relative speed is also provided by the length of this "tail," When plots are made with every rotation, an even more accurate indication of relative course and relative speed is given by the direction and intervals between dots.

Accurate courses and speeds can be readily computed from a plot on which quarter minute times are noted. The viewing screen can then be used as a maneuvering board.

Use of VG for Air Plot

Used with SK, air plotting can be carried out on the VG screen in the same manner as it is usually performed on an air plot board. Again, great advantages will result from the elimination of dead time and the constant plotting of all targets. If it is not possible to plot all contacts appearing on the screen, the "tail" will indicate the general course and speed of all aircraft. Quarter minute time should be used but plotting done with each rotation of the antenna. Tracks will turn out to be clearer and straighter than those made with the usual operator-plotter team. Moreover, plots will not be missed and fades will be at once apparent.

Several disadvantages must be understood and the gear operated accordingly. Identification will ordinarily be impossible on VG. Information as to identity of the contact will have to be obtained from the master radar. However, once a target is designated friendly, an accurate plot will serve to keep its identity certain.

Difficulty is also encountered in use of the electronic range marks when SC-SK radar is being used. With Range Mark Intensity turned fully clockwise, the range marks may not appear at all. It is necessary then to reduce the Video Gain until the marks appear. It may not be possible to get signals and marks at the same time.

Interceptions can be made from VG with some advantages over an air plot board interception. However, poor target definition and long persistence has limited the possibilities where particularly close interception is required as in night fighter direction. Evasive maneuvers of the bogey are sometimes hard to follow. The VC with a 12-inch scope is much more satisfactory.

Use of VG for Navigation

When within range of land, the VG can be used to obtain navigational fixes. The SP-SM is the best master radar to use for this purpose with the SG being almost as effective.

Contour charts on tracing paper must be prepared in advance for land to be encountered. With a pantograph these charts can be drawn quickly and easily to correspond with the VG range scale on which they will be used. The range scale to be used will depend entirely upon the operations to be undertaken. The 80-mile scale will be most useful range for general navigation but for shore bombardment, or inshore piloting, lower scale will be better.

Accuracy of VG fixes will not be as high as with the VPR or when otherwise making use of the master radar. However, fixes can be obtained very quickly and can be of considerable use in C.I.C.

PERFORMANCE

Performance of the VG is in all cases inferior to the master radar with which it is being operated. Target definition is poorer resulting in worse bearing and range resolution. Also faint targets visible on the master radar will often be lost on the VG though it is frequently possible to coach the VG operator onto this target from the master set. Range and bearing accuracy is also inferior to that of the master radar.

TROUBLES

Burning in Permanent Patterns.--This hazard has frequently been mentioned and it must always be borne in mind. Targets with no relative motion, land, range marks, and the center expand circle create images which can burn in permanent black patterns. These images must be avoided or reduced whenever possible. The screen must always be erased before securing it.

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Changing Cathode Kay Tube.--This is a process requiring considerable practice since it involves realignment of the optical system. Technicians should be given an opportunity to practice this and no one else should attempt it.

Cracking of Lenses.--Several cases of cracking of the parabolic condenser lens have been reported. The operator should report any failure of the blower motor immediately as continuous air delivery might prevent such casualties.

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ECHO BOX

INTRODUCTION

HOW IT WORKS

HOW TO TEST OVER-ALL RADAR EFFICIENCY

RINGTIME MEASUREMENT POINTERS

OTHER USES


Figure 4 OBU-1. The typical echo box (OBU-3).

Introduction

Before the development of the echo box, radar operators had no way of testing the efficiency of their sets. The echo strength of a so-called "standard target" such as the pineapple tower in Honolulu--as seen from Pearl Harbor, was once thought to be significant. In the early days of radar few appreciated the role of weather as a factor influencing the performance of radar. Now, however, we know that a radar may be in poor materiel condition and give fair ranges under conditions of "anomalous" (nonstandard) wave propagation. Furthermore, it is quite possible


Figure 4 OBU-2. Atmospheric variations cause variations in radar performance.

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that a set may be in 40 condition and still fall far below the typical standard of performance. Nonstandard propagation and other variables that influence the performance of radars have been dealt with at length in RAD 1A and to some extent in this manual: suffice it to say, it is not possible for you to judge the efficiency of your radar except by testing it with an echo box.

How It Works

The echo box, as the name implies, is a device that returns an echo whenever a pulse from the transmitter is fed into it. This echo incidentally is a standard echo in the truest sense of the word--if it changes, a change in over-all radar system efficiency is indicated.


Figure 4 OBU-3. Simplified cross-section of echo box.

Essentially the echo box consists of simply a cylinder, the size of which is varied by a piston. The piston moves in and out as the echo box is tuned by its tuning knob. Energy from the radar transmitter is fed into this "tuned cavity" in one of two ways: (1) A small pick-up antenna can be placed in the vicinity of the radar antenna--the pick-up antenna being connected to the echo box by a coaxial cable.

(2) A so-called "directional coupler" can be installed in the wave guide--it picks up energy which is then fed through a coaxial cable to the echo box.

