FM transmission receiving device null of color television

摘要

PURPOSE:To decrease a noise in an FM demodulated chromaticity signal by forming two types of FM modulated waves, which are a positive-phase FM modulated wave and an antiphase FM modulated wave, by the difference frequency between an input and an output in a one-line delay line, switching the FM modulated waves by a subcarrier, and making the switched FM modulated waves into FM demodulation. CONSTITUTION:The frequency difference (for a frequency shift) between the input and the output of a one-line delay line 28 is obtained at an intermediate frequency step, and the frequency difference is made into two types of frequency differences, which are a positive-phase frequency difference and an antiphase frequency difference. Further, the two frequency differences are switched with electronic switches 32 and 33 by a switch pulse, in which subcarrier signals cos omegasct and sin omegasct orthogonally cross, obtained from a FM demodulator 4 for every 1/2fsc, demodulated in FM demodulators 34 and 35 for respective cos omegasct side and sin omegasct side, and made into the chromaticity signal. On the other hand, the sum frequency of (the sum of the input and the output of) the one-line delay line 28 is demodulated at an FM demodulator 36, and the high frequency component of the output is used as the high frequency component of a luminance signal. Thus, the influence of the noise due to the FM demodulation of the chromaticity signal can be minimized, and the mixing of the high frequency component of the luminance signal into the chromaticity signal can be suppressed.