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APPENDIX A
Glossary of Radar Terms

This glossary was compiled largely by selecting terms from the following sources:

Radar Electronic Fundamentals NavShips 900,016
Radar System Fundamentals NavShips 900,017
Glossary of Terms used in Connection with Radiation Laboratory Radar H. Shapiro, 15 November, 1943
Glossary of Radar Terms AN/APQ-13 Instruction Book
Radar Technical Bulletin No. 4 Eng. 129
The following additional publications give definitions also suited to radar:
Symbols and Abbreviations BuShips Specification 16S12(RE)
U. S. Navy Symbols--  
Report No. 58 from Ship's Statistics Report--Matériel Branch of BuShips
Glossary of Physics Weld
American Standard Definitions of Electrical Terms AIEE

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GLOSSARY OF RADAR TERMS

A Band--A frequency band used in Mark III IFF. Transpondors that operate in this band are continually tuned through it, causing responses to a particular interrogating frequency to be transmitted at 3-second intervals. These responses are coded in that the pulse duration is varied by the coding mechanism. See G Band.

"A" Indicator--An indicator on which a time sweep produces a horizontal range scale on which echo signals appear as vertical deflections (also called "A" scan and "A" scope).

Absolute Altimeter--An electronic instrument which furnishes altitude data, in feet, with respect to the surface of the earth, as distinguished from an aneroid altimeter whose readings are based on air pressure and therefore functions with respect to sea level. See Altimeter.

AC--Alternating current.

Acceleration Merit--Ratio of acceleration (in degrees/sec.2) to angular lag (in degrees) in a servo system.

Acorn Tubes--Small receiving tubes, made in the shape of acorns, and having good high frequency characteristics.

AEW--Aircraft early warning radar. A high-power set installed in aircraft for long-range detection.

AFC--Automatic Frequency Control.

AGC--Automatic Gain Control.

AGL--Airborne gun laying; radar for plane-to-plane fire control.

AI--Aircraft interception. Radar which enables a night fighter to detect and close with an enemy aircraft.

Aided Tracking--A system of tracking a signal in azimuth, elevation, or range in which a constant rate of motion of the tracking mechanism is maintained by mechanical means so that an equivalent constant rate of motion of the target can be followed.

Air Gap--An air space between two objects which are electrically or magnetically related. For example, the space between electrodes of a spark gap or the space separating sections of an iron core transformer. It is used to provide a high impedence path for electron flow and a high reluctance path for magnetic flux.

AJ--See Anti-Jamming.

Alignment--(1) The process of adjusting the tuned circuits of. a tuned radio-frequency receiver to a predesignated natural frequency.

(2) The process of adjusting two or more components of a system so that their functions are properly synchronized; for example, antenna orientation and PPI sweep.

Alternating Current (AC)--Current that is continually changing in magnitude and periodically reversing in polarity.

Altimeter--An instrument that indicates the elevation of an aircraft above a given level. A barometric or aneroid altimeter does this by measuring the weight of air above it and thus indicates height above sea level, or some other selected reference plane. A radio altimeter, usually referred to as an absolute altimeter, utilizes the time interval between the transmission of a radio signal and the return of its echo from the ground to measure absolute altitude.

Altitude--(1) Corrected altitude is the true height above sea level. (2) Absolute altitude is the true height above the ground.

Ambient Temperature--The temperature of the surrounding cooling medium, such as gas or liquid, which comes in contact with the heated parts of the apparatus, e. g., temperature inside airplane or in a compartment of a ship.

Amplidyne Generator--A special type of DC generator used as an electromechanical amplifier. A small amount of field power can control a large power output, and the response of the output voltage to changes in field excitation is very rapid. The amplidyne generator is used with radar equipment to control the speed and direction of rotation of the antenna driving motor.

Amplification--The process of increasing the amplitude (either current or voltage or both) of an electrical signal.

Amplifier--A device for increasing the power, voltage or current of a given input, in which the output of a local source of power is controlled by the input signal.

Amplitude--In connection with alternating current or any other periodic phenomena, the maximum value of the displacement from the zero position.

Amplitude Balance--A control for balancing the amplitude of signals on separate traces.

Amplitude Distortion--A condition in which the output voltage of an amplifier is not directly proportional to the input voltage over the complete range of the input voltage.

Amplitude Modulation (AM)--An operation in which the amplitude of a radio wave is made to vary in accordance with the signal containing the intelligence to be transmitted; the frequency and phase angle of the radio wave remain constant.

Angle Component Solver--A machine which resolves an electrical vector into its components. See Electrical Resolver and Resolver.

Angular Rate--Rate of change of bearing.

Anode--Any electrode of a vacuum tube or cathode ray tube operated at higher d-c potential than the cathode (e.g., plate, screen grid, focusing anodes, accelerating anode, etc.).

Anomalous Propagation--See Trapping.

Antenna--A conductor or a system of conductors for radiating or receiving radio waves.

Antenna Assembly--The complete equipment associated with projecting radar waves into space and receiving them, consisting in general of a mounting base, gears and motors for rotating the antenna, synchros, potentiometers, the antenna proper, and the reflector, together with associated switches, such as those used in sector scanning, and the switch used to set up a ship's head marker on the PPI tube.

Antenna Bearing--The generated bearing of the antenna as delivered to the indicator or PPI; generally true bearing, but may be relative, depending on operating conditions. (A separate circuit is generally used to indicate the transmission of relative bearings.)

Antenna Control--Control governing rotation of antenna--direction, speed, servo, slewing, etc.

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Antenna Disconnect Switch--Safety switch or interlock plug to remove driving power from antenna to prevent rotation while work is being performed on it.

Antenna Matching Device--A device which matches the antenna to its transmission line by introducing an impedance which together with the impedance of the antenna equals the characteristic impedance of the line.

Antenna Pedestal--Support for antenna assembly containing training motor, gears, synchros, rotating joint, etc.

Antenna Reflector--That portion of a directional array, frequently indirectly excited, which reduces the field intensity behind the array and increases it in the forward direction.

Antenna Switching Unit--The TR box.

Anti-Aircraft Fire Control Radar--Equipment for precision long-range fire control, and for defense against low-flying planes such as dive bombers and ground attack planes.

Anti-Hunt--A feedback signal or network in a servo mechanism acting to prevent "hunting" or oscillation of the system. Special types of anti-hunt circuits are: Anticipators, Derivative, Velocity Feedback, and Dampers.

Anti-Jamming (AJ)--(1) The art of minimizing the effect of enemy counter-measures in order to permit the echoes from targets detected by the radar to be visible on the indicator. (2) The controls or circuit features incorporated to minimize jamming.

Anti-T-R Box--A device similar to a T-R box used to tune the transmitter section of the r-f line so that returning echoes do not enter the transmitter. Also called the R-T box or ATR box.

Aperture (of an Antenna)--Diameter of the reflector (dish). Usually measured in terms of wavelengths.

Aquadag--A colloidal suspension of graphite deposited on the inner side walls of cathode-ray tubes to serve as an electrostatic shield or as an accelerating anode.

Array--A number of antenna elements arranged so as to produce a concentration of energy in a desired direction.

Artificial Line--A circuit made up of lumped constants (inductors, capacitors and/or resistors) which is used to simulate the delay or pulse-forming characteristics of a long transmission line.

ASC--Automatic sensitivity control.

Astigmatism--Variation of focus along trace of CRT.

ASV--Aircraft to surface vessel. Radar to detect surface vessels from patrol aircraft.

ATR Box--See Anti-T-R Box.

Attenuation--Reduction in the strength of an electrical impulse or signal.

Attenuator--A device for reducing the amplitude of a signal. RF attenuators are of two general types. The first, or "cut-off type," operates on the principle of a wave guide below cut-off. The second, or "dissipative type," introduces dissipative elements to absorb energy. In coaxial-line dissipative attenuators the loss may be introduced either in the form of series resistance or shunt conductance. Examples of the former are the platinized glass rod and carbonized rod attenuators. Shunt conductance types are ordinary lossy cable and sand loads.

Automatic--Applicable to any system which carries on its function without manual control.

Automatic Frequency Control (AFC)--The control of the frequency of a generating system within a narrow range. Usually control of local oscillator frequency as a means of keeping the receiver accurately tuned.

Automatic Gain Control (AGC)--A type of circuit used to maintain the output of a receiver constant, regardless of variations in the signal strength applied to the receiver. In radar, the echo from any selected target, which is within the range gate, is used to control the gain of the whole receiver, so that echoes from other than the selected target appear to vary more than usual.

Automatic Gain Stabilization (AGS)--A circuit used with superregenerative receivers for the purpose of maintaining optimum sensitivity by keeping the noise pulse level constant. Such a circuit is desirable because it prevents the receiver from becoming so sensitive that the noise pulses would trigger the transmitter which is usually associated with a superregenerative receiver in IFF and radar beacon equipment.

Automatic Sensitivity Control (ASC)--A circuit used for automatically maintaining receiver sensitivity at a predetermined level. Similar to AGC, but it affects the receiver constantly rather than during the brief interval selected by the range gate.

Automatic Tracking--Tracking in which the servo mechanism follows the signal automatically, and keeps the radar beam oriented on the target.

Automatic Train--Automatic training of the antenna in azimuth by automatic following of the target.

Automatic Volume Control (AVC)--A circuit which develops a d-c voltage proportional to the amplitude of the carrier wave for the purpose of varying the gain of the receiver so that a constant volume of sound is heard. The operation of this circuit is independent of both the carrier frequency and the modulation imposed on the radio waves. In radar, if the modulation of the received carrier wave, that is the echo pulses, is not used, then there is no signal available for use in an AVC circuit. Therefore, the term AVC has no meaning when applied to radar, and Automatic Gain Control should be used instead.

Auxiliary Control Unit--Unit containing supplementary controls to main control and general control.

Auxiliary-Normal--A control used for selecting the source of main power to system.

Azimuth--Angular position or bearing in a horizontal plane measured from a zero degree relative or true north to the target in a clockwise direction from 0 to 360°.

Azimuth Rate--Rate of change of true bearing.

Azimuth-Stabilized PPI--A PPI presentation in which 12 o'clock on the tube face is made always to represent true north, irrespective of the heading of the vessel carrying the indicator. The stabilization is effected by introducing synchro voltages from the compass into the servo system that drives the PPI coils.

B Indicator--A type of presentation in which signals appear as bright spots on a rectangular grid. Azimuth is shown horizontally and range vertically. Also called B scan and B scope.

B+ (B plus)--Symbol used to designate the point in a circuit to which the positive terminal of the d-c supply is to be connected.

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Babs--Beacon system for controlling the blind approach of aircraft.

Back Bias--An AJ circuit used to aid the receiver in discriminating against signals of duration longer than a normal echo pulse.

(1) Unamplified back bias is a degenerative voltage developed across a fast time constant circuit within an amplifier stage itself.

(2) Amplified back bias is a degenerative voltage developed across a fast time constant circuit within a stage of an amplifier and fed back into a preceding stage.

Back Swing--That portion of a pulse which occurs near the end of the pulse, during which the voltage shifts in a direction opposite to that of the main body of the pulse.

Balance (Bal)--AJ control of video balance.

Band Pass or Band Width (Δ f or B)--The number of cycles per second expressing the difference between the limiting frequencies at which the desired fraction (usually half power) of the maximum output is obtained. Term applies to all types of amplifiers.

Base Line--The horizontal (or vertical) line formed by the movement of the sweep on a cathode-ray tube. Sweep usually used.

Battery--Two or more dry cells or storage cells connected together to serve as a d-c voltage source.

Battle Short--A switch for short-circuiting the safety interlocks and lighting a red warning light.

Bazooka--A device used to match an unbalanced high frequency transmission system into a balanced system or vice versa.

Beacon--See Radar Beacon.

Beaded Transmission Line--A transmission line using beads to maintain the inner conductor coaxial with the outer.

Bead Support--Ceramic or plastic beads used to support the inner conductor in coaxial transmission lines.

Beam Current--The electron stream flowing from cathode to the fluorescent screen and then to the second anode in a cathode-ray tube. This current is usually on the order of the 25 microamperes.

Beam Width--The angle between half-power intensities in lobe pattern. See Lobe.

Bearing--The direction of the line of sight from radar antenna to target. Azimuth angle of train. See True and Relative.

Bearing Buzzer--Circuit to indicate transmission of bearing to remote station.

Bearing Cursor--Mechanical bearing line on PPI for reading target bearing.

Bearing Mark--Electronic bearing line on PPI. See SHM.

Beat Frequency--A frequency resulting from the combination of two different frequencies in a non-linear device, such as a vacuum tube or a crystal. It is numerically equal to the sum or difference of these two frequencies.

Beat Frequency Oscillator (BFO)--See Local Oscillator.

Beaver Tail Beam--A fan-shaped beam.

Bedsprings--See Billboard Type Antenna.

Bias--A d-c potential applied between control grid and cathode of a vacuum tube. It determines the zero signal level about which the grid operates.

Billboard Type Antenna--A large broadside array with flat reflector.

Blanking Pulse--A square wave (positive or negative) used to switch off a part of a radar system electronically, for a predetermined length of time. See Unblanking Pulse.

Bleeder--See Bleeder Resistor.

Bleeder Current--A current drawn continuously from a power supply to improve its voltage regulation or to increase the value of voltage drop across a particular resistor.

Bleeder Resistor--A resistive network used to draw a fixed current from a power supply, for purposes of regulation. Also used to provide a slow discharge path across high voltage capacitors.

Blind Zones--Areas in which echoes cannot be received.

Blip--Echo indication on a type A scope. The indication is produced by a short, sharply-peaked pulse of voltage.

Block Diagram--A diagram in which the essential units of any system are drawn in the form of rectangles usually, and their relation to each other indicated by appropriate connecting lines.

Blocking Capacitor--A capacitor used in some branch of a circuit for the purpose of preventing the flow of direct current, or limiting the flow of low-frequency alternating current, without materially affecting the flow of high-frequency alternating current.

Blocking Oscillator--A circuit containing a vacuum tube and a transformer which produces pulses at a predetermined repetition rate. May be free running or under control of a synchronizing voltage.

Blocking Oscillator Driver--A circuit which develops a square pulse used to drive the modulator tubes, and usually contains a line-controlled blocking oscillator that shapes the pulse into the square wave.

Blooming--The expansion of the spot on a cathode-ray tube due to maladjustment of bias, focus and intensity.

Blower--A motor-driven fan used to supply air for cooling purposes.

Blower Alarm--Indicator light which lights if unit overheats due to blower failure.

Blown Fuse Indicator--Neon warning light, across fuse, which lights when fuse is blown.

Bolometer--A piece of test equipment used to measure high-frequency current or power. The sensitive element absorbs r-f power, its temperature changes, and consequently its resistance is altered.

Bond--Electrical interconnection made with a low-resistance material between chassis, metal shield cans, cable shielding braid, and other supposedly equipotential points, in order to eliminate undesirable interaction resulting from high impedance paths between them.

Bootstrap Driver--A special type of vacuum tube circuit used to produce a square pulse to drive the modulator tube. The duration of the square pulse is determined by a pulse-forming line. The circuit is called a bootstrap driver because voltages on both sides of the pulse-forming line are raised simultaneously with voltages in the output pulse, but their relative difference (on both sides of the pulse-forming line) is not affected by the considerable voltage rise in the output pulse.

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Breakdown Voltage--The voltage at which the electric field produced becomes strong enough to break down or ionize the insulation, gas, or air separating two conductors, thereby causing current to flow between them.

Bridge--An electrical network consisting usually of four branches, often represented in the form of a diamond-shaped figure. One pair of diagonally opposite corners is connected to the input and the other pair to the output circuit. Used in many types of measurements, in rectifiers, and in some oscillators. See Wein Bridge Oscillator.

Brightness Control--See Intensity Control.

Brilliance Control--See intensity Control.

Broadside Array--A directional antenna system designed to give the maximum radiation in a direction perpendicular to the plane of the array, as in the SC and SK antennas.

BTO--Radar equipment designed to allow bombing through overcast.

Bug--(1) The moving element of a DRT (Dead Reckoning Tracer). (2) A diamond-shaped marker for reading bearings against graduated scale of fixed or moving bearing dials.

Buncher--The element in a velocity-modulated tube which alternately slows down and speeds up the electrons so that they are formed into groups or bunches at some point along the path of the electron beam.

Bups--Ultraportable S-band beacon for Army plane and ground cooperation.

Burn-Out--Loss of crystal sensitivity when excessive power is applied to it.

Buzzer--Warning device to indicate bearing or range transmission, overheating, etc.

By-Pass Capacitor--A capacitor which provides an alternating-current path of comparatively low impedence around some circuit element.

C indicator--A type of radar indicator in which the signal appears as a bright spot with azimuth angle as the horizontal coordinate and elevation angle as the vertical coordinate. Also called C scan and C scope.

C & I--Control and Indicator. Range operator's position in Mark 4 radar.

Calibrate--Position to which a control may be set to check frequency, range marks, or other functions against a standard.

Calibration Markers--Indications on the screen of a radar indicator which divide the range scale into accurately known intervals for range determination, or checking against mechanical indicating dials, scales, or counters.

Capacitance--The property of two or more bodies which enables them to store electrical energy in an electrostatic field between the bodies.

Capacitance Coupling--A method of coupling between two electrical circuits in which a capacitor's property of passing an alternating current or voltage and blocking direct current or voltage is utilized. See RC coupling.

Capacitance Divider--A circuit made up of capacitors for measuring accurately the value of a high-voltage pulse by making available only a conveniently small fraction of the total pulse voltage for the measurement.

Capacitor--An electrical circuit element which consists of two electrodes or sets of electrodes in the form of metal sheets or plates separated from each other by an insulating material called a dielectric.

Capacitor-Start Motor--An a-c split-phase induction motor in which a capacitor is connected in series with an auxiliary winding to provide a means of starting. When the motor gets up to speed, the capacitor is disconnected by a centrifugally operated switch, and the motor runs as an ordinary single-phase induction motor. Such motors are used for rotating heavy spinners and for operating the lobe switching mechanisms in radar antennas.

Carbon Pile Regulator--A device whose resistance decreases in accordance with the pressure or compression applied. It is used to regulate the output of small generators.

Carrier--A pure radio-frequency wave which is used as the vehicle for conveying intelligence by radio.

