| 摘要 |
PURPOSE:To accurately perform the detection of dropout period, by providing a specific means which detects and uses an FM signal having a frequency two times that of an FM video signal being a part of an FM demodulator output. CONSTITUTION:An FM video signal from an input terminal 1 passes through a band filter 2 and a delay type FM demodulator 3 and obtains an FM signal output having a frequency two times the frequency of a base band video signal and an input FM viceo signal. The video signal is separated at a low pass filter 4 and applied to an output terminal 5, and the FM signal is separated at a high- pass filter 14, amplified at an amplifier 15, applied to a discriminating circuit 62a for the presence/absence of a prescribed frequency signal, where dropout is detected and outputted at a terminal 7. Thus, the conventional limiter circuit matching is not required, the time constant of a retrigger multivibrator 11 can be shortened, and a short dropout can surely be detected. |
