Foundations of Amateur Radio

The shaving of the Yak progresses, it's now making noise! Before you get too excited, the noise is one-way, it's barely distinguishable from hash and it's fragile, so keep that in mind as we dive into the world of .. something.

If you have no idea what I'm talking about, you're in good company, half the time I'm struggling, but today I'm working on a project to bring software defined radio to the masses, well, radio amateurs who haven't dipped their toes yet and I'm calling this effort Bald Yak.

In case you're unfamiliar, the Bald Yak project aims to create a modular, bidirectional and distributed signal processing and control system that leverages GNU Radio. It's called Bald Yak because by the time I'm done, the Yak is likely well and truly shaved.

So, last time we congregated around the campfire I discovered that what I need to build is something that has a collection of things that talk to each other across a network. Seems pretty obvious now that I say it, but it wasn't always that way, remember, I'm inventing this from scratch, or so I tell myself. I will note that the deeper I dig, the more it looks like a lack of documentation, which really comes with no surprise, but I persist, if only to determine that it can be done, that I can do it, and that I understand how it works.

The underlying drive for all this is for me to gain a deep understanding of the whole ecosystem, since I firmly believe that we're well and truly committed to software driven radio.

So, what did I discover? First of all, thank you to all of you who sent messages with your own ideas on how to make two devices talk to each other. I explored at least a dozen of them.

I'll give you some highlights. First cab off the rank is OpenWebRX, radio in a web browser, very popular. I installed it, ran it, configured it, got noise, was able to pick a band across the network and decoded plenty of stuff. Looked like a contender until I discovered two significant issues. One is that it expects a menu entry for each slice of frequency range, with 2.4 MHz being the widest possible for an RTL-SDR dongle, so its 1.7 GHz range would need 708 entries. Someone made a good start, but if you want to tune to something that overlaps two entries, you need another menu entry. Then there's the weird flex that it doesn't decode FM Broadcast in stereo. There's a whole description on why not, but I lost interest. I also tried OpenWebRX+ which adds a bunch of functionality, but not enough to overcome those fundamental problems.

I explored several other web based tools, one looked really promising right until it demanded that I install some random binary off the Internet .. hard pass.

I didn't go down the path of AllStarLink across the room, mainly because I have no desire to start the rounds of configuration, or manage the lack of ability to change frequency, to name two issues.

I did fire up RTL-TCP and managed to connect to it from my Mac using SDR++, it even worked, but boy, the SDR++ user interface is hard work, too many buttons and not enough consistency, like why do I need to set the gain for each mode, and why doesn't it support SoapySDR on MacOS?

RTL-TCP is a tool that essentially puts an RTL-SDR dongle on the network. It's excellent, once you figure out how to make it work inside Docker, has great documentation, talks to GNU Radio, everything you'd want, except that it's only one-way and it only talks to RTL-SDR dongles.

I started comparing SoapySDR to RTL-TCP and then landed back with SoapySDR, since it does the same job, with a bonus that I discovered by accident, since the documentation is .. let's call it .. challenged.

One of the things that people who contacted me missed, probably because it was obvious to me, was the notion that I want to use automatic service discovery, something that has myriad names, ZeroConf, Bonjour, Avahi, mDNS and plenty others. I tried many of them as search terms with GNU Radio and found nothing.

Then I tried the same with SoapySDR and discovered that it supports mDNS out of the box. It's not something I'd seen before, since all the examples I found previously hard code an IP address into the flow graph, which means that it might work on my computer and network, but it won't work on yours until you change things, hardly something I want to inflict on unsuspecting users.

So, the way it works is that you run a thing called "SoapySDR Server" on the machine with the RTL-SDR dongle, and GNU Radio running Soapy Source with the remote driver can find it .. most of the time. There's still plenty of hair pulling here, a flow graph that ran yesterday stopped working today, until I rebooted the server twice, no other changes, so fun.

To be honest, it feels a little like Windows 95 Plug and Play, or as we used to call it, Plug and Pray, excellent idea, shame about the implementation.

Then I came across a flow graph by Handiko YB1SDL who created a git repository with the title "How to Stream the Audio Out from GNU Radio into VLC Media Player" .. which of course was catnip to an aspiring geek like me.

Turns out that VLC can listen on a UDP port and GNU Radio can send data to it. The quality of the audio is very poor as noted by Handiko, but I think that's due to neither of us understanding how to scale it properly, but that's par for the course.

So, right now I have three devices talking to each other, a SoapySDR Server with an RTL-SDR dongle on a single board computer, a GNU Radio flow graph running in a Docker container on my main server, and VLC running on my Mac.

What does this buy me?

Well, the Mac audio is a bonus, I'd like to be able to listen to the radio, but GNU Radio talking to an unnamed server that's just sitting on the network is precisely what I envisaged when I started this whole malarkey.

Mind you, it's not stable enough to show and tell, and I have no idea what it does if there's more than one radio on the network, but that's more opportunity to explore.

I'll also note that this is precisely why I'm doing all this in GNU Radio, so I can learn how it works.

There's one other thing. I'm documenting all this so it inspires you to start playing with this ecosystem, because ultimately I picture this environment as the radio equivalent of a massive bag of LEGO scattered all over the living room floor, something which brings me all kinds of joy.

So, what are your GNU Radio adventures like, and what have you tried and where are you stuck?

I'm Onno VK6FLAB