DISCRIMINATORA circuit in which amplitude variations are derived in response to phase or
DISTILLED WATERWater that has been purified through a process of evaporation and
DOPPLER EFFECTIn radar, the change in frequency of a received signal caused by the relative
motion between the radar and the target.
DOPPLER FREQUENCYDifference between transmitted and reflected frequencies; caused by the
DOUBLE-MODINGIn a transmitter output tube, the abrupt and random change from one frequency to
DRY-AIR SYSTEMProvides dehumidified air for electronic equipment that is moisture critical.
DUCTINGTrapping of an rf wave between two layers of the earth's atmosphere or between an
atmospheric layer and the earth.
DUPLEXERA radar device that switches the antenna from the transmitter to the receiver and vice
DUTY CYCLEIn a transmitter, ratio of time on to time off.
ECHOThe rf signal reflected back from a radar target.
ECHO BOXA resonant cavity device that is used to check the overall performance of a radar system.
It receives a portion of the transmitted pulse and retransmits it back to the receiver as a slowly
ELECTRICAL POWER SYSTEMProvides the necessary input power.
ELECTRONIC COUNTER-COUNTERMEASURES (ECCM) CIRCUITSSee Antijamming
ELECTRONIC EQUIPMENT DEHYDRATORProvides alternate dry-air input in the event of
failure of the central dry-air system. May include a compressor.
ELECTRONIC FREQUENCY COUNTERAn instrument that counts the number of cycles (pulses)
occurring during a precise time interval.
ELECTRONIC SCANNINGScanning in which the axis of the beam is moved, relative to the antenna
axis, in a desired pattern.
ELECTRONICS DRY-AIR BRANCHA common line for providing dry air to various electronic
equipment, such as search radar, fire-control radar, and repeaters.
ELEVATION ANGLEThe angle between the horizontal plane and the line of sight.
EMERGENCY POWERTemporary source of limited electrical power used upon the loss of the
normal power source.
EXTERNALLY SYNCHRONIZED RADARRadar system in which timing pulses are generated by a
master oscillator external to the transmitter.