CQ / Hello World…

A quick introduction: by day, I'm a DevOps Engineer at Red Gate, a software company in Cambridge, UK. Outside of work, I enjoy both amateur radio (hence the callsign, M0VFC) and community broadcast radio at Cambridge 105. This blog aims to span all those interests - so feel free to ignore the posts that aren't relevant!

Feel free to get in touch on Twitter (@rmc47).

73 / Best wishes,

Strawberry Fair on Cambridge 105 Radio

7 June 2017 | Comments

Hot on the heels of of Radio Local, Strawberry Fair is one of Cambridge 105 Radio's biggest outside broadcasts of the year. We run one of the live music stages of the UK's largest free music festival, focussing on local artists ranging from solo acoustic acts to full ska and rock bands.

Big 10 at Strawberry Fair. Photo: Jon Watts

During the 12 hour broadcast, we hosted 16 artists. We're fortunate to have an excellent team which allows us to do this while having seamless broadcast coverage throughout:

The split of "live" and "broadcast" is something we started a couple of years ago, with excellent results. It means I can do some (very quick!) sound checks with bands as they set up while the broadcast continues uninterrupted, and without me having to think about it.

From an equipment point of view, we achieve this with a Behringer X32 Compact (plus S16 digital snake) as the front-of-house mixer, and X32 Rack in Flossie, our outside broadcast van, as the broadcast mixer. FOH sends three stereo groups to the van: vocals, instruments, and drums. That allows broadcast to achieve a better balance on air, where there's no live sound from the drums or backline, without needing to do a complete remix on the fly. Broadcast sends a mixbus back to FOH with our music playout system and the presenters' radio mics that we can feed to the front of house speakers during changeovers.

Backhaul was once again primarily via IP, this time using a tethered 4G connection to the Raspberry Pi. It proved remarkably reliable, though we did have to drop back at one point to our Band 1 analogue FM link.

Radio Local - behind the scenes

30 May 2017 | Comments

Over the weekend of 27-28th May, live art collaboration Hunt & Darton were commissioned to perform "Radio Local" at the Cambridge Junction as part of the Watch Out festival. Cambridge 105 Radio, as well as broadcasting the output, provided much of the equipment and engineering behind the project.

Hunt & Darton on stage at Radio Local

This presented some new challenges compared to many of our outside broadcasts:

As well as these, the broadcast was to run for a solid 24 hours!

4am weather on Radio Local

At its core, audio mixing was handled by a Behringer X32 Rack in the van. This gives a compact mixer with an incredible amount of routing flexibility. We didn't need anything like the number of inputs available, but the ability to quickly route arbitrary combinations of channels to arbitrary outputs in software is excellent for this sort of event. Clean feed for the phone line? No problem. Need to reduce output to the PA speakers, but not the broadcast feed? Fine.

Another advantage of the X32 is the ability to control it over a network. In the van, we ran X32-Edit, and Hannah the producer used an Android tablet with Mixing Station XM32. This let her drive the show, but gave us the ability to jump in if we needed (very rarely - she was great!)

On stage, a Behringer S16 digital snake provided audio connectivity back to the X32 over a single Cat5E cable. Along with Ethernet and mains, that meant only three cables between the stage and the van - handy in a public space where trip hazards need to be avoided.

Audio playout used the open-source Rivendell suite, running on a laptop in the van. That meant that a complete loss of the stage feed would still retain playout capability. A VNC server on that laptop allowed three other laptops, one for each of the presenters and producer, to control it remotely. The presenters could see what was lined up next, and how long was left to run on a track, as well as firing jingles and sound effects from the cart wall.

The "jingle shed" used another laptop running Audacity, coupled with a small mixer and USB audio interface. After recording, jingles were saved into a Rivendell dropbox folder over the network, and ingested automatically.

Telephone calls were provisioned using a voice over IP line from Andrews & Arnold, and terminated on an instance of Asterisk running on a Linux server (which also handled various network routing functions). This sent incoming calls to an analogue telephone adaptor where they rang a traditional phone handset. When ready to go to air, a blind transfer to another extension moved the call to an instance of MicroSIP on the van PC. This was configured to auto-answer. Send audio was a post-fade mix bus containing all channels except the phone, and receive audio appeared as a channel on the mixer.

The broadcast output fed a Raspberry Pi with Cirrus Logic audio card running LiquidSOAP, streaming it back to the main Cambridge 105 studio over the internet.

Finally, our internet connectivity came from the Junction to the van via a pair of Ubiquiti Nanostation M5 5.8GHz WiFi links; a Ubiquiti UniFi UAP-AC Lite provided local WiFi access for variouis mobile devices, but all laptops, mixers, and so on were hard wired.

In summary, we used two mixers, seven laptops, four ethernet switches, two Raspberry Pis, one server, one tablet, and countless cables - but it all worked!


12 February 2017 | Comments

My first Summits on the Air (SOTA) activation was, apparently, 31st December 2007. It involved a 10m telescopic aluminium mast, 40Ah car battery and Icom IC-7000 lugged to the trig point on Detling Hill. Fine for a small summit like that, but entirely impractical for more challenging hills.

Since then, I've refined the equipment I carry. It's not as minimal as some folks, but it's working well for me at the moment:

The key bits are:

All of the above packs into the blue rucksack, which also contains a CamelBack water pack. Including water, it weighs around 8.5kg.