Foundations of Amateur Radio

I recently expressed the notion of using a PlutoSDR as a replacement for an oscilloscope, a spectrum analyser, and perhaps even a vector network analyser. I can add signal generator to that list and you get the notion that this one device might replace a bunch of tools in your shack.

So .. I set out to come up with a minimum viable product to see what I might discover.

There are days when you get out of bed with a spring in your step, only to end the day exhausted and thoroughly defeated. Given the chance, the next day, you get out of bed and try again.

Fortunately for me, I have a full head of hair and my yak shaving barely made a dent and as a bonus, I learnt something, which is always nice.

The short version is that you should use a USB Y-adaptor or splitter to ensure that your PlutoSDR has enough juice to power a USB Ethernet dongle.

That statement alone is worth at least a combined fifteen hours of Yak Shaving.

Without this turning into a PlutoSDR specific troubleshooting saga .. for reasons I don't understand, plugging the power supply into the Pluto power socket and a USB Ethernet dongle into the accessory port doesn't work, but plugging both into a Y-adaptor and that into the accessory port makes all the blinkenlights work, even those on your network switch. As I said, fifteen hours.

So, what does this buy me, other than an appreciation for subtlety? It gives me network access to my PlutoSDR, which makes it possible to connect to it using GNU Radio running on a different computer, which then allows me to experiment.

Before starting this side-quest into connecting to my Pluto, I went on the hunt for some example code. Jon Kraft, who is a senior staff Field Applications Engineer at Analog Devices, whom I came across first on YouTube, where he's been playing with beam-forming and other nifty RF phenomena, also has a GitHub repository with some PlutoSDR examples for use with GNU Radio.

These examples are pretty straight forward, essentially connecting to a PlutoSDR, setting the centre frequency and extracting a bunch of RF and visualising it. Essentially what you'd want in some testing gear.

After playing around for a bit with Jon's examples, I'm able to see radio spectrum, across the network, on my screen, using GNU Radio.

Eagle eyed observers will note that I already achieved this with an RTL-SDR dongle and indeed I did. A few differences. I have access to a frequency range between 70 MHz and 6 GHz and I have the ability to transmit.

Of course this doesn't yet get us to the point of replacing test gear, but I think it paves the way to a collection of experiments that will.

If 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, my oscilloscope and other tools adventure is an example of what Bald Yak might facilitate. In radio terms there's very little to distinguish this type of tool from a transmitter running your favourite mode, and it allows me to experiment with a different radio back-end.

Full disclosure, I'm still trying to work out how to do this using SoapySDR, because if you remember, that will allow me to connect to any device, for now, this is using a PlutoSDR source and sink.

While we're on the subject of Soapy, I did start digging into SoapyAudio and the idea of making a more universal module that will allow amateur radios for both receive and transmit using Soapy, but I came unstuck when I discovered that the example plug-in code is essentially an empty file with the programming equivalent of "here be dragons". I'll likely come back to it, but not today.

Now, I do need to make some disclaimers because I know that there are plenty of caveats I've glossed over here. I think much of it is covered with the word "calibration".

A PlutoSDR is not a laboratory grade device. It isn't calibrated in any way, it's likely unstable, connectivity across the network is likely to be choppy, and plenty more issues like this.

In other words, if you come away from this thinking we're going to be building something to replace measuring gear you can buy for the price of a small car, you're going to be disappointed.

However, if you're here for "Wow, cool, you can do that, for a couple of hundred bucks?", you've come to the right place.

Also, I'm aware of the Analog Devices "IIO Oscilloscope",  that it's extensible, and even has a plug-in specification, but what it doesn't have is GNU Radio, which is I want to use for a whole lot of reasons, least of which that it isn't hardware dependent.

As I've said before, when I have something to show-and-tell, you'll be the first to know.

In the meantime, you could do worse than look for Jon Kraft's GitHub or his RadioKrafter YouTube efforts and have some fun yourself, that's Jon, no "H" and Kraft with a "K".

I'm Onno VK6FLAB