Radio Waves: December 8, 2023

Radio via Software

Chances are, you’ve actually used one without realizing it. I’m referring to a Software Defined Radio, and it is the design most — if not all — modern radios, including automotive and home models, use to receive and process the signal that comes from a radio station’s transmitter. 

I would venture to guess that the only hardware-based radios still being manufactured are those small portables that are in production based upon decades old designs such as the old “transistor” radios of the 1960s and ‘70s.

In the past, most radios used physical hardware to receive, tune and process the signal. If you looked inside older tuners you might have seen a part with fins that move when you turn the dial. The fins, which made up the variable (tuning) capacitor, are what allowed the radio to select the channel. Generally speaking, the more fins the better the reception, though there were exceptions. Today the tuning is handled by software, and in most cases, no moving parts are involved at all.

Technically, the definition of a Software Defined Radio as defined by the SDR Forum is “radio in which some or all of the physical layer functions are software defined.” That’s leaves a lot of room for various implementations; in practice, an SDR is a radio in which everything in the tuning and signal processing stage is handled by a software program.

I have a portable Sony radio that is definitely SDR … you can tell by the way the stations “jump” into place as you turn the tuning dial, rather than easing in as an analog radio would do. The advantage for manufacturers of radios using SDR is obvious … rather than design improvements necessitating designing new parts and changing production schedules, all that is needed is a software update. It also lowers the cost of manufacturing dramatically.

“Most newer generation radios are SDR, even though you can’t really tell from the outside, explains Hank Landsberg of Henry Engineering. “They work like any other radio but the circuitry is all-digital, often starting at the antenna jack. The only place the signal becomes analog is at the speaker output.”

As the software has improved, reception has improved as well, which is one reason automotive manufacturers can get decent reception out of those little antennas that in the past would have given no signal. or static at best. According to Landsberg: 

“Newer generation SDR-based car radios offer incredible selectivity, as well as sensitivity. This means they can receive closely-spaced stations that couldn’t be heard on older analog radios. Even a low power FM station that’s adjacent to a higher-powered commercial station can be tuned in. SDR designs can successfully receive weak signals that were previously not listenable due to excessive noise or interference.”

 It also allows the ability to tune different bands using the same parts, and that’s where the fun starts. While every radio currently available for your car or home is SDR, what hobbyists consider SDR is totally different. For while your home or car radio is designed to tune traditional AM or FM, an SDR dongle that you attach to your computer through your USB port can tune — with the appropriate software — shortwave, police, aircraft, or even CB radio channels.

Hobbyist SDRs include, as part of the software, a graphical representation of the signal so  you can see the way the station is processed, adjacent signals, or even interference in real-time. And as designs have improved, hobby SDRs are looking more more like traditional radios.

One such radio showed up on my Facebook feed recently, in the form of a YouTube video at The radio, available at United Kingdom supplier sells for slightly less that $100 at press time and is essentially a fully portable SDR that picks up every band. I have not evaluated it myself, so I am not recommending it, but it certainly looks intriguing. Maybe Santa will be nice to me and send one along.

Otherwise, or perhaps even better for now, are the USB dongles that can cost as little as $30. With that you can play on the cheap, using your computer. Landsberg uses one from Nooelec called the NESDR Smart, but there are many on the market. 

That portable looks so sweet though …

If you have experience with a hobby-style SDR, send me a note – I’d love to pick your brain. In the meantime, I think I’ve found another hobby to add to long list of radio-related collections…

Next week: the old school.