| 摘要 |
A voltage variable oscillator feeds an FM modulated signal to be transmitted to an orthomode transducer connected to a dual polarization antenna, another port of the orthomode transducer feeding received FM signals to a single ended mixer, the output of which is passed through an FM receiver. The orthomode transducer leaks a portion of the transmitted wave to the single ended mixer, for use in lieu of a local oscillator, thereby limiting the requirements to a single microwave oscillator. The output of the FM receiver is applied to a cancellation circuit where the transmitter modulation is cancelled from the FM receiver output in response to delayed transmitter input signals. The output of the cancellation circuit comprises the receiver output, and is used as the signal input of a phase sensitive demodulator, the phase reference input of which is the delayed transmitter modulation, the phase sensitive demodulator controlling the gain of a variable gain amplifier so as to provide complete closed loop automatic gain control, limiting the frequency excursion of the oscillator in such a fashion as to permit complete cancellation of the transmitter input modulation from the receiver output modulation, despite any variations in circuit scale factor. In a system employing more than one transceiver having the same receiver IF frequency, an automatic frequency control loop is provided in one of the transceivers, and nominal or stabilized frequency control is applied in the other, whereby one frequency is slave to the other separated by the IF frequency; in addition, means are provided in conjunction with the cancellation circut to accommodate the opposite polarity of the discriminator output in two different transceivers communicating with one another resulting from discrimination of opposite sidebands.
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