Wednesday 14 November 2018

EMF Hub going into hibernation

Now EMF 2018 is a distant memory, I will be switching off the bridges that form the EMF Hub sometime in December. The Brandmeister Talkgroup will remain active, however the crosslinks to AllStar, TeamSpeak and Echolink will be shutdown.

Thanks to everyone that used the hub or showed an interest.

We will return sometime in 2020 for the next instalment of Electromagnetic Field!

Sunday 30 September 2018

Post-EMF Update

It's been almost a month since EMF took place, and as I've almost finished unpacking I thought I'd best put up a brief update.

The EMF Hub proved to be fairly successful, with offsite Amateurs connecting from Ireland, Holland and Germany as well as the UK to chat with attendees at EMF. The majority of offsite users were using DMR to connect to the Hub, with a few connecting via Echo Link and IRN.

The hub also proved useful for on-site communications and allowed users to use both FM and DMR radios to communicate.

There were a handful of niggles. The DMR Gateway had issues receiving a Motorola hand held, and a different Motorola hand held  occasionally had issues receiving the hub. Chinese DMR radios worked flawlessly. I suspect this is because Motorola probably follow the specifications more closely. When I find the time I will do a bit more troubleshooting.

Saturday 25 August 2018

Update: Less than one week to go!

I've neglected to provide any updates for a while. Rest assured that things are full steam ahead. The hardware is complete, and I've been focussing on some software tweaks to improve the experience.

See you in a week!

MB6IEF and MB7AEF racked up, ready to deploy on site.

Monday 6 August 2018

Update: MB7AEF on the bench, and a successful FM <-> DMR QSOs

Tonight I got MB7AEF the FM side working. It's not quite as polished as MB6IEF as I still need to make up an enclosure, but I had a successful FM to DMR QSO with GM7RYR, the keeper of GB7EE in Edinburgh who has kindly added the EMF Hub as a static Talkgroup.

The photo shows a rather messy "bench". MB7AEF is on top of the PSU to the left with MB6IEF on the right. Not shown is the Raspberry Pi or USB Sound Card.

Saturday 4 August 2018

Update: MB6IEF Nearing Completion

MB6IEF, the DMR side of the on-site gateways is now nearing completion and is now on the "bench" (also known as my kitchen table) for testing.

During testing K8TCP saw the activity and connected to the hub via IRN (Teamspeak) and a successful QSO was held IRN <-> DMR with audio sounding great both ways.

The test "Bench"

Friday 3 August 2018

Minor Update: Radios are now programmed for MB6IEF and MB7AEF

This evening I finished off programming the Tait 8105 UHF Radios for use with the EMF Hub.

Programming involves setting the correct Frequencies and also configuring the GPIO options that allow the Controllers to operate the radios and send / receive the audio from the appropriate point in the audio chain - these differ for FM and DMR.

A terrible photo showing a Tait 8105 with its front cover attached being programmed

MB6IEF and MB7AEF programmed up and labelled. 

Update: DMR IDs issued for GB2EMF, MB6IEF and MB7AEF

DMR IDs have been issued for GB2EMF, MB6IEF and MB7AEF.

If you own a DMR radio that translates DMR IDs to Callsigns and Names, remember to flash your radio before coming to EMF!

Call SignDMR IDUsernameCountry
GB2EMF2345324GB2EMFUnited Kingdom
MB6IEF2345444MB6IEFUnited Kingdom
MB7AEF2345445MB7AEFUnited Kingdom

Thursday 2 August 2018

Minor Update: DMR MMDVM Modem and Screen flashed to the latest versions

This evening I started off sketching out the mounting holes for the STM32 Nucleo-F446RE Microcontroller that the MMDVM Modem sits on top of. Fortunately before I got the drill out I realised it wasn't accurate - the mounting holes in the STM32 Nucleo are randomly scattered around the board making it challenging to measure.

So I threw my toys out the pram and decided to put the callipers and ruler down for the evening and turn my hand to the software side.

I've flashed the Nucleo to the latest version of the MMDVM firmware which should improve performance and fix any bugs that have been fixed since it was last flashed over a year ago.

I also flashed the latest ON7LDS version of the firmware to the Nextion LCD, which has fixed the kerning issue and added a couple of extra features.

Nextion LCD with ON7LDS Firmware

The STM32 Nucleo - Note the top two screws are not in the same horizontal posistion

Wednesday 1 August 2018

Work In Progress: MMDVM Modem to control the DMR side of the EMF Hub

Today I spent some more time on the EMF Hub hardware, getting close to finishing the enclosure for the MMDVM Modem - the controller that will drive the DMR side of the on-site EMF Hub.

This involved cutting out holes for a USB and DB15 connector as well as the 2.4" Nextion LCD. I really do hate measuring and cutting enclosures, its not something I excel at, but I think the holes turned out reasonably well.

I've mounted the connectors and display but the box doesn't actually contain the modem yet, just a USB to serial adapter so I could test the screen prior to mounting the modem - a job for tomorrow.

For whatever reason the kerning seems a little off on the display. The firmware was last updated over a year ago, so hopefully flashing it will improve things.

The important stuff - Connectors for the Host and the Radio 
The bling - a 2.4" Nextion Display

Monday 30 July 2018

Completed: DC Power Distribution Unit

I have completed the DC power distribution unit for the EMF Hub.

It takes DC In from a 13.8V, 23A power supply and splits it into 4x Anderson PowerPole outputs and 3x 5V USB Outputs. It also has a Voltmeter / Ammeter on the front panel for added bling.

