| 摘要 |
PURPOSE:To hold always a carrier level of an output signal of an FM modulator by connecting an output section of an FM modulator to a band-pass filter via a variable gain automatic control amplifier and controlling the gain of the amplifier so that the output level of the band-pass filter is constant. CONSTITUTION:The variable gain automatic control amplifier 7 connected between the FM modulator 4 and the band-pass filter 6 is subjected to gain control by using a carrier signal extracted at the filter 6 so as to make the carrier level constant. Thus, even if the level of the input signal to the FM modulator is excessive and the frequency shift is large, the carrier level of the FM modulator output section 2 is kept always constant. For example, a supervisory circuit 8 supervises the output carrier level of the FM modulator and controls the gain of the variable gain automatic control amplifier 7 to keep the carrier level of the FM modulator output signal constant.
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