Around 2010 someone discovered that a cheap European DVB-T television tuner, the Realtek RTL2832U, could be told to hand over its raw I/Q samples instead of decoding television. That accident produced the RTL-SDR: a software defined radio receiver covering roughly 500kHz to 1.75GHz for about $30.
It remains the best value in the entire field, and it is the right place to start if you want to put real-world radio into your work.
The Tech Prepper on the current hardware and software combination — RTL-SDR v4 with SDR++.
Buy the right one
This is the most important paragraph here, because the market is full of near-identical-looking dongles of wildly different quality.
Buy an RTL-SDR Blog V4. Around $30–40. It has a proper R828D tuner, a 1ppm TCXO (temperature-compensated oscillator, so it does not drift as it warms up), better filtering, an aluminium case that acts as shielding and a heatsink, bias-tee power for active antennas, and an SMA connector.
Avoid the generic $12 ones. They work, technically. They also drift badly, have poor shielding, overheat, and use MCX connectors that nothing else uses. The $20 difference buys you not spending an evening wondering why your signal moved.
One real gotcha with the V4: it needs driver version 2.0.2 or newer of librtlsdr. Older drivers will appear to work and produce nothing but noise. If you buy a V4 and get static, this is almost certainly why.
You also need an antenna, and the kit version — dongle plus a dipole set with a tripod and extendable elements — is worth the extra few dollars. Which brings us to the thing people get wrong.
The antenna matters more than the radio
A $400 SDR with a bad antenna performs worse than a $30 SDR with a good one. This is the single most common beginner mistake and it is worth internalising before you buy anything else.
Two rules:
Length should match the frequency. A quarter-wave antenna is 75 / frequency-in-MHz metres long. For 1090MHz (aircraft) that is about 6.9cm. For 162MHz (marine AIS) about 46cm. For FM broadcast around 100MHz, about 75cm. The dipole kit’s extendable elements exist so you can set this; set them.
Position beats everything. Radio at these frequencies is roughly line-of-sight. An antenna at a window, or ideally outdoors and high, will outperform a better antenna on your desk by an enormous margin. For aircraft especially, the difference between “a few planes” and “everything within 150 miles” is usually a window.
Install SDR++
SDR++ is the current best starting point — cross-platform (Windows, macOS, Linux), actively developed, clean interface, and it handles the V4 properly. Download from sdrpp.org.
Alternatives worth knowing: SDRangel (more features, steeper curve), GQRX (Linux/macOS, simple and solid), SDR# (Windows only, long-time standard), and CubicSDR.
First run:
- Pick RTL-SDR as the source, hit refresh, select the device
- Set sample rate to 2.4 MSPS
- Tune to a strong local FM broadcast station, set mode to WFM, bandwidth 150–200kHz
- Press play
If you hear a radio station, everything works. Do this before anything else — it is the one signal guaranteed to be strong enough to confirm your whole chain.
Then learn to read the waterfall. The display shows frequency horizontally and time scrolling vertically, with brightness as signal strength. It is the single most useful skill here: you learn to recognise signals by their shape. FM broadcast is a wide fuzzy block. A digital data burst is a sharp rectangle. FSK looks like two parallel lines. Narrow FM voice is a thin spike that comes and goes.
Five things to decode on your first afternoon
1. Aircraft (ADS-B), 1090MHz. The best first project. Install dump1090 (or readsb), point it at your dongle, and you get live aircraft positions from their own broadcasts — no API, no account. It serves a web map and also re-broadcasts SBS text on port 30003, which is how other software consumes it. We wrote about FltCast, an LED matrix tracker built on exactly this.
2. Everything on 433MHz with rtl_433. This one is addictive. rtl_433 decodes hundreds of consumer devices — weather stations, tyre-pressure sensors, doorbells, remote thermometers, utility meters. Run it and discover how much your neighbourhood is broadcasting:
rtl_433 -F json
For installation work this is gold: a genuine, live, local data source with no network dependency.
3. Marine AIS, 161.975 / 162.025MHz. Ships transmit position and identity the same way aircraft do. AIS-catcher or rtl-ais decodes it. Only interesting if you are near water, and extremely interesting if you are.
4. NOAA weather satellite images, 137MHz. The most satisfying thing an RTL-SDR does. Polar-orbiting satellites broadcast analogue APT images as they pass overhead. Record a pass with a V-dipole antenna, decode with noaa-apt, and you have a photograph of the clouds above you that you received from space with a $30 dongle. Use a tracking site to find pass times.
5. Radiosondes, around 400MHz. Weather balloons, launched twice daily worldwide, transmitting telemetry as they rise to 30km. radiosonde_auto_rx decodes them, and people chase and recover the payloads.
What it cannot do
It cannot transmit. This is a receiver. Transmitting requires different hardware and, in most bands, a licence.
It has 8-bit samples. Limited dynamic range, so a strong nearby signal can swamp a weak one. The usual fixes are an attenuator, a band-pass filter, or just turning the gain down.
It stops at ~1.75GHz and does not go below ~500kHz without a direct-sampling mode (the V4 has one for HF, via a Q-branch tap — enable it in SDR++ for shortwave).
And it is not a spectrum analyser. The amplitude readings are relative, uncalibrated and gain-dependent. Fine for “is there a signal”, useless for “how strong in dBm”.
Where this goes creatively
Radio is an invisible layer of the environment that is genuinely there, genuinely local, and almost never used as a material. A piece that listens to the aircraft overhead, the ships in the harbour, the weather stations on the street, or the raw noise floor of a room is reading the actual place it is in — and it keeps working when the Wi-Fi does not.
The tradition is older than the dongle: Christina Kubisch’s Electrical Walks hand audiences induction headphones to hear electromagnetic fields in a city; Joyce Hinterding builds antennas as sculpture; Alvin Lucier’s Sferics recorded natural radio emissions. An RTL-SDR is the cheapest entry to that lineage there has ever been.