Virtual Radio

Foundations of Amateur Radio

There is a feeling of anticipation in the air, the year has started, there are so many different ideas bubbling through my mind that I feel like an excited puppy dog wagging its tail.

I've been playing with a wonderful piece of software called GNU Radio, more on that in a moment.

So, I have for a while been dissatisfied with the offerings of SDR software. There is lots of development going on, lots of new toys being invented and many different hives of activity in this area.

It's not unlike the progression from reel-to-reel based radio broadcasting via VHS tape, to computers with audio files. There are lots of solutions solving specific problems, but there are also a group of solutions looking for a problem and only time will sift out which one is worth the effort.

In amateur radio we deal with valves, resistors, capacitors, inductors, transistors, integrated circuits, crystals, connectors, solder and many, many different physical things.

I'm a computer guy, have been since I was in primary school. I grok computers, more-so than any aspect of anything else. Amateur radio was intended as an escape from this world, but initially to my dismay, but now to my delight, computers are making serious inroads into the hobby. Not just as peripherals that take care of logging, messaging, propagation forecasting and the like, but as integral parts of the radio.

I looked at GNU Radio several years ago and wasn't able to understand what it did and how it worked. I didn't have enough in the way of radio skills or vocabulary to get started, but in learning about my hobby I now have a much better understanding.

GNU Radio is a tool, a piece of open source software, that allows you to build circuits inside a computer that process information. Not unlike how filters, amplifiers and oscillators do this inside a physical radio.

If you want to change the behaviour of a radio, you need to alter a circuit by changing components, or re-design the circuit entirely and re-build it. Hours of planning, soldering, testing and the like, just on a hunch or an idea. It's how we've been doing development for centuries.

GNU Radio allows you to tweak a radio on the spot, in real-time, and see what it does. The feedback loop is immediate. You build up a sequence of blocks, an oscillator, a filter, a combiner, splitter, decoder, spectrogram, waterfall, whatever and if you need it do do something else, you either swap out one of the blocks, or change one or more parameters, better still, replace a fixed parameter with a slider so you can change it while it's running to see what happens.

For example, displaying a Lissajous figure in the real world involves two signal generators, cables, an oscilloscope, power, gain settings, timing, several hundred, if not thousand dollars worth of gear. In GNU Radio it involves two signal source blocks and an oscilloscope block, joined together. All there, three blocks, two lines and it's working.

Making an FM receiver in GNU Radio involves a source of radio frequency information, say a $20 RTL-TV dongle and an FM decoder block. You can display it on a waterfall with a third block, or listen to it with an audio block.

To make matters even more interesting, you can build your own blocks, transmit if your radio is capable and test all of this without ever needing to go to the local electronics store or heat up a soldering iron.

I have no doubt that this changes amateur radio for me and I'm fairly sure it will do the same for you.

I'm Onno VK6FLAB