| 摘要 |
A double super heterodyne FM receiver having a first local oscillator for deriving a first intermediate frequency signal from an FM input signal, tuning means for varying the frequency of the first local oscillator to tune the FM receiver to a predetermined frequency, a second local oscillator for deriving a second intermediate frequency signal from the first intermediate frequency signal, an FM detector for demodulating the second intermediate frequency and means for processing the demodulated signal, means for deriving the direct current component of an output signal occurring at a point after the FM detector, first control means for controlling the frequency of the second oscillator in response to the direct current component so that the direct current component is reduced to substantially zero to thereby lessen shock noise during the tuning of the receiver, second control means responsive to the tuning means being operated to tune the FM receiver so that the control means controls the means for deriving the direct current component to thereby derive a first low frequency range as the direct current component, the control means also being responsive to the tuning means no longer being operated so that a second low frequency range less than the first low frequency range is derived as the direct current component. The receiver may also include a stereo demodulator whereby shock noise and accordingly multi-stage coupling capacitance in the output stages may be eliminated by feeding the direct current component back from a point after the stereo demodulator to control the frequency of the second oscillator.
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