2013-04-21

Uniden GMR3040 squelch adjustment


I bought a bunch of Uniden GMR3040 two-way radios at US.

This model seems to be cursed by a squelch calibration defect - so that the radio is always receiving a static noise. In high-end devices the user can select the squelch level, but on this consumer devices it is factory set, and good luck with that.

So I had the option of returning them for warranty repair or try to fix it at home.

I opened it in the hope of finding some pots. And there they were.

Then it was just a question of try one by one to see what were they for.

RT404 Adjusts the squelch. That is the only thing I needed. Problem solved.

I figured out two more adjustments:

RT401 is able to adjust the frequency about +-70KHz.
L401 adjusts the FM demodulation.


You can see the frequency sweep while I give a full turn to RT401. This is measured with a calibrated RTL.


There are some more pots on the board. Probably for battery voltage measurement, VOX threshold, etc. If you know what any of them are for please leave a comment and I will update this article.

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