Duplex microwave equipment with a single microwave oscillator.

摘要

A microwave communication equipment comprises a frequency modulated microwave transmitter and a superhetrodyne receiver. Since the microwave osillator (12) is expensive it is desirable to use the oscillator (12) of the transmitter for frequency change (16) in the receiver but this introduces unwanted modulation into the received signals. This invention adds a cancellation signal (23,24,26) into the received signals so as to cancel the unwanted send-baseband introduced in the first frequency change. The output of a discriminator (20) passes to a correlator (27) which also receives send-baseband from delay (23). The output of correlator (27) adjusts controllable attenuator (25) to adjust the level of modulation applied to oscillator (12) and hence the level of unwanted modulation applied via mixer (16). The control loop transfers to microwave oscillator (12) either the modulation stability of VHF oscillator (26) in a preferred embodiment or the demodulation stability of receiver discriminator (20).