1402885 Radio navigation STANDARD TELEPHONES & CABLES Ltd 24 July 1973 [3 Aug 1972] 36231/72 Heading H4D In a receiver for a Doppler-effect beacon which radiates sequentially from an aerial array the received bearing input signal frequency is changed to a predetermined fixed frequency (whatever the bearing) such that for all bearings the ensuing spectrum contains its two most powerful lines one on each side of the fixed frequency. In the embodiment a voltagecontrolled local oscillator VCO is coarsely controlled by a wide-band discriminator WBD and then by a differential detector DD fed from narrow-band filters NBF1, NBF2. A counter CO yields a measure of bearing (azimuth or elevation).
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