There are fuses protecting the overall current, and also the current to the USB DC/DC convertor - I would have liked to have fused each PowerPole individually, but ran out of room inside the enclosure.

Front of PSU + DC Distribution
Rear of PSU + DC Distribution

Originally the DC distribution was designed to handle a maximum of 40A, but I've dropped it down to 20A as I'm not comfortable with the PowerPoles which are connected with cable rated for 20A being protected by the fuse sized for a total load of 40A. This isn't a huge issue as the PSU is only rated for 23A and the total load of the EMF Hub will be well below 20A.

I need to replace the resistor in series with the LED as its currently brighter than the sun and will likely light up the entire EMF Field at night.

I was also hoping to add relays to individually switch 2 of the 4 PowerPoles, but again room was an issue so I had to give up on that - I totally underestimated the size of the crimp connectors and "Bend Radius" of the thick cables required to carry the required current.

I plan to revisit this in the future, but its fairly low down the list of priorities. Maybe it will be ready for EMF 2020?? If I were to do this again I would:

  • Use a Laser Cutter to create front / rear panels for an ABS box, which will result in a much neater finish and engraved labels / logos
  • PCB Mount the PowerPole and USB Connectors to cut down on internal wiring.
  • Fuse each PowerPole individually 
  • Add relays to the 2 of the 4 PowerPoles, and allow switching them from the front panel or via IP
  • Add voltage / current monitoring to each of the PowerPoles, exposing it over IP
  • Add failsafe timers so if a radio has been transmitting (Using more current) for X minutes continuously, the power is switched off - useful for scenarios where software or a repeater controller has crashed

Saturday 28 July 2018

DMR GPS to APRS possible via the EMF Hub

I've done some testing and confirmed that it's possible for a GPS enabled DMR radio to transmit its location to the EMF Hub where it will then be relayed to APRS-IS and displayed on websites such as

As there is no Open Source code for handling GPS reports from DMR Radios, I'm pushing the GPS data frames direct to Brandmeister where they handle the conversion and processing.

To get DMR GPS --> APRS working correctly, you will need a supported DMR radio, and you will need to configure your Brandmeister "SelfCare" account correctly.

The specialist routing of the GPS frames to Brandmeister is handled by a custom version of HBlink

So far this is only tested on a TYT MD-390G. I will create some documentation on configuring this radio for the EMF Hub shortly.

73 for now

Thursday 26 July 2018

The EMF Hub duplexer has arrived

The Duplexer has arrived for the EMF Hub 9 days after it was ordered - pretty impressive as it came all the way from China, preconfigured for our allocated frequencies.

The duplexer allows the two radios (FM and DMR) to share a single antenna.

Monday 16 July 2018

NoVs Issued

The NoVs for MB6IEF and MB7AEF have been issued by Ofcom!

Once again thanks to the ETCC and also to WSPR / MM0MRU for facilitating this, your assistance is much appreciated!

Sunday 15 July 2018

NoVs are now pending Ofcom Issue

The NoVs for MB6IEF and MB7AEF have been submitted to Ofcom for approval.

Big thanks to the ETCC and also to WSPR / MM0MRU for facilitating this, your assistance is much appreciated!

Wednesday 11 July 2018

New hardware acquired for the EMF Hub

With EMF Camp less than 2 months away its time to convert the pile of radios and wires that are occasionally allowed to sit on the kitchen table into something a bit more functional that will survive the trip to EMF, so Ive started to purchase the additional hardware required.

  • 13.8 Volt, 23 Amp Power Supply
  • DC Cabling for 5, 10, and 25 Amp loads
  • N Type and BNC connectors + CoAx for making patch leads
  • Fuses holders + fuses
  • DC Bus Bars
  • Crimp Connectors
  • Rack Mount Shelves
  • UHF Duplexer

Still Pending
  • Mast / Antenna Stand

Sunday 20 May 2018

EMF Hub Monitor "widget" now available

I've created a 'widget' to embed the Live Monitor into existing sites. You should see it on the right-hand side of this blog (assuming you're not using a mobile device). It looks like this -

To add the widget to your own site, you can use the following as a guide:
.resp-container {
    position: relative;
    overflow: hidden;
    padding-top: 56.25%;

.resp-iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    border: 0;

<p> See who's transmitting on the hub:</p>
<div class="resp-container">
    <iframe class="resp-iframe" src=""></iframe>

Saturday 19 May 2018

EMF Hub Monitor now in BETA

I've created a tool to show who's talking on the hub. You can see it here -

It's currently a work in progress, so it may malfunction or be down from time to time. Depending on the crosslink the user is keyed up on, you may only see their callsign.

The backend, known as the "Hub Events Collector" (HEC) is written in Python. It collects events, such as someone pushing the PTT from the various crosslinks and pushes them to an MQTT server. Its written in away that allows plugins so in theory it can collect from other sources and push to other destinations.

All the events are available publicly via MQTT if anyone wishes to build their own 'app' with the data.

I am not a web developer and could do with someone else picking this up, so I can spend more time on the 'back end'.  Please get in touch if you would like to help out.

Monday 7 May 2018

Added Auto-reconnect functionality

I've added some functionality to automatically reconnect clients that link into the hub via SIP (IRN and the MP3 Stream).

If no audio stream is received from a client for 60 seconds the connection will automatically be terminated and re-attempted shortly after. This should make the hub more resilient.

The code is available on Github if anyone wants to take a look.