FM receiver having improved audio quality in response to Rayleigh faded received signals
First Claim
1. In an FM receiver having an improved audio output response to Rayleigh faded received signals including means for amplifying a received FM signal, means for limiting said amplified FM signal, and discriminator means for converting the limited FM signal into an audio signal, the improvement comprising:
- means for generating a control signal corresponding to the average magnitude of the received signal; and
AGC means for controlling the magnitude of amplification provided by said amplifying means so that a predetermined level of limiting by said limiting means is maintained in response to said control signal, said predetermined leveloof limiting being within the range of 5-20 dB of limiting.
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Abstract
The present invention minimizes noise pops due to Rayleigh fades by controlling receiver gain relative to the average received signal strength so that only a predetermined level of limiting occurs prior to the recovery of the audio information. The amount of limiting is selected so that a significant Rayleigh fade will cause the amplified IF signal to drop below the limiting level and enter the linear amplification region. During the fade the magnitude of the signal provided to the discriminator decreases thereby decreasing the discriminator'"'"'s output and minimizing the magnitude of the audio pop. Additional minimization of the subject noise pops is achieved by utilizing a discriminator which has a square law transfer characteristic so that the recovered audio level will decrease 2 dB for every 1 dB decrease in input signal level.
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Citations
21 Claims
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1. In an FM receiver having an improved audio output response to Rayleigh faded received signals including means for amplifying a received FM signal, means for limiting said amplified FM signal, and discriminator means for converting the limited FM signal into an audio signal, the improvement comprising:
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means for generating a control signal corresponding to the average magnitude of the received signal; and AGC means for controlling the magnitude of amplification provided by said amplifying means so that a predetermined level of limiting by said limiting means is maintained in response to said control signal, said predetermined leveloof limiting being within the range of 5-20 dB of limiting. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A receiver having an improved audio output response to Rayleigh faded received FM signals comprising:
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means for amplifying the received FM signal; means for limiting said amplified FM signal; discriminator means for converting the limited FM signal into an audio signal; and means for maintaining a predetermined limiting level relative to the average amplitude of the received signal, said predetermined level of limiting being within the range of 5-20 dB of limiting. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15)
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16. A method for minimizing noise bursts in the audio output of an FM receiver due to Rayleigh faded received signals comprising the steps of:
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receiving an FM signal; amplifying the received signal; limiting the amplified signal prior to converting the FM signal into an audio signal; and maintaining a predetermine level of limiting relative to the average amplitude of the received signal, the predetermined level of limiting being within the range of 5-20 dB of limiting. - View Dependent Claims (17, 18, 19, 20, 21)
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Specification