Build Your Own non-ICOM Dstar Repeater
After years of avoiding Dstar due to the high cost of an ICOM repeater, I discovered a repeater
could be built for a fraction of the cost. I did buy an ICOM handie-talkie and mobile to use with
my new repeater. However that too may change as some new projects are developed that will
allow digital signals to be generated without the need for an ICOM radio.
If you are the only Dstar radio owner in your area, a simpler solution may be to build a hot spot
or simplex node. There isn't any need to repeat your signal if your the only one around. A hot
spot is constructed just like this repeater except with only one GM300 and without the
duplexer. The GMSK modem has software settings for either simplex or duplex.
My repeater was made from two Motorola UHF GM300 mobile radios including an Astron RS-20
power supply and small duplexer. A GMSK modem, Dell GX-270 computer, some affordable
software and an Internet connection.
The GM300 mobiles are 25 KHz models and widely available with the commercial narrowband mandate
rapidly approaching. This radio has the famous 16 pin accessory connector and all required connections
are available without soldering connections inside the radio. The only modification needed was to make
sure jumper JU551 on the logic board is set to position A. This allows flat receive audio to be sent to pin
11. Don't overlook this modification as you will not be able to decode the digital data with it in the wrong
Flat transmit audio is sent to the radio on pin 5. No jumper change is needed for flat transmit audio.
I have also used the Motorola R1225 repeater module which can be programmed for 12.5 KHz
Dstar transmit deviation is around 1200-1500 Hz and is considered a 12.5 KHz mode. I have not
noticed any difference between using the R1225 in 25 KHz or 12.5 KHz mode.
Here is the MoenComm StarBoard GMSK modem. The enclosure
is a die-cast aluminum project box. I bought too many and have
extra if you are interested.
The USB cable is connected to the computer and also provides
power to the modem. A DB9 connector has the radio
Pin 3 PTT
Pin 5 Flat Tx Audio
Pin 7 Ground
Pin 8 COS (not needed for the StarBoard)
Pin 11 Receive Audio
Pins 15 & 16 (jumper if you want the speaker to work)
The GM300 mobile radio was designed for commercial
service and not for ham radio rag chewing. The PA heatsink
kept the radio cool for the commercial users that might
make a 45-60 transmission but not for a long-winded ham.
The transmitter I am using is a 45 watt UHF model turned
down to around 30 watts. An important feature of the GM300
transmitter for ham radio use, is the thermistor located in
the PA. If it gets too hot, the radio will begin to reduce power
output to reduce heat.
I still add forced air cooling to all of my repeater projects.
You can see another example of my desire to keep things
cool on my Mitrek repeater cooling page.
Here you can see a small thermostat snap disc fastened to
the transmitter PA. The disc will close at about 110F. They
are available on eBay for around $ 13.00 each.
Here is a picture showing the 16 pin connectors and antenna
Each cable only required three connections to the transmitter and
receiver. However extra wires were included just in case.
The modems I used before the StarBoard required COS from the
receiver. You can see that extra wire hanging from the connector.
Here are some good links for getting started building your own
I have just scratched the surface of the DIY non-ICOM repeater process. The important
thing to remember is if I can do it, so can you!
randy at wb0vhb.com
Motorola 16 Pin Connections