ICOM 51A DMR Radio

ICOM documentation for this radio.  Don Race KW2AIR - one of my oldest friends, gifted me this radio to get started in Digital Mode Radio (DMR).

To get DMR working you need a DMR capable radio (this one is D-STAR), and an internet connected repeater or hotspot to contact via the transmitted signal. 

This page is dedicated to the ICOM 51A Plus Radio, the Pi-Star (Pi Zero W w/ MMDVM modem) hotspot and D-STAR.


Cloning Software Instructions CS-51
ID-51 Basic Instructions 1
ID-51 Basic Instructions 2

D-STAR Handheld Radio Selection Chart
D-STAR Handhelds Radio Spotlight
ID-51A D-STAR Brochure
ID-51A Photo
RS-MS1A Device Requirements-Android Only Remote Control via Bluetooth or cable

Apple App Store RS-MS1I - compatible with ID-52, probably not compatible with ID-51A.



The access point needs a computer to process the output of the modem (MMDVM) to and from the internet.  The smallest and least expensive such computer is a Raspberry Pi Zero.  The latest version (W) includes wi-fi connectivity and deletes the Ethernet port on previous versions. 

When the components necessary to construct the Raspberry(s) are no longer in short supply, this unit is available at an MSRP of $15.00 USD.  Then you need a case, power supply, and the MMDVM 'hat' (that's the term Pi uses for the GPIO connected device(s).  GPIO (General Purpose Input Output) is a architecture that has been around since before computers got small.  It was used extensively in electronic test equipment interconnection to automate complex tasks.  In essence it is an extended address and data buss that can be shared by a large number of devices.  In an access point the MMDVM is the primary GPIO client.


MMDVM (Multi Mode Digital Voice Modem) is a chip that connects the internet on one side to a radio (in this case internal to the 'hat') on the other side.  Incoming RF signals (voice or data) are converted into outbound IP (Internet Protocol) routed data, and inbound IP is converted to RF digital voice and data outbound.  The MMDVM in my access point can be configured to utilize the following DMR (Digital Mobile Radio) modes:


D-Star Users - Display's current users on all reflectors or by reflector.

D-Star Gateway - D-Star registration system.  My D-Star Registration Site W7AES

D-Star Info - Reflector list and repeater downloads for ID-51A Plus radio.

Repeater Book - Find repeaters various ways including 'closest to me'.


I installed the access point on the cover of a Netgear Gigabit Switch that is mounted on the shack wall.

pi-star installed 1  pi-star installed 2

In this location, the unit is pretty close to the high power HF path.  Time will tell if its a problem or not.

Since the output power of the MMDDV is very low (about 0.1W) I wasn't expecting particularly long range connectivity. 

My first test was to use the 'rubber ducky' antenna supplied with the hotspot and drive the ID-51A around kerchunking the hotspot. 

I made it 0.15 miles

Max Range 'Rubber Ducky' Antenna

Then I connected the MMDVM to my Tram 6Db VHF/UHF antenna.

Tram 6db VHF/UHF Antenna

And then I tried it again.

Just in case you are interested.  This is what an antenna can do for you.

My plan is to NOT connect the Tram except for testing.  The reason?  Its a publicly accessible access point, that has been published.  It will easily service anyone in the park, although I may install a slightly better antenna just to get 100% coverage of the park.  I'll keep the Tram on my high(er) powered VHF/UHF radio.


As an Electronics Technician my only exposure to UHF radio was the gargantuan dinosaur vacuum tube URC 9 aboard CGC Cape Jellison.  It worked for very short range comms with aircraft to coordinate search patterns etc. but on the high seas you just don't get to use it for much else.  Since the MMDVM has the ability to receive and transmit in the 420-450 Mhz (UHF) range, I decided to explore that portion of the spectrum with this access point.

It has been a while since I have had to think about the difference between a repeater and a hot spot, so here is a quick recap. 

Simplex comms are carried out between two radios on the same or different transmit/receive frequencies. One station transmits while the other receives, then they swap roles to carry on a conversation.  The receiver of one radio must be tuned to the transmit frequency of the opposite radio and vise versa. The conversation consists of one party transmitting at a time, with no facility for interruption by the other party.

Duplex comms are different from simplex in that each pair of radios has separate transmit and receive frequencies which are isolated from each other by sufficient bandwidth (and often notch filters) to allow the receiver to receive continuously while it's associated transmitter is transmitting without creating a feed-back-loop.  Both parties can speak and hear each other at the same time.  This is akin to natural speech or telephone systems.

There are a number of methods for radios to interact with each other.  In the strictly RF domain, direct comms are nearly always simplex.  In order to extend the service area and enable portable low power hand held radios to communicate effectively, repeaters have been developed to simultaneously receive on one frequency and re-transmit on another frequency.  In this scenario comms are simplex.  The purpose of the dual frequency is to allow instant re-transmission of the signal from a more powerful location so that more of the hand held units within the service area can participate.

Adding the digital domain comes in at least two flavors.  In one, an operator is remote from the transmitter and performs control and communication via a separate circuit,  which may be a phone line, or a different RF path through any number of devices used to connect the operator to the radio site.  In this scenario the control and data circuit is dedicated and often shielded for security and reliability.  In a different scenario the control and communications circuit between the operator and the radio may be routed through the public internet.  Within the internet there exist many protocols that guarantee connectivity and security.  For example the DNS (Domain Naming System) routes messages around internet physical outages to the extent possible, on a routine basis making guaranteed connections as long as there exists a route between each end.  Another example is SSH (Secure Socket Shell - {Shell has long been abbreviated as 'sh') a protocol used to authenticate and encrypt all of the address and data packets (fragments of the conversation) once the connection has been established.  Conducting an ssh conversation is (for practical purposes) private.

Now we come to the idea of an access point (AP).  This is where the MMDVM (Multi Mode Digital Voice Modem) comes into play.  This device converts (MODEM stands for Modulator Demodulator) voice to and from a digital format.  The MMDVM chips in use on typical Amateur Radio access points also contain one or more radios which they use to obtain the voice from a near by radio as input/output on one side, and the internet on the other.  A computer (typically the smallest least expensive computer that will do the job is chosen) connects the MMDVM to the internet through the mechanisms available to any modern computer, IP (Internet Protocol) etc.  The access point is by its nature a simplex device, however the MMDVM chip can be used to control a repeater (remember the two frequency simultaneous transmit/receive function?) For this reason the configuration of the MMDVM includes options for separate input/output frequencies, however when used as an access point there is no operational reason to configure it this way.