Power adjustment problem with converted 900 Maxtracs

[kchafin]

Hi:

I've converted three 900 Maxtracs to the ham band successfully using conductive pen method and it has worked great. I intend to use these radios as link radios on a repeater. I'm having trouble adjusting the power. When I adjust the power output using the RSS on all three radios, it goes down to the level I ask for. As soon as I set the power value in the radio and try to use it, the power output is full power. I cannot make the power change no matter what I set it for with the RSS. When I adjust the frequency with the warp adjustment in the RSS that works fine. Any idea on why I can't adjust the power? If I can't adjust the power with the RSS, I'm thinking of dropping the voltage on the 9.6V line to the PA with a resistor to force the PA to a lower power. If anyone has an idea of where I'm going wrong I would appreciate any assistance you could give me.

Thanks,

Ken
W6CPA

[PETNRDX]

This gets discussed periodically.
The "operating system" of the radio won't control the power out when you go out of band.
There are several ways to "adjust" the power control voltage.
All are hardware fixes.
I personally like the LM317 variable voltage regulator.
Others just use resistors.
This also happens to different versions of the GM300/MAXTRAC/RADIUS radios when you move below about 145 mhz, etc.

[kchafin]

Thanks for the info. I was unaware of this. I like the LM317 idea. I'm going to give it a try.

73,

Ken

[PETNRDX]

If you do a search of the forums there is probably suggestions on how to do it.
I just cut the power control line, built a LM317 circuit, and used a trim pot to get the exact power I wanted.
The odd thing about this seems to be that some radios do it and some don't.

[Big BOB]

Another reason you want to modifiy the control line is because of a timing circuit they use for the PA. If the radio is being used as a repeater or link where the transmitter stays on for exteneded periods the PA will shut down. It is not controlled by temperature, but instead by a preset time

[Max-trac]

....and put a big fan on it too. They get hot even when running lower power....

[w1ksz]

I have only found one of the three 900 MHz radios I converted has exhibited this anomaly. It was a trunking radio.

73, Dick, W1KSZ