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 DVRPTR.net 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!

Disabling internal controller on TKR-820

From Mark, N9WYS:

Remove the internal signaling unit. (I'm looking at the TX/RX Unit in the service manual, Page 83, and the Signaling Unit, Page 76.) Unplug both cables from the signaling unit and add the jumpers to the connector.

On CN6 of the repeater TX/RX Unit, or at the cable connector end for CN1 of the Signaling Unit, apply a jumper to pins 2&3, 8&9, 10&11.

Pin 2  = PTT
Pin 3  = KEY
Pin 8  = AFD
Pin 9  = DET
Pin 10 = AC
Pin 11 = GND

That way, if the external crashes, you can plug the internal back in and still be operational.  If the external controller is wired CORRECTLY to the 15 pin accessory plug, it WILL work properly. 

I've used the solid copper 24g telephone wire to short the connections, secured with black tape.  My personal preference was to insert the jumper wires into CN1 connector at the Signaling Unit end of the cable… to reverse the modification, all one needs to do it remove the jumpers and plug the Signaling Unit back in.

NEVER use the internal controller with an external controller. You are
asking for problems.

DVRPTR to TKR-820 cabling

Here's how I've cabled my DVRPTR.net board to a TKR-820 UHF repeater accessory port:

TKR, purpose, DVRPTR
3, tx mod in, 1 red
4, rx dis out, 4 black
8, PTT, 3 grey
11, grnd, 2 green
13, cos/rus, 6 blue

Also connect pin 1 to pin 11 on the TKR to disable the internal controller. You also should jumper the controller so that you don't create an unintended audio path.

Kenwood TKR-820 DSTAR LSB-208

I found this service bulletin one time, but I haven't been able to find it online since. I'm uploading it here so others will be able to access it. It is a simple mod for TKR-820 repeaters used for DMR or DSTAR. By removing a capacitor on the display unit, the output waveform to the modem is less distorted. I've seen only minor improvement in error rates, but every little thing helps.

To access the capacitor, you remove the top and bottom covers. Then remove the left and right top screws holding the front face in place. Tilt it down, and you have access to the capacitor. You do not need to take the knobs off, or remove the from face from the unit. Total time is less than 15 minutes to complete.

Good luck!

Ham radio with a low power radio

If you've been following my posts lately, you've seen more of a move from the "farm life" to the "ham life"...ham being amateur radio. I've re-kindled my interest in amateur radio. I sold the radio I purchased a year ago on ebay and bought a used Elecraft KX3. This is a truly modern software defined radio. It's quite the wonder...talk to the world with a radio that fits in your hand and an antenna made from 40 feet of wire.

Besides the technology differences between the FT897 I had before and the KX3, there's a shift in operational thinking. The FT897 is a 100 watt, bulky, mainly fixed based unit. Yes, you could mount it in the car and take it camping...but it certainly isn't something you want to pack around for a while. The KX3 is small - it fits in your hand. It is low power - 10 watts or so if you connect it to external power, but it shines running 5 watts or less off of 8 AA batteries.  While I do operate from my home office, I also enjoy sitting on the porch and listening for new people to meet.

In my few weeks of ownership, I've noticed a shift in my operating patterns. I'm spending more time doing CW (morse code). I'm still doing a little PSK. And I've made 3 voice contacts with a piece of wire temporarily strung up to a low tree branch. This weekend I worked a special event station in Georgia after hanging up my wire on my Mom's porch. It was pretty cool...

Sure, I can Skype all over the world. Need to get a message to a friend? Facebook or LinkedIn is probably my first choice. But when it comes to meeting new people, ham radio, and especially low power (aka QRP) operations are the way to go.