Since the release of the MMDVM in early 2016, Johnathan Naylor’s (G4KLX) creation has hit the ground running throughout the ham community. This simple creation has put the power back into the hands of radio operators around the world allowing them to build and tinker with digital voice systems, breaking down the barrier of needing expensive commercial hardware. The MMDVM is a hardware and software component that can interface radios to a computer, like a raspberry pi, turning normal analog radios into digital radios, much like a TNC for packet radio. The MMDVM-Repeater board is a lot like a hotspot, except it doesn’t have a radio built onboard. Instead, it uses cables to wire directly into the IO pins of the radio(s) you choose. The MMDVM/Raspberry-Pi combo will turn a single analog radio into a high powered hotspot or 2 radios into a fully featured digital voice repeater. The MMDVM_Host software counterpart is opensource and feature rich giving users access to the following digital modes:
Yaesu System Fusion
P25 Phase I
After following this article you will be able to put together a multimode amateur digital repeater or high powered hotspot that can be connected to the internet for world wide digital communication. Through proper coordination, given digital’s IP connectivity and features, Ham radio operators around the world can build fully connected systems, allowing remote parts to have access to RF communication. A connected digital environment allows us to leverage MESH networks like Broadband Ham Net or ARDEDN in events where the internet may not be reliable. Think about it, the ham community can build a large network that has the ability to be “offline” and still allow for clear digital voice communication. How cool would that be! If its easy and cheap to build and can be done in areas with no internet, that’s helping humanity. Baby steps though, lets just get this digital node built.
- Rasperry Pi 0 or Pi3
- Micro SD card
- MMDVM board = STM32-DVM OR Zum MMDVM (Discontinued) OR Micro-Node TEENSY
NOTE: Actually I'm using an MMDVM repeater boad produced by BI7JTA at cost of 52 USD
- TX/RX with a 9600buad port, I'm using Motorola GM-340 series.
Choose a radio carefully keeping in mind duty cycle and heat dissipation, EXTREMELY IMPORTANT. A cooling fan will be an absolute must! Motorola radios are great, but have drawbacks if you don’t have access to programming software. The old Icom/kenwood sitting in the corner collecting dust is a viable option. Many people are using the Yaesu DR-1X repeater for duplexed operations (must not be firmware updated, i.e. FR model, or the DR2).
- A cable to connect from your radio(s) to the MMDVM.
You can buy this cable already made from BI7JTA for a small extra cost or you can built your own.
- The Pi-Star Image for the SD card
Other items include, a dummy load and SWR/Wattmeter for testing, power supply, and an antenna when you are ready for the air. Please help keep the finite airwaves clear of testing and un-needed traffic. Please use a dummy load during all your initial tests and any future tweaks you may need to do, and of course, Motorola R.I.B. to program your radio.
These 7 items will give you:
a) Ability of up to 5 different digital modes, P25, DMR, D-Star, Yaesu Fusion, NXDN, along with some cross-mode capabilities with on the fly PTT access. Meaning, just key up your radio and it handles the rest.
b) A web interface that can be accessed from a smart phone or computer to control the node remotely with real-time activity.
C) “high-powered” hotspot or repeater. Anything deployed, no matter the coverage, helps add to the infrastructure. Just be sure to advertise the repeater/node. Sharing is caring!
Program the radio: Pick a frequency and program your radio(s). Not sure what frequency to use? Please check your radio band plan. Just make sure you don’t over step any local repeaters, national calling frequencies, or Satellite Frequencies. In other words, please use common sense. As part of programming your radio, if you are using CDM/commercial radios, make sure all your settings are set to FLAT AUDIO.
Boot the PI up: Now that you have the cable made, radios programmed, and the Pi-star image burned to the SD card, put the SD card in the PI and boot it up with a network cable plugged into your local network. *Leave the radio(s) unplugged from the MMDVM for now.* We dont want to accidentally key the radio with no antenna or burn anything up with bad SWR etc…
Navigate to the dashboard: If your PI is booted and has network connectivity all you need to do is open a web browser on a computer or your phone and go to…
Default credentials– Username: pi-star Password: raspberry
Setup Pi-star: This video by W1MSG is an excellent video that goes over the initial setup of pi-star.
Basically the video walks through filling out the required fields, enabling modes you want and configuring those modes. Pi-Star is an amazing, super easy, straight forward tool. Even if you have never used it before, once you are logged in, its easy to get around the interface.
Key up and test it: Once pi-star is configured, go to the dashboard and plug your radio(s) into the MMDVM, making sure you have a dummy load or an antenna plugged in. Key up on the frequency you chose on the digital mode you chose. You should see on the dashboard in Green “RF” and the red PTT light on your MMDVM light up.
One snag I ran into was by default TXINVERT was set to on or ‘1’. I was hearing digital noise, but nothing was decoding it. I fixed it by going into expert mode in pi-star (pi-star.local/admin/expert) and setting it to off or ‘0’ under MMDVMHost. TXINVERT and RXINVERT depends on the radio you use. This may require trial and error.
Adjust the pots: If everything seems to work at this point, the next step is to tune the mmdvm’s adjustable audio pots. This is a very tedious process and requires A LOT OF PATIENCE. Most of the time, the pots are already set from the factory and usually don’t need adjusting. But if you are seeing constantly high BER or not getting audio back, you will need to adjust the pots. There are 3 ways you can tune the pots to achieve desirable BER/Audio. DMR is the most picky and requires even more patience.
Open firewall ports : Opening ports may be optional depending on your network. Most of the time uPnP if implemented on your network properly is “good enough”. However, if you notice other devices cant link inbound or features like callsign routing are not working, you many need to open ports.
UDP 62031 — Homebrew repeater protocol
UDP/TCP 20001-20009 — DPLUS
UDP 30001 — D-EXTRA
UDP 30051,30062 — DCS client
UDP 40000 — D-Star call routing
TCP 9007 — IRCDDB
UDP 20011-20014 — Dstar repeater
For more information: Brandmeister page & Dstar101
Below I/O setting for Motorola GM-340/GM-950
photo courtesy of BI7JTA
photo courtesy ofBI7JTA
photo courtesy of BI7JTA
If you own already your YSF reflector and your WiresX room using an HRI-200 interface then you can link the nets together via super Hot Spot.
Procedure is very easy. Open the wiresX software on your PC then open File menu, open Transceiver and into frequencu box use the same ISO frequency of your Super Hotspot.
Job done. Enjoy and have fan.