| 摘要 |
PURPOSE:To attain both actions of a station selecting action and an FM negative feedback action only with one frequency mixer and one voltage controlled oscillator respectively by overlapping a demodulating signal to the tuning voltage impressing terminal of a voltage controlled oscillator so as to be the negative phase and operating this as an FM negative feedback circuit. CONSTITUTION:By a frequency mixer 3, a high frequency FM modulating signal is converted to an intermediate frequency signal, an unnecessary signal is removed from the intermediate frequency signal by a band pass filter 7, a modulating signal is demodulated from the intermediate frequency signal to remove the unnecessary signal by a frequency discriminating device 10 and a demodulating signal is negative-fed back to a tuning voltage impressing terminal 5 of a voltage control oscillator 4. Thus, one frequency mixer for selecting a station and one voltage controlled oscillator are respectively used, the demodulating signal is overlapped to a tuning voltage impressing terminal for control of a voltage controlled oscillator so as to be the negative phase, this is operated as an FM negative feedback circuit, and whereby, both actions of a station selecting action and a threshold extension action can be executed.
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