GMRS Repeater

Well my latest project is to set up a GMRS repeater for the Cedar Rapids metro area. I picked up a pair of Motorola GM300 mobile UHF radios, duplexer, and Zetron repeater controller. FCC issued our license which is WQPY702. The repeater pair is 462.600/467.600 no tone.  Now all we need is a site to put up the antenna.

I also bought some UHF Ericsson MDX mobile radios surplused from the West Virginia State Police off of Ebay. The first problem is to program them to our system. 

Programming the MDX radios requires GE TQ 3370 radio interface box which 1. is very expensive and 2. impossible to find.  I downloaded the schematic for the interface and determined its nothing more than a MAX232 level converter.

This is what I came up with:

Here is the microphone connector on the FRONT of radio.

Note Pin 1 is the lower right, programmer connections a Pin 4, Pin 5 and Pin 7. I used some pins from a DB9 male serial connector for the connection to the radio microphone connector.

The programming cable to the PC is a straight through 2-2, 3-3, 5-5, 6-6

Here is my perf board version of the MAX232 schematic:

To program you need to find a copy of the ProGrammer software. It took a few days Googling to find it but it's out there.

When the ProGrammer software prompts you to turn on radio simply hold volume down while pressing power button and the radio will display "PROGRAM".

That's all.