Glossary of Terms


"A" BAND - The universal IFF Mark III frequency band is designated "A" band by the Navy. (This same band is designated "I" band by the Army.) The Army uses the term "A" band to designate a frequency band used in the Mark II IFF system.

AI -- Abbreviation for Aircraft Interception -- a function of some radar sets.

A Scope

"A" SCOPE -- An indicator on which signals caused by targets appear as vertical deflections on a horizontal range trace. By means of a calibrated scale the approximate range of any target can be read instantly. Approximate azimuth and/or elevation data may be obtained by observing the direction of the antenna when a signal is at maximum intensity. Much more accurate azimuth and elevation data can be obtained by means of pip matching on a modified form of "A" scope. (See PIP MATCHING). It is possible also to get an estimate of the size of targets from an "A" scope. This type scope is often used for tuning up sets and is the basic display in many. The vertical defection shown above at the start of the trace is caused by the transmission of the radar pulses.

ASV -- Abbreviation for Air to Surface Vessel; ASV sets being used in planes for the function of detecting objects on the surface of the sea.

ASV Scope

ASV SCOPE -- There is a vertical double "A" scope that is used by some ASV sets and is called an "ASV SCOPE". (This type of indication is not confined to ASV sets, and not all ASV sets use it.) Indicates range of target as well as position of target to right or left or radar-equipped plane. Signals appear as horizontal deflections in the two vertical traces. When the plane is pointed directly at the target, both signals are of equal length. This pip matching is used when homing.

B BAND -- Army designation for a frequency used in the IFF Mark II system.

B Scope

B SCOPE -- An indicator with horizontal and vertical coordinates, giving range vertically; and azimuth, or bearing, horizontally. Signals appear as bright spots.


C Scope

C SCOPE -- An indicator with horizontal and vertical coordinates giving elevation vertically; and azimuth, or bearing, horizontally. Signals appear as bright spots.


Expanded Scopes

EXPANDED SCOPE -- An arrangement by which a small part of the sweep on an indicator can be spread over a larger area so that a more accurate measurement can be made. Sometimes part of a sweep is expanded on the same indicator; usually part of a sweep on one indicator is made to appear in expanded form (i.e. over a larger area) on a separate indicator.

G BAND -- An Army and Navy designation for a tunable spot frequency band used in the Mark III IFF system. Only fighter planes carry the G band, and it is used in GCI and SCI operations to separate friendly fighters from other friendly or enemy aircraft.

GCI -- Abbreviation of Ground Control of Interception -- a function of some radars, the sets being used to control fighter planes from a ground station.

G Scope
G SCOPE -- A spot error indicator on which a single signal, only, appears as a bright spot from which horizontal wings sprout -- the wings growing as distance to the target diminishes. That is, the shorter the range to the target, the longer the wings. Azimuth is given horizontally, and elevation vertically. The information for moving the spot is obtained by some form of lobe switching arrangement. (See lobe switching).

H Scope

H SCOPE -- A modified B scope. Azimuth is given horizontally, and range vertically. The signal appears as two bright spots, displaced laterally with reference to each other. The slope of the line that can be imagined as joining the dots gives an indication of target elevation. When the line tilts upward (from left to right) the target is upward in relation to the axis of the H-scope-equipped plane. When the line is horizontal, the target is at the same elevation. When the line tilts downward, the target is downward. The H scope is often designated by the term "double dot" scope.


HR Scope

HR SCOPE -- An indicator with a display somewhat similar to an "A" scope. Range is given as on an ordinary "A" scope, and height can be estimated. This is done by having the target appear as two signals by the use of two sets of antennas at different elevation angles, and by estimating the size-ratio of these two signals and referring to a table that converts size-ratio to height. An HR can also be used to estimate the size of the approaching formation of planes.

I BAND -- Army's designation of the universal Mark III frequency band. See A BAND.

IFF -- Abbreviation of Identification of Friend or Foe -- a function of some radars.

INDICATOR -- All radar signals are displayed on the face of a CATHODE RAY TUBE. This face is a flat surface at the end of the tube and is called the INDICATOR, SCOPE, or SCREEN. The word INDICATOR also is used to refer to the whole cathode ray tube, as well as the component of a radar set that houses the cathode ray tube and contains associated circuits. For various types of display afforded by an indicator see A SCOPE, ASV SCOPE, B SCOPE, C SCOPE, H SCOPE, HR SCOPE, J SCOPE, PPI, EXPANDED SCOPE and MOVING SPOT INDICATOR.

INTERROGATOR -- A pulse type transmitter used to challenge transpondors for IFF purposes in an IFF system. The interrogator is part of the interrogator-responsor unit.

IR -- Abbreviation of Interrogator-Responsor. See INTERROGATOR. The IR is the part of an identification system (IFF) which challenges doubtful aircraft or ships and receives and displays the recognition signal.