Cascade Amplifier--An amplifier of several stages, the output of one being the input of the next.

Cat Whisker--A wire which touches the crystal in a crystal detector.

Catcher--That electrode in a velocity modulated vacuum tube on which the spaced electron groups induce a signal. The output of the tube is taken from this element.

Cathode--That electrode in a vacuum tube which, when heated, provides the primary source of electrons in the tube.

Cathode Follower--A vacuum tube and its associated circuit in which the output signal is taken from the cathode circuit rather than the plate circuit. This provides a low impedance voltage source. There is no polarity reversal in this type of operation and the voltage gain of the stage is never greater than one.

Cathode Ray--The electron stream that flows in a cathode ray tube and which after acceleration may be focused and deflected. See Beam Current and Cathode-Ray Tube.

Cathode-Ray Oscilloscope--A test instrument which, when properly adjusted, makes possible the visual inspection of a-c signals. It consists usually of three major parts--an amplifier, time base generating circuits, and cathode-ray tube (CRT) for translation of electrical energy into light energy.

Cathode-Ray Tube--A vacuum tube in which an electron beam is accelerated and focused in an electron gun. This electron beam is then made to strike a layer of fluorescent material which converts the electron energy into light energy. By inserting a changing field, either electric or magnetic, between the electron gun and the fluorescent screen, this spot of light may be deflected or moved in accordance with the field variations.

Cavity Resonator--A hollow metallic cavity in which electromagnetic oscillations can exist when properly excited. These determine the oscillating frequencies of klystrons, McNally tubes, and Sheppard tubes. Frequency is determined by the physical dimensions of the resonator.

Center Expand--Movement of start of PPI sweep from center of CRT so as to give a hole in center of the pattern.

Centering Control--A control used for positioning the image on the screen of a CRT, by either changing the d-c potential on the deflection plates in the electrostatic system or changing the direct current flowing through the deflection coils in the magnetic system.

Ceramic Bead--A wafer type insulator used to support and insulate the center conductor of a coaxial line.

Challenge--To cause an interrogator to send out pulses, putting the IFF system in operation.

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Channel--A group of circuits through which a signal passes. Each circuit may, in some fashion, alter the appearance of this signal.

Characteristic Impedance--The ratio of the potential difference applied to a transmission line to the resultant current at the point where the potential difference is applied when the line is of infinite length.

Charging Current--(1) Current that flows to charge a pulser capacitor. (2) Current that flows to restore energy to a storage battery.

Cheese Antenna--Truncated parabolic reflector with horizontal enclosures at top and bottom giving rectangular opening for radiation.

Choke--An inductance normally used to impede alternating or transient currents without affecting appreciably the direct current.

Choke Flange--A flange put around a transmission line to prevent energy from feeding back along the outside of the line.

Choke Joint--A type of joint for connecting two sections of waveguide together. It permits efficient energy transfer without the necessity of an electrical contact at the inside surfaces of the guide.

CIC--Combat Information Center. See RadSix.

Circuit--One or more electrical parts (vacuum tubes, resistors, coils, capacitors) so interconnected as to permit current to flow when a voltage is applied.

Circular Scan--Method of scanning of lobe of antenna radiation through 360° in a single plane.

Circularity--Control on a PPI to give equal radial deflection on all bearings.

Clamping Circuit--A circuit which maintains either amplitude extremity of a waveform at a certain level of potential.

Clipper--A vacuum tube and its associated circuits which does not pass certain unwanted portions of a signal. A clipper is usually thought of as passing only the peak (positive or negative) of the signal. It can be arranged to clip any amount of the positive or negative half cycle by proper biasing.

Clutter--The obliteration of targets on the screen of a radar indicator due to atmospheric conditions or other targets. Ground, cloud, or sea clutter.

Coarse--Control for making rough adjustment of intensity, gain, tuning, etc.

Coaxial Cable--A two-conductor cable in which one conductor is a shield or tube and the other is centrally located within it. Its major feature is low loss at high frequencies. It is available in both flexible and rigid types.

Coaxially Fed Linear Array--A beacon antenna having a uniform azimuth pattern. Each element consists of three dipoles of the slotted type, with Ag/2 spacing between the elements.

Coder--A beacon circuit which takes the trigger pulse output of the discriminator, forms it into a series of pulses, and then feeds these pulses to the modulator circuit.

Coding Disc--Disc with small projections for operating contacts to give a certain predetermined code to the transmission.

Coho--A type of local oscillator which is used to provide a reference phase in a coherent pulse doppler system. It is locked in phase to the transmitter pulse every time a pulse is sent out. See Stalo.

Coil--An electrical circuit element consisting of a number of turns of wire so arranged physically as to offer impedance to the flow of alternating current through them. The impedance is a function of the frequency and the inductance, which in turn depends on the number of turns and method of winding.

Coincidence Amplifier--An amplifier which has an output only when two pulses are applied to the tube simultaneously.

Co linear Array--An antenna having a string of ½ wavelength elements excited in phase.

Collector--An electrode in a velocity modulated vacuum tube on which the spent electron bunches are collected. It serves approximately the same purpose as the plate in a more conventional tube.

Color Code--The system of colors used to specify the electrical value of a radio part or identify terminals and leads.

Combiner--Circuit for mixing video, trigger and scan data from synchronizer for modulation of link.

Compass Bearing--Bearing measured relative to magnetic north.

Compass Error--Angle between N-S compass line and true meridian.

Compass Transmitter (Flux Gate)--Contains the Flux Gate, the sensitive element of the Gyro Flux Gate Compass System, which picks up the directive force of the earth's magnetic field.

Computer--An instrument for calculating various quantities such as range, speed, altitude, etc., from the information supplied.

Concentric Cable--See Coaxial Cable.

Conical Scanning--A type of antenna beam scanning in which the tilt angle is fixed so that the axis of the r-f beam generates a cone whose vertex angle is usually from 5 to 10 degrees.

Console--Main operating unit of a radar in which indicators and general controls are installed.

Contamination--Deposition of cathode emitting material on grid of tube causing unwanted grid emission.

Continuity Test--An electrical test to determine the existence of a broken connection.

Control--A knob, dial, switch or screw driver adjustment for operating an electrical installation.

Control Central--See Timer.

Control Grid--That electrode in a vacuum tube on which the signal is usually impressed. The control grid is the electrode nearest the cathode.

Control Panel--A panel where switches, potentiometers, meters, etc., are installed for controlling and protecting electrical equipment.

Control Transformer--See Synchro Control Transformer.

Conversion Gain of the Crystal--The ratio of the available i-f power output to the available r-f power input. Is always less than unity.

Converter--See Mixer.

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Converter Unit--A unit of a radar system in which is located the mixer of a superheterodyne receiver, and usually two stages of i-f amplification. The converter unit usually is placed relatively close to the radar antenna. See Preamplifier (2).

Copper Oxide Rectifier--A rectifier made up of copper discs coated on one side with cuprous oxide. The cuprous oxide-copper discs have a unidirectional current characteristic, that is, they allow current to flow in only one direction. One common use is to obtain a-c voltage readings on a d-c instrument.

Corner Reflector--A device made in the form of three planes mutually perpendicular--as the three sides of a cube that meet at a corner. It is very effective in returning a strong radar echo.

Corona--A luminous discharge due to ionization of the air surrounding a conductor around which exists a voltage gradient exceeding a certain critical value.

Cosecant Squared Beam--A radar beam pattern designed to give approximately uniform signal intensity for echoes received from distant and nearby objects. Such a beam is generated by a spun barrel reflector. The beam intensity varies as the cosec2 of the elevation angle.

Counter Circuit--Receives uniform pulses representing units to be counted and produces a voltage in proportion to their frequency.

Countermeasures--See Radar Countermeasures.

'Counting Down' Circuit--See Frequency Divider.

Coupling--The means by which signals are transferred from one electrical circuit to another. Coupling can be direct through a conductor, capacitive through a capacitor, or inductive through a transformer, or any combination of these.

Cross-Level Angle--The angle between the plane of the ship's deck and a horizontal plane, measured in the plane perpendicular to the side of the level angle lying in the ship's deck. This quantity is positive if the right side of the deck, as seen by an observer facing the target, is raised. See Level Angle.

CRT--Cathode-ray tube.

Crystal--(1) An electrically conductive, or semi-conductive mineral which has the property of rectifying small high frequency voltages. It is used as a detector or mixer in certain receivers.(2) A plate of quartz or other material demonstrating a piezo-electrical characteristic. When properly combined with other electrical parts it will generate a voltage when mechanically stressed. It can be used to produce radio frequency oscillations and when put to this use has a very stable frequency characteristic.

Crystal "Burn-Out"--The impairment of a crystal by exposure to excessive r-f power.

Crystal Check--Measurement of forward and backward crystal resistance.

Crystal Detector--A system composed of a metal wire and a crystal, which offers a higher resistance to currents in one direction than to currents in the other direction.

Crystal Mixer--A housing containing the crystal, inputs for signal and local oscillator, and i-f output. Used in heterodyne detection for converting the received radar signal to a lower frequency before amplification.

Crystal Oscillator--An oscillator circuit using a quartz crystal or the mineral tourmaline and which depends for its operation on the principle of piezoelectricity. The quartz crystal exhibits the properties of a very high Q circuit when properly cut, which determines the frequency of oscillation and establishes a high order of frequency stability.

Crystal-Video Receiver--A broad-tuning receiver consisting of a crystal detector and a high-gain video amplifier. Usually an intercept receiver.

Curdio--Current conditions of radio propagation conditions. Cursor--See Bearing Cursor.

Cursor Target Bearing--Target bearing as measured by a PPI cursor.

Cutler Feed--A resonant cavity at the end of a waveguide, which feeds r-f energy to the reflector of the spinner assembly.

Cut-Off--(1) Value of grid bias required to reduce plate current to zero. (2) The longest space wavelength which can be conducted down any given waveguide.

CW-Doppler--Comparison of transmitted and echo frequencies to give an aural indication of moving target. No range information is provided; rate information available only when a single target is in the beam.

CW-OFF-CCW--A control. Rotation clockwise; off: rotation counter-clockwise.

Cycle--In periodic phenomena, one complete set of recurring events.

D Indicator--A type of radar indicator which combines types B and C indicators. The signal appears as a bright spot with azimuth angle as the horizontal coordinate and elevation angle as the vertical coordinate. Each horizontal trace is expanded slightly vertically by a compressed time sweep to facilitate separation of signal from noise and to give a rough range indication.

Damping Diode--A vacuum tube which damps the positive or negative half cycle of an a-c voltage.

Dark Trace Tube--A cathode-ray tube with a screen composed of a halide of sodium or potassium. The screen normally is nearly white, and wherever the electron beam strikes, it is tuned a magenta color which is of long persistence. The screen can be illuminated by a strong light source so that the reflected image may be made intense enough to be projected.

DB--Decibel.

DC--Direct current. Unidirectional current.

D.C.--Insertion--See Clamping Circuit.

D.C. Restorer--See Clamping Circuit.

Dead Spot--An area within or from which little or no signal is received.

Debug--To clear away the difficulties arising from improper design or construction of a set, and so to make it operate satisfactorily.

Deception--The deliberate production of false or misleading echoes on enemy radars by the radiation of spurious signals synchronized to the radar, or by the reradiation of the radar pulses from extraneous reflectors. Small targets may be made to appear like large ones, or echoes may be made to appear where no genuine target exists.

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Decibel (db)--A unit used for comparing the power levels of two signals or of a signal to a fixed reference level of power. Also, a measure of power, current, or voltage gain.

Deck-Tilt Correction--When the spinner base is tilted with respect to the horizontal, changing the elevation of the reflector causes a small rotation about a true vertical axis. Thus a bearing error is introduced since bearing is read directly from the rotation of the spinner base. Removal of this error is called the deck-tilt correction.

Decoder--Unit made up of circuits for separating triggers, video, scan data, etc., as received over link from synchronizer.

Decontaminate--The process of restoring the original condition of low emission to the grid of contaminated oscillator tubes in radar equipment. The remedy is effected by heating the grid to a white heat which is sufficient to boil the contaminating material from the surface, and yet not sufficiently hot to melt the grid.

Decoupler--Circuit for eliminating the effect of common impedance coupling. Main use is in power supply or measuring circuits to isolate signal circuit from supply.

Decoy--A reflecting object used in radar deception, such as a spar buoy that looks like a periscope, a group of streamers hung from a captive balloon, etc.

Deflection Coils--Coils placed about the yoke of a magnetic cathode-ray tube to cause the displacement of the electron stream by the magnetic field produced within the tube as the result of current flowing in the coils.

Deflection Plates--Two pairs of parallel plates with each pair set at right angles to one another and parallel to the axis of the electron stream in an electrostatic cathode-ray tube. They are used to cause the displacement of the electron stream by the electric field produced between each pair.

Deflection Sensitivity--In a cathode-ray tube, the ratio of the displacement of the electron beam at the point of impact to the change in the deflecting field. It usually is expressed in millimeters per volt applied between the deflection plates, or in millimeters per gauss of the deflecting magnetic field.

Degeneration--Feeding back into an amplifier a signal of polarity opposite to that of the input signal. This system reduces the overall gain of the amplifier but increases stability. It improves frequency response and lowers distortion.

Dehydrating Unit--Used for removing moisture from the air supplied to radar transmission lines or enclosures.

De-Icer--Heating circuit to melt ice from antenna assembly.

Delay Circuit--A circuit, usually a multivibrator, which introduces a time delay in passage of pulse or signal from one part of a circuit to another.

Delay Line--An artificial transmission line used to introduce a small time delay.

Delay Unit--A unit of a radar system in which pulses may be delayed a controllable amount. Used in providing expanded indicator presentations, etc.

Delayed PPI--A plan position indicator in which the start of the sweep is delayed a variable or a fixed time after the PPI trigger, allowing distant targets to be displayed on a short range scale that provides an expanded presentation.

Delta (Δ)--Greek letter usually indicating a small quantity or smallchange in a large quantity.

Demodulation--The process of obtaining the modulating component of a modulated radio wave.

Depression--Sensitivity-Time Control adjustment of initial gain at zero range.

Desiccant--The chemical contained in a desiccator. Silica Gel.

Desiccator--Small units containing a chemical which absorbs water from the air. Used to keep the air inside of a piece of equipment dry.

Destructor--See Detonator.

Detection--See Demodulation.

Detector--That stage in a receiver at which demodulation takes place.

Detonator--A small unit containing a charge of some explosive used to damage the interior of a piece of equipment so that the enemy cannot use or reconstruct the equipment, should it fall into his hands. Sometimes called destructor.

Deviation Alarm--Unit which gives warning indication when synchro error exists due to failure of excitation, amplifier, etc.

DG Synchro Amplifier--Synchro differential generator driven by servo system. Generally used with OSC servo or deck tilt correction.

DF--Generally refers to radio direction finders. Is also sometimes used by the British for radar instead of RDF. Sometimes written D/F.

DG--Synchro differential generator.

Dial Light--Illumination of bearing scale.

Dielectric--An insulator; a term applied to the insulating material between the plates of a capacitor.

Differential Synchro--See Synchro Differential Generator and Synchro Differential Motor.

Differentiating Circuit--A circuit which produces an output voltage substantially in proportion to the rate of change of the input voltage or current. Differentiating circuits employ time constants that are short compared to the duration of the pulse applied.

Diffraction--Deviation of rays of a wave motion from a straight course when partially cut off by an obstacle or passing near the edges of an opening, or through a small hole. Its effect is more marked as wavelength increases.

Dimmer--Control for varying the intensity of illumination on pilot, scale, or dial lights.

Diode--An electronic vacuum tube in which two elements--cathode and anode or plate--are used. Used for rectifying alternating voltages.

Diode Clipper--A two-element vacuum tube and associated biasing circuit which can be adjusted to remove any unwanted portion, positive or negative, of a signal. See Clipper.

Diode Mixer--A diode in r-f line which mixes incoming radio frequency and local oscillator signals to produce an intermediate frequency. See Mixer.

Diode Rectification--Half-wave rectification by means of a diode which depends on the fact that a diode passes current in one direction only.

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Diplexer--(Not Duplexer.) Permits the same antenna system to be used simultaneously or separately by two transmitters.

Dipole Antenna--Two metallic elements, each approximately ¼ wavelength long, which radiate the r-f energy fed to them by the transmission line.

Dipole Disk Feed--An antenna consisting of a dipole near a disk, which is used to reflect energy to the dish.

Direct Current (DC)--Unidirectional current.

Direct Wave--The component of the ground wave that is transmitted directly from transmitter to receiver. See Sky Wave.

Directional Antenna--Any antenna system or array which either receives or radiates r-f energy more efficiently in one direction than in any other.

Directional Coupler--Wave guide coupling device to permit measurement of direct wave or incident power. Also provides coupling for echo box.

Director--A parasitic element which reinforces radiation on a line pointing to it from the antenna.

Discriminator--(1) Radar: A circuit that produces a response which depends on the frequency of the input signal. Used in AFC circuits. (2) Beacon: A circuit which accepts pulses of proper duration and rejects others.

Dish--A paraboloidal antenna reflector.

Display--A CRT screen and dials which present the information obtainable by the radar set; for example, range, bearing, elevation.

Distance--See Range.

Distributed Capacitance--Capacitance between circuit elements or between tube elements, as distinguished from a lumped capacitance or capacitor. Also the capacitance of a transmission line per unit length of line.

Doorknob Tube--The Western Electric 316A triode tube or other of similar shape designed for u.h.f. use. Resembles a doorknob in shape.

Double Bounce Calibration--A method of calibration used to determine the zero set error by using round-trip echoes. The correct range is the difference between the first and second echoes. See Radar Maintenance Bulletin, page MK 3/4 5-12.

Double-Diode Limiter--A special type of limiter, which is used to remove all positive signals from a combination of positive and negative pulses, or to remove all the negative signals from such a combination.

Double-Layer Phosphor--Phosphor compound of 2 layers e.g., (1) zinc sulphide activated with silver, and (2) a mixture of zinc sulphide and cadmium sulphide activated with copper. Layer 1 emits short persistent blue light from electron impact, and layer 2 receives the blue light and converts it to yellow light of longer persistence. Used on Long Persistence Screens.

Double Moding--Frequency jumping, changing abruptly from one frequency to another, at irregular intervals.

