| 摘要 |
PURPOSE:To simplify the circuit constitution, by using positively a sound SIF signal of television broadcast system so as to eliminate the need for an SIF detecting circuit and an FM modulation/demodulation circuit required in conventional systems. CONSTITUTION:An oscillating frequency of a local oscillator 50 is selected as (4.5MHz+f3), since the SIF frequency of the NTSC system is 4.5MHz, in taking the center frequency of a recorded sound FM signal as f3. In applying an output of the local oscillator 50 and the SIF signal to a mixer 51 having a load of center frequency f3 to take a difference between both the frequencies, the deviation and a sound FM signal with unchanged deviation and emphasis characteristic and f3 as the center, and the signal is recorded on a video track in the spectrum as shown in Figure by applying the said signal to a recording amplifier 7. The center frequency of a BPF53 is taken as f3 at the reproduction, the sound FM component only is extracted and the sound reproducing FM signal equivalent entirely to the SIF signal at the receiving is obtained from a mixer 54. |
