| 摘要 |
An improved FM communication system is disclosed in which noise bursts and pops in the audio output of the receiver, due to weak and Rayleigh-faded signals, are minimized by selectively attenuating the audio signal in the receiver. The amount and rate of attenuation for the receiver noise reduction circuits is determined by a control signal derived form either the average discriminator noise at frequencies above 3 kHz, or from a received RF signal strength indicator, or a combination of both. The audio output is attenuated during weak signals or Rayleigh fades only when the attenuation control signal increases above a predetermined signal-to-noise ratio threshold. Also described are further improvements to noise attenuation devices used in combination with the receiver noise reduction circuits to enhance audio quality in particular applications, e.g., FM repeater systems which may incorporate multiple transmitters in a simulcast configuration.
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