Double Stub Tuner--An impedance matching device for a transmission line, consisting of two adjustable length stubs spaced a fixed distance apart.

Doublet Trigger--A trigger signal consisting of two pulses spaced by a fixed amount for coding.

Double-Tuned Stage--A stage of the i-f strip of a receiver which has two coupled tuned circuits. Double tuned stages at present are tuned synchronously (in line) and ordinarily are critically coupled.

Drift--The change of frequency in an oscillator during warm-up period.

Driven Element--An element which receives power from the transmitter through the transmission line.

Driver--(1) The circuit in the transmitter which produces a pulse to be delivered to the control grid of the modulator tube. (2) A unit driving another unit, as PPI Driver, etc.

Drooler--A circuit which distorts a square type of pulse by reducing the sharpness of leading and trailing edges, and tending to round the top of the pulse.

Drop-Bar--A protective device used to ground a high voltage condenser when opening a door.

Dropping Resistor--A resistor connected in a circuit which uses up a part of the voltage, thus leaving less voltage for the remainder of the circuit.

DRT--Dead Reckoning Tracer. A mechanical device on which a moving spot of light, or "bug," automatically indicates the approximate geographical position of own ship. The direction of motion of the bug is controlled by synchro data from the gyro compass, and the rate of motion is controlled by either the pitometer log or the dummy log.

Dummy Load--A device in which the output power can be absorbed, used for simulating conditions of operation for test purposes. Usually a load to simulate an antenna. Also called Dummy antenna and Sand load.

Duplexer--A coaxial-line device consisting of a Protective Tank for the purpose of protecting the receiver from the transmitted pulse, and a Decoupling Tank used to keep the echo out of the transmitter. Use TR and ATR for microwave device of same nature. Sometimes called Reprod.

Duration--A control for adjusting the time duration of reduced gain in Sensitivity-Time Control circuit.

Duty Cycle--The ratio of pulse length to pulse interval. Usually expressed in per cent.

Duty Cyclometer--A test meter which gives direct reading of duty cycle.

Duty Factor--The ratio of pulse interval to pulse length. Reciprocal of duty cycle.

Dynamotor--A rotating piece of machinery having a d-c motor and a d-c generator on the same shaft. Low voltage d-c is supplied to drive the motor. This rotation causes the generator to generate a higher d-c voltage.

Dynatron--Oscillator which makes use of negative plate resistance of a tetrode caused by secondary emission from the plate. Not the same as Transitron which is a negative trans-conductance oscillator not dependent on secondary emission.

Dynode--Elements of electron multiplier or storage tube.

E Indicator--A modification of type B radar indicator. The signal appears as a bright spot with range as the horizontal coordinate and elevation as the vertical coordinate.

E Units--See Radar Signal-Noise Ratio.

Eccles-Jordan Circuit--A direct-coupled multivibrator circuit possessing two conditions of stable equilibrium. Also known as a flip-flop circuit.

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Echo--The signal reflected by a distant target to a radar set. Also the deflection or indication on the screen of a cathode-ray tube representing a target.

Echo Box--A high Q resonant cavity which receives r-f energy through a pickup during the transmitted pulse and reradiates this energy through the same pickup immediately after the pulse. The reradiated energy is picked up by the radar set. Since the energy from the echo box dies off exponentially, it will appear on an A-scope indicator as a flat-topped pulse, resulting from the saturation of the receiver by the high energy return, followed by an exponential curve. The time from the end of the transmitted pulse to the point at which the echo-box signal is lost in noise is called the "ringing time" of the echo box. The echo box may be used to demonstrate graphically on the PPI scope the form of the antenna pattern, and to test the overall performance of the radar set.

Echo Box Antenna--A small dipole supported on a bracket near the radar antenna, used to pick up the radar pulse and to feed the echo box oscillations back to the radar antenna.

Echo Suppression--IFF control used to disable the responsor for a short time to prevent reception of echoes from nearby targets that are produced by the interrogator pulse.

EEI--Expanded elevation indicator.

Electric Field Intensity--Property of a radio wave measured in terms of the e.m.f. it produces, e.g., if 20 microvolts are generated between the ends of a conductor 1 meter long when the radio wave cuts across it, the field intensity is said to be 20 microvolts per meter.

Electrical Resolver--A special type of synchro in which a single winding is put on the stator and two windings whose axes are 90° apart on the rotor.

Electrode--A terminal at which electricity passes from one medium into another.

Electromagnetic Energy--Forms of radiant energy found, for example, in radio waves, heat waves, light waves, X-rays, gamma rays, and cosmic rays.

Electromagnetic Field--The portion of space in which the energy radiated in a radio wave can be detected. The field of energy always consists of a moving magnetic field and a moving electric field that act at right angles to each other. The direction in which the field moves is perpendicular to the line of action of both components of the field.

Electron--The negatively charged particles of matter. The smallest particle of matter.

Electron Emission--The liberation of electrons from an electrode into the surrounding space.

Electron Gun--A group of electrodes in a vacuum tube, most commonly a cathode-ray tube, used to produce an electron beam of controllable intensity and to focus this beam to a small spot. This gun consists of a cathode and heater combination from which electrons are emitted thermionically, a grid for controlling the number of electrons that flow in the beam and hence the brightness of the luminous spot on a cathode-ray tube screen, and a means of focusing the beam.

Electron Multiplier--A vacuum tube in which electrons liberated from a photo-sensitive cathode when light strikes it are attracted successively to a series of electrodes, called dynodes. Each electron liberates others as it strikes each dynode, causing a great increase, or multiplication, in the number of electrons flowing in the tube. Amplification on the order of 1,000,000-fold is possible with such an arrangement.

Electronic Instrument--An instrument which utilizes for its operation the action of an electronic (thermionic) tube.

Electronic Coupling--The method of coupling electrical energy from one circuit to another through electron flow in a vacuum tube.

Electronic Switch--A vacuum tube used as an on-off switch in some channel.

Electronics--That branch of science and technology which relates to the conduction and control of electron flow through gases or in a vacuum.

Elevation--Angular position in a plane perpendicular to the earth's surface. The horizon is usually minimum elevation and the zenith is maximum elevation. It is usually expressed in degrees. That is, the horizon is 0° and the zenith is 90°. It is occasionally expressed in mils, 0° being equal to 0 mils and 90° being equal to 1600 mils.

Elliptically Polarized Waves--Result from the superposition of two plane-polarized wave systems which are propagated in the same direction and have the same wavelength or frequency.

Emergency--Normal--A control used to select the source of antenna training power.

Emergency--Off--A control not normally intended to turn off system power.

EMF--Electro-motive force. (Voltage.)

End-Fire Array--A directional antenna system designed to give the maximum radiation in a single direction lying in the plane of the array (e.g., Yagi array).

Error--(1) Error voltage in servo control or training. (2) Error in synchro bearing.

E-Wave--A "mode" in which electromagnetic energy can be transmitted in a wave guide. An E-wave is a wave in which the magnetic field in the tube is everywhere transverse, i.e., perpendicular to the length of the tube, but in which the electric field in addition to having a transverse component, also has a longitudinal component parallel to the length of the tube. Also called a TM-wave.

Evasion--Tactics that are designed to take advantage of the limitations of radar to prevent or postpone radar detection, or to avoid revealing the true position of an attacking force.

Expanded Sweep--(1) A sweep in which the movement of the electron beam across the screen is speeded up during a selected portion of the sweep time. See R Indicator. (2) In fire control radar, a range scale shorter than the longest scale provided, but extending from zero range rather than having its part delayed, as the precision sweep is. See Precision Sweep.

Exponential Sweep--A sweep whose speed varies exponentially with time. The sweep starts fast and decreases in speed as it approaches the end.

F Indicator--A type of radar indicator in which a single signal appears as a bright spot. Azimuth angle error appears as the horizontal coordinate, and elevation angle error as the vertical coordinate. Cross-hairs on the indicator face permit bringing the system to bear on the target.

Face--The front or viewing surface of a cathode-ray tube. The inner surface of the face is coated with a material which gives off light under the impact of a stream of electrons.

Fade Chart--A graph on which the null areas of an air-search radar antenna are plotted as an aid to estimating target altitude.

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Fanning Beam--A narrow antenna beam which is repeatedly scanned over a limited arc.

Fast Time Constant (FTC)--A type of coupling circuit used in radar receivers to permit discrimination against echo pulses of duration longer than the transmitted pulse.

Feed--Means of supplying to the antenna the energy carried by the r-f line.

Feedback--Transfer of energy from one point in an electrical system to a preceding point, such as from the output back to the input. See Regeneration and Degeneration.

Feedback Time Constant--The time constant of an RC combination introduced into a circuit to determine the amount of delay in the feedback circuit. Determines also that the feedback is of the proper phase.

Ferret--An aircraft fitted with RCM equipment to be used in radar reconnaissance. U. S. Army term.

Fidelity--Refers to width of video or audio response, which in turn determines the accuracy with which the input is reproduced in the output.

Field--Magnetic field of motors, generators, etc. See Electromagnetic Field or Magnetic Field.

Filament--Directly heated cathode of a vacuum tube.

Filter--Any combination of resistance, inductance, and capacitance which presents a low impedance to a certain frequency or group of frequencies, and at the same time presents a high impedance to other frequencies or to d-c.

Filter, Band Pass--A filter so designed that it tends to pass a band of frequencies and attenuates all frequencies outside of the band.

Filter Choke--A coil of high inductance used to suppress more or less completely the alternating current components in the output of a rectifier.

Filter, High Pass--A filter so designed that it tends to pass all frequencies above a certain frequency and attenuates all frequencies below that frequency.

Filter, Low Pass--A filter so designed that it tends to pass all frequencies below a certain value and attenuates all frequencies above a certain value.

Fine--Refers to control for fine adjustment of tuning, intensity, etc.

Fire--In a gas tube, to ionize, i.e., to become conducting.

Fire Control Radar--System providing highly accurate range, bearing, and elevation data to fire control computers.

Fixed-Frequency IFF--A class of IFF equipment which responds immediately to every interrogation, thus permitting the response to be displayed on plan position indicators. Compare A-Band and G-Band.

First Detector--See Mixer.

Fixed-Tuned--A circuit which is permanently tuned to a certain frequency.

Flash Pulsing--Transmission of short bursts of radiation at irregular intervals by a mechanically controlled keyer.

Flat--Sensitivity-Time Control adjustment of maximum depression of gain.

Flat Line--An r-f transmission line, or part thereof, having a low standing wave ratio.

Flicker--A random mode jump or breakdown condition observed in certain magnetrons, as a result of which the tube gives no power for one or two pulses at the prescribed frequency. The occurrence of this condition is random and varies from a very low rate to more than ten times per second, for different tubes.

Flip-Flop Multivibrator--See Start-Stop Multivibrator.

Fluorescence--The property of emitting light as the immediate result of electronic bombardment.

Fluorescent Screen--The thin coating of chemical material on the face of the cathode-ray tube. This material is chosen for its ability to transform electron energy into visible light. When the screen is bombarded by high velocity electrons, light is given off. The color of light emitted is dependent on the type of material used on the screen.

Fluxgate--The magnetic azimuth-sensitive element of the fluxgate compass system which is activated by the earth's magnetic field. It is maintained in a horizontal plane by stabilizing it on an electrically-driven horizon gyro.

Fluxgate Amplifier--Amplifies the induced rotor voltages of the coupling synchro in the master indicator, and thus provides sufficient energy to drive the induction motor. Also contains oscillators for Flux Gate, and for the induction motor.

Flux-Gate Compass--A gyroscope-stabilized compass used for supplying stabilization information concerning the geographical orientation of the PPI pattern. A "lubber line" produced on the PPI indicates the plane's heading once each rotation of the sweep. Consists of the following units: a Gyro-Stabilized Flux Gate Transmitter, an Amplifier, a Master Indicator, and from one to six Magnesyn (synchro) Remote Indicating Repeaters.

Fluxmeter--An instrument for measuring the intensity of a magnetic field.

FM Doppler--A type of radar involving frequency modulation of both carrier and modulation. For example, carrier frequency modulated 200 kc by a sine wave which is swept at a low rate between 0.5 to 10 kc. Range, bearing, and rate direction are indicated by left-right deflection on radial sweep.

Focus--In the cathode-ray tube, making appropriate electrical adjustments so as to give a sharp image of sweep line or signals on the face of the tube.

Focusing Anode--One of the electrodes in a CRT, the potential of which may be varied to focus the electron beam. Varying the potential changes the electric field and thereby alters the path of the electrons to change the spot size.

Foe--Designation light to indicate foe on IFF.

Fordio--Forecast conditions of radio propagation conditions.

Four-Axis Stabilization--See Stabilization.

Framing--Shifting of pulses on trace.

Free-Running Multivibrator--A multivibrator so arranged that it does not need a trigger pulse to start operation. Application of filament and plate voltages is all that is required.

Frequency--The number of cycles per second which an electric current, a sound wave, or a vibrating object completes.

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Frequency Converter--A circuit or device which changes the frequency of an alternating current. See Detector and Mixer.

Frequency Distortion--Exists when all the frequency components of an input voltage are not amplified to the same degree.

Frequency Divider--A circuit or device designed to divide a frequency to a submultiple of that frequency.

Frequency Modulation--A system of modulation in which the deviation in frequency above and below the mean, or carrier frequency, is at each instant proportional to the amplitude of the signal being transmitted, and the number of complete deviations per second above and below the mean or carrier frequency is equal to the frequency of the signal being transmitted. Phase and amplitude remain constant.

Frequency Pulling--Small changes in frequency of an oscillator caused by changes in load impedance.

Frequency Response--The measure of the effectiveness with which a circuit or device transmits the different frequencies applied to it.

Frequency Scanning--Type of system in which output frequency is made to vary at a mechanical rate over desired frequency band.

Frequency Splitting--One condition of operation of a magnetron which causes rapid alternating from one mode of operation to another. This results in a similar rapid change in oscillatory frequency and a consequent loss in power at the desired frequency.

Friend--Designation light to indicate friend on IFF.

Front-to-Back Ratio--The ratio of the resistance of a crystal to current flowing in the normal direction to the resistance to current flowing in the opposite direction. A term used in connection with checking crystals used as mixers in microwave receivers.

FTC--Fast Time Constant video coupling.

Fuse--An overcurrent protective device. Consists of a wire or strip of fusible metal inserted in a circuit. The strip melts when the current becomes too large.

Fuse Alarm--Light which indicates blown fuse.

G Band--A frequency band used in Mark III IFF. Transpondors that operate in this band are fixed-tuned, so that immediate responses are obtained which can be displayed on a PPI. See A-Band.

G Indicator--A type of radar indicator in which a single signal only appears as a bright spot on which wings grow as the distance to the target is diminished. Azimuth angle appears as the horizontal coordinate, and elevation angle as the vertical coordinate. This has been referred to as the Mark VI indicator and as the Spot Error Indicator.

Gain--(1) In an amplifier stage or system, the ratio of output voltage, current, or power to input voltage, current, or power. Often expressed in decibels. (2) In an antenna, a measure of the degree to which the radiation pattern becomes unidirectional. This is an important characteristic when it is desired to send as much energy as possible to one point only. It is given as the ratio of the energy density in the optimum direction to that from an equal source radiating isotropically.

Gap Coding--A means for inserting gaps, or periods of non-transmission, in a system that normally transmits continuously. The spacing and duration of the periods of silence from the code. System is used in some radar beacons.

Gang--To couple mechanically two or more variable components (capacitors, switches, and potentiometers) to facilitate operating from a single control knob.

Gap-Motor--Spark-gap modulator drive motor.

Gaseous Tube--An electronic tube into which a small amount of gas has been introduced.

Gassiness (of a Tube)--The presence of gas in a vacuum tube, usually in relatively small amounts, due to leakage from outside, or evolution from the inside walls or elements of the tube.

Gate--A square voltage wave which switches a circuit on or off electronically; usually by application to a grid or cathode.

Gate-Producing Multivibrator--A rectangular-wave generator designed to produce a single positive or negative gate voltage when triggered and then to become inactive until the next trigger pulse.

GCA--Ground control of the approach of an aircraft to an airfield.

GCI--Ground control of interception. A technique that is accomplished by cooperation between a land-based radar set and fighter aircraft equipped with their own radar sets.

GCL--Ground control of the landing of aircraft.

General Control Unit--Remote control unit associated with operator's console which permits full control of all necessary operating functions.

Generator--(1) A rotating machine which converts mechanical energy into electrical energy. (2) A radio device which develops an a-c voltage at a desired frequency and of a desired shape when energized with d-c power.

Getter--An alkali metal introduced into a vacuum tube during manufacture and fired after the tube has been evacuated to react chemically with any gases which may have been left in manufacture. The silvery deposit on the inside of the glass envelope of a tube, usually near the tube base, is the result of getter firing.

Ghost Signals--Signals appearing on the screen of the radar indicator, the source of which cannot readily be determined.

GL--Gun laying. Information supplied by GL equipment (range and bearing) is used to direct guns and to control their firing fire control radar equipment.

Glide Path--A radar beam for blind or instrument landing of aircraft.

Goniometer--A device used in RDF for the comparison of signal amplitudes. It consists of two equal mutually perpendicular stator coils, having a common axis, and a rotor coil which rotates about this axis.

GMCM--Guided Missile Countermeasures.

Grass--In radar, random interference caused primarily by circuit noise. The interference appears as sharp, closely spaced discontinuities in the base line of radar indicators. If the equipment is operating properly, the height of the grass is substantially level across the screen, and not sufficiently great to cause bad interference to echoes from targets within range.

Grid Bias--See Bias.

Grid Pulsing--A method of pulsing in which the oscillator is biased so negatively that no oscillations take place, even with full plate voltage applied, until application of positive keying pulse to grid.

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Ground--A conducting connection, whether intentional or accidental, between an electric circuit or equipment and earth, or to some conducting body which serves in place of the earth.

Ground Clutter--Radar echoes reflected from terrain, which obscure relatively large areas of the radar indicator.

Ground Range--The distance from an object on the ground to a point on the ground directly beneath an aircraft.

Ground-Reflected Wave--The component of the ground wave that is reflected from the ground.

Ground Return--See Ground Clutter.

Ground Speed--The speed of an aircraft relative to the earth.

Ground Wave--The portion of a radio wave that is propagated through space and is, ordinarily, affected by the presence of the ground. The ground wave is somewhat refracted by the gradual change with altitude of the dielectric constant of the lower atmosphere.