Basically this is all there is to an echo box, but most have an output meter built in as an additional refinement--this is, of course, for use in making periodic comparisons of average pulse power.

The echoes of the box are detected by the radar receiver and displayed on the various indicators as a characteristic pip extending from zero range out to several thousand yards. If the pick-up dipole has been placed in a fixed position with respect to the radar antenna, the echo box echo will be seen best in one direction only (when the radar antenna is pointed at the pick-up antenna). If the pickup antenna is attached to the radar antenna and rotates with it, or if a directional coupler is used; the echo will be seen extending in all directions from zero range to several thousand yards.

How To Test Over-all Radar System Efficiency

Testing the over-all system efficiency requires only a moment and should be done by the radar operator at the time a new watch is set or whenever he has reason to believe his set is "below par." The procedure is as follows:

1. Turn on radar and allow sufficient time for it to warm up thoroughly.

2. Turn off AJ controls and STC.


Figure 4 OBU-4. Echo box echo on "A" scope. Its duration is measured in yards and called "ringtime."

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Figure 4 OBU-5. Ringtime as it appears on the PPI scope

3. Rotate the radar antenna until it is pointed in a direction relatively free of targets out to several thousand yards.

4. With echo box connected to the directional coupler, adjust its tuning knob until the output meter reads a maximum.

5. Check calibration of radar range circuit.

6. Set receiver gain as you would for short range search.

7. Look at the echo box echo on the radar indicator (A scope preferred) and adjust the receiver tune control until the echo box echo is saturated to the greatest possible range.

8. Measure the "ringtime" (the greatest range at which the echo box echo can be seen) several times and average the readings.

9. Record the date and time, the output meter reading, the ringtime, the difference between the actual ringtime and the expected ringtime (the latter is determined by the technician or the materiel officer).

10. If the ringtime is low, the technician should be called to investigate the trouble. A loss of more than about 150 to 250 yards of ringtime begins to be quite significant (this depends on the model of echo box used)--especially with regard to small targets such as periscopes and aircraft. The radar materiel officer will inform the operators of the expected ringtime and he may request that he be called if the loss of ringtime is larger than some specified figure--like 150 yards.

11. Having completed the check, the radar operator may now secure the echo box by detuning it.

CONFIDENTIAL


Figure 4 OBU-6.

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Figure 4 OBU-7. Measuring ringtime on "A" scope--receiver gain not a critical factor within reasonable limits.

Ringtime Measurement Pointers

In measuring ringtime on the A scope, the range should be read at the point where the echo just disappears in the grass--the antenna should be stopped. Be sure you don't confuse the echo box ring with sea return or other nearby echoes. The characteristic behavior of the ring as the receiver gain is varied will distinguish it from other echoes.

When the PPI scope is used, the ringtime should be measured to the point where it is barely distinguishable from noise--not where it ceases to be solid white. Receiver gain should be set so that flecks of "snow" cover about half the scope area. Ringtime can be measured on the PPI with the


Figure 4 OBU-8. Setting the step.


Figure 4 OBU-9. Measuring ringtime on PPI. A. When directional coupler is used. B. When pick-up dipole is used and is not mounted on antenna so as to rotate with it. Note that measurement is made at outermost fringe of echo.

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Figure 4 OBU-10. Ringtime seen on B' and * J" scope.

antenna rotating or stopped but it is generally easier when the antenna is in motion.

In most cases, a number of operators will be making ringtime measurements. These men should practice together until they can make readings that agree closely with one another.

The expected ringtime will depend upon the pulse length in the case of some radars--so be sure you take this into account and use the one which corresponds to the ringtime you have been told to expect. Furthermore, the expected ringtime will depend upon whether it is the pick-up antenna or the directional coupler that is "connected to the echo box" (there is more loss in the long coax necessary when the pick-up antenna is used). It is quite possible to use the pick-up dipole in

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over-all system check. This technique has two advantages and one big disadvantage when compared to the test previously described.

Advantages--(1) You test not only the transmitter and receiver, but the antenna and transmission line too. (2) You can see a rough outline of your antenna pattern (and therefore spot your minor lobes) on the PPI, if pick-up is fixed with respect to antenna.

Disadvantage--Variations in weather affect the loss in the longer coax rather unpredictably, making precision comparisons impossible.

Other Uses

The echo box is a valuable piece of test gear. In addition to its most important function (ringtime measurement), it can be used to make a "spectrum analysis" (to determine if frequency modulation or double moding is occurring and to measure pulse duration) to make periodic power comparisons, and discover and isolate to some extent obscure troubles that might go unnoticed. Naturally these test functions are out of the realm of radar operation but they are mentioned for information anyway.

You now have a quick, scientific means of checking the over-all system efficiency. There is a natural tendency question to question testing equipment of this type--especially when good radar conditions (nonstandard atmosphere) offset and conceal reduced efficiency. The equipment is fundamentally simple and ruggedly and reliably made. It is intended to serve you and is worthy of your confidence. Use it.

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