GM300 PA Swap?? Help please.

[eagle844]

I have a GM300 M04GMC29C3. WE know that is a 2 watt radio. I have a GM300 UHF that does 40watts with a dead receiver. Is there a way to swap the PA? I would like to have the wattage, 2 watts just does not do it on UHF.

Thanks so much for your help,

Mike

[wavetar]

The easiest thing to do would be to swap the RF board into the 40-watt unit & then go through the 'new RF board' alignment in the service portion of the RSS.

[Will]

Use the replace power amp section in the alignment section of the RSS.
This sets the transmitter power outpot at several points across the band.

This is all you would need when replacing power amps, even different power PA decks.

[eagle844]

So, Let me get this straight.
Option 1-- Replace the RF board and go through the alignment.
Option 2-- Replace the PA and go through the PA alignment.

How do I make sure the alignments are good without any test equipment?

Thanks much,

Mike

[wavetar]

So, Let me get this straight.
Option 1-- Replace the RF board and go through the alignment.
Option 2-- Replace the PA and go through the PA alignment.

How do I make sure the alignments are good without any test equipment?

Thanks much,

Mike

I've never put a 40 watt PA onto a low-powered GM300 model...but if Will says it works, then it's a safe bet it does. My suggestion does require a lot more RSS alignment, and requires a very specific procedure, so go for swapping the PA.

If you have no test equipment whatsoever, then you have no way of knowing if the alignments are good. At the very least, you'd want a good watt meter with proper 50-ohm load to check the TX power at each of the softpot TX power frequencies.

[Bill_G]

If you don't have test equipment, then swapping rfpa sections is the easier way to go. You still have to take the whole radio apart, but at least your freq and dev settings will stay intact. Where your tx power will land is hard to say, but it should work without any problems.

[chartofmaryland]

This should work,

The only thing that comes to mind is there may not be enough control voltage to tell the PA to come to full power even with alignment.

Worth the try, I have converted a number of 25 watt to 40 watt and found the output voltage kept the unit from reaching much more than 36 watts without some minor modifications to get the whole 40 watts, where with the factory unit the output went from 6-51 watts as a true 40 watt model. I also added the R1225 heat sinks to those 40 watt units so with the lumpy heat sink the RF board was kept happy.

Give it a try and follow the alignment as this best sets the voltage control of the PA.

Also, what is the fate of the 2 watt RF boards?

CoM

[eagle844]

Fate? Well, the 2watt radio works great, except the wattage. It do all I need it to do and for features. I just cannot talk more than very, very short distance. So, I need the wattage. Even if the watts were not a full power model, it still would work better than that 2 watt.

The 25 or 40 watt radio has a dead RF receiver. I am not sure what is wrong with it. I did place a meter across some diodes and did get an open reading on the specific ones that I read about. The article was saying that if the radio get too much RF exposure that several diodes and a crystal would go bad and need to be replaced.

On that note, my goal was to make a more powerful radio to use and not have both setting on a shelf.

I do not know much about the GM300's. But from my understanding about the Maxtrac's, the RF board does 2 watts. The PA does the rest and makes the final wattage 25 or 40. Is this the same with the GM300's?

So, My best option would be the PA swap. This would be the easiest without test equipment. I do not mind getting less wattage than a factory models.

Thanks so much,

Mike

[PETNRDX]

The RF boards on the Maxtrac, Radius, and GM300 don't put out anywhere near two watts.
I don't recall from memory, but it is more like a half a milliwatt out from the RF board.
The PA's first gain stage puts out something like 300 milliwatts. (all versions )
Then on the 2 watt PA there is a "final" stage that can put out around 4 W.
The 20 and 40 W PA's have additional sections that increase the 2 to 4 watt out up to either 25 or 40.
Your best bet is to have someone with the test equip. swap the PA's for you if you are unsure.
In any case, the PA swap is likely easier than RF board.

[Will]

PETNRX is correct.
The RF Power Amplifiers do have more stages and a different output transistor depending on the power output rating.

The LPI 2 watt PA will do up to 8 watts. The bottom line is: The RF board IS the same.

So, Let me get this straight.
Option 1-- Replace the RF board and go through the alignment.
Option 2-- Replace the PA and go through the PA alignment.

How do I make sure the alignments are good without any test equipment?
Thanks much,
Mike

Just replace the Power Amplifier, PA, and do the PA alignment. Option 2.

You will need a wattmeter and a dummy load on the radio for the alignment and tests.

[Satelite]

Hello :
Sorry to butt in .
The topic is pretty much on target but i just wanted to point out to the original poster that along with the watt meter and dummy load that a DOS type computer with the proper RSS program and RIB and Cable will be needed to set the pa wattage settings ect.
Satelite