How to Make a MMDVM Digital Repeater

Since the release of the MMDVM in early 2016, Johnathan Naylor's (G4KLX) creation has put the power back into the hands of radio operators around the world. This simple hardware and software combo can interface radios to a computer—like a Raspberry Pi—turning normal analog radios into digital radios.

After following this guide, you will be able to put together a multimode amateur digital repeater or high-powered hotspot that can be connected to the internet for worldwide digital communication.

What is MMDVM?

MMDVM stands for Multi-Mode Digital Voice Modem. It's a hardware board that works with the MMDVMHost software to convert analog audio to and from digital voice formats. It supports the following digital modes:

• D-Star
• DMR
• Yaesu System Fusion
• P25 Phase I
• NXDN 4800
• POCSAG (paging)

The MMDVM-Repeater board differs from a hotspot board in that it doesn't have a radio built onboard. Instead, it uses cables to wire directly into the I/O pins of one or two external radios.

Hotspot vs. Repeater

Feature	Hotspot	Repeater
Radios	1 (low power)	1 or 2 (full power)
Coverage	Room/house	Neighborhood/city
Duplex	Simplex only	Simplex or duplex
Purpose	Personal access	Community infrastructure

What You'll Need

Hardware

1. Raspberry Pi (3B+, 4, or 5)
2. Micro SD card (16GB+ recommended)
3. MMDVM board (choose one):
   • STM32-DVM
   • Zum MMDVM
   • Micro-Node TEENSY
4. 1 or 2 analog radios with a 9600 baud port or discriminator tap:
   • A simplex node uses 1 radio
   • A duplexed node uses 2 radios + a duplexer
5. Cables to connect your radio(s) to the MMDVM board
6. Cooling fan — duty cycle management is critical

Software

• WPSD (formerly Pi-Star) — the recommended firmware image
• MMDVMHost — the modem host software
• stm32flash — for firmware updates

Choosing a Radio

This is the most critical decision. Keep these factors in mind:

• Duty cycle: The radio will be transmitting continuously. Consumer-grade radios overheat quickly.
• Cooling: A fan is mandatory for repeater operation.
• Programming: Motorola radios are excellent but require proprietary software. Older Icom or Kenwood radios are viable alternatives.

Popular choices:

Radio	Use Case	Notes
Yaesu DR-1X	Duplex repeater	Must not be FR-model or DR-2X
Motorola CDM series	Single or duplex	Needs programming software
Icom IC-F series	Single or duplex	Easy to cable
Kenwood TK-x90 series	Single or duplex	Good 9600 baud port

If you don't have access to programming software for commercial radios, look for radios with front-panel programming capability.

Step 1: Prepare the Raspberry Pi

Flash WPSD to your micro SD card:

# Download the latest WPSD image
wget https://wpsd-swd.w0chp.net/WPSD-SWD/WPSD-Images/releases/...

# Flash to SD card (replace /dev/sdX with your card device)
sudo dd if=WPSD-*.img of=/dev/sdX bs=4M status=progress

Insert the SD card, connect the MMDVM board to the GPIO header, power on, and SSH in:

ssh pi-star@pi-star.local

Default credentials: pi-star / raspberry.

Step 2: Cable the Radio

Connect your radio to the MMDVM board. The wiring depends on your specific radio, but the general pinout is:

MMDVM Pin	Radio Connection
TX Audio	Modulator input
RX Audio	Discriminator output
PTT	PTT line
GND	Ground
COR/COS	Carrier detect

For a 9600 baud radio, connect directly to the flat TX/RX audio ports. For a discriminator tap radio, you'll need to tap into the unfiltered audio before the de-emphasis circuit.

Step 3: Configure MMDVMHost

SSH into the Pi and edit the configuration:

sudo nano /etc/mmdvmhost

Key settings to configure:

[General]
Callsign=YOUR_CALL
Duplex=0          ; 0 for simplex, 1 for duplex
Timeout=300

[DMR]
Id=1234567        ; Your DMR ID
Enable=true

[D-Star]
Enable=true
Module=C

[System Fusion]
Enable=true

[P25]
Enable=true

[NXDN]
Enable=true

Save and restart the service:

sudo systemctl restart mmdvmhost.service

Step 4: Connect to the Network

Configure your network connection in the WPSD web interface:

1. Navigate to http://pi-star.local/ and log in (default credentials).
2. Go to Admin → Expert → MMDVMHost.
3. Configure your network connections (DMR Master, D-Plus, YSF Reflector, etc.).
4. Save and restart.

Step 6: Test Your Repeater

Verify the modem is detected:

sudo wpsd-detectmodem

Expected output:

Detected MMDVM_HS Port: /dev/ttyAMA0 (GPIO) Baud: 115200 Protocol: V1
Modem Data: MMDVM_HS_Dual_Hat-v1.6.1 ...

Make a test call using a digital radio on the configured frequency. Check the WPSD dashboard to confirm traffic is flowing.

Duplex Operation

For a full duplex repeater, you need:

1. Two radios — one for receive, one for transmit
2. A duplexer — to allow both radios to share the same antenna
3. Frequency separation — typically 5 MHz (2m) or 10 MHz (70cm)

Set Duplex=1 in /etc/mmdvmhost and configure the TX and RX frequencies separately.

Quick Reference

Step	Command
SSH into hotspot	ssh pi-star@pi-star.local
Edit config	sudo nano /etc/mmdvmhost
Restart service	sudo systemctl restart mmdvmhost.service
Flash firmware	sudo stm32flash -R -w firmware.bin /dev/ttyAMA0
Detect modem	sudo wpsd-detectmodem

Troubleshooting

No traffic showing on dashboard:

• Check that your radio is on the correct frequency
• Verify the MMDVM cable connections
• Check sudo journalctl -u mmdvmhost for errors

Radio overheating:

• Reduce TX power
• Add or improve cooling
• Reduce TX percentage in MMDVMHost config

Modem not detected:

• Check GPIO pin connections
• Verify firmware is flashed correctly
• Try a different baud rate in /etc/mmdvmhost

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This guide is based on N5AMD's excellent digital voice resources. Always check local regulations and obtain proper coordination for repeater operation.