Building a MMDVM multi-digital mode repeater

Building a MMDVM multi-digital mode repeater- DRAFT 24/2/2017


Very draft. Will write more as I go.

Everything has arrived and I am starting to put it together.

Facebook and Yahoo

How to do everything

_Interfacing the CDM 1250 to MMDVM board.pdf in Yahoo files. For 1.01 board and updated files. (Good but had trouble connecting via the network. Will go back to full desktop)

DMR-UTAH MMDVM XFCE Raspberry Pi Image  *
*        by Chris Andrist, KC7WSU         *
* *
*  Another, includes CDM1550LS code plugs Posts on a number of guides. more guides. mmdvm/MMDVM_homebrew2.pdf

MMDVM hardware MMDVM and Duo Adrino. Arrived! Another source for modem. Bulk order kit.


List of suitable radios:

Radios I have:

MOTOROLA CDM1550LS+ UHF 403-470MHz Mobile Radio, 25W, AAM25RHF9DP6AN. Nice radios but steep learning curve programming them. However, mainly just need frequencies.

TTY MD-390 Seems OK for relatively inexpensive hand-held. I need a DMR TRX to test repeater. Again, programming not simple, but with a couple of others' code plugs, it seems to work ok.

SDR# and DSD+, SDR RX for DMR, DSTAR and other modes. Cheap way to get second RX for testing. Still working on getting it going.

ICOM IC-FR4000 repeater. Was given the repeater and will try to get it working too.

Other bits needed

  • Software- See tutorial- Github. On Windows and written to RPi SDcard.
  • Connectors for TRX- cheap repeater cable for connectors-eBay- arrived. Plugs are 16 pin, TRX are 20 pin. Just use in centre pins, with unused pins on outside on both sides.
  • Programming software for TRX-ether-Downloaded and running.
  • Programming cable for radio-eBay- Arrived. Steep learning curve for Motorola software.
  • Raspberry Pi- I think 2 is easier than 3- see tutorial. Have program on RPi and am contemplating the .ini configuration file
  • Duplexer - I have one that needs to be reduced in frequency. It uses BNC connectors on the cables. I bought some male to female BNC connectors on eBay. Adding one extra connector will electrically lengthen the cable in a simple manner. Should be close enough. Cavities need modifying by solding an extra piece to the resonator, which lows the frequency. Have done one of four and it works fine. They are pass-reject cavities, with a little piston trimmer capacitor to tune notch. Cavity frequency is changed with a screwed capacitive hat.

Tuning modem: Inexpensive tools

Tuning of the modem is covered in page 5 of F5UII's guide. An oscilloscope and spectrum analyser are used. However, many people don't have access to this equipment. However, there may be simpler and/or free ways to do this.

The RX input to the modem is modulated audio. The output to the TX audio that goes straight to the input of the amplifier????

Audio oscilloscope and spectrum analyser software

Many available. Probably work well with high quality 192 kHz USB soundcard. I have Asus Xonar.

Spectrum Lab:

SDR based spectrum analyser and tracking generator $120!

For tuning cavities and possibly modem.

Hotspots DIY


I have bought a DV4mini to get access to didital radio networks via handheld.


Seems ok, but not sure on DMR (via DMR+).
Access to Brandmeister seems limited?
Not pursued much, mainly interested in repeater.

Official? DMR sites Recently appeared??

Online streaming

Hose line is an online streaming platform for the HAM radio Digital Mobile Radio (DMR) Brandmeister network.

Handy to see who is active.

Looks useful


  1. Hi,
    Did you ever get the ICOM IC-FR4000 repeater working with a MMDVM?


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