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GM300 Mod levels

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GM300 Mod levels

Postby sambo521 » Wed Nov 08, 2017 1:24 pm

Hey Guys,
I have two GM300 vhf radios that appears to be setup for 12.5Khz spacing.
The mod measures 2.5Khz on my service monitor, and going into mod alignment in RSS I max out the mod and all I get is +/- 3khz deviation.
The model number of both radios are: M43GMC29C2AA with a HLD8031A RF Board.
This should be a +/-5Khz capable radio unless I'm missing something.
Any suggestions?

P.S. It's entirely possible someone has altered these radios either by software or physically.
Sam Hunter

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Re: GM300 Mod levels

Postby jackhackett » Wed Nov 15, 2017 12:56 pm

There should be two pots on the RF board, R164 for Reference Mod and R302 for VCO Mod. You may just have to adjust them, but if someone did a conversion on it they would probably have changed some of the associated fixed resistors. As I recall they didn't generally go all the way down to 2.5kHz without changing some resistors.
If it was converted it would probably also have the IF filters changed as well. Have a look here and see if the radio has the D or F filters (should be marked on them) and check the resistor values against the charts. ... -kits.html

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