Absolute Altitude: The altitude of an object relative to the ground beneath it.
Acceptable Degradation: The allowable reduction in system performance. For a fire control radar, the acceptable degradation is usually expressed as a reduction in range; for example, the maximum lock-on range might be degraded by 25 percent without loss of essential defense capability.
Acquisition: The process between the initial location of a target and the final alignment of the tracking radar on the target. Operational phase of a fire-control or track radar during which the radar system searches a small volume of space in a pre-arranged pattern. A procedure by which a fire control tracking radar attains initial lock-on. Usually, the approximate target coordinates are supplied to the tracking radar and it searches a predetermined volume of space to locate the target.
Active Electronically Scanned Array: [AESA], an active phased array radar.
AFC: [Automatic Frequency Control] An arrangement whereby the frequency of an oscillator or the tuning of a circuit is automatically maintained within specified limits with respect to a reference frequency. A magnetron drifts in frequency over a period of time. The AFC of a radar makes the local oscillator shift by an equal amount so the IF frequency will remain constant.
AGC: [Automatic Gain Control] A method for automatically obtaining an essentially constant receiver output amplitude. The amplitude of the received signal in the range gate determines the AGC bias (a DC voltage) which controls the receiver gain so as to maintain a nearly constant output even though the amplitude of the input signal changes.
Air-Control Panel: Panel that monitors the dry-air input at each user equipment. [Environmental Alarm Manufacturers].
Altitude: Vertical distance of an aircraft or object above a given reference, such as ground or sea level.
Ambiguous Returns: Echoes that exceed the PRT of a radar and appear at incorrect ranges. Also see Pulse Repetition Time [PRT].
Amplifier: An electronic device used to increase signal magnitude or power. See also GaAs FET Amplifier, Klystron Amplifier, Traveling-Wave Tube Amplifier. [RF Equipment Amplifier Manufacturers].
Transistor RF Amplifier Schematic
Amplitude Modulation: [AM] A method of impressing a message on a carrier wave by causing the
carrier amplitude to vary proportionally to the message waveform. Read more on Amplitude Modulation in the main engineering dictionary.
Amplitude Shift Keying: [ASK] A method of impressing a digital signal upon a carrier signal by causing the carrier amplitude to take different values corresponding to the different values of the digital signal.
Angle Jamming: ECM technique, when azimuth and elevation information from a scanning fire control radar is jammed by transmitting a jamming pulse similar to the radar pulse, but with modulation information out of phase with the returning target angle modulation information.
Angle Noise: Text in review.
Angle of Reflection. The angle between the reflected wave and the normal.
Angular Error: The error in angle of an object reported by the antenna.
Angular Rate: The rate of change of the bearing of an object.