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    • 7. 发明授权
    • FM communication system with improved response to Rayleigh-faded
companded signals
    • FM通信系统对瑞利衰落的压缩信号的响应改善
    • US4893347A
    • 1990-01-09
    • US90982
    • 1987-08-28
    • Bruce C. EastmondDonald L. Linder
    • Bruce C. EastmondDonald L. Linder
    • H04B1/10H03G3/20H03G3/34H04H20/67
    • H03G3/3052H03G3/344H03G3/345H04B1/1027H04H20/67
    • An improved FM companding 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 prior to expansion. The amount and rate of attenuation for the noise reduction circuits is determined by a control signal derived from 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. Preferably, attenuation increases at a rate greater than the decrease in the received signal strength. The invention includes a circuit for modifying the expansion characteristics of the expandor to minimize signal clipping in the output audio stage of the receiver due to limited dynamic range.
    • 公开了一种改进的FM压扩通信系统,其中由于弱和瑞利衰落的信号,接收机的音频输出中的噪声突发和流行通过在扩展之前选择性地衰减接收机中的音频信号来最小化。 噪声降低电路的衰减量和速率由通过频率高于3kHz的平均鉴别器噪声或接收到的RF信号强度指示符或两者的组合导出的控制信号确定。 只有当衰减控制信号增加到高于预定的信噪比阈值时,音频输出在弱信号或瑞利衰减期间被衰减。 优选地,衰减以大于接收信号强度的降低的速率增加。 本发明包括用于修改扩展器的扩展特性的电路,以使接收机的输出音频级中的信号限幅最小化,这是由于有限的动态范围。