| 摘要 |
PURPOSE:To give compensation to the phase modulation component of the IF signal and prevent the occurrence of buzz and buzz beat, by detecting the horizontal synchronous component contained in the aural FM detection signal and then giving contrarily the phase modulation to the local signal with the video signal when the horizontal synchronous component exists. CONSTITUTION:Both the IF signal sent from front end 2 and the local oscillation signal from 2nd local 6 are applied to mixer 5 to produce the aural IF signal. This IF signal is detected through aural FM detecting circuit 8 after amplified through aural IF amplifier 7, and then this detected output is applied to synchronous component detecting circuit 10 to detect the frequency component of an integer-fold the synchronous signal out of the detection output. And at the moment the frequency component is detected, the detection signal is applied to phase control signal producing circuit 11. And then the phase modulation is given contrarily to the video signal sent from video detector 4 to give the control to the oscillation signal to be applied to mixer 5 from local 6. Thus the compensation is given to the phase modulation component of the intermediate frequency signal. In this way, the occurrence of the buzz or buzz beat can be avoided for sound multiple demodulating circuit 9. |