Grounded-Grid Triode Mixer--A triode in which the grid forms part of a grounded electrostatic screen between the anode and cathode, and is used as a mixer for centimeter wavelengths.

Guide Wavelength--The wavelength of electromagnetic energy conducted in a wave guide. The guide wavelength for all air-filled guides is always longer than the corresponding free-space wavelength.

Guided Propagation--See Trapping.

Guillemin Line--The network used in high-level pulse modulation for generating a square pulse with steep rise and fall.

Gyro Compass--A type of compass in which the axis of a gyroscope is made to point constantly to geographic or true north. Also called the Master Gyro Compass. A synchro system is used to repeat the compass indications at suitable locations throughout the ship.

Gyro Repeater--The indicator driven by the synchro system associated with the master gyro compass.

Gyroscope--An instrument which utilizes a rotating mass to maintain a stable equilibrium.

H Indicator--Intensity modulated signals on a CRT with range vertical and azimuth horizontal. Tangent of echo tilt angle proportional to sine of angle of elevation.

Half Wave Element--A conductor of such length as to be resonant at a given frequency.

Harmonic--A multiple of any particular frequency.

H. Center--A control for adjustment of horizontal position of CRT pattern.

Hard Tube--See High-Vacuum Tube.

Heading--True or magnetic compass direction in which the ship or aircraft is pointed. Also called Ship's head.

Heater--(1) Space heater for control of temperature and reduction of humidity. (2) Element of a vacuum tube which indirectly heats the cathode.

Heaviside Layers--Layers of ionized gas, believed to exist in the region between 50 and 400 miles above the surface of the earth, which bend radio waves, of frequency below about 40 megacycles, back to earth under certain conditions. Also called the Kennelly-Heaviside layer.

Height--The vertical distance of the target above the horizontal plane through the point upon which the range keeper or data computer bases its solution. Usually measured in feet.

Helical Scan--The scanning motion in which a point on the r-f beam describes a distorted helix. The antenna rotates in azimuth while the elevation angle changes from horizontal to vertical.

Helipot--Trade name for a potentiometer wound in a helical form so that the variable arm may make several revolutions.

Helmholtz Coil--A phase-shifting network consisting of fixed and movable coils. With a constant input, fixed in phase, the output may be continually shifted in phase from 0° to 360°. Used to determine range in certain radar equipment.

Heterodyne Reception--Reception by combining received radio frequency with locally generated oscillations. Beat frequency may be audible or may be IF which is further amplified and demodulated. See Superheterodyne.

HF--High frequencies (3000 to 30,000 kilocycles).

High Pass Video (HVP)--Filter in video circuit used to permit only the higher frequency components of a signal to pass.

High-Vacuum Tube--A vacuum tube evacuated to such a degree that its electrical characteristics are essentially unaffected by gaseous ionization.

High Voltage--Refers to control, meter, rectifier, etc., for vacuum tube plate supply.

Hollow Waveguide--See Waveguide.

Homing Antenna--A type of directional antenna array useful when it is desired to fly directly to a target.

Hood--A shield placed over a CRT to eliminate extraneous light and thus make the image on the screen appear clearly.

Horizontal Polarization--Electric field (E vector) parallel to the horizon. An antenna in which the dipoles are horizontal is horizontally polarized.

Horizontal Spot Limit-Left (Right)--Control of tracking spot on "B" Indicator.

Horn--A type of radiator or feed used to direct radiation from a wave guide.

Hunting--Mechanical oscillation in a servo system due to improper adjustment of control voltage, servo amplifier, or feedback.

HVP--See High Pass Video.

H-Wave--A "mode" in which electromagnetic energy can be transmitted in a wave guide. An H-wave has an electric field which is entirely transverse, i.e., perpendicular to the length of the wave guide, and a magnetic field which has a longitudinal component in addition to its transverse component. Also called TE waves.

I Indicator--A type of radar indicator used to depict range and direction for a system with a conically scanning antenna. The signal appears as a bright circular segment with radius proportional to range. The circular length of the segment is inversely proportional to the error of aiming the system, and its position indicates the bearing of the target. True aim results in a complete circle. This has been referred to as RTB Indication and as Broken Circle Indication.

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IAVC--Instantaneous Automatic Volume Control. A radar receiver circuit which uses the echo amplitude- of each returning signal to vary the receiver gain. The action of the circuit is delayed for a time approximately equal to the pulse duration so that echoes from isolated targets are not affected. However, if signals are received continuously for a period longer than the pulse duration, the receiver gain is decreased, but it returns to normal shortly after the end of this longer signal.

Iconoscope--A cathode-ray tube with a photo-mosaic and scanning electron beam which converts a visible image into fluctuating electrical currents. Used as a camera tube in television.

IF--Intermediate frequency.

IFF--Identification, Friend, or Foe. Generic term applied to systems or equipment used for the recognition of ships or aircraft detected by radar.

IFF Coordinator--Unit for coordination of IFF Trigger, Range Indicator Trigger and Radar and IFF displays on "A" Indicator.

Identification--The process of indicating your own friendly character. See Recognition.

Illumination--Lights for meters, range dials, bearing dials, etc. Also refers to radar beam being directed on a target.

Image Frequency--An undesired signal capable of beating with the local oscillator signal of a superheterodyne receiver which produces a difference frequency within the bandwidth of the i-f channel.

Impedance--The total opposition which a radio part or circuit offers to the flow of alternating current at a particular frequency. Impedance is a vectorial combination of resistance and reactance and is measured in ohms.

Impedance Matching--See Matching.

Impedance Transformer--An impedance matching device used to provide a maximum transfer of energy from one circuit to another.

Incident--Refers to a wave travelling in a direction toward the load.

Indicator--That component of a radar set by which the data obtained by the set is presented for visual observation.

Inductance--That property of a circuit which tends to oppose any change in current. Inductance is effective only when varying or alternating currents are present; it has no effect on direct current of constant amplitude.

Inductive Coupling--A form of coupling in which energy is transferred by induction from a coil in one circuit to a coil in another circuit. Varying magnetic lines of force produced by the flow of varying direct current or alternating current through one coil causes an a-c voltage to be induced in the other coil.

Inductive Kick--Refers to the fact that when the current through an inductor is broken abruptly, the collapse of the magnetic field through the windings of the coil may generate across the coil a voltage many times higher than the impressed voltage.

Inductor--A circuit element designed so that its inductance is its most important electrical property; a coil.

In-Line Tuning--Method of tuning the i-f strip of a superheterodyne receiver in which all the i-f amplifier stages are made resonant to the same frequency. This type of tuning results in a narrow i-f bandwidth. Compare Stagger Tuning.

Input (In)--Used to indicate signal, power, trigger, etc., fed in to a unit or circuit.

Input Impedance--The impedance between the input terminals of a network.

Instantaneous Automatic Volume Control--See IAVC.

Integrating Circuit--A circuit which produces an output voltage substantially in proportion to the frequency and amplitude of the input voltage. In a few special cases, the waveshape of the output is approximately the mathematical integral of the waveshape of the input.

Intensifier Electrode--An electrode provided in some types of electrostatic cathode-ray tubes which permits additional acceleration of the electron beam after it has been deflected. The advantage of this extra electrode is that it permits greater intensity of the trace without materially reducing the deflection sensitivity of the tube.

Intensifier Pulse--A pulse or gate voltage used to turn a cathode-ray beam on and off at a specified time.

Intensity Control--That control which, by varying the bias on a cathode-ray tube, controls the beam current of the tube and hence the amount of light generated by the fluorescent screen.

Intensity Modulation--In a cathode-ray tube, causing the intensity of the light generated to vary in accordance with the modulating signal.

Intercept Receiver--See Search Receiver.

Interception--The detection of radar signals by use of a special receiver and associated apparatus.

Inter-Electrode Capacitance--The capacitance which exists between two electrodes in a vacuum tube. Although this is usually a very low value, it becomes extremely important in ultra-high frequency circuits. See Distributed Capacitance.

Interference--Confusing- signals accidentally produced on a radar indicator by the effects of either friendly or enemy electrical apparatus or machinery, or by atmospheric phenomena.

Interlock--A safety switch which de-energizes high voltage when doors, access covers, or other openings are opened.

Intermediate Frequency (i-f)--In a superheterodyne receiver, the frequency to which all incoming carrier frequencies are converted before being fed to the i-f amplifier. See Local Oscillator.

Intermediate Frequency Amplifier--That section of a superheterodyne receiver which is designed to amplify signals with high efficiency at a predetermined frequency called the intermediate frequency of the receiver.

Intermittent Pulsing--Transmission of short bursts of radiation at irregular intervals.

Intermittent Scanning--One or two 360° scans of antenna beam at irregular intervals to increase difficulty of detection by intercept receiver.

Interrogator--A pulsed radio transmitter which emits signals on some frequency in the IFF band, and which is associated with the radar equipment whose echoes must be recognized.

Inverse Feedback--Intentional negative feedback or degeneration introduced in an amplifier or single vacuum tube stage for the purpose of reducing the distortion, increasing the stability, and improving the frequency response. See Degeneration.

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Inverted--Changed in sign, e.g., a positive voltage pulse is inverted to obtain a negative pulse.

Inverter--(I) A polarity inverting amplifier. (2) A rotating machine acting both as motor and generator, used to change a d-c input voltage to an a-c output voltage.

Ionosphere--A body of ionized gas which exists in the outer portion of the earth's atmosphere. See Heaviside Layers.

IR--Interrogator-Responsor.

Iris--A commonly used impedance matching device in a waveguide transmission line system. It consists of an aperture placed in a waveguide section. The relative size of the aperture with respect to the waveguide controls the effective electrical length of the section.

Isolation Diode--A diode used to pass signals in one direction through a circuit, but to prevent signals from being transmitted in the opposite direction.

Isotropic Radiator--A radiator which sends out energy equally in all directions.

J Antenna--A type of vertical ½-wave antenna, end fed by a ¼-wave matching stub.

J Indicator--A type of radar indicator which is a modification of type A indicator. The time sweep produces a circular range scale near the circumference of the cathode-ray tube face. The signal appears as a radial deflection of the time trace. No bearing indication is given.

Jamming--Intentional transmission of r-f energy in such a way as to interfere with reception of signals by another station.

Jitter--Instability of signals or trace on a cathode-ray tube caused by variation in the synchronization of components, leading to variations in the position of the observed pulse along the sweep.

Junction Box--An enclosed distribution panel for connecting or branching one or more electric circuits without the use of permanent splices. K Indicator--A modification of type A scan used for aiming a double-lobe system in bearing or elevation. The entire range scale is displaced in the direction of the antenna lobe in use. One signal appears as a double deflection from the range scale, and the relative amplitudes of these two pips serves as an indication of the error in aiming the antenna.

Keep-Alive--An auxiliary electrode in the T-R tube, to which a negative d-c potential is applied. The keep-alive voltage is on continuously in order to furnish sufficient ions for almost instantaneous discharge across the main gap with small leakage power to the crystal.

Keeper--A piece of magnetic material placed across the pole pieces of a permanent magnet to enable it to maintain its magnetic strength by providing a low reluctance path for the magnetic field.

Kennelly-Heaviside Layers--See Heaviside Layers.

Keyer--Name sometimes given to the modulator of a radar set.

Kidney Joint--A flexible joint, or air-gap coupling, used in the waveguide of certain radars, and located near the transmitting-receiving position. The kidney joint, so called because of its shape, consists of two flanges facing each other but spaced 3/8 to ½ inch apart. The face of each flange extends about ¼ wavelength perpendicular to the waveguide and then has a skirt about a ¼ wave deep about the outside.

Killer Circuit--That vacuum tube or tubes and associated circuit in which is generated the blanking pulse used to temporarily disable a radar set. The circuit is usually triggered from a pulse obtained from another piece of radar equipment. This disabling is essential in order to eliminate interference arising from the use of two pulsing systems in close proximity to one another.

Killer Pulse--See Killer Circuit.

Kilo (k)--A prefix meaning 1,000, as kilocycle, kilowatt, etc.

Klystron--A tube in which oscillations are generated by the bunching of electrons as the result of velocity modulation of the electron stream. This tube uses the transit time of the electrons between two electrodes as a means of controlling the delivery of pulsating energy to a cavity resonator in order to sustain oscillations within the cavity.

Knocker--A subassembly in radar equipment, comprising synchronizing and triggering circuits. The knocker is used to drive the r-f pulse generating equipment in the transmitter and to synchronize the cycle of operation in range units and range indicators with the transmitted pulse. Term is used only with some Fire Control radars.

I. Indicator--A time sweep produces a vertical range scale and signal appears as left and right horizontal deflection of equal amplitude when target bearing is zero degrees relative.

LAB--Low altitude bombing.

Land Return--See Ground Clutter.

Leakage--(1) An undesirable flow of current through or over the surface of a dielectric material.

(2) That portion of a magnetic field which is not utilized most effectively. For example, the field appearing at end pieces of an electromagnet.

Leaky Waveguide Antenna--An antenna constructed of a long waveguide with radiating elements at intervals along its length. It can be made to have a very sharp pattern.

Level Angle--The angle between the horizontal plane and the deck plane measured in the vertical plane through the line of sight. (Positive when the deck toward the target is below the horizontal plane).

LF--Low frequencies (30 to 300 kilocycles).

Lighthouse Tube--Parallel element tubes suitable as local oscillator or r-f amplifier, etc., in microwave region.

Limiting--Removal by electronic means of one or both extremities of a waveform at a predetermined level.

Limit Ratio--Ratio of peak value to limited value, or comparison of such ratios.

Line Balance Converter--See Bazooka.

Line Pulsing--A method of pulsing a transmitter in which an artificial line is charged over a relatively long period of time and then discharged through the transmitter tubes in a short interval determined by the line characteristics.

Line Stretcher--An impedance matching device for coaxial transmission lines.

Line Voltage--Voltage level of main power supply to equipment.

Linear Array--Single line of dipole antennas.

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Linear Scan--A radar beam which traverses one arc or circle only. For example, a beam which is oscillated back and forth over a 30° angle in the horizontal without being elevated.

Linear Sweep--A periodic voltage, applied to the horizontal deflecting plates of the cathode-ray tube, which increases linearly with time up to a maximum value and then falls abruptly to zero. This causes the spot to sweep across the screen at a uniform velocity.

Line of Position--A locus of the possible positions of a ship.

Line-of-Sight--The straight line which joins observer and point of aim (on target).

Line-of-Sight Coverage--The distances to which radar and television sets are commonly said to be limited because the radiated waves do not follow the curvature of the earth. The horizon range based on the height of the antenna. Refraction effects on radar beams, similar to mirage effects observed with visible light, can take place under certain atmospheric conditions, resulting in greatly increased coverage. See Trapping.

Line-of-Sight Stabilization--See Stabilization.

Linear Time Base--See Linear Sweep.

Link--Refers to radio link which transmits synchronized video, trigger, and scan data to remote decoder and repeater.

Lissajous Figures--Patterns produced on the screen of a CRT by combination of sine wave signal voltages, of various amplitude and phase relations, on horizontal and vertical deflection plates.

Load Divider--Unit for distributing regulated or unregulated power to various units.

Load Set--Adjustment of load relay.

L. O. Injection--An adjustment used to vary the magnitude of the local oscillator signal that is coupled into the mixer.

Lobe--Refers to the two or three dimensional polar representation used to indicate the distribution in space of antenna field strength intensities. The curve shows points of equal field strength, power, or voltage as desired.

Lobe Pattern--See Fade Chart.

Lobe Switching--Any method (electrical or mechanical) of alternately shifting the lobe of an antenna system from one direction to another. The difference in direction between the two or more positions is predetermined. It is used in conjunction with a receiver or indicator switching system to provide more accurate angular (bearing or elevation) position data.

Local Oscillator (LO)--An adjustable-frequency oscillator used in a superheterodyne receiver. The output of this oscillator is mixed with a desired r-f carrier to form a signal of lower, or intermediate, frequency.

Lock--Indication of locking position of a control.

Locking--(1) Controlling the frequency of an oscillator by means of an applied signal of constant frequency. (2) Automatic following of a target by a radar antenna.

Long Persistence Screen--A cathode-ray tube screen in which the phosphorescent characteristic of certain chemicals is utilized. Fluorescent and phosphorescent compounds are combined and bombarded with electrons. The fluorescent material translates electron energy to light and the phosphorescent material gives off additional amounts of light when the fluorescent light strikes it. The total effect is to provide a screen in which the decay time of the light is relatively long, usually several seconds.

Loran--Long range navigation system. See Ships 278.

Lord Mount--A vibration insulating mount, made in two types: cup type and flush type shear mounts. Load ratings are from 1 to 90 lb. for both types, depending on application.

Lossy Line--A cable used in test measurements which has a large attenuation per unit length.

Lower--Refers to voltage, gain, frequency, etc., adjustment.

Lubber's Line--A prominent fixed line on the compass, drift sight, pelorus, or PPI made parallel to the ship's keel to furnish a reference for indicating ship's heading.

M Indicator--A modification of type A scan in which the horizontal time base is slightly displaced in a vertical direction by insertion of a step which serves as an adjustable range marker. A ranging circuit is used for controlling the position of the step along the trace, and range is indicated on counters when the step and an echo are brought into coincidence.

Magnetic Circuit--A complete path for magnetic lines of force. It includes the magnet producing the lines of force.

Magnetic Field--The space occupied by continuous lines of force linking the north and south poles of a magnetomotive force.

Magnetic Focusing--A method of focusing an electron stream by which the electrons are brought to a point through the action of a magnetic field.

Magnetic Lines of Force--Imaginary lines used for convenience to designate the direction in which magnetic forces are acting as a result of a magnetomotive force.

Magnetron--An ultra-high frequency oscillator tube. Because of its available high peak power it is often used as a transmitter tube in radar sets.

Main Control Unit--Unit associated with Transmitter-Receiver Unit containing controls not necessary to operator but essential for energizing, adjustment, etc.

Main Power--Line power supplied to complete system.

Main Sweep--On some fire control radars, the longest range scale available.

Maintenance Controls--Those necessary for correct setup of equipment and not available to operator.

Manual--Used with gain, train, tuning, etc. Operation by hand without using any other source of power.

Marker--Electronic range or bearing indication on radar indicator.

