| 摘要 |
A circuit is provided for detecting the level of noises in received FM signals in an AM/FM receiver which includes at least an FM intermediate-frequency amplifier, an FM detector connected thereto, an AM intermediate-frequency amplifier and an AM detector connected thereto. This FM noise level detecting circuit includes a frequency converter receiving the output of the FM detector for converting noise components contained in the output of the FM detector into a noise signal of the AM intermediate-frequency, which is in turn outputted to the AM intermediate-frequency amplifier, so that the converted noise signal is amplified by the AM intermediate-frequency amplifier and then detected by the AM detector to produce a DC signal. The signal thus obtained is not only representative of the level of the noise contained in the received FM signal, but also representative of the received FM signal strength.
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