Monday, December 1, 2014

Cabling a DVRPTR board to a CDM1550 for a DSTAR Repeater

I'm playing with a couple of CDM1550 radios to be used as another DSTAR repeater. I've had pretty good luck with the Kenwood TKR-820, although it can be very finicky. You're using early 80's technology with the Kenwood, where you're using 21st century tech with the CDMs.

Here's how I've cabled my board to two CDM1550 Motorola UHF radios:

CDM1550 (T=transmitter, R=Receiver), purpose, DVRPTR
T5, tx mod in, 1 red
R11, rx dis out, 4 black
T3, PTT, 3 grey
T7 and R7, grnd, 2 green
R15, cos/rus, 6 blue
T10/R10, ignition sense, connect to 12V

You'll also have to do some programming in the CDM:
1. Turn on the flat tx audio when using the external ptt line
2. Set accessory port 3 to be PTT when low
3. Set the tx power low (I'm using 10 watts, and keyed down for 20 minutes wasn't too hot on the heatsink)
4. Set the transmitter timeout to 180 seconds for each channel
5. Set the on/off to be the front panel button and also the ignition sense wire

You need to take pin 10 to 12V so that if the power supply goes off, the radios will power back on by themselves. Without this pin connected, a power failure will cause the radios to stay off when the power returns!

A big advantage of the CDMs is the ease at programming the frequencies. With the right software, it is a breeze. The problem, the software isn't cheap. Luckily I have the software available from my work at the fire station. 

For my setup, I put both the transmit and receive frequencies in both radios as simplex channels. That way, if my transmitter finals go bad, I can swap the accessory plugs, change the selected frequency on each radio, and be back on the air. Of course, if the finals go out, it likely is because of an antenna system failure or because I ran the transmitter too hard!

UPDATE: Here's a pdf version of the wiring diagram that Tom KJ9P created. Thanks Tom!

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