| 摘要 |
PURPOSE:To simplify and miniaturize a noise detecting circuit by detecting echo distortion while AGC over an FMIF signal is increased and by detecting the lowering of an electric field when the AGC increase becomes ineffective owing to a drop in signal level. CONSTITUTION:When antenna-received electric field is above a prescribed voltage in case of multipath reception, an AM component generated as fluctuations of amplitude of an AGC amplification output owing to echo distortion is detected and smoothed 11, and the AM half-wave component is detected 12 and smoothed 13 to be inputted to NOR gate 14 as an echo distortion detection signal. Next, when the antenna-received electric field is below the prescribed voltage, the echo distortion is detected while AGC over an IF signal amplified by FMIF amplifier 8 is increased; and if the AGC increase becomes ineffective owing to a drop in signal level, a decrease in amplitude is detected by AM detector 10, smoothed 18 and phase-inverted 19 to generate a voltage-drop detection signal. Consequently, the noise detecting circuit is simplified and miniaturized. |