Marker Oscillator--Source of range markers. Masking--See Clutter.

Master Gain--Control of overall gain to all associated indicators.

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Master Gyro Compass--See Gyro Compass.

Master Multivibrator--A master oscillator using a multivibrator circuit.

Master Oscillator--A timing oscillator which controls other circuits.

Master PPI--PPI unit associated with a system console.

Matching--Connecting two circuits or parts together with a coupling device in such a way that the impedance of either circuit will be equal to the impedance existing between the coupling terminals to which that circuit is connected.

Matching Stub--A device placed on an r-f transmission line which varies the electrical length of the line. The impedance of the line can be adjusted in this manner.

Mattress Antenna--Vertical or horizontal half-wave antennas arranged in rows, with the rows one above the other. A flat sheet-metal, expanded metal, or wire screen is used behind the array as a reflector.

Maxima (Minima)--The regions of maximum and minimum return from the transmitted pulse caused by additive and sub-tractive combinations of the direct and reflected waves. A plot of this data is usually known as a Null Pattern or Fade Chart.

Maximum Set--A control for sweep calibration at maximum range.

McNally Tube--A velocity modulated vacuum tube designed to produce low-power uhf oscillations. It is used as a local oscillator in some radar receivers.

Mega (m)--Prefix meaning one million, as megacycle, megawatt, etc.

MEW--Microwave early warning radar. Gives long-range warning of approaching aircraft, and allows continuous plotting, in range and azimuth, of multiple targets. AN/CPS-1.

MF--Medium frequencies (300-3000 kilocycles).

MG--Motor generator.

Micro--Prefix meaning one millionth, as microfarad, microsecond, etc.

Microphonic Noise--Noise caused by mechanical vibration of the elements of the tubes.

Microsecond--One millionth of one second.

Micro-Switch--Trade name for a small switch which can be operated with very small pressure and very small displacement. They may be either normally open or normally closed.

Microwaves--Radio waves having wavelengths shorter than 50 centimeters.

Minimum Set--A control for sweep calibration at a low end of range scale.

Mirror Reflection Echoes--Multiple reflection echoes that are caused by the radar beam being reflected from a large flat surface, as the side of an aircraft carrier, and subsequently striking other nearby targets.

Mixer--The stage in a superheterodyne receiver in which the incoming modulated radio-frequency signals are mixed with the local oscillator signals to produce the intermediate-frequency signal. The mixer may be either a vacuum tube or a crystal. Also called First Detector and Converter.

Mode--Different types of electromagnetic waves that may be sustained in a given resonant system. Each type is designated as a particular mode and has its own electric and magnetic field configuration.

Model Terminology--(1) Experimental, Model Shop, or Breadboard Models produced by manufacturer, at his expense, for establishing electrical performance. (2) Developmental Model. Manufactured under contract to establish new or radically revised specification. (3) Preliminary Model. Production contract for "hand-made" model to determine contractor's ability to meet established specifications. These are additional equipments over requirements. (4) Preproduction Model. Prototype of production and completely interchangeable. Considered and accepted as one of production equipments.

Modulated Wave--A radio frequency carrier which varies either in frequency or amplitude in accordance with the waveform of the modulating signal.

Modulation--The variations in frequency or amplitude of an r-f carrier which contain the information or signal being transmitted. Also the process of modulating an r-f carrier.

Modulation Generator--See Timer.

Modulator--That component of a radar set which turns on and off (keys) the transmitter. The pulse width of the transmitter is controlled by the modulator.

Momentary--Used with key switch for Radiation and Challenge operation. The circuits are active only while key is depressed, and they become inactive when the switch is let go.

Monitor--A term used with meter, cathode-ray tube, antenna, receiver, etc., which are used to check the operation and performance of a system by examining a small part of the output.

Motor Boating--Regeneration in an audio, video, or r-f amplifier causing a low-frequency oscillation and resulting in intermittent operation of the amplifier.

Motor-Generator (MG)--Rotating machine used to convert ship power to form suitable for energizing system.

MTI--Moving Target Indication. See CW, FM and Pulse Doppler.

Multielement Parasitic Array--An array of dipoles and parasitic reflectors, arranged so as to produce a radar beam of desired directivity.

Multiple Reflection Echoes--Echoes returned from a real target by way of reflection from some object in the radar beam. Such echoes appear at a false bearing and false range, and may therefore be very alarming in some circumstances.

Multiple Trip Echoes--See Second Trip Echoes.

Multivibrator--A form of relaxation oscillator, essentially a two-stage amplifier with feedback. Will oscillate of its own accord, or through an external synchronizing voltage.

N Indicator--A modified type A scan with two traces horizontally displaced to permit pip matching in a lobe-switching system, with a range step in each trace to permit direct measurement of range. A combination of types K and M scans.

Nautical Mile--6080.27 feet (as contrasted with statute or land mile, 5280 feet). The length of one minute of arc of the equator. 6000 feet or 2000 yards is used in the Navy for all gunnery, navigation and radar applications. Standard frequency for calibration is 81.967 kc, since the time required for one cycle at this frequency equals the time required for a radio wave to go out to and return from a target 2000 yards away.

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Negative Feedback--See Degeneration.

Network--Any combination of capacitance, inductance and/or resistance electrically interconnected.

NMP--Navigational Microfilm Projector. A device for superimposing on the PPI pattern the virtual image of a chart projected from microfilm. By changing the lens system, the scale of the projected chart can be altered to match either of two range scales on the radar indicator. See VPR.

Noise--A random voltage appearing at the output terminals of a receiver with no impressed signal, if the amplifier has sufficient gain. It is due to random motion of electrons in the grid circuit of the first amplifier tube, to fluctuations in emission, shot noise at the plate, etc. On the A scope, noise appears as random spikes ("grass") on the sweep line.

Noise Figure--The figure of merit for sensitivity of a receiver. Defined as the ratio of the input power to kTB (where k is Boltzmann's constant, T the temperature in degrees Kelvin, and B the bandwidth in cps) when the output signal power equals the output noise power. Noise figure normally is expressed in db.

Non-Linear Coil--A coil having an easily saturable core possessing high impedance at low or zero current and low impedance when current flows and saturates core. Peterson Coil.

Notch--Rectangular depression in sweep trace used as a range mark.

Null--An area in the antenna pattern of a radar where the field strength is very low because of the interference between direct radiation and radiation reflected from the sea. The positions of the nulls are fixed by the geometry of the system; no kind of device put on the antenna can change the locations of the nulls.

O Indicator--A type A scan modified by the inclusion of a notch for measuring range.

Off-Center PPI--A modified type of PPI presentation in which the center about which the sweep trace rotates can be moved off the face of the cathode-ray tube as a means of expanding the presentation in order to provide better resolution. The pattern is stabilized so that true north always remains at 12 o'clock on the screen.

Off-On--Circuit Control.

Omnidirectional--A type of antenna that radiates equally in all directions, insofar as technological limitations permit. Omnidirectional antennas are used primarily with IFF and radar beacons.

On Time--Adjustment of "on" period of multivibrator in some types of timing circuits.

One-Axis Stabilization--See Stabilization.

One-Cycle Multivibrator--See Start-Stop Multivibrator.

One Speed--A synchro system in which the rotor of the synchro generator turns one revolution for each revolution of the shaft whose position is to be reproduced remotely.

Operate--Position of a control that indicates normal operating condition.

Operational Controls--Those necessary for operation of equipment.

O.S.C. Bus--Own ship's course gyro supply. Voltages derived from synchro at master gyro compass.

O.S.C. Excitation--Own ship's course synchro excitation.

O.S.C. 1 Speed--Own ship's course single speed synchro data. Synchro geared 1:1 to gyro compass.

O.S.C. 36 Speed--Own ship's course 36-speed synchro data. Synchro geared 36:1 to gyro compass.

Oscillation--(1) A condition whereby alternating voltages are generated in a circuit. (2) One complete cycle of a periodically recurring phenomena.

Oscillator--A vacuum tube and associated circuit which generates an a-c signal when d-c power is applied.

Oscillatory Circuit--A circuit in which oscillations can be generated or sustained.

Oscilloscope--See Cathode-Ray Oscilloscope.

Out (Output)--Used to indicate the signal, power, trigger, etc., fed out of a unit or circuit.

Output Impedance--The impedance between the Output terminals of a circuit measured at a definite frequency or at a predominant frequency in the range which the device is to handle.

Over Current Raise--Relay adjustment.

Overload--Type of relay or adjustment.

Overshoot--Excessive potential attained by a portion of the main body of a pulse.

Own Ship Course (OSC)--The direction prescribed for the ship's movement, or the direction in which the ship sails from one place to another.

P Indicator--See PPI.

Panoramic Adaptor--A special oscilloscope used with a search receiver to assist the RCM operator in interpreting the signals that are detected.

Pan-Rangic--Intensity modulated "A" type of indication with slow vertical sweep applied to video. Stationary targets give solid vertical deflection and moving targets give broken vertical deflection.

Parabolic Reflector--A metallic sheet formed so that its cross section is in the shape of a cylindrical parabola. The antenna elements are placed along the line that runs through the focal point of the parabola, parallel to the leading edge of the reflecting sheet. See Paraboloid.

Paraboloid--A reflecting surface formed by rotating a parabola about its axis of symmetry. Paraboloidal reflector or dish.

Paraphase Amplifier--See Phase Inverter.

Parasitic Antenna--An antenna that is excited by radiation from other antennas rather than by electrical connection with them.

Parasitic Oscillations--Oscillations which occur at other than the desired frequency in oscillators, or random oscillations in audio and radio frequency circuits. These oscillations are always undesirable.

Parasitic Reflector--A parasitic antenna so placed that the radiation from the driven antenna is reduced in one direction and reinforced in the opposite direction. See also, Director, Reflector (2).

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Pattern--(1) The geometrical figure used to show the directional qualities of the antenna assembly. (2) Position on selector switch of monitor scope.

Peak--The maximum instantaneous value of a varying voltage, current, or power.

Peaking Circuit--A circuit used to sharpen a wave of any form, whereas a differentiating circuit is designed to sharpen a square wave.

Pedestal Pulse--A square wave pulse or gate upon which may be superimposed a video signal or sweep voltage.

Pencil Beam--An antenna beam in which energy is confined to a narrow, approximately conical portion of space.

Pencil Mixer--A form of crystal mixer.

Perdio--Performance data relative to radio ranges and reception.

Persistence--The measure of the length of time during which phosphorescent light is emitted from the screen of a cathode-ray tube. Long persistent screens are used on intensity-modulated indicators, as the PPI, while test oscilloscopes and deflection type radar indicators use short persistent screens. The persistence of the screen is indicated by the final number in the type designation of the tube. A 5CP1 is of short persistence, and a 7BP7 is of long persistence.

Persuader--Element of storage tube directing secondary emission to electron multiplier dynodes.

Phantastron--A very stable triggered gate-producing circuit using a pentagrid tube.

Phantom Signals--Signals appearing on the screen of a CRT Indicator the cause of which cannot readily be determined and which may be caused by circuit fault, interference, propagation, jamming, etc.

Phase Angle--The time difference, expressed in electrical degrees, between the occurrence of the positive peaks of two sine waves of the same frequency.

Phase Detector--A circuit which detects both the magnitude and the sign of the phase angle between two sine-wave voltages or currents.

Phase Distortion--Exists in an amplifier when the relative phases of the various frequency components in a complex input voltage are not preserved in the output voltage.

Phase Inverter--A stage of amplification giving two output signals, equal in amplitude but differing in phase by 180 degrees.

Phase Modulation--A form of FM in which only phase is varied while amplitude and frequency remain constant.

Phosphor--A chemical compound which has the property of giving off light when bombarded by fast-moving electrons. Phosphors are used to coat the inner face of cathode-ray tube screens. See Phosphorescence and Fluorescence.

Phosphorescence--The property of emitting light for some time after excitation by electronic bombardment.

Photoelectric Tube--Vacuum tube in which electron emission results from light energy striking light-sensitive cathode.

Photo-Sensitive--Capable of emitting electrons when illuminated by light rays.

Pigtail--A short flexible lead connected to a part or terminal.

Pillbox Antenna--A narrow cylindrical parabola antenna reflector with plain parallel plates covering the ends.

Pill Transformer--An impedance matching device for coaxial transmission lines, consisting of a quarter wavelength of enlarged center conductor which can be adjusted longitudinally.

Pip--A short, sharply peaked wave of current or voltage. The echo indication on a type A scope.

Pitch--The motion of a ship in which the bow rises and falls as a result of oscillation about a transverse axis.

Pitch Angle--For any system of stabilization. The angle between the ship's deck and a horizontal plane, measured in a vertical plane including the fore and aft axis of the ship. This quantity is positive if the ship's bow is depressed.

Plan Position Indicator--See PPI.

Plane Polarized Wave--In such a wave the electric intensity is everywhere parallel to some plane and the magnetic intensity is everywhere perpendicular to that plane.

Plate Pulsing--A method of modulating a transmitter in which the plate voltage is normally low until the application of a pulse of full plate voltage to produce oscillations.

Plumbing--Refers to all ultra-high frequency r-f transmission line systems.

Polarity Selector--Control box for selection of polarity of trigger, signal, etc.

Point--To control motion in elevation--as a gun or an antenna.

Polarized Wave--A wave in which the electric lines are parallel. If the electric field is vertical, the waves are known as vertically polarized; if horizontal, horizontally polarized.

Polyplexer--See T-R Box.

Poly-Rod Antenna--An antenna made of a tapered rod of polystyrene. Usually excited by a wave guide.

Polystyrene--A plastic insulating material most useful at ultra-high frequencies.

Port--Left side of an aircraft or ship when facing the nose or bow.

Positive Feedback--See Regeneration.

Positive-Grid Multivibrator--A type of multivibrator which has one or more grids connected to the plate voltage supply usually through large resistance.

Potential--The difference in voltage existing between one point in a circuit and another point.

Potentiometer--A resistor having a tap which can be continuously varied over the entire length of the resistor as a means of changing the resistance between two points in a circuit.

Power--The time rate of transferring or transforming energy.

PPI (Plan Position Indicator)--An indicator on which echoes appear as bright arcs. The sweep moves radially from the center of the tube face, and the sweep line rotates synchronously with the antenna. Thus, the radial distance at which the echo appears is an indication of range, and the angular distance measured clockwise from 12 o'clock is an indication of bearing.

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PPI Driver--Unit containing necessary power supply, sweep, marker gate, and other circuits essential to the operation of a separate repeater PPI scope.

PPI Repeater--Unit which repeats PPI indication at a location remote from the radar console.

Preamplifier--(1) The r-f amplifier stage or stages in a superheterodyne receiver which amplify the incoming modulated r-f signal before it is converted to the r-f signal by the mixer. The preamplifier is often located near the receiving antenna. (2) The two or three stages of the i-f amplifier that immediately follow the mixer in some microwave receivers, mounted in a unit near the antenna, and separate from the rest of the receiver.

Precision PPI--The model VF repeater PPI, which displays targets on both a 5-inch PPI scope and 5-inch B scope. Any area of the PPI pattern 30° in angular width and 4000 yards long in range can be displayed on the expanded B scope. A highly accurate ranging circuit is provided to measure ranges out to 40,000 yards.

Precision Range Unit--Extremely accurate range unit for fire control radar.

Precision Sweep--Delayed expanded sweep for high resolution and range accuracy. A type of R scope.

Predicter--A form of computer.

Pre-Plumbed System--Fixed, non-tunable wave guides or coaxial transmission lines.

Presentation--The form which the radar echo signals are made to take on the CRT screen, which is dependent on the nature of the sweep circuit utilized. Examples: A-scope presentation, PPI scope presentation.

Presentation Selector--Selection of CRT indicator display.

Pressurized--The filling of the r-f line with air at a pressure greater than atmospheric. Its purpose is two-fold: (l) to prevent breakdown of the components at high altitudes and (2) to protect against transmission losses caused by materials in the atmosphere, such as dirt and water.

Pre-T-R--Additional T-R Box to provide increased attenuation of transmitted pulse so as to prevent damage to crystal mixer.

Pre-Trigger--Trigger used to initiate sweep ahead of transmitted pulse.

Probe--A projecting rod placed in the slotted section of the RF line, and used to pick up RF energy, in the determination of standing wave ratio (SWR).

Projection PPI--Model VG repeater PPI. A unit in which the image of a 4-inch dark-trace cathode-ray tube is projected on a 24-inch horizontal plotting surface. The echoes appear as magenta-colored arcs on a white background. Also called a Skiatron.

Pseudo-Synchronizer--Unit for supplying simulated data for testing decoder.

Pulling--See Frequency Pulling.

Pulsating Current--A current which changes in value but not in direction.

Pulse--A momentary sharp change in a current or voltage, followed almost immediately thereafter by sharp return to normal.

Pulse Amplifier--A circuit which amplifies the pulse waveform without materially altering its shape. Video amplifier.

Pulse Analyzer--A special oscilloscope used with a search receiver for the purpose of measuring the pulse repetition rate and pulse width of intercepted radar signals.

Pulse Doppler (Coherent)--A radar system for distinguishing between fixed and moving targets by detecting the frequency difference between echo and coherent c-w oscillator locked in phase with transmitted pulse. Video pulses from one repetition period are stored and mixed out of phase with pulses from the next period. Echo signals from fixed or slow-moving targets are cancelled, and only echoes from fast-moving targets remain in the receiver output to be displayed on the PPI.

Pulse Doppler (Non-Coherent)--Uses doppler beats between the moving target and clutter at the same range to give MTI by aural indication of target in range gate.

Pulse Duration--The elapsed time between the start and finish of a single pulse. See Pulse Length.

Pulse-Forming Line--A combination of circuit components used to produce a square pulse of controlled duration. See Guìllemin Line.

Pulse Interval--Time between corresponding points of successive pulses.

Pulse Length--The duration of the pulse in microseconds at .85 of peak voltage value is the nominal length used in peak power calculations, while duration at ½ of peak voltage is maximum length used for receiver band with calculations.

Pulse Modulation--Transmission of r-f energy in short pulses.

Pulse Repetition Rate (PRR)--The number of pulses transmitted per second.

Pulse Timer--Unit which automatically causes radar to emit short series of pulses at intermittent intervals.

Pulse Transformer--A special type of transformer -designed to pass pulse currents and voltages as distinguished from the usual sine-wave type of transformer. Its major features are high-voltage insulation between windings and to ground, low capacitance between windings, and low reactance in both windings.

