| 摘要 |
PCT No. PCT/JP81/00207 Sec. 371 Date Aug. 23, 1982 Sec. 102(e) Date Aug. 23, 1982 PCT Filed Aug. 31, 1981 PCT Pub. No. WO83/00974 PCT Pub. Date Mar. 17, 1983.The present invention relates to the improved demodulation system which improves the noise characteristics for the demodulation of a wideband television FM signal. An adapter for improving the ratio C/N is provided at the output of a bandpass filter (7), and the output of said adapter is applied to a discriminator (14) which demodulates the FM signal, through a limiter (13). The adapter has a variable bandpass filter (8), the center frequency and the bandwidth of which are controllable, and said variable bandpass filter (8) is inserted in an FM signal path. The bandwidth of the variable bandpass filter (8) is controlled so that said bandwidth is wide when the input carrier level is high, and said bandwidth is narrow when the input carrier level is low. The center frequency of the variable bandwidth filter (8) is controlled so that said center frequency follows to the instantaneous frequency of the color sub-carrier component (3.58 MHz). A phase detector (10) is coupled with the input and the output of said variable bandpass filter (8) in order to derive the color sub-carrier component, and the output of said phase detector controls said variable bandpass filter through a narrow-band bandpass filter.
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