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APPENDIX I GLOSSARY - 14190_162
APPENDIX I GLOSSARY - 14190_164

Neets Module 18-Radar Principles
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AI-3 DISCRIMINATOR—A circuit in which amplitude variations are derived in response to phase or frequency variations. DISTILLED WATER—Water that has been purified through a process of evaporation and condensation. DOPPLER EFFECT—In radar, the change in frequency of a received signal caused by the relative motion between the radar and the target. DOPPLER FREQUENCY—Difference between transmitted and reflected frequencies; caused by the Doppler effect. DOUBLE-MODING—In a transmitter output tube, the abrupt and random change from one frequency to another. DRY-AIR SYSTEM—Provides dehumidified air for electronic equipment that is moisture critical. DUCTING—Trapping of an rf wave between two layers of the earth's atmosphere or between an atmospheric layer and the earth. DUPLEXER—A radar device that switches the antenna from the transmitter to the receiver and vice versa. DUTY CYCLE—In a transmitter, ratio of time on to time off. ECHO—The rf signal reflected back from a radar target. ECHO BOX—A 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 decaying transient. ELECTRICAL POWER SYSTEM—Provides the necessary input power. ELECTRONIC COUNTER-COUNTERMEASURES (ECCM) CIRCUITS—See Antijamming Circuits. ELECTRONIC EQUIPMENT DEHYDRATOR—Provides alternate dry-air input in the event of failure of the central dry-air system. May include a compressor. ELECTRONIC FREQUENCY COUNTER—An instrument that counts the number of cycles (pulses) occurring during a precise time interval. ELECTRONIC SCANNING—Scanning in which the axis of the beam is moved, relative to the antenna axis, in a desired pattern. ELECTRONICS DRY-AIR BRANCH—A common line for providing dry air to various electronic equipment, such as search radar, fire-control radar, and repeaters. ELEVATION ANGLE—The angle between the horizontal plane and the line of sight. EMERGENCY POWER—Temporary source of limited electrical power used upon the loss of the normal power source. EXTERNALLY SYNCHRONIZED RADAR—Radar system in which timing pulses are generated by a master oscillator external to the transmitter.






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