Pulsed Oscillator--An oscillator which is made to operate repetitively, usually at a low duty cycle (i.e., having the pulses short compared with the intervals between them).

Push-Pull Amplifier--A system driving two tubes with equal voltages which are always of opposite polarity (180° out of phase).

Pyramid Wave--A triangular wave the sides of which are approximately equal in length.

Q Factor--A figure used to express the efficiency of coils and capacitors and resonant circuits. It expresses the ratio between the total energy in the circuit and the energy that is dissipated. A high-Q circuit is very selective of the frequencies that it will pass, and oscillations set up in such a circuit will persist for a relatively long time because the energy in the oscillations is dissipated slowly. The numerical value of Q is commonly found by dividing the inductive reactance or capacitive reactance by the resistance of the circuit.

Quarter-Wave Support--A method of insulating the inner from the outer conductor of a coaxial transmission line. A quarter-wave metallic stub is used in place of dielectric insulators.

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Quarter-Wave Transformer--A quarter-wave section of line used to match the impedance of one circuit to another. It can be used as an interstage coupling device or in transmission lines. The input is placed across the open end and the output tapped off at the point, determined by test, which provides the proper impedance match. Also used as a voltage step-up or step-down transformer by tapping both the input and output signals at proper points along the line.

Quartz Crystal--See Crystal.

Quench Frequency--An a-c voltage applied to an electrode of a tube used as a super-regenerative detector. It alternately varies the sensitivity of the detector, thereby preventing any sustained oscillation. The quench frequency is usually low in comparison with the signal frequency to be received.

Quench Oscillator--That circuit in a super-regenerative receiver which produces the quench frequency signal.

Quiescent State--The time during which a tube or other element of an electric circuit is not performing its active function in the circuit.

R Indicator--Expanded Type A Presentation. Also called R scope or R scan.

Racon--See Radar Beacon.

Radar--Originally Radio Detection and Ranging. It has since been expanded to include all types of echo-ranging radio equipment.

Radar Beacon--A receiver-transmitter combination which sends out a coded signal when triggered by the proper type of pulse. A vessel or aircraft can determine its range and bearing from the beacon by tuning the radar to the beacon frequency.

Radar Countermeasures (RCM)--The means employed to obtain information about enemy forces from his use of radar, and to prevent him from obtaining any accurate or useful information about our forces through the use of his radar. Countermeasures methods are of four types: interception, jamming, deception and evasion. See Radseven and Radeleven.

Radar Distribution Switchboard (RDS)--Switching panel for connecting video, trigger, and bearing from any one of five systems to any or all of 20 repeaters. Also contains order lights, bearing cutouts, alarms, test equipment, etc.

Radar Indicator--A unit of radar equipment which provides a visual indication of the reflected energy received, using a cathode-ray tube or tubes for such indication. The radar indicator comprises, besides the cathode-ray tube, the sweep and calibration circuit, and associated power supplies.

Radar Receiver--An instrument which amplifies radio frequency signals, demodulates the r-f carrier, further amplifies the desired signal and delivers it to the indicator. It differs from the usual radio receiver in that it is more sensitive, has a lower noise level, and is designed to pass a pulse type of signal.

Radar Repeater Adapter--Unit which takes one video and trigger input and delivers several standard PPI video and trigger outputs suitable for driving PPI Repeaters.

Radar Selector Switch--A manual or motor-driven switch which transfers a PPI Repeater from one system to another, switching video, trigger and bearing data.

Radar Signal-Noise Ratio--Ratio between echo height and average height of grass.

E Units Ratio Description
E-1 1 to 1 Barely Perceptible
E-2 2 to 1 Weak
E-3 4 to 1 Good
E-4 8 to 1 Strong
E-5 16 to 1 Very Strong or Saturating

Radar Test Scope--A combination synchroscope and oscilloscope provided with fast sweeps, which enables the examination of wave forms and voltages throughout the radar set.

Radar Transmitter--A unit of radar equipment in which the radio-frequency power for radar action is generated and keyed. Corresponds to radio transmitter in communications.

Radex--An exercise designed to train radar operators to read through jamming and to acquire skill and confidence in the use of anti-jamming techniques and equipment. Sometimes loosely used to include the whole field of radar antijamming.

Radiation--(1) The process wherein a transmitting antenna system converts the r-f output of the transmitter into radio waves which travel away from the station. (2) A control. On-Off-Momentary switch for operating the transmitter.

Radiation Pattern--See Lobe and Pattern.

Radiation Resistance--A fictitious resistance which may be considered to dissipate the energy radiated from an antenna.

Radio Beacon--A radio transmitting station, usually in a fixed geographic location, which emits a distinctive or characteristic signal for enabling mobile stations to determine bearings or courses.

Radio Frequency--Any frequency in the spectrum of electromagnetic waves having a value below that of heat but above the highest audio frequency: abbreviated r-f.

Radio-Frequency Amplifier--A vacuum tube and associated circuit designed to provide amplification at radio frequencies.

Radio Wave--A combination of transverse electric and magnetic fields, each building up and collapsing at a radio frequency and capable of traveling through space at the speed of light. See Electromagnetic Field.

Railing--A pattern on type A Indicator caused by pulse interference or pulse jamming.

Raise--Refers to voltage, gain, frequency, etc.

Random Pulsing--Continuous varying PRR accomplished by noise modulation or continuous frequency change.

Randomized Jitter--Jitter by means of noise modulation.

Radome--A general name for radar turrets which enclose antenna assemblies.

Range--The number of miles between any two points, usually measured in yards or nautical miles. A nautical mile is 6080.27 feet, but for convenience in radar and navigation, the nautical mile is said to be 6000 feet, or 2000 yards long. The statute mile is 5280 feet long.

Range Buzzer--Circuit to remote indicator for calling attention to range transmission.

Range Calibrate--Calibration of range counter or dial against electronic markers.

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Range Coding--A method of coding a beacon response in which the reply consists of a group of pulses extending out in range from the range of the beacon. The coding lies in the arrangement of these pulses as they show on the scope.

Range-Height Indicator--See RHI.

Range Gate--A gate voltage used to select echoes from a very short range interval.

Range Marks--Pips or complete traces superimposed on the video signal and supplied to a cathode ray tube at specific intervals. They are used for calibration purposes.

Range Mark Offset--Displacement of range mark on a type "B" indicator.

Range Rate--Control of rate of range change.

Range Ring--Accurate adjustable ranging mark on PPL Corresponds to a range step on type M indicator.

Range Selector--Control for selection of range scale.

Range Step--Vertical displacement on "M" Indicator sweep to measure range.

Range Unit--A radar system component used for control and indication (usually counters) of range measurement.

Range Zero--Alignment of start of sweep trace with zero range.

RASD--Radar antenna stabilization director.

Rate--Used with range, bearing, elevation, etc.

RC Coupling--Coupling between two circuits by means of a resistance-capacitance network.

RCM--Radar countermeasures.

RC Network--A circuit containing resistances and capacitances.

Reactance--Impedance offered to the flow of alternating current by the inductance or capacitance of a radio circuit or part thereof. Reactance is measured in ohms, and depends upon the frequency of the alternating current as well as upon the actual magnitude of the inductance or capacitance. A capacitor has capacitive reactance while a coil has inductive reactance. Capacitive reactance causes current to lead the voltage and inductive reactance causes current to lag behind the voltage in phase.

Reactance Tube--A vacuum tube used to change the reactance of a circuit.

Read--Target Indication indicator light.

Ready--Indication of completion of standby condition.

Receiver--Unit for converting r-f energy into video or audio frequencies.

Receiver Gain--Control of output of receiver. See Gain.

Receiver Gating--Applying operating voltages to one or more i-f stages during only the interval when reception is desired.

Receiver Tune--A control for adjustment of receiver L.O. frequency.

Recognition--The process of determining the friendly or enemy character of others. See Identification.

Recovery Time (of Receiver)--The time required for the receiver to recover to within approximately 3 db of full sensitivity, after the main transmitted pulse stops.

Recovery Time (of TR)--Time required, after an r-f pulse has fired the gap in the TR cavity, for the ions to recombine. Time after the end of the gap discharge when a received signal is 3 db down from one received a long time after the ions have recombined.

Rectification--The conversion of alternating current into unidirectional current by means of a tube or crystal.

Rectifier--A device which passes current more easily in one direction than in the other. Common types of rectifiers include two-element vacuum tubes, gaseous tubes, crystals, and copper-oxide devices. Used in Rectifier Power Units, High Voltage Rectifiers. Regulated Rectifiers, etc.

Reflected--Refers to a wave traveling in a direction away from the load.

Reflectometer--Unit for measuring standing waves of voltage and power.

Reflector--(1) A device to redirect radiation in a desired direction or directions. (2) A parasitic element which reinforces radiation on a line pointing from it to the antenna. (3) An anode in a reflex klystron tube which reflects the electrons back toward the grid. Also called a repeller.

Reference Voltage--In a synchro servo system, the a-c voltage used to determine the in-phase or 180° out-of-phase condition in order to provide directional sense.

Reflex Klystron--A klystron in which a single cavity is used both as buncher and catcher. The bunched electrons pass through the cavity and are then reversed in direction by means of a negatively charged repeller electrode.

Refraction--The bending of light or radio waves which takes place when the energy passes from one medium into another. The variation of the transmission properties of air caused by temperature inversion and cold-wave fronts may cause a certain amount of refraction to radio waves. However, for convenience the radiation from radar equipment is often assumed to travel in straight lines.

Regulated Rectifier--Unit for supplying d-c power at constant voltage in spite of load or line supply voltage variations.

Regeneration--A method of increasing the amplification of an amplifier by feeding a portion of the amplifier output back to the amplifier input in such a way that reinforcement of the input signal is obtained.

Regenerative Receiver--A radio receiver which employs controlled regeneration to increase the amplification provided by a vacuum tube stage.

RE J--A] controls for tuning the band elimination, or rejection, filters through the i-f band of the receiver.

Relative--The angle between the vertical plane through the fore and aft axis of own ship and the vertical plane through the line of sight, measured in a horizontal plane clockwise from the bow. A bearing measured with respect to own ship's heading.

Relaxation Oscillator--An oscillator in which a capacitor is charged slowly through a resistor and then discharged rapidly through a tube.

Relay--An electromagnetic device which permits control of the current in one circuit by a much smaller current flowing in another circuit. This is accomplished by causing an electromagnet to open or close a switch.

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Remote Caging Control (of Fluxgate Compass)--A device (manual or electrical) for caging the gyro of the gyro fluxgate compass system, when it is not in use. The gyro is caged to protect the gyro assembly from damage when the system is not operating. The caging mechanism is operated before the power is shut off.

Remote PPI--See PPI Repeater.

Remote-Local--Shift of control from main control to general control at Indicator Console.

Repeller--Element of Reflex klystron oscillator. See Reflector (3).

Reset--Overload relay reset.

Resistance Coupling--A type of coupling in which a resistor and capacitor provide a path for signal energy between two circuits. See RC Coupling.

Repetition Rate (PRR)--The number of pulses sent out by the transmitter per second.

Resolution--1. Range. The minimum range difference between two targets on the same bearing that will allow the operator to obtain data on either target. 2. Bearing. The minimum angular separation between two targets at the same range that will allow the operator to obtain data on either target. 3. Elevation. The minimum angular separation between two targets at the same range and bearing that will allow the operator to obtain data on either target.

Resolver--An electro-mechanical unit, similar to a synchro, used to resolve incoming voltages into their sine and cosine components as referred to angle of shaft rotation. Resolvers may be supplied with two stator and two rotor windings for resolution of the sine and cosine components of the vector sum of two quadrature inputs.

Resonance--In a circuit containing both inductance and capacitance, a condition in which the inductive reactance is equal to the capacitive reactance at a particular frequency. In parallel resonance, the impedance presented appears as a high value of pure resistance. In series resonance, the impedance presented appears as a low value of pure resistance. When two bodies, or two currents, or two voltages which are coupled oscillate at the same frequency they are said to be in resonance.

Resonance Indicator--Meter indicating condition of resonance. Used with Reflectometer, Wave meter, Echo Box, etc.

Resonant Cavity--See Cavity Resonator.

Resonant Charging Choke--Modulator inductor which, with the effective capacitance of a pulse-forming network, is used to set up an oscillation of a given charging frequency in order to charge the line to a high voltage.

Resonant Frequency--The frequency at which resonance occurs in an LC tuned circuit. That frequency of vibration which causes maximum amplification of applied vibration.

Resonator--A resonant cavity, the frequency of oscillation of which is determined primarily by the physical dimensions.

Responsor--A radio receiver, associated with the radar equipment, which receives the reply returned from the Transpondor and produces an output suitable for feeding to a display system. The Responsor usually is combined into a single unit with the Interrogator.

Retrace--The return of a trace on the screen of a CRT to its starting point. Usually blanked out. Sometimes called Flyback or Backtrace.

RF--Radio Frequency.

RF Choke--A choke of low inductance, used to prevent radio-frequency currents from passing from one circuit to another.

RF-IF Converter--See Preamplifier.

RF Line--The system of metallic tubes (wave guides and/or coaxial lines) which conducts r-f energy from one point to another. Also referred to as "plumbing."

RF Plumbing--Radio-frequency transmission lines and associated equipment.

RHI--Range-Height Indicator. Intensity modulated radar indicator which displays elevation on vertical axis and range on horizontal axis.

Rhumbatron--A re-entrant hollow-cavity, velocity modulated oscillator.

Ring Oscillator--A type of oscillator used in some radars in which any even number of tubes are arranged in a ring. Between each pair of adjacent tubes is a tuned quarter-wave line functioning as a balanced tank circuit. The open ends of each line are connected either to two grids or two plates, alternating around the ring. Coupling between plate and grid circuits is chiefly through the internal capacitance of the vacuum tubes. The balanced nature of each tank circuit puts equal r-f voltage of opposite polarity on adjacent tubes.

Ribbon Marker--Intensified annular segment of precision PPI (model VF). indicating ß-scope area.

Ringing Oscillator--An oscillator circuit containing an LC resonant combination in the cathode circuit. Usually used to provide range marks.

Ringing Time--See Echo Box.

Roll--The motion of a ship in which it inclines first to one side and then to the other; an oscillation about the fore and aft axis of the ship. Owing to the structure of the ship there is no roll without pitch, but it is theoretically possible to have pitch without roll.

Roll Angle--(For any system of stabilization.) The angle between the ship's deck and a horizontal plane, measured in a plane perpendicular to the fore and aft axis of the ship. This quantity is positive if the starboard side of the ship is raised.

Rope--Metal foil about 400 feet long, untuned and effective for passive jamming from 50 to about 350 mc.

Rotary Spark Gap--A device in which several electrodes mounted on a wheel are rotated past a fixed electrode, producing periodic spark discharges. Used in radar modulators.

Rotating Joint--A device for permitting one section of a transmission line to rotate continuously with respect to the other and still maintain r-f continuity.

Rotoflector--A rotating reflector, elliptically shaped, used to reflect at right angles a vertically directed radar beam so that it illuminates in a horizontal direction.

Rotor--The rotating member of a machine.

Round Trip Echoes--Multiple reflection echoes produced when the radar pulse is reflected from a target strongly enough that the echo is reflected back to the target where it produces a second echo. As many as four round trips have been observed, producing on the indicator a series of pips on the same bearing which are at the true range, twice the true range, etc. These echoes decrease markedly in size on each succeeding round trip because of the great attenuation involved in the several reflections.

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RPD--Radar Planning Device. A system in which a topographical relief model and a narrow beam of light are used to simulate PPI presentations by photographing the light and shadow areas on the model.

RPPI--Repeater Plan Position Indicator. See PPI Repeater.

RR Equipment--Radio recognition equipment. See IFF.

RT Box--A standard TR tube contained in a cavity with no output circuit. The RT box is placed on the line between the TR and the magnetron, and A/4 away from the TR box. It is part of the duplexing system and prevents radar echoes from feeding into the magnetron.

Sand Load--An attenuator used as a terminating section on a transmission line to dissipate power. The space between inner and outer conductors is filled with a sand and carbon mixture which acts as the dissipative element.

Saturate--Overloading a vacuum tube to the limit of its emission and amplifying capabilities.

Saturated Signal--The maximum possible signal that may be observable on a CRT.

Saw-Tooth Wave--A voltage or current wave which increases linearly to a maximum and then falls off to a minimum in a relatively short period of time. The retrace or backtime is usually less than 10% of the total cycle time.

Saxophone--A vertex-fed linear array antenna giving a cosecant-squared radiation pattern.

Scale-of-Two Circuit--A system for dividing by two the number of input pulses. A frequency divider.

Scan Converter--Unit for converting electronic scan data to synchro bearing data.

Scanner--A type of antenna in which a paraboloidal reflector is made to oscillate back and forth about a center position. The oscillation may be in a horizontal or a vertical plane or in a combination of both.

Scanning--1. The process of directing the r-f beam successively over all points in a given region of space. 2. The process of deflecting the beam of a cathode-ray tube to all parts of the screen as a means of forming a pattern.

Scatter-Band--The band of frequencies within which the principal operating frequency of any given transmitter tube type is permitted to vary.

Scattering Cross Section of a Target--The ratio of the power reflected from, to the power incident on a given target. It depends on size, configuration, aspect, and composition of the target, and the wavelength and polarization of the r-f energy.

Schwarzchild Antenna--A rapid-scanning antenna. SCI--Ship-controlled interception.

Screen--See Fluorescent Screen and Long Persistence Screen.

Screen Grid--An electrode placed between the control grid and plate of a vacuum tube for the purpose of increasing the gain of the tube and of reducing the capacitance between these two electrodes.

Sea Return--The indication on a radar indicator caused by radio waves being reflected by the surface of the sea.

Search--Refers to a radar system whose primary function is detection with moderately accurate range, bearing, elevation, and target composition data. Dual Search--Two separate search systems combined on one mount. General Search--Combined air and surface search. Height-Finding Search--Long-range early warning and elevation of aircraft in addition to long range surface search. High Resolution Search--System with high range and azimuth resolution for navigation, station keeping and standby fire control. Long-Range Search--High-power system for detection of planes at extreme range. Panoramic Search--Complete hemispheric search (short range) with range, bearing, and elevation data. Range-Only Search--Omnidirectional or wide-angle search primarily for warning or range data. Bearing obtained by optical means. Surface Search--Detection of surface targets and low-flying planes at maximum range. Zenith Search--Detection of aircraft in region 20° to 90° elevation and 360° azimuth.

