Sir Clive Sinclair, ever the brightest British electronics entrepreneur, made his first substantial profits from selling tiny personal radios by mail order to impressionable schoolboys like me, back in the early 1960s. For the man who went on to sell us the Spectrum home computer in 1982, and so make his first million, that radio was an auspicious start. Although in 1985 we thought his C5 lightweight electric car was a leap into the absurd, perhaps he was just being a little too prescient.

Sinclair’s radio used analogue circuitry with transistors, then considered to be at the leading edge. At the same time, the more serious radio transceivers used by radio hams and the military were often still based on valves (vacuum tubes), relatively little changed since the Second World War, and both bulky and delicate.

The revolution which packed those ungainly valve sets into compact, robust and battery-powered radios, bringing us Radio Caroline and portable music, is now being overtaken by a new revolution which (almost) does away with the radio altogether.

Software-defined radio (SDR) basically converts the analogue radio signals to digital at the antenna. From there on, all the signal processing that used to be performed by intricate analogue circuitry is done digitally, typically by a computer, or by more specialised signal-processing systems such as those found in a modern graphics processing unit (GPU).

As a radio ham, the bits of our house which are not crowded by books and Macs usually have ham radio gear. There are the VHF/UHF transceivers, hand-held walkie-talkie-style FM sets, several HF transceivers of different sizes and capabilities, even a couple of specialist single-band sets for 6 and 4 metre wavelengths.

With an SDR, which could be as small as an iPhone or even a USB stick, you can perform better than all those on any frequency from a few Hertz to microwave (above WiFi).

Like so many expensive and speculative developments, SDR originated in, and has been largely funded by, the defence industry. Those who periodically press for defence R&D funding to be cut should bear this in mind. However much we might all regret putting our taxes into the development of weapons, the tens of billions of dollars invested in the GPS network are another good example of defence spending which has changed our lives for the better.

Even without a licence to transmit anything, SDR offers great capability with its capacity to tune in to any frequency and process any radio signal. Want to listen to digital broadcast radio, monitor CB frequencies, and look for WiFi hotspots? One little system will do the lot.

Inevitably there is a dark side: it is also hugely attractive to hackers. As SDR systems become more widespread, exploits involving all forms of radio, such as breaking into car security systems and over-hearing radio telemetry are inevitable. Let’s hope that the respective industries are hardening their security up in preparation.

There are also some potentially highly innovative areas which await developers. Radar systems have previously been relatively expensive, and only found on marine vessels and aircraft, although ground penetrating radar is starting to show its potential on land. Radar systems are heavily dependent on the sort of signal-processing which SDR should be capable of, given a suitably directional antenna.

So far most SDR hardware has been reliant on wired connection. Imagine an iPhone-sized SDR which connected to your iPhone wirelessly, for example. There is already one iOS app for SDR, although it is aimed at the experimenter rather than consumer. WebSDR.org keeps a list of over a hundred SDR systems which can be accessed over the Internet, although you can of course only receive through those, not transmit.

Indeed the only real limitation to what SDR can achieve (other than legal restrictions) is the need for an antenna. As a radio ham I have chatted with other hams in Australia using very low power (technically known as ‘QRP’), but the antenna which I used was a few metres high and hardly the sort of thing to walk round with! Mercifully this becomes much less of an issue as the radio waves become shorter, up in the microwave bands, where much of the action is with modern wireless communications.

I am sure that a few with the vision of Clive Sinclair will be along very shortly to show you some truly new and exciting applications for SDR.