| 摘要 |
A communication circuit comprises sources of program material, carrier frequency signal sources and first modulators for modulating the carrier frequency signal sources with the program material sources. Each of the first modulators has a first input terminal, a second input terminal and a first output terminal. Terminal apparatus for demodulating program material-modulated carrier frequency signals include automatic gain control (AGC) circuits having AGC bandwidths. One of the program material sources is coupled to the first input terminal of a respective first modulator through a second modulator having a third input terminal, a fourth input terminal and a second output terminal. A source of signals having a frequency in the AGC bandwidth is coupled to the third input terminal. The source of program material is coupled to the fourth input terminal. The second output terminal to the first input terminal.
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