Localizer Range Rate Measurement System,
FEDERAL AVIATION ADMINISTRATION WASHINGTON DC SYSTEMS RESEARCH AND DEVELOPMENT SERVICE
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The FAA Wind Shear Project Office has determined that groundspeed is a desirable parameter for a wind shear detection system. This report describes range rate measurement equipment that meets both the accuracy and response time requirements for groundspeed on final approach. The cost of the described equipment is considerably less than current shelf hardware, e.g., INS and Doppler navigators, that also meet these measurement requirements. The described system provides one-way differential ranging, operating on the Doppler principal. The localizer carrier antenna pattern is modulated by a 5 KHz precision frequency controlled tone. This signal is received by the aircrafts ILS localizer receiver, and its demodulated tone is processed to measure the Doppler shift of the tone. The unique differential ranging processing method used in this equipment, which accurately measures frequency differences of less than one thousandth of a Hertz, is described in more detail. This system has been successfully flight tested several times, and copies of flight check recordings are shown in this report.