Search Receiver--A special calibrated receiver which can be tuned over a wide frequency range in order to detect and measure r-f signals transmitted by the enemy.

Searching Gate--A gate pulse which is made to search back and forth over a certain range.

Searchlight Control Radar (SLC)--Equipment for directing searchlights onto aircraft.

Searchlighting--Directing the radar beam continuously at any given object or target, instead of illuminating it once during each scan period.

Seasoning--Overcoming a temporary unsteadiness of the magnetron which may appear when it is first installed.

Secondary Emission--Emission of electrons from a tube element other than the cathode when the element is bombarded by high-velocity electrons.

Secondary Indicator (of Flux Gate Compass)--A repeater unit which duplicates at a remote station the indications of the master indicator of the gyro flux gate compass system.

Second Detector--See Detector.

Second Trip Echoes--Echoes returned from targets so distant that the time required for the radar pulse to go out to the target and return to the set is longer than the interval between pulses. These echoes show up at false ranges, and the apparent range can be changed by varying the pulse repetition rate.

Sector Scan--A type of scanning in which the antenna pattern is made to scan back and forth through a sector of a circle.

Selectivity--The degree to which a radio receiver is capable of receiving signals of one frequency or band of frequencies while at the same time discriminating against signals of all other frequencies.

Selector Switch--A switch arranged so that a conductor may be connected to any one of several other conductors.

Self-Bias--A means of biasing the grid without applying a negative voltage derived from a special power supply, as by using a cathode resistor or a grid leak.

Self Pulsing--A special type of grid pulsing which automatically stops and starts the oscillations at the pulsing rate by a special circuit.

Selsyn--A trade name. See Synchro.

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Sensitivity--A measure of the ability of a receiver to amplify a signal. It is measured by the input signal required to produce a certain fixed output signal. The lower the input signal for a given output, the higher the sensitivity.

Sensitivity-Time Control (STC)--A circuit which reduces receiver sensitivity for the first few thousand yards of each sweep, and then gradually restores it to normal. Helpful in reducing the effect of sea return and side lobes.

Separation--Horizontal spacing of pattern, lobe, signal, trace, etc.

Separator--Circuit at receiving end of link which separates video, trigger, and scan data.

Service Outlet--Outlet for providing servicing power conveniently on the front of the equipment.

Service Phone--Servicing phone jack.

Service Switch--Line switch in service power.

Servicing Block--A block diagram containing wave forms, terminals, signal paths, tubes, and other data useful for servicing.

Servo Amplifier Unit--A unit of a servo system in which information from a synchro is amplified in order to control the speed and direction of the servo motor output.

Servo System--A complete electromechanical system for amplifying and transmitting accurate mechanical position. Servo motor, Servo generator, Servo amplifier, etc.

Shaping--Adjustment of PPI pattern set up by rotating magnetic field.

Sharpener Amplifier--A peaking circuit plus an amplifier.

Shepherd Tube--The Shepherd-Pierce tube, type 723A. A microwave local oscillator, all-metal velocity modulated tube.

SHF--Super-high frequencies (3.000 to 30,000 megacycles).

Shield--A grounded metal can or housing placed around a radio part to prevent its electric and magnetic fields from affecting nearby parts, or to prevent other fields from affecting it.

Ship Heading Marker (SHM)--An electronic radial sweep line on PPI indicating heading of own ship.

Ship's Head--See Heading.

Shock Mounting--Placing a component on rubber supports to insulate it from jarring or shock which might disturb its operating characteristics or damage the equipment.

Short Circuit--An abnormal connection of relatively low resistance, whether made accidentally or intentionally, between two points of different potential in a circuit.

Short Gate Gain--Video gain on short-range gate.

Shot Effect--Noise caused by the random impact of electrons in a vacuum tube. This causes slight instantaneous variations in the output current of a tube.

Shunt--Any parallel-connected part, or the act of placing one part in parallel with another.

Sickles Calibrator--A range calibrator using a circular-sweep tube, and which is stabilized by a crystal oscillator.

Sidebands--When the amplitude or frequency of a high-frequency wave is varied at a comparatively low-frequency rate, the high-frequency wave is said to be modulated. The resultant wave has a component wave of the high-frequency plus other frequencies that depend on the modulation frequency or rate. These are the sidebands.

Side Lobe--A portion of the beam from a radar antenna, other than the main lobe, and usually much smaller.

Signal--A radio wave or alternating current which carries intelligence of any form. More generally, any alternating current having other than a power-line frequency.

Signal Generator--A test instrument used to produce a modulated or unmodulated r-f carrier signal at a known frequency and in some cases at a known voltage. It is used as a signal source during alignment of a radio receiver and in locating the defective part in an improperly operating receiver.

Signal-to-Noise Ratio (S/N)--The ratio of the amplitude of a desired signal at any point to the amplitude of noise signals at that same point. The higher the signal-to-noise ratio, the less noise, or grass, there is to interfere with the observation of target indications.

Silica Gel--A chemical having moisture absorption properties, used in connection with the dehydrator in removing moisture from the air supplied to the transmission line in radar equipment.

Silverstat Regulator--A multi-tapped resistor, the taps of which are connected to single-leaf silver contacts. Variation of voltage causes a solenoid to open or close these contacts, shorting out more or less of the resistance in the excitor circuit is a means of regulating the output voltage to the desired value.

Single Stub Tuner--A short section of transmission line terminated by a movable short-circuiting plunger. Used as an impedance matching device.

Siting--The proper location of a radar antenna in order to obtain optimum performance.

Size--Control of size of PPI indication by varying PPI sweep length.

Skiatron--A type of PPI in which the image of a dark-trace tube is projected on a screen larger than the tube face.

Sky Waves--Radio waves which travel up into the sky from the transmitting antenna and are bent back to earth by the Ionosphere.

Slant Range--The distance in a straight line fre>m a radar set to a target.

Slewing Motor--Motor drive of antenna control synchro or handwheel.

Slicer--A circuit which effectively amplifies a portion of the incoming pulses lying between two closely spaced amplitude levels.

Slip Ring--Device for making electrical connections between stationary and rotating contacts.

Slotted Section--A slot in a transmission line along which a probe is moved to measure SWR.

S/N--Signal-to-noise ratio.

Snow--The low, fairly regular indications on the PPI caused by noise.

Soft Tube--(1) A high-vacuum tube which has become defective because of the entry of a small amount of gas. (2) An electronic tube into which a small amount of gas has purposely been put in order to obtain desired characteristics. A gaseous tube.

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Solid Dielectric Cable--Made by extruding a flexible dielectric over the inner conductor, with braided copper wire to form the outer conductor, which may be tinned or plated. For microwave work, most cables are nominally 50 ohms. For IF and video, 70-ohm cable is more generally used.

Sonar--Underwater sound navigation and ranging equipment.

Spaghetti--Heavily varnished cloth tubing sometimes used to provide additional insulation for radio circuit wiring.

Spare--Designation of spare fuse, tube, etc.

Spark Gap--An arrangement of two electrodes between which a disruptive discharge of electricity may take place, such that the insulation is self-restoring after the passage of the discharge.

Spark Gap Modulator--A modulator in which the high current switch takes the form of a spark gap. The spark gap may be either of the triggered or the rotary type.

Spark Pulse Modulator--A modulator which generates pulses at high power level directly from a pulse-forming line. The spark may occur in air, or in a gas-filled tube.

Spectrum Analyzer--A test instrument used to show the distribution of the energy contained in the frequencies emitted by pulsed magnetrons to measure the Q of resonant cavities or lines and to measure the cold impedance of a magnetron.

Spinner--Name applied to the rotating antenna assembly on certain types of microwave radar sets.

Spiral Scanning--A point on the r-f beam traces out a spiral. The motion is obtained by rotating the paraboloid rapidly about a horizontal axis, while tilting it more slowly about an axis at right angles to the first.

Square Wave--Any periodic wave rectangular in shape. Specifically, a rectangular waveform in which the positive and negative portions are of equal amplitude and duration.

Square-Wave Amplifier--A resistance-coupled or RC amplifier, the circuit constants of which are such as to amplify a square wave with the minimum amount of distortion. In effect, a wide-band video amplifier.

Squeezable Waveguide--A waveguide used in rapid scanning, the dimensions of which can be altered periodically.

Squegging Oscillator--An oscillator usually operating at radio frequency, which oscillates briefly arid then cuts itself off due to grid current. This action is repeated periodically. A self-pulsing oscillator.

Squitter--The irregular transmission of pulses that results from self-triggering of an IFF transpondor when the super-regenerative receiver becomes so sensitive that it is operated by noise pulses instead of by interrogating pulses received in the normal manner.

SSI--Sector Scan Indicator.

Stabilization--A system for maintaining a radar beam in a desired direction in space despite the roll and pitch of the ship or aircraft. 1. One-axis stabilization--Same as Line-of-sight stabilization. 2. Two-axis stabilization--This is the same as line-of-sight stabilization except that provision is made for adding the deck-tilt correction to the train order. By this means the spinner is kept pointed at the target irrespective of the roll and pitch of the vessel or aircraft as long as the true bearing of the target does not change. Rotation occurs about two axes; namely, the level axis and the train axis. 3. Three-axis stabilization--This is the same as two-axis stabilization except that provision is made for rotation of the antenna about a true horizontal cross-level axis. More precisely the level axis and the line-of-sight are both maintained in a horizontal plane. As in two-axis stabilization, provision is made for adding the deck-tilt correction. Rotation occurs about three axes; namely, the level axis, the cross-level axis, and the deck-train axis. 4. Four-axis Stabilization--A stable-base system in which elevation stabilization is added. 5. Line-of-sight Stabilization--A method of compensating for roll and pitch of the vessel or aircraft by changing the elevation of the spinner in order to keep the radar beam pointed at the horizon. 6. Stable-base Stabilization--A method of maintaining the spinner base in a true horizontal plane by compensating for roll and pitch directly. The deck-tilt error does not occur when this method is used. In a stable-base system, rotation occurs about three axes; namely, the roll axis, the pitch axis, and the train axis. If it is desired to raise the radar beam above the horizontal, a fourth axis called the elevation axis must be added above the spinner base. 7. Tilt Stabilization--Stabilization by use of a gyroscope of the tilt angle of a spinner. Also called "line-of-sight" stabilization.

Stable Element--A gyroscopic instrument which maintains a true vertical, and develops angles of deviation of the ship's deck from the true horizontal. The unit may be rotated in train, and has outputs of level and cross-level which may be used as input data to computers used in stabilization systems, or the outputs may be fed to the antenna directly.

Stable Platform System--See Four-axis Stabilization.

Stable Vertical--A gyroscopic instrument which is similar to the stable element except that it is not rotated in train and has outputs of roll and pitch only.

Stacked Dipole Antenna--Generic term applied to a number of antenna designs in which antenna directivity is increased by providing a number of identical dipole elements, excited either directly or parasitically. The resultant radiation pattern will depend on the number of dipole elements used, the spacing and phase difference between the elements, and the relative magnitudes of the currents.

Stagger Tuning--Method of aligning the i-f stages of a superheterodyne receiver in order to produce wide bandwidth. This is accomplished by peaking alternate i-f transformers at slightly different frequencies. Compare In-line Tuning.

Stalo--An extremely stable c-w oscillator used as a local oscillator in the superheterodyne radar receiver in an MTI system. See Coho.

Standby--Condition of equipment which will permit complete stable operation within a short period of time.

Standard Atmosphere--A condition of the atmosphere in which the temperature and the moisture content of the air decrease uniformly with height. In the standard atmosphere, the air temperature decreases with increasing altitude from 15° Centigrade at sea level at the rate of 6.5°C. per kilometer. Although this condition is postulated as "standard," it is not necessarily normal at any particular location. The atmosphere is likely to be of standard composition when strong, gusty winds are blowing because the turbulence created prevents both stratification of the air and establishment of non-standard temperature and humidity gradients.

Stand-Off Insulator--An insulator used to support a wire, or other radio component, at a desired distance away from the structure on which the insulator is mounted.

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Standing Wave--A distribution of current and voltage on a transmission line formed by two sets of waves traveling in opposite directions, and characterized by the presence of a number of points of successive maxima and minima in the distribution curves. Since standing waves indicate that power is being lost in transmission, efforts are made to keep standing waves to a minimum.

Standing Wave Indicator--An instrument containing a detecting device (bolometer, thermocouple or crystal) which enables one to determine the ratio of the maximum voltage to the minimum voltage of the combined incident and reflected waves. The deflection or current reading is proportional to the time average of the square of the voltage at any given point. Other SW detectors may read voltage directly.

Standing-Wave Ratio (SWR)--The ratio of the current (or voltage) at a loop or maximum to the value at a node or minimum. It is determined by the terminal and by the characteristic impedances.

Starboard--The right side of an aircraft or ship when the observer is facing its nose or bow.

Start-Stop Multivibrator--A biased rectangular wave generator which operates for one cycle when a synchronizing trigger signal is applied.

Stator--The portion of an electrical machine which contains the stationary parts of the magnetic circuit with their associated windings.

STC--Sensitivity-Time Control.

Step--Range mark offset on type M presentation.

Step-by-Step--A system used for data transmission on older ships and on ships that have only d-c power available. The system consists of special d-c motors that are driven by a rotary switch which is controlled by the shaft whose position it is desired to duplicate at a remote location.

Stiffness Factor--Static accuracy--angular lag between input and output of a servo system.

Storage Tube--A cathode-ray tube of special design in which signals can be stored or retained for a short time, after which the signals may be recovered without appreciable loss of identity.

Stow--Locking of antenna to prevent rotation while servicing.

Stray Capacitance--Capacitance existing between adjacent conductors or wiring. Coupling effects cause it to be detrimental at high frequencies. See Distributed Capacitance.

Strobe--An intensified spot in the sweep of a deflection type indicator, used as a reference mark for ranging or expanding the presentation.

Strut--A tuning strut is a thermally controlled tuning member of the Nehr L.O. which changes the cavity dimension.

Strut Time Constant--Time required for tuning to reach 64% [(1-ε-1)] of its final value after the application of unit step-function voltage to the tuning strut.

Stub--Device for matching, loading, or tuning in r-f system. See Matching Stub.

Stub Angle--A right-angle elbow for the coaxial r-f transmission line which has the inner conductor supported by a quarter-wave stub.

Stub-Supported Line--A type of coaxial line in which the inner conductor is positioned coaxially by short-circuited quarter-wave stubs.

Superheterodyne Receiver--A type of radio receiver in which the incoming modulated r-f signals are amplified in a preamplifier (in some cases; but not necessarily in all receivers of this type), then fed into the mixer for conversion into a fixed, lower carrier frequency called the intermediate frequency of the receiver. The modulated i-f signals undergo very high amplification in the i-f amplifier stages and are then fed into the detector for demodulation. The resulting audio or video signals are usually further amplified before use.

Super-Refraction--See Trapping.

Super-Regenerative Receiver--A type of regenerative receiver in which weak periodic oscillations are caused by the use of a quench frequency signal. This quench signal is fed to the receiving tube where it constantly varies the gain of the tube by varying an electrode voltage.

Suppressor Pulse--A pulse used to disable an IFF or beacon transpondor during intervals when interference would be encountered. See Killer Circuit.

Suppression--Suppression of noise, etc.

Surge--A transient variation in the current and/or potential at a point in the circuit.

Sweep--The steady bright line produced on the screen of a cathode-ray tube by the repeated deflection of the electron beam across the screen. The time base on which the range of an echo is measured in a radar indicator. Main, expanded, precision, etc.

Sweep Amplifier--A vacuum tube stage designed to increase the amplitude of the sweep voltage.

Sweep Circuit--A circuit which produces at regular intervals an approximately linear, circular, or other form of movement of the beam of the cathode-ray tube.

Sweep Displacement--Vertical displacement of sweep when used with IFF.

Sweep Generator--A sweep circuit.

Sweep Length--A control for adjusting the magnitude of sweep voltage.

Sweep Voltage--A voltage having a wave form suitable for deflecting an electron beam in a CRT back and forth across the fluorescent screen.

SWR--Standing wave ratio.

Synchro--A type of wound-rotor a-c motor used for repeating angular motion both as to speed and total angle. The trade name "Selsyn" is often used synonymously with synchro, and is an abbreviation of the term "self-synchronous," and indicates the normal use of the equipment. See OP 1303, U.S. Navy Synchros.

Synchro Control Transformer--A synchro in which the electrical output of the rotor is dependent on both the shaft position and the electrical input to the stator.

Synchro Differential Generator--The synchro unit which receives at its primary terminals an order from a synchro generator, modifies this order mechanically by any desired amount by the angular position of the rotor, and transmits the modified order from its secondary terminals to other synchro units.

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Synchro Differential Motor--A motor which is electrically similar to the synchro differential generator except that a damping device is added to prevent oscillations. Both its rotor and stator are connected to synchro generators, and its function is to indicate the sum or difference between the two signals transmitted by the generators.

Synchro Generator--A synchro which has an electrical output proportional to the angular position of its rotor.

Synchro Motor--A synchro in which the rotor shaft position is dependent on the electrical input.

Synchronism--The relationship between two or more periodic quantities of the same frequency when the phase difference between them is zero.

Synchronizer--That component of a radar set which generates the timing voltage for the complete set. See Timer.

Synchroscope--An oscilloscope on which recurrent pulses or waveforms may be observed, which incorporates a sweep generator that produces one sweep for each pulse. The sweep usually is very fast in order to permit display of short pulses.

Tail--A small pulse, following the main pulse and in the same direction; or the slow decay, following main body of pulse.

Tail Clipping--Any method of sharpening the trailing edge of a pulse.

Target--Any distant object which will reflect a sufficient amount of signal to be evident at the searching set.

Target Alignment--Alignment of spot indication in center of scope when beam is directly on target (G Indication).

Tell Tale--Warning indicator which shows loss of synchronism between PPI rotation and antenna rotation.

Temperature Alarm--Warning indicator light or buzzer which indicates overheating.

Terminal--A point to which electrical connections are made.

Test Amplifier Unit--Used to amplify output of echo box, bolometer, or other test equipment.

