EI2GCD Galway City Digital Gateway

Consideration was given to building up 2 metre Echolink Gateway but with the times that are in it, it seemed more logical to go digital instead. There is an interest in Digital Communications in the Galway/Mayo area and plenty of opportunity for experimentation.  To Date Joe EI3IX, John EI7FAB, Aengus, EI4ABB and myself seem to be the only ones active on DMR although there are two more registered in the DMR listings locally.

A number of ‘Homebrew’ DMR Repeaters have been built using various commercial hardware but powered by the MMDVM modems and so this set up seemed to be the best choice.  The ‘modem’ package is made up of an Arduino Due micro with a ZUM MMDVM modem board as the front end, and a Raspberry Pi-3 running the MMDVM Host software. The software is written by KB5RAB. This system was recommended by John Anderson, MI0AAZ, who has been instrumental in setting up many Repeaters and Gateway systems in Northern Ireland.




Raspberry Pi and associated software is not really my area of expertice. Not being all that computer literate, it was a good decision to seek assistance with the programming. With the aid of Team viewer and John, MI0AAZ at the other end, it was possible to configure the Arduino Due board first. This was not overly time consuming and I could have been talked through that part. The configuration of the Raspberry Pi was different. It was great to be able to watch and have each step explained as the set up progressed. None of the quickness of the hand deceiving the eye where one learns nothing.

The MMDVM image was written onto a 16GB SD Card and plugged into the Raspberry Pi. The Arduino Due was plugged into one of the USB ports of the RPi and then the power applied to the RPi. LEDs came on but seemed to be static. It was necessary to find the IP address of the Raspberry Pi to connect the laptop to the system. A remote connection was made to the Raspberry Pi after a few attempts and the system screen appeared on the laptop. It wass from here that the configuration took place. 

A number of updates to the software were performed and then the system configuration file was updated with my information. it is important to go through this section with a clear head. The connection to the network is wholly dependant on this file. All details such as the callsign, DMR number, and location need to be entered here. The different modes of operation were entered here also. In my case D-Star, DMR and Yaesu Fusion.

The Raspberry Pi, was connected to the internet and booted into the program. On checking the Brandmeister Dashboard it was found that the software had connected and both DMR and Fusion servers and showed no errors. D-Star required another registration number and this had not come through at the time and so was not included.  Initially the setup was performed via an Ethernet Cable but, on completion, the system is totally operational via WiFi connection from the shack. Once operational there will be a large MMDVM sign above the Transmitter symbol in Galway. Some further registration has to be performed with the Gateway's Callsign before this can happen.

The GM350 needed two minor modifications to ensure clean error free digital audio.
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The circuit of the GM 350, when configured for flat audio, is AC coupled with a 1uF Capacitor, the demodulator also has a second 1uF capacitor in circuit. The true demodulator output which is DC coupled is available at one pin of the IF chip.  This modification takes the true DC coupled demodulator output and routes it to the accessory connector pin. Conveniently the DC level can then be fed into the MMDVM interface board bypassing the 47uF capacitor at its input. This means that the whole demodulator to ADC chain is then DC coupled and the audio signals remain flat even with small frequency errors. Having done this modification the BER was significantly improved remaining at 0% for most of the time. It will also be necessary to change the setting of RXINVERT in MMDVM.ini as this modification inverts the sense of the received signal.


See below, result after the capacitor is bypassed

Because the signal is now DC coupled it will be necessary to carefully adjust the receive level pot on the interface board  to ensure the signal remains in the range 0- 3.3V. This is best done with an oscilloscope but it can be done by trial and error whist receiving.

The pinout of the accessory plug located at the back of the GM350 is shown below. Note that pin 10, this ignition sense, can be used to switch on the GM350 whn power is applied. Useful if there should be a power cut especially on a high site.


The Gateway was brought down to John, EI8JA, who set the critcal levels on the transmit side. If overdriven or undermodulated there would be an increase of Bit Error Rates (BER).  The levels on Fusion and D-Star in both transmit and receive were also carefully optimised on transmit and receive also.

Using the MMDVM calibrate tone of 1200 Hz it is possible to advance the input level until the trace below is achieved on the TX output. In DMR, the frequency modulation deviation must be 2.75 kHz.


Special thanks to John EI8JA for his assistance here. The D-Star and Fusion modes were calibrated and put on air to test them. Whilst doing this an almost identical set up was calibrated for the Mayo Gateway EI2DOD.

On return to Galway it was decided to substitute the Pi-Star image as this was much easier to set up manually by somebody not as "au fait" with Computer programming. A few minor teething problems were encountered but nothing that couldn't be resolved with John MI0AAZ on team viewer. The system finally booted up and showed connection on the Brandmeister Server. Noting these settings, it was easy enough to Team view into the Mayo system and set it up. A considerable amount of time was saved and the Mayo system went straight on air.

On connection all the relevant status indicators lit up and the Gateway showed signs of running normally.



It was necessary to check that all was connected on the Brandmeister server. The map showed the system up and running.


Both DMR and Yaesu fusion were tested resulting in very clear two way communication. It was possible to change the YSF networks by pressing the DX or X buttion on the Yaesu Fusion equipment. The default is IE YSF Ireland. Screens from the FTM 400 illustrate the ability to change YSF Reflectors by Pressing the DX or X button.




On DMR, the UK Call TG 2350 was used to establish contacts as this area is considerably busier than the Irish Call TG 2722. The Dashboard on the P-Star filled quickly.


As can be seen, both DMR Slot 2 and YSF showed connection from EI5DD. After 24 hours the mutli-mode gateway seems to be stable and trouble free. It remains to make a small unit to house the components and a cooling fan for the radio as a precautionary measure to ensure that constant use does not overheat the system.

Specifications of the Galway City Gateway 

Callsign  EI2GCD

Location Galway City

Frequency 144.850

Time Slot 2

 Colour Code 1

default Talk Group TG 2722 ( Ireland Call ) 

Default Yaesu Fusion Server IE YSF Ireland

Sysop Steve EI5DD - reports welcomed

wrights1@eircom.net