| 摘要 |
A communication circuit comprises a plurality of sources of program material, and a plurality of modulators for supplying a plurality of carrier frequency signals. Each modulator is modulated by a respective one of the sources of program material. Each of the program material sources is coupled to a respective modulator. The program material-modulated carrier frequencies are coupled in the circuit. Terminal apparatus is provided for demodulating at least one of the program material-modulated carrier frequency signals. The terminal apparatus includes automatic gain control (AGC) circuitry having an AGC bandwidth. The terminal apparatus is coupled to the circuit. One of the program material-modulated carrier frequencies is coupled in the circuit through a variable attenuator having an attenuator control signal input, a program material-modulated carrier frequency input, and a variably attenuated program material-modulated carrier frequency output. An oscillator generates at an oscillator output a signal having a frequency within the AGC bandwidth. Said one of the program material modulated carrier frequencies is coupled to the program material-modulated carrier frequency input. The oscillator output is coupled to the attenuator control signal input. The variably attenuated program material-modulated carrier frequency output is coupled in the circuit.
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