Software Defined Radio is one of the best value rabbit holes in tech. For about £20 you can pick up an RTL-SDR dongle, plug it into a USB port, and suddenly you're receiving aircraft transponders, weather satellites, and your neighbour's wireless doorbell.
What you need to get started
The hardware barrier is genuinely low. An RTL-SDR Blog V4 dongle is the go-to starter kit — it covers roughly 500kHz to 1.75GHz which is more than enough to keep you busy for months. Pair it with a cheap telescopic antenna to begin with, you can always upgrade later.
On the software side, SDR++ is where I'd start. It's cross-platform, actively maintained, and doesn't require a PhD to configure. For more serious signal processing, GNU Radio is the industry standard — it has a steeper learning curve but the visual flow graph editor makes it approachable.
What can you actually receive?
Quite a lot, as it turns out:
- •ADS-B — aircraft transponders. Run dump1090 and you'll have a live map of every plane overhead within minutes.
- •NOAA weather satellites — with a simple V-dipole antenna you can decode actual satellite imagery as the birds pass overhead.
- •ACARS — aircraft data link messages. Surprisingly readable and occasionally entertaining.
- •DAB/FM radio — obviously, but it's a good sanity check when you're starting out.
- •ISS SSTV — the International Space Station occasionally transmits slow-scan TV images. Catching one never gets old.
The antenna is everything
I cannot stress this enough. A £200 SDR with a bad antenna will be beaten by a £20 dongle with a good one every single time. Once you've got the basics down, spend your money on antenna improvements before anything else.
For a general-purpose outdoor antenna, a discone covers a wide frequency range and is hard to beat for the price. If you're specifically interested in HF (below 30MHz), you'll need an upconverter or an SDR that natively covers HF — the RTL-SDR doesn't go that low on its own.
Where to go from here
Once you've exhausted the obvious targets, look into trunked radio systems, POCSAG pager decoding, and AIS (ship transponders if you're near water). There's also a whole world of amateur radio digital modes — FT8, WSPR, JS8Call — that are fascinating to decode even if you're not licensed to transmit.
The community around SDR is genuinely excellent. The RTL-SDR blog, the SDR++ Discord, and the amateur radio subreddits are all worth bookmarking.
Happy hunting.