What is a software-defined radio?

A software-defined radio (SDR) is a radio whose tuning, filtering and decoding are done by software on a computer instead of by circuits in a box. The hardware’s only job is to catch a slice of the radio spectrum and hand it to the computer as numbers. The software then becomes whatever radio you need: FM, DAB+, aircraft, weather stations, the remote for a toy car. The cheapest way in is an RTL-SDR USB dongle, which receives up to about 1.7 GHz (from as low as 100 kHz on the better models), cannot transmit, and costs under $100 with an aerial.

A TV stick that turned out to be a radio

The dongle everyone starts with began life as a cheap USB digital TV stick. Inside are two chips: a tuner (usually a Rafael Micro R820T2 or R828D) that picks a stretch of spectrum, and a Realtek RTL2832U that was meant to decode DVB-T television from it.

In 2012, Linux developers worked out that the Realtek chip has a mode that skips the TV decoding entirely and streams the raw radio signal straight down the USB cable, about 2.4 million measurements a second. Linux TV-driver developer Antti Palosaari is credited with the find, and the Osmocom project wrote the first open-source driver (RTL-SDR Blog). A cheap TV stick became a general-purpose radio receiver overnight, and a whole hobby grew up around it. Purpose-built versions such as Nooelec’s NESDR Smart, the one we use, and the RTL-SDR Blog V4 keep the same Realtek chip but add the things the TV sticks skimped on: a metal case, a steadier clock, better filtering and an SMA aerial socket.

That history matters for two reasons. It explains why the hardware is so cheap. And it means the stick can still be a TV tuner, so you can watch free-to-air TV on a laptop with no login or subscription, which is the subject of our companion guide.

What “software-defined” actually means

An ordinary radio is built to do one thing. An FM radio has circuits that tune between 87.5 and 108 MHz and a circuit that turns FM into sound, and that is all it will ever do.

An SDR does as little as possible in hardware:

1. The tuner shifts the part of the spectrum you asked for down to a low frequency.
2. The converter measures that signal millions of times a second and turns it into a stream of numbers, called I/Q samples. Think of them as a recording of the radio waves themselves, not of any sound.
3. The software does everything else: picks out one station from the slice, filters away the rest, works out how the signal was encoded, and turns it into sound, pictures or data.

Change the software, and you have changed the radio. The same stick is an FM receiver in one program, a digital radio in another and a weather-station decoder in a third.

The window you are looking through

The RTL-SDR captures about 2.4 MHz of spectrum at once. (Boxes quote up to 3.2 MHz, but faster rates tend to drop samples; the RTL-SDR Blog guide puts the stable limit at about 2.56 MHz and suggests 2.4.) Picture a window 2.4 MHz wide that you can slide anywhere the dongle tunes: roughly 0.1 to 1,750 MHz on ours. Anything inside the window is on screen at once; anything outside it isn’t, until you move the window.

That one number explains a lot of what follows. A whole FM station fits in the window ten times over. A DAB+ digital radio block fits, just. A digital TV channel, at 7 MHz wide, doesn’t fit at all.

What you need

• An RTL-SDR dongle with an aerial. Ours is below. A kit with a telescopic aerial is the easiest start.
• A computer. Windows, Mac or Linux. Any machine from the last ten years is fast enough.
• A short USB extension lead. Computers are electrically noisy, and moving the dongle 50 cm away from the case makes a visible difference.
• Free software. We start everyone on SDR++ (sdrpp.org), which runs on all three systems. SDR# from airspy.com is the long-standing Windows favourite. Two specialist programs appear in the examples below: welle.io for DAB+ and rtl_433 for remote sensors.

SDR dongle

Nooelec NESDR Smart v5 bundle

What we use it for: learning SDR — FM, DAB+, 433 MHz sensors and the occasional TV experiment.

Chips

Realtek RTL2832U with an R820T2 tuner

Receives

100 kHz to 1.75 GHz (below about 25 MHz by direct sampling, which needs a suitable aerial such as a long wire)

Frequency accuracy

0.5 ppm temperature-compensated clock, so it doesn’t drift as it warms up

Connects by

USB, which also powers it

Aerial socket

SMA (see our connector reference)

Transmits

No. Receive only

Driver

None on a Mac. On Linux, the free rtl-sdr tools. On Windows, SDR++’s built-in driver or the WinUSB driver installed with Zadig (see On Windows)

In the box: the dongle in an aluminium case, a magnetic aerial base on a 2 m cable, and three whips that screw into it: a telescopic one you can set to any length, and fixed ones for 433 MHz and UHF (Nooelec). Note that these are single whips, not a two-armed dipole; the aerial section below explains what that changes.

