| 摘要 |
PURPOSE:To reduce distortion and noise due to band limit of an FM wave, by synthesizing modulated audio subcarriers, after a video signal passes through an amplitude limit circuit so as not to prevent an instantaneous amplitude of the video signal through a pre-emphasis circuit from exceeding a prescribed value or more. CONSTITUTION:A video signal of a waveform (a) becomes a waveform (b) after passing through a pre-emphasis circuit 21, and a waveform (e) through an amplitude limit circuit 28. The frequency shift at the output side of an FM modulator 24 is within a band of a BPF25 and no instantaneous amplitude is lowered. Thus, the waveform becomes a waveform (f) through a de-emphasis circuit at the reception side and almost no distortion is appeared. On the other hand, an audio subcarrier signal obtained from a terminal 11 is applied to a synthesis circuit 23 after the circuit 28, then no effect is imposed by them. As conventionally, without the LIM28, the demodulation waveform is as (c), and a distorted waveform (d) is obtained after the reception, but by providing the LIM28 additionally, when a limited band of transmission circuit like satellite communication is effectively used, unpleasant distortion or click is eliminated. |
