NOISE BLANKER WITH VARIABLE RATE-SHUT-OFF AND/OR VARIABLE BLANKING THRESHOLD LEVEL

摘要

NOISE BLANKER WITH VARIABLE RATE SHUT-OFFAND/OR VARIABLE BLANKING THRESHHOLD LEVELABSTRACTA noise blanker circuit for a stereo radio receiver isdisclosed herein. The noise blanker circuit detects noiseimpulses in a received radio signal. When the magnitudes ofthese detected noise impulses exceed a predetermined thres-hold level corresponding noise blanking pulses are producedwhich are coupled to a gate means. The gate means receivesthe received radio signal and selectively passes and blocksthis signal in response to the noise blanking pulses suchthat the output of the gate means is essentially free ofnoise impulses. A manually adjusted actuator is providedfor selectively altering the predetermined threshold levelof the noise blanker circuit such that the most efficientmode of noise blanking can be implemented. In addition,rate shut-off circuitry is provided to prevent the pro-duction of noise blanking pulses when the detected noiseimpulses occur at a repetition rate exceeding a maximumrepetition rate. The manually adjustable actuator alsoselectively determines the value of this maximum allowablerepetition rate and thereby also selectively implements themost efficient mode of noise blanking. The manually adjust-able actuator is illustrated as comprising either the tonecontrol actuator or the stereo-monaural selection switchactuator of a radio receiver, whereby control of the noiseblanker circuit is implemented without adding an additionalcontrol to the stereo radio receiver. In addition, anembodiment of the present invention illustrates the use of astereo decoder means of the stereo radio receiver to selectthe predetermined threshold level and/or the maximum repetitionrate of the noise blanker circuit.