Know before you buy: it receives only, so it can’t interfere with anything, and it can’t do what some listings imply about “hacking” car keys. Its 8-bit converter is basic, so a strong local station can drown a weak one nearby. The metal case runs warm in use; that is normal. Because it keeps the R820T2 tuner the old TV sticks used, it can also go back to being a TV tuner (here’s how).

See it on Amazon AU (paid link)

Getting set up

Jump to your computer: Windows · Mac · Linux

The first part is the same on every computer:

1. Plug the dongle in through the USB extension lead, and screw on the aerial.
2. Install the driver (if any) and the software from the section for your computer, below.
3. Open SDR++ (or GQRX), choose “RTL-SDR” as the source and press Play. You now have a waterfall: frequency left to right, time scrolling downwards, signal strength as colour. Every signal you meet below is a shape on that waterfall before it is anything else.
4. Set the gain properly. Turning the gain to maximum is the most common beginner mistake. Start low, raise it until the background noise on the waterfall just starts to lift, then back off a notch. Too much gain doesn’t make weak stations louder; it fills the screen with ghosts of strong ones. There is no single right number to copy: it depends on your aerial and how strong the stations are where you are. The guides agree on the method instead. The RTL-SDR Blog quick-start guide notes that SDR# starts the gain at zero, where you’ll probably hear only very strong FM stations, and says to raise it until other signals appear. The SDR++ manual says to tune a known clear FM station and set the gain roughly for a hiss-free sound, then fine-tune it on a weak station for the biggest gap between the signal and the background hiss; sometimes, it adds, turning the gain down brings a signal up. It also rates the dongle’s own RTL AGC and Tuner AGC switches as less effective than setting the gain in the software.
5. Set the aerial to the right length for what you want to hear. The next section explains how; for FM, pull the telescopic whip out to about 75 cm.

Only one program can use the dongle at a time, on any computer. Close one before you open the next.

On Windows

Windows treats the dongle as the TV tuner it was sold as. SDR programs need it on a generic USB driver, WinUSB, instead.

• The driver. Sources disagree on whether you have to swap it yourself. The SDR++ manual says the RTL-SDR drivers are built into SDR++ and Zadig isn’t needed; the RTL-SDR Blog guide says to run Zadig first for every program, SDR++ included. Both routes are documented, so try the simpler one first: open SDR++ and see whether it lists the dongle. If it doesn’t, swap the driver with Zadig (zadig.akeo.ie): choose Options › List All Devices, pick Bulk-In, Interface (Interface 0), make sure the target is WinUSB, and click Replace Driver. Pick the wrong device here and that device stops working, so check the USB ID reads 0BDA 2838.
• SDR++: download sdrpp_windows_x64.zip from sdrpp.org, unzip it into a folder of its own and run sdrpp.exe. SDR# (airspy.com) is the long-standing Windows-only alternative.
• DAB+: welle.io has a Windows installer on its download page.
• 433 MHz sensors: rtl_433 has ready-made Windows builds on its releases page. Unzip one and run it from a Command Prompt; it uses the same WinUSB driver.
• TV later? Once Zadig has swapped the driver, the dongle stops being a TV tuner on Windows until you undo it. The TV guide explains.

On a Mac

No driver is needed. macOS leaves the dongle alone, and SDR programs talk to it directly. We used an Apple silicon Mac mini.

• Check the dongle (optional). With Homebrew, brew install librtlsdr installs the dongle’s command-line tools (Homebrew formula), and rtl_test -t should name the tuner. Ours said Found Rafael Micro R820T tuner.
• GQRX is the simplest place to start. Download the .dmg for your Mac from its releases page (arm64 for Apple silicon, x86_64 for Intel), choose the device RTL-SDR at 2.4 MSPS, and set the mode to WFM (stereo). GQRX found our dongle straight away, and the command-line rtl_fm tool recorded triple j on 105.7 MHz.
• SDR++ has a native Apple silicon build (sdrpp_macos_arm.zip) and an Intel one on its nightly download page.
• If macOS won’t open an app because it can’t check the developer, open System Settings › Privacy & Security and click Open Anyway (Apple).
• DAB+ is the awkward one. welle.io’s newest Mac build is version 2.4, and it is Intel-only (welle.io releases), so an Apple silicon Mac needs Rosetta 2, Apple’s translator for Intel apps. macOS offers to install it the first time you open an Intel app, or run softwareupdate --install-rosetta (Apple). Apple says that from macOS 28 Rosetta will only support some older games, so treat this as a stopgap. We didn’t install Rosetta, so DAB+ on our Mac is untested. CubicSDR is in the same position: its last Mac build, 0.2.5 from 2018, predates Apple silicon (CubicSDR releases).
• 433 MHz sensors: brew install rtl_433 (rtl_433).

