Telecommunications – Transmitter and receiver at separate stations – Single message via plural carrier wave transmission
Patent
1987-08-28
1990-01-09
Griffin, Robert L.
Telecommunications
Transmitter and receiver at separate stations
Single message via plural carrier wave transmission
455 72, 455212, 455205, H04B 1500, H04B 110
Patent
active
048933473
ABSTRACT:
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.
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Eastmond Bruce C.
Linder Donald L.
Griffin Robert L.
Krause Joseph P.
Motorola Inc.
Parmelee Stephen G.
Smith Ralph E.
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