IRT -- An abbreviation for Interrogator-Responsor-transpondor, when all are combined in a single unit. An IRT system is an IFF device.

J Scope display

J SCOPE -- Also called CIRCULAR SWEEP SCOPE. It is an A scope with the trace around the outer rim of the face of the indicator, instead of horizontally across the indicator. The signal appears as a radial deflection in the moving trace. Like an ordinary A scope, range data are given, but greater accuracy and simplicity are attained.


Lobe Switching

LOBE SWITCHING -- The act of moving the


lobe of an antenna in space -- the transmitted beam being directed a few degrees to the right and left of (or above and below) the target. Lobe switching is commonly done by either moving one antenna, or else having two antennas. In either case, the direction of maximum intensity of the antenna system is moved so that two signals from these two antenna positions are shown on the indicator -- one signal from each position. To do pip matching the radar operator directs the antenna system until the signals or pips are of equal height -- in which case the antenna is then pointing directly at the target. (See PIP MATCHING). Lobe switching and the resulting pip matching are commonly used to measure azimuth and elevation errors. For example, in the scope picture above, the signal from the right lobe is higher and hence shows that the target is to the right of the antenna. The comparison may also be done electrically, in which case the imperfection of the matching is usually indicated by a meter or by a moving spot indicator.

Moving Spot Indicator

MOVING SPOT INDICATOR -- Also called SPOT ERROR INDICATOR. Used to measure error (departure of target from center line of radar beam) in gun fire control sets. A single signal, only, appears as a bright spot on the indicator. This spot has the same angular relationship to the center of the indicator as the target has to the center of the radar beam. The azimuth error angle appears as the horizontal coordinate; elevation error angle, as the vertical coordinate. If the spot is in the center of the indicator, then the center of the radar beam is pointed directly at the target. This indicator is always associated with some form of lobe switching. The comparison of echo intensities for different directions is done electrically so that a deviation of the spot from center results from any lack of balance in the signal intensities.


PIP -- A term used to designate the signal on an indicator. Usually the signal is shaped like a triangle, with the base on the line of the sweep -- as in picture of two pips above.

Pip Matching

PIP-MATCHING -- A method of accurately determining the azimuth or elevation of a target. Usually the transmitted beam is alternately directed a few degrees to the right and left of (or above and below) the target. A signal, or pip, from each direction appears on the scope. The operator moves the antenna until these double pips are of equal height. The antenna is then pointing directly at the target. Pip-matching is done by lobe switching. (See LOBE SWITCHING).


PPI Scope

PPI -- Plan Position Indicator. The sweep is a radius on the tube face (from the center to the rim of the tube), and the sweep moves around through 360 degrees. This type of presentation gives the azimuth of the target by the direction of the radial line, and range by the distance of the target's signal from the center point of the tube.

RACON -- Same as RADAR BEACON, RDF BEACON, and RESPONDOR BEACON. A racon is a transpondor used for radar navigation. Radar beacons are divided into several groups: (1) ROOSTER -- An airborne radar beacon which will enable other radar-equipped aircraft to home on it. (2) EUREKA -- A battery-operated lightweight portable radar beacon which may be dropped in a container by parachute. It is interrogated by a Rebecca IR unit. (3) REBECCA -- An airborne interrogator for the Eureka-type beacon. (4) JELLYFISH -- A battery-operated lightweight radar beacon designed to be carried by an aircraft on a bomb rack. It is dropped into the water, moors itself automatically and switches itself on.


RECEIVER -- Unit of a radar set which amplifies the returning signal and reduces it to the stage necessary for visual representation on the indicator.


RESPONSOR -- A pulse type receiver used to receive from a transpondor the reply to an interrogation in IFF operations. Responsors are invariably used with interrogators, and are a part of an IR unit. Respondors are sometimes termed "responders".


SCI -- Ship Control of Interception -- a function of some radar sets, the sets being used to direct fighter planes to an interception course.

SCR -- Abbreviation of Signal Corps Radio, indicating radar set is an Army model. The Navy uses a different designation system for sets.

SPINNER -- Sometimes means REFLECTOR, sometimes means the whole assembly -- reflector, antenna, mount for the reflector, and so on.

TRANSMITTED PULSE -- The signal on the indicator made by the transmitted pulses of energy that are sent out by the transmitter at the start of operations. The way the transmitted pulse (or pulses, since each transmitted pulse appears at the same place on the scope) looks on a scope is shown in the scope pictures in this glossary. See A SCOPE, for an example.

TRANSPONDOR -- A pulse type receiver-transmitter used to receive an interrogating signal and automatically to transmit a reply for reception by a responsor. Transpondors fall into two categories: (a) IFF transpondor -- used solely for identification purposes; (b) Racons (radar beacons) -- used for radar navigation.


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