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NOISE BLANKERS/NEW AND OLD

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    K0YNE
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    BACK IN THE OLD DAYS, PROBABLY JUST TWO  OR THREE DECADES AGO, NOISE BLANKERS WERE
    PRIMARILY DESIGNED TO ELIMINATE OR REDUCE THE EFFECTS FROM SPARK PLUG NOISE. FORD
    VEHICLES WERE EXTREMELY BAD ABOUT SPARK PLUG INTERFERENCE IN MOBILE HAM RADIOS.
    IN THOSE DAYS, THE NOISE BLANKER WAS GENERALLY FIXED AS TO THE TIME LENGTH OF THE SPARK.
    THE NOISE BLANKER WAS FOUND IN THE AUDIO CHAIN AND COULD HAVE BEEN AFTER DETECTION.
    THESE WERE GOOD TO EXCELLENT NOISE CANCELLING CIRCUITS, SO AN OPERATOR COULD ELIMINATE OR GREATLY REDUCE THE POP OF THE SPARK IN THE SPEAKER.
    IN LATER YEARS, THE CIRCUIT WAS MOVED FROM THE AUDIO AREA AND EMPLOYED NEAR THE RF AND MIXER STAGES, THUS REDUCING OR ELIMINATING SPARK PLUG NOISE AND OTHER LESS COMPLEX NOISE WAVE FORMS WITH ADJUSTMENTS TO SHORTEN OR LENGTHEN THE NOISE'S TIME PERIOD.  THIS WAS AND IS
    NOW MUCH MORE BENEFICIAL , BECAUSE NOW THE DISRUPTING INTERFERENCE CAN BE REMOVED AND
    THE “IF” AMPLIFIERS CAN RECOVER THE GAIN WITHIN THE CHAIN. AT THIS POINT THE AGC (AUTOMATIC GAIN CONTROL) WON'T BE MASKED BY THE ENGINES POPPING NOISE FROM SPARK PLUGS AND THE AGC CAN RESUME ITS RISE AND FALL WITHIN THE BAND PASS AND ALLOW GAIN THRU THE AMPS TO AMPLIFY WEAK SIGNALS AGAIN OR LOWER THE GAIN ON STRONG SIGNALS.

    THE CIRCUITRY IS SIMILAR TO THE “GREEN SCREEN TECHNOLOGY”  WHEN SIGNALS ENTER THE RF AMP AND MIXER CIRCUITS TO BE PASSED DOWN THRU THE “IF” (INTERMEDIATE FREQUENCY) CHAIN , AND IF THERE IS A SPARK PLUG INTERFERING FOR EXAMPLE, THEN AS IT LEAVES THE RF AMP AND INTO THE MIXER, THE IF SIGNAL IS SAMPLED AND PASSED THRU AN INVERTER STAGE. THE INVERTER STAGE KEEPS THE AMPLITUDE OF THE INVERTED SIGNAL AND 180 DEGREES OUT OF PHASE  AS THE SIGNAL IS FOUND TRAVELING DOWN THE IF BANDPASS. SINCE THE SAMPLED INVERTED NOISE PULSE WILL BE BEHIND
    IN “TIME” COMPARED TO THE SIGNAL IN THE BANDPASS OF THE “IF”. A SLIGHT DELAY WILL HAVE TO
    BE PLACED IN THE BAND PASS OF THE “IF” AT THE POINT WHERE THESE TWO SIGNALS THAT ARE 180
    DEGREES OUT OF PHASE WITH EACH OTHER, BUT AT THE SAME AMPLITUDE AS EACH OTHER.
    WHEN THE TWO ARE REJOINED ALONG THE “IF” BANDPASS CHAIN, THE TWO SIGNALS MET AND THE
    180 DEGREE DIFFERENCE PROVIDED A CANCELLATION OF THE OFFENDING “POP” OF THE SPARK PLUGS.
    PAUL K0YNE

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