| 摘要 |
PURPOSE:To allow the titled system to be used as an FM carrier lower than a low frequency carrier for a conventional system by providing a doubler means before an FM demodulation means in the FM demodulation system demodulating a low carrier FM modulation signal recorded on an information recording medium so as to suppress a bead disturbance due to moire existing in a demodulation signal. CONSTITUTION:The doubler means consists of a phase shift circuit giving a phase delay of npi/2 (n=0, 1, 2,...) and a multiplier. The input FM signal is divided into two, the one is subject to no modification and the phase of the other signal is shifted by the phase shifter 1 to be any of 0 deg., pi/2, pi, 3/2pi,... and the result is inputted to the multiplier 2. The output of the multiplier 2 is a signal doubling the input signal. The output of the multiplier 2 is divided further into two, the one is subject to no change and the other is delayed by a time tau at a delay device 3 and inputted to the multiplier 4. A demodulated signal and a carrier component multiplied by 4 is generated at the output of the multiplier 4. The carrier component multiplied by four is eliminated from the video signal and the result is extracted at the next LPF 5.
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