Eliminating Clock Noise In a ACC RC-96 controller
By Jeff DePolo WN3A

A friend of mine has an RC96 on a Micor repeater.  He complained about a slight amount of clock noise on the Tx audio.  It was there all the time, whether or not the squelch was open.  Now, I've had switching noise on RC85 and RC96's as the caps in the negative supply started to age, but this was different.  It was fairly low-level, but noticible if you listened for it. Anyway, long story short, I found the source of the noise.  I thought I'd pass it along in case you have the similiar noise on yours.

The noise was getting into the "direct Tx in" line (DVR connector pin 1). Left unterminated, the trace that goes to that pin makes a very nice antenna and sucks in a lot of clock noise.  Terminating it with a 4.7K resistor got rid of the noise completely. I found a convenient spot on the board to install the resistor; if you don't want to go through the aggrevation, just put the resistor in a DIN plug between pin 1 (TX audio mixer input) and pin 2 (the audio ground pin) on the DVR connector and plug it in.

                                                --- Jeff

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Jeff DePolo WN3A    Engineering Consultant
 

This page prepared by Kevin Custer  W3KKC

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