Noise reducing circuitry for single sideband receivers

Details Noise reducing circuitry for single sideband receivers Noise reducing circuitry for single sideband receivers

1982-05-06

1984-08-14

Bookbinder, Marc E.

Telecommunications

Receiver or analog modulated signal frequency converter

Squelch

455223, 455311, H04B 110

Patent

active

044661290

ABSTRACT:
Improved noise reducing circuitry for high frequency signal sideband (SSB) receivers is described that substantially eliminates interference caused by impulse noise from a noise source 160. The SSB receiver includes first and second mixers 102 and 106 intercoupled by a crystal filter 104 having a passband that is approximately the same as the noise bandwidth of the antenna circuitry 100 when the SSB receiver is tuned to the lower frequency in its frequency band. A second intermediate frequency (IF) signal from second mixer 106 is coupled to an IF amplifier 122 and a noise amplifier 126. An envelope decector 128 is coupled to the output of noise amplifier 126 and provides an output signal having a magnitude proportional to the envelope of the noise amplifier output. Automatic gain control circuitry 132 is coupled to the output of the envelope detector for generating a gain control signal that reduces the gain of noise amplifier 126 as the magnitude of the envelope detector output increases. An impulse detector 130 is also coupled to the envelope detector output for detecting the presence of impulse noise and generating mute control signal pulses when impulse noise is detected. The mute control signal pulses are coupled to an attenuator 124 which attenuates the output of IF amplifier 122 so that the impulse noise does not create audible interference in the speaker 154 of the SSB receiver.

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