Test--Referring to points of wave-form or voltage test.

Test Equipment--An assortment of instruments provided with a radar set to enable the maintenance man to determine accurately whether the set is performing properly in its various functions.

Test Lead--A flexible insulated lead used chiefly for connecting meters and test instruments to a circuit under test at a test point.

Test Prod--A sharp metal point provided with an insulated handle and means for electrically connecting the point to a test lead. It is used for making a touch connection to a circuit terminal.

Tetrode--An electronic vacuum tube in which four elements--cathode, control grid, screen grid, and plate--are used.

Thermal Agitation--Term applied to noise caused by random motion of free electrons in a conductor, which produces minute voltages across the terminals.

Thermal Time Delay Switch--An overcurrent protective device which contains a heater element, and thermal delay.

Thermionic Emission--The evaporation of electrons from the body of a solid at high temperatures.

Thermistor--A sensitive resistor, used in the thermistor bridge, whose resistance varies significantly with temperature.

Three Axis Stabilization--See Stabilization.

Thirty-Six Speed--A synchro system in which the rotor of the synchro generator turns 36 revolutions for every revolution of the shaft whose position is to be reproduced remotely. The 36-speed system is used to provide finer position control than is possible with a 1-speed system alone.

Thyratron--Trade name for gaseous triode tube. The time at which current through the tube starts to flow is determined by the grid voltage. The amplitude of current flow is independent of the grid voltage once the tube begins to conduct.

Thyrite--A material that has high resistance when low voltage is impressed on it and low resistance when the voltage is high. Used in connection with the magnetron to prevent backswing.

Ticket Tube--Material used as a waveguide for low or medium power microwave radar equipments. The material is a hollow brass pipe, rectangular in cross-section, with inside dimensions of approximately 3/8" by 2¾".

Tilt--The angle which the reflector makes with the horizontal.

Tilt Stabilization--See Stabilization.

Time Base--The voltage generated by the sweep circuit or circuits in the radar indicator. The waveshape of the voltage generated is such as to cause to be described on the screen of the cathode-ray tube a trace which is either linear with respect to time, or, if non-linear, is still at a known timing rate.

Timer--In radar, a generic term for an assembly of electric circuits and associated equipment which provides the following: (1) trigger pulses, (2) sweep circuits, (3) intensifier pulses, (4) gate voltages, (5) blanking voltages, and (6) power supplies. An important feature of a timer is that the various output events are synchronized with respect to each other.

Time Cancel--Control of variable reflector in an MTI radar system to adjust PRR to length of delay line.

Time Constant--Refers to AJ control for adjustment of circuit time constant (product of RC.)

Torque Amplifier--Used in gyro flux gate compass system to amplify the error signal developed between the magnesyn in the master indicator and the autosyn in the torque unit.

Torque Unit--A unit attached to the base of the spinner in H2X (AN/APS-15 radar) which turns the stator of a synchro so that the direction of the antenna is always referred to true north. Used for azimuth stabilization of the PPI pattern.

TR Box--Transmit-receive resonant cavity to keep transmitted pulse out of receiver. See Duplexer.

Trace--Visible line which appears on the screen of a CRT.

Track--(1) The geographical path of a moving body, or the path relative to the medium in which the body is moving. (Since own vessel, target, and torpedo all move in the same medium, track is taken to mean path relative to the water, and current is not considered.) (2) The actual course or direction between stations on the surface of the earth that an aircraft has traveled.

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Tracking--(1) The process of following a target by means of radar indications. (2) The term used to indicate that all tuned circuits in a receiver are properly aligned throughout the entire tuning range.

Tracking Spot--Moving spot on a type B indicator for target indication.

Train--To control motion in azimuth or bearing, as a gun or an antenna.

Train Angle--(For two-axis stabilization.) This is the angle, measured clockwise in the ship's deck as seen from above, from the forward end of the fore and aft axis of the ship to a plane perpendicular to the deck, through the target. In three-axis stabilization, this plane is perpendicular to the horizon.

Train Indicator Unit--Contains bearing synchros and training controls.

Train Order--Training a spinner on a target is generally accomplished by means of a hand crank or motor and a servo system. The voltage sent through the servo system resulting in rotation of the spinner about its own axis is called the train order.

Trainer--A system used for training radar operators. Simulates signals received under operating conditions in the field.

Training Control Amplifier (TCA)--Control of power supplied to antenna training motor.

Trans Off-On--Control of high voltage to transmitter.

Transformer--A component composed of two or more coils in close proximity to one another. The flow of alternating current, or pulsating direct current, through the first coil, or primary causes a magnetic field to build up and collapse in accordance with the current flow. This building up and collapsing of the magnetic field induces a voltage in the second or secondary coil. The amplitude of the secondary voltage is primarily dependent on the turns ratio of the windings. Transformers are used to couple from one circuit to another when d-c isolation is desired. Also to step-up or step-down a-c voltages.

Transient--The instantaneous surge of voltage or current which usually occurs at random intervals.

Transit Time--The time required for an electron to leave the cathode and arrive at the plate in a vacuum tube.

Transitron Oscillator--A pentode vacuum tube used as a generator of sinusoidal oscillations. The negative resistance characteristic of the screen grid of a pentode is used.

Transmission Line--Any set of conductors used to carry signals or energy from one location to another.

Transmitter--A term applied to that part of a radio or radar set where the r-f oscillations are generated and/or amplified. See Radar Transmitter.

Transmitter Pulse--The r-f pulse generated in the transmitter. Sometimes called direct pulse, initial pulse, radar pulse, or main bang.

Transpondor--A combined receiver-transmitter, fitted in all friendly aircraft and ships, which receives a challenge pulse from an Interrogator and automatically returns a signal on the same frequency (or a different frequency; depending on the IFF system in use). The form,and duration of the reply signal are controlled by a coding system.

Traveling Wave--The resulting wave, guided or unguided, which carries energy from one point to another in space.

Trapping--A type of radio wave propagation in which the radiated rays are bent excessively by refraction in the lower layers of the atmosphere. This bending creates an effect much as if a duct or waveguide had been formed in the atmosphere. The duct, which may be either elevated or ground based, is able to guide part of the radiated energy over distances far beyond the normal radar range.

Trapezoidal Generator--A vacuum tube stage designed to produce a trapezoidal voltage wave.

Trapezoidal Wave--A waveform of trapezoidal shape. (A square wave on which a saw-tooth is superimposed.) It is the voltage wave necessary to give a linear deflection current through the coils of a magnetic CRT.

Traveling Detector--A probe mounted on a slider and free to move along a longitudinal slot cut in a waveguide or coaxial transmission line. The traveling detector is connected to auxiliary measuring apparatus and forms a means of examining the relative magnitude of any standing waves that may be present in the system.

Triggatron--High-pressure triggered spark-gap modulator.

Trigger--Any short pulse, positive or negative, which can be used to set into motion a chain of events. Used to synchronize the operation of the various units of a system. 1. Calibration Trigger: Trigger supplied to range calibrator. 2. Coordination Trigger: Trigger supplied to IFF coordinator. 3. Delayed Trigger: Trigger supplied by Delay Unit to give delayed operation, as with delayed sweep. 4. IFF Trigger: Trigger supplied to IFF interrogator. 5. PPI Trigger: Trigger supplied to PPI unit. 6. Pre-Trigger: Trigger delivered to sweep and indicators ahead of the time of the transmitted pulse. 7. Radar Trigger: Trigger supplied to the system from the modulator or transmitter pulse. 8. Range Indicator Trigger: Trigger supplied to the "A" scope, Range indicator. 9. STC Trigger: Trigger supplied to the sensitivity time control circuit of the receiver. 10. Synchronized Radar Trigger: Radar trigger which has passed through a delay line so as to be coincident with the corresponding video.

Triggered Spark Gap--A fixed spark gap in which the discharge passes between two electrodes and is struck (started) by an auxiliary electrode, the trigger, to which low-power pulses are applied.

Trimmer Capacitor--A small adjustable capacitor, usually adjusted with a screw driver, and used in the tuning or trimming circuits of radio receivers and other radio apparatus to permit accurate alignment of these circuits.

Triode--An electronic vacuum tube in which three elements--a cathode, control grid, and plate--are used. Used as an amplifier.

Trodio--Tropospheric observations of temperature and moisture conditions affecting radio or radar propagation.

Trombone--A U-shaped adjustable coaxial line matching assembly.

Troposphere--That part of the earth's atmosphere below the stratosphere in which temperature generally decreases with altitude, clouds form, and convection is active. Region which causes refraction and trapping.

True--(1) Bearing of target with true north as reference. (2) Designation of synchro data from the system which gives antenna true bearing.

Truncated Paraboloid--A paraboloid in which a portion of the top and bottom has been cut away in order to reduce the vertical aperture and thus broaden the vertical width of the radar beam.

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Tube Hours--Designation of tube life meter.

Tunable Echo Box--An echo box consisting of an adjustable cavity operating in a single mode. If calibrated, the setting of the plunger at resonance will indicate the wavelength.

Tune Set--Control for manual adjustment of receiver to desired frequency.

Tuned Circuit--A circuit consisting of inductance and capacitance which can be adjusted for resonance at a desired frequency.

Tuning--The process of varying the inductance or capacitance in an LC circuit to provide resonance at a desired frequency.

Turnstile Antenna--Consists of two linear antennas, lying in a plane, and crossing one another without electrical contact at their centers. If the angle between the two is 90°, the length of each element equal to a half wavelength, and the currents 90° out of phase, the directional pattern in the plane of the antenna elements is nearly circular.

Two-Axis Stabilization--See Stabilization.

UHF--Ultra-high frequencies (300 to 3,000 megacycles).

Unblanking Pulse--Voltage applied to CRT to overcome bias and cause trace to be visible. Intensifier pulse.

Under Current Raise--Relay adjustment.

Units of Radar System--Antenna Assembly, Antenna Pedestal, Auxiliary Control Unit, Bearing Indicator Unit, Converter Unit, Dehydrating Unit, Delay Unit, Deviation Alarm, DG Synchro Amplifier Unit, Directional Coupler, Echo Box, Echo Box Antenna, Elevation Indicator, General Control Unit, IFF Coordinator Unit, Indicator Console, Line Switch. Line Transformer, Load Divider, Main Control Unit, Manual Elevation Unit, Modulator Unit, Monitor Receiver, Monitor Scope, PPI Unit, PPI Driver Unit, PPI Repeater, Pre-Amplifier. Power Equipment, Pulse Synchronizer Unit, Pulse Timer, Radar Distribution Switchboard, Radar Receiver. Radar Repeater Adapter Unit, Radar Selector Switch, Radar Transmitter, Range Calibrator Unit, Range Indicator Unit, Range Unit, Rectifier Power Unit, Receiver, Reflectometer, Regulated Rectifier Unit, Servo Amplifier Unit (Train, Elevation, PPI, Cross Level, Level, Roll, Pitch, O.S.C., etc.), Stable Element, Standing Wave Indicator, Synchroscope, Test Amplifier Unit, Train Indicator Unit, Training Control Amplifier Unit, Transmission Line, Transmitter, Transmitter-Receiver Unit, Trigger Delay Line, Trigger Unit, Vacuum Tube Voltmeter, Video Amplifier Unit, Voltage Regulating Transformer, Waveguide, Wires and Cables.

Unstabilized--Refers to an antenna of which the base is locked in deck plane, so that no correction can be applied to offset roll and pitch of the ship.

V Center--Vertical centering of scope pattern.

Vacuum Tube--A device consisting of a number of electrodes mounted in an envelope or housing from which practically all air has been removed. Also called an electronic tube.

Vacuum Tube Voltmeter--A test instrument which utilizes the rectification characteristic of a vacuum tube for measuring voltages without materially affecting the circuit to which the instrument is connected.

Variac--A type of manually adjusted autotransformer generally used to adjust line voltage input.

Velocity Control--Variation of sweep rate on MTI velocity indicator CRT.

Velocity Merit--Ratio of velocity (in degrees per second) to angular lag (in degrees) over linear range of the servo system.

Velocity Modulation--The speeding up or slowing down of electrons in an electron stream to produce "bunches" of electrons whose energy is taken up in a "catcher" cavity to produce high-frequency oscillations.

Velocity Modulated Tube--A vacuum tube oscillator which produces high frequency oscillations induced by the fields associated with "bunches" of electrons in transit.

Velocity of Light--A physical constant equal to 2.99796 × 1010 centimeters per second. More conveniently, the velocity of light can be expressed as: 186,280 statute miles per second; 161,750 nautical miles per second; 328 yards per microsecond.

Vertical Polarization--Electric field (E vector) perpendicular to the horizon. An antenna in which the dipoles are vertical is vertically polarized.

Vertical Spot Limit--Control of tracking spot on a type B indicator.

VHF--Very high frequencies (30 to 300 megacycles).

Vibration Isolation--The property of a shock mount by which the applied vibration amplitudes are attenuated. The vibration frequencies generally encountered are 1000-3000 vibrations per minute, on aircraft, and 300-1200 vibrations per minute on ships.

Vibrator--A device used to change d-c power to a-c in order that the alternating voltage so produced may be stepped up or down by a transformer, and used to supply power to radio equipment. This device uses a vibrating vane driven by a coil as a means of opening and closing contacts which cause the output current to alternate in direction. By suitable arrangement, a vibrator can also be used to rectify alternating currents.

Video--1. A term used to include a wide band of frequencies extending from approximately 60 or 100 cycles per second out to several megacycles per second. 2. The output voltage of a detector, or the signal voltage applied to a radar indicator.

Video Amplifier--A wide-band amplifier capable of amplifying video frequencies. Used for amplifying pulses in radar and television. See Pulse Amplifier.

Video Equalizer--Control for change of video gain with sweep radius or sweep rate.

Video Frequency--See Video.

VLF--Very low frequencies (10 to 30 kilocycles).

Voltage Divider--A group of resistors, capacitors, or inductors placed in series and having one or more fixed or adjustable contacts along its electrical length in addition to the customary two end terminals. The total available voltage is applied between the two end terminals and desired portions of this voltage are obtained from any two terminals on the voltage divider.

Voltage Doubler--A rectifier circuit which gives a pulsating d-c output nearly double the a-c input from the power transformer, or voltage source.

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Voltage Regulating Transformer--Saturated-core type of transformer which holds output voltage to within a few percent (± 5%) with input variations up to ± 20%. Considerable harmonic distortion results unless extensive filters are employed.

VPR--Virtual PPI Reflectoscope. A device for superimposing a virtual image of a chart on the PPI pattern. The chart is usually prepared with white lines on a black background to the scale of the PPI range scale. See NMP.

VR Tube--Gas-filled electronic tube which has the property of maintaining a nearly constant voltage across its terminals over a considerable range of current through the tube. Used in electronic voltage regulators.

VTVM--Vacuum tube voltmeter.

Wattmeter--An instrument for measuring electric power, and provided with a scale usually graduated in milliwatts, watts, or kilowatts.

Wave--A disturbance which is propagated in a medium in such a manner that at any point in the medium the displacement is a function of the time, while at any instant the displacement at a point is a function of the position of the point.

Wave Front (of an Impulse)--That part of a wave (in time or distance) between the initial point of the impulse and the point at which the impulse reaches its crest value.

Waveguide--A hollow pipe, usually of rectangular form, used as an r-f transmission line. The dimensions of the pipe are determined by the wavelength to be transmitted by the pipe. There are other types of waveguides, such as solid dielectric cables, through which it is possible to transmit energy. Waveguides may be straight, twisted, curved, tapered, or flexible.

Waveguide Elbow--A bend in a waveguide.

Waveguide Plunger--A movable shorting plate, used to vary the length of a resonant section of waveguide.

Waveguide Switch (Coaxial Switch)--A transmission line switch for transferring Transmitter-Receiver Unit from one antenna to another or to a Dummy Load.

Wavelength--A wavelength is the distance traveled in one period or cycle by a periodic disturbance. If the distance between corresponding phases of two consecutive waves of a wave train. Wavelength is the quotient of velocity by frequency.

Wavemeter--An instrument for measuring wavelength.

Wave Shape--The graph of the wave voltage or current as a function of time.

Wein Bridge Oscillator--A sine-wave oscillator which utilizes a resistance-capacitance bridge to provide the regenerative feedback voltage. The RC bridge is electrically connected as a Wein Bridge circuit.

Whisker--The sharpened metal wire in contact with the crystal in a crystal mixer.

Window--Metal foil strips dispersed by rocket, shell, or aircraft for the purpose of jamming by multiple false targets.

Wing Spot Generator--An electric circuit which grows wings on the video target signal of a type C indicator. These wings are inversely proportional in size to the range.

Wings Level--Sensitivity of wing amplifier in type C indication.

Wobbulator--RCA frequency-modulated signal generator.

Woggle Joint--A flexible joint in a transmission line or waveguide.

X Axis--The horizontal axis of a cathode-ray oscilloscope, as distinguished from the vertical, or Y axis, and the intensity modulation, or Z axis. It is usually an adjustable linear time base.

Y Axis--The vertical axis. Used to describe deflection of the electron beam in the vertical direction in cathode-ray oscilloscope tubes, as opposed to deflection on the X, or horizontal axis.

Yagi Antenna--A type of directional antenna array usually consisting of one driven ½-wavelength dipole section, one parasitically excited reflector, and several parasitically excited directors.

Yaw--The angular difference between course and heading. The amount that a ship is "off her course" at any given instant. Measured to the right or to the left, in degrees, from course to heading.

Yoke--A group of coils placed around the neck of an electromagnetic cathode-ray tube for purpose of deflection. They are wound and shaped to provide a uniform magnetic field in the area through which the electron beam passes. The magnitude of the field, and hence the amount of deflection, varies in accordance with the current through the coils.

Z Axis--An attempt to show a third dimension on the two-dimensional screen surface of a cathode-ray tube by applying the third variable to the control grid of the tube, this variable showing up as a change in intensity.

Zero Set--Control for adjusting range counter to give correct range.

Zone Blanking--A method of turning off the CRT during part of the sweep of the antenna.

Zone Plate Antenna--A rapid scanning antenna, in which the reflector consists of arcs of confocal parabolas with focal lengths which differ by ?/2 and which lie close to a circle centered at the focus.

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Table of Contents

Transcribed and formatted by Larry Jewell & Patrick Clancey, HyperWar Foundation