On Linux

The one catch on Linux: the kernel’s own TV driver, dvb_usb_rtl28xxu, grabs the dongle the moment it is plugged in, and an SDR program can’t open the dongle while the TV driver holds it.

• Install the tools. On Debian, Ubuntu and Linux Mint, the rtl-sdr package brings rtl_test and rtl_tcp (Debian) and a device rule that lets an ordinary user open the dongle (rtl-sdr). GQRX is in most distributions’ software manager as gqrx-sdr (Debian, GQRX); SDR++ comes as a .deb for your Ubuntu or Debian version from its nightly download page. We used both on Linux Mint, and GQRX had triple j (105.7), 2Day (104.1) and ABC Classic (92.9) loud and clear in stereo.

• Deal with the TV driver, one of two ways. The easy way is to let the SDR program unhook it: the rtl-sdr library can detach the kernel driver when it opens the dongle and hand it back when it closes, if it was built that way (rtl-sdr source). Linux Mint’s was, so we did nothing. If a program instead complains that the kernel driver is active, block the TV driver (RTL-SDR Blog guide):

  echo 'blacklist dvb_usb_rtl28xxu' | sudo tee /etc/modprobe.d/blacklist-dvb_usb_rtl28xxu.conf

  Then unplug the dongle and plug it back in. The block also stops the dongle working as a TV tuner, so if you want TV as well, read the TV guide first.

• DAB+: welle.io recommends installing it from Flathub (welle.io releases).
• 433 MHz sensors: sudo apt install rtl-433 on Debian, Ubuntu and Mint (rtl_433).

Or use the dongle from another computer

The rtl_tcp tool, part of the rtl-sdr tools (Homebrew’s librtlsdr on a Mac, the rtl-sdr package on Linux), shares the dongle over your home network (rtl_tcp source). On the computer the dongle is plugged into, run rtl_tcp -a <server address>, where <server address> is that computer’s own address on your network (without -a, it only listens to itself). On the other computer, choose RTL-TCP as the source in SDR++, enter the same address and port 1234, and press Play. We served our dongle from the Linux laptop this way and checked that the samples arrived on another computer; we haven’t yet tried SDR++ on Windows as the receiving end. At 2.4 MSPS the stream is about 38 Mbit/s, so use a network cable, or drop the sample rate to 1.024 MSPS on Wi-Fi. Keep it on your home network: never open the port to the internet.

Why the aerial’s length matters

The aerial is the one part of an SDR you can improve for free, and most of the improvement comes from getting its length right. A gain setting can’t make up for an aerial that is the wrong size for the signal.

Every signal has a wavelength

A radio wave travels at the speed of light, about 300,000 km a second. Its frequency is how many waves pass each second. Its wavelength is the distance from the top of one wave to the top of the next. Divide one by the other and the conversion is one line:

Wavelength in metres = 300 ÷ frequency in MHz

An FM station on 100 MHz has a wavelength of 300 ÷ 100 = 3 metres. A 433 MHz weather station’s is 300 ÷ 433.92 = 69 cm. Low frequencies have long waves; high frequencies have short ones.

Match the aerial to the wave

An aerial picks up a signal best when its length matches the wavelength, in the same way a guitar string rings loudest at its own note. At the right length the aerial resonates: the energy arriving from the wave builds up in it instead of washing through, and more of it reaches the dongle.

A full wavelength is not the best length. Half a wavelength is, and that is what the classic two-armed SDR aerial, called a dipole, is designed for. A half-wave dipole resonates cleanly, and at its centre, where the cable joins, it presents an impedance of about 70 Ω (ARRL gives 72 Ω). That is close to the 50 Ω a dongle with an SMA socket expects (RTL-SDR Blog), so the signal passