72 OCEAX ELECTRONIC NAVIGATIOXAL AIDS 



"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). 



ANTENNA. — A conductor or a system of conductors for radiating or receiving 

 radio waves. 



AZIMUTH. — Angular position or bearing in a horizontal plane measured from 

 0° to 360°, relative or true north, to the target in a clockwise direction. 



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 

 syncro voltages from the gyrocompass into the servo system that drives the 

 PPI coils. 



SWEEP BASE LINE. — The horizontal (or vertical) line formed by the movement 

 of the sweep on a cathode-ray tube. Sweep usually used. 



RADAR BEARING. — The direction of the line of sight from Radar antenna to 

 target. Azimuth angle of train. 



BEARING CURSOR. — Mechanical bearing line on PPI for reading target bearing. 



BLIND ZONES. — Areas in which echoes cannot be received. 



CALIBRATION MARKERS. — Indications on the screen of a Radar indicator which 

 divide the range scale into accurately known intervals for range determina- 

 tion, or checking against mechanical indicating dials, scales, or counters. 



RADAR 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 

 effective in returning a strong Radar echo. 



RADAR 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. 



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. 



GROUND CLUTTER. — Radar echoes reflected from terrain, which obscure rela- 

 tively large areas of the Radar indicator. 



HOOD. — A shield placed over the scope to eliminate extraneous light and 

 thus make the image on the screen appear clearly. 



INTERFERENCE. — Confusing signals accidentally produced on a radar indicator 

 by the effects of electrical apparatus or machinery, or by atmospheric 

 phenomena. 



MARKER. — Electronic range or bearing indication on Radar indicator. 



/vi;CROSECOND. — One-millionth of one second. 



PIP. — The flgure presented on the oscilloscope of a Radar caused by the echo 

 from an aircraft or other reflecting object. 



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. 



PPI REPEATER. — Unit which repeats PPI indication at a location remote from 

 the Radar console. 



PULSE DURATION. — The elapsed time between the start and finish of a single 

 pulse. 



PULSE REPETITION RATE (PRR). — The number of pulses transmitted per second. 

 Pulse repetition frequency (PRF) . 



RADAR INDICATOR. — A unit of Radar equipment which provides a visual indi- 

 cation of the reflected energy received, using 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 de- 

 livers it to the indicator. It differs from the usual radio receiver in that it is 

 designed to pass a pulse type of signal. 



RADAR TRANSMITTER. — A unit of Radar equipment in which the radio-fre- 

 quency power is generated and keyed. Corresponds to radio transmitter in 

 communications. 



RADOME. — A general name for Radar turrets which enclose antenna 

 assemblies. 



