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Supercon 2022: Sam Mulvey Shows You How To FM Radio


Sam Mulvey built his own radio station in Tacoma, WA. Is there a better way to meld ham radio practice with a colossal number of DIY electrical and computer projects? Sam would say there isn’t one! This 45-minute talk is basically the lessons-learned review of setting up KTQA 95.3 – the radio station on the hill.

Sam starts out the talk by introducing you to LPFM. And maybe you didn’t know that there’s a special type of license issued by the US FCC allowing non-profit community radio stations up to 100 W, covering an radius of around 5 km. It’s like running a pirate radio station, but by jumping through a few legal hoops, made legal.

Trash on the Radio

Putting a radio station together on a budget requires a ton of clever choices, flexibility, and above all, luck. But if you’re willing to repair a busted CD player or turntable, scrounge up some used computers, and work on your own amplifiers, the budget doesn’t have to be the limiting factor.

Being cheap means a lot of DIY. For instance, Sam and friends made a custom console to support all the gear and hide all the wiring. Some hot tips from the physical build-out: painted cinderblocks make great studio monitor stands, and Cat-5 can carry two channels of balanced audio along with power, with sufficient isolation that it all sounds clean.

But not everything in the KTQA studio is cheap. Sam spends the money when it counts, and first splurge was quality microphones. And thanks to the rise of podcasting and streaming, items that used to be clear DIY choices like microphone stands and sound dampening material are now into Sam’s buy-vs-build category.

Open Source on the Airwaves

Sam then goes through all of the software that runs the station. Perhaps not apparent to those outside the scene, the Linux audio ecology has grown up enough that it can meet the needs of the professional studio. All the usual suspects are here, from Jack to Audacity and ffmpeg. Using an open production toolchain allows Sam to write some of his own tools too, and that includes a studio automation tool, VU meters over websockets, and a dead-air detector.

SDR tools are in abundance for monitoring their local output for making sure they’re not overmodulating or stomping on other nearby signals. But Sam is also planning to do a live comparison of their coverage when running in stereo vs mono by “FM Wardriving” around Tacoma to see which comes in best.

Finally, Sam talks about future projects – hooking the entire studio management up to MQTT to make wireless “On the Air” lights and coordinate other services, and playing around with the RDSS radio data service, because when you have your own radio station, why not?

A Dream Fulfilled

Sam has always wanted to be on the air, and is a hacker at heart. The community radio scene enables him to do it all. It looks like tremendously fertile ground for all sorts of fun and mayhem. And an FCC window for LPFM licensing is coming up soon, so if you’re at all interested in getting your junk on the air, look around for a local LPFM station and volunteer, and if you haven’t got one, you might just have to make one. Start now!

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