Definitions of Radar Terms
"A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M",
"N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"

"R" to "Ra", "Re" to "Rz"

Receiver: A unit that converts rf echoes to video and/or audio signals pertaining to RADAR.

Receiver Bandwidth: The difference between the limiting frequencies within which receiver performance in respect to some characteristic falls within specified limits. (In most receivers this will be the difference between the two frequencies where the intermediate frequency (IF) amplifier gain falls off 3 dB from the gain at the center IF frequency.) See also Receiver Selectivity.

Receiver Selectivity: The degree to which a receiver is capable of differentiating between the desired signal and signals or interference at other frequencies. (The narrower the receiver bandwidth, the greater the selectivity).

Receiver Sensitivity: The degree to which a receiver can usefully detect a weak signal; the lower limit of useful signal input to the receiver. A characteristic which determines the minimum strength of signal input capable of causing a desired value of signal output.

Recovery Time: In a radar, the time interval between the end of the transmitted pulse and the time when echo signals are no longer attenuated by the tr gap.

Reflecting Object. In radar a air or surface contact that provides an echo.

Reflection: The turning back (or to the side) of a radio wave as a result of impinging on any conducting surface which is at least comparable in dimension to the wavelength of the radio wave.

Reflex Klystron: A microwave oscillator that is tuned by changing the repeller voltage.

Relative Bearing: Bearing of a target measured in a clockwise direction from "dead ahead" of a ship or plane.

Resolution: In radar, the minimum separation in angle or in range between two targets which the radar is capable of distinguishing.

Return. The RF signal reflected back from a radar target; echo.

RF: (Radio Frequency) A term indicating high frequency electro-magnetic energy.

RFI: (Radio Frequency Interference) Any induced, radiated, or conducted electrical disturbance or transient that causes undesirable responses or malfunctioning in any electrical or electronic equipment, device, or system. (also RFI).

Ring Around: A condition in which a repeater jammer's total gain, from receiver antenna to transmitter antenna, exceeds the antenna isolation resulting in the repeater amplifying it's own internal noise. Akin to positive feedback in an amplifier that causes unwanted oscillations. The condition where radio frequency interference signals from a transmitter of one radar enter the receiving circuits of another radar.

Rope: An element of chaff consisting of a long roll of metallic foil or wire which is designed for broad, low frequency response. See Chaff.

Ringing: Rf oscillations caused by shock excitation of a resonant circuit (cavity).

Ring Time. In radar, the time during which the output of an echo box remains above a specified level.

R-Scope: (Range Scope) Also called an A-scope, A-Scan or PPI display. A cathode-ray oscilloscope [CRT] used in radar systems to display vertically the signal amplitude as a function of time (range) or range rate. Targets are displayed as perpendicular deflections on the time scale. Sometimes referred to as Range (R)-Scope. Note; the A-Scope display is obsolete, and is shown in the right side-bar.

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