Hipo, These radios should work well for you but you will need to watch the heat issue. I put mine in a 5 RU deep cabinet and fabricated a tray mounted in the rear of the cabinet on which I placed a 10mm fan blowing directly on the cooling fins. I also placed a 40mm fan on the back of the cabinet and a 40mm hole, with louvers, in the front side of the cabinet. I can e-mail you pictures during the weekend if you desire. The tray makes a great location to mount the mini controller and fuse bank. Use ball bearing fans for maximum life.
If the heat is still an issue, you can remove the final and use just the driver. This will produce 5 to 10 watts output to drive a 100% duty cycle PA. Just pull the final, jumper the base to collector points on the board, and remove the B+ choke at the collector. You will also need to replace a couple of resistors in the current sensing circuit. Just compare the 10 watt version to the 40 watt version's schematic and you'll see the differences. You'll still need the fans as the driver produces a lot of heat. You shouldn't need to retune the front end unless you are operating outside the programming range of the radio. In this instance, I've had good luck touching it up with just a SINADDER and RF generator. As for the squelch, I'd suggest disabling both the squelch and PL and using an aftermarket unit like the ComSpec CTCSS board to create PTT. It improves the system PTT sensitivity by about 6dB, minimizing momentary drop-outs due to mobile flutter. I got 6dB SINAD key-up sensitivity on the crossband link radios I built using this configuration. Use the flat unfiltered descriminator audio from the receiver to feed the controller/transmitter audio input. Refer to the service manual for the correct jumpers and settings as I can't recall and am not home to look it up. Good luck, Scott Madison, W1NB --- In [email protected], "hb9ibg" <[EMAIL PROTECTED]> wrote: > > Hello friends > I have recently obtained a few Motorola GM300 radios in faily good shape > and very reasonable price. I plan to take them to my home country,CX, > where where they will hopefully replace ageing equipment in several > repeaters. > I would like to find the alignement procedures, in particular for the > receiver. I bought the original Service Manual, nothing in there. > I have made a test bench repeater in a back to back configuration, > seems to work beautifully, but I have read in the past that high > TX temp might be an issue. > I have noticed that setting the squelch past the closing point reduces > sensitivity, is it possible to leave only the CTCSS and the squelch > fully open? > I plan to use some kind of controller because ID every 10min is > mandatory in CX. > > I am usually on HB9GE-R Echolink repeater, 6 hours at least time > difference.(node 193835) > Many thanks > Hipo >
