| 摘要 |
PURPOSE:To make inconspicuous a noise due to echo distortion by attenuating high- frequency components to a prescribed amount by detecting the peak value of an AM component included in an IF signal by detecting the AM component by an AM detector and then by holding the detected peak value. CONSTITUTION:When echo distortion is generated owing to a multipath, an AM component appears in IF signal (a) AGC-amplified by an IF amplifier. This AM component is extracted as a sine wave by removing an FM component by AM detector 7 to extract a half-wave component. Further, detector 7 extracts the half- wave component. Then, smoothing circuit 15 smooths the signal. Its smoothing output is waveform-shaped 16 into a DC signal by waveform shaping circuit 16 over the period when the AM component is detected. For example, if the output rises at level H, high-cut filter 11 is put in operation via the switch of control circuit 9 to attenuate the high frequency component of an FM demodulation output from IF amplifier 3 by a prescribed amount, thereby making inconspicuous a noise due to the echo distortion. |
