"What can I actually receive? An RTL-SDR beginner's guide to real signals"
What can I actually receive? An RTL-SDR beginner's guide to real signals
Every software-defined radio beginner hits the same wall: the dongle works, the spectrum looks alive, and you still have no idea what is actually up there. This guide lists the signals a sub-A$100 RTL-SDR setup can genuinely receive from an Australian location, with the frequencies, the antenna question, and the software that decodes each one.
The hardware baseline
Two of our products cover the entry spectrum (we sell these, disclosed as our own stock):
- RTL-SDR V4 Receiver Kit with dipole antenna (A$55) — the recommended first buy. The V4 adds a built-in bias tee and improved filtering over the original design, and the kit's dipole is what you'll use for FM, ISM and satellite work in week one.
- RTL-SDR R820T2 bare dongle (A$39) — the budget option if you already have antennas or want to experiment.
Setup is documented by the vendor in the RTL-SDR quick start guide, and the V4-specific user guide covers the driver and software steps for the improved tuner.
What you can realistically receive
ADS-B aircraft positions (1090 MHz). Planes broadcast their position on 1090 MHz; software plots them on a live radar map. This is the classic first project and works from a window. The RTL-SDR ADS-B tutorial and the open-source dump1090/readsb decoder ecosystem (see the readsb project on GitHub) are the standard starting points. Antenna matters enormously here: the stock dipole will show dozens of aircraft within 100 km; a dedicated ADS-B 1090 MHz outdoor antenna (9 dBi) plus a mast-mounted spot is the difference between "a few planes" and "every plane in the FIR".
NOAA weather satellites (137 MHz, APT). Polar-orbiting NOAA satellites transmit automatic picture transmission on 137 MHz; a good pass yields a real weather image you decoded yourself. The RTL-SDR NOAA satellite tutorial and the tracking-and-decoding guide to NOAA weather satellites walk the full pipeline, including orbit prediction and the WXtoImg/SatDump decoding step.
ISM band devices (915 MHz in Australia, plus 433 MHz). Wireless doorbells, weather stations, tyre-pressure sensors, key fobs. SDR# (Windows) or GQRX (Linux) make these easy to spot and record. Frequency etiquette: the ISM allocation is shared, receive-only hobby listening is lawful, and transmitting is not — more below.
ACARS aircraft datalink (131.525 MHz VHF). Text messages between aircraft and ground — maintenance reports, weather requests, gate assignments. Decodable with multimon-ng or SDR# plugins; the Signal Identification Wiki's ACARS page documents the protocol and frequencies.
POCSAG pagers (various, 148–153 MHz in AU). Yes, pagers still run — hospitals, some security and emergency services — and the text is usually unencrypted. The RTL-SDR POCSAG decoding tutorial covers multimon-ng setup. Treat anything you decode as someone else's operational traffic: read what's plainly broadcast, don't redistribute personal data.
Broadcast FM (88–108 MHz). Trivially received, useful mainly as a sensitivity test and a first signal for kids. RTL-SDR is unfiltered below ~24 MHz, so expect FM broadcast overload to desensitise other bands — an LNA + FM/ADS-B filter set (A$29.90) fixes both problems at once for any serious listening.
The antenna, honestly
The stock dipole is fine for FM, 433 MHz ISM and 137 MHz satellites with favourable geometry. For ADS-B, height and a purpose-cut antenna matter more than receiver quality — a 9 dBi collinear at roof height outperforms every other upgrade. Start indoors, get one signal decoded, then invest.
Software shortlist
- SDR# (Windows) — the de-facto default; the quick start guide above installs it.
- GQRX / SDR++ (Linux, macOS) — cross-platform, lighter.
- dump1090/readsb + adsbfi/tar1090 map — ADS-B plotting.
- SatDump or WXtoImg lineage tools — NOAA APT images.
- multimon-ng — POCSAG and ACARS.
Lawful-use note
Receiving these signals in Australia is lawful for hobby purposes; transmitting on any of these bands without authorisation is not. Don't rebroadcast pager or ACARS content containing personal data. This post is general information, not legal advice — the ACMA class licence pages and the cited guides are the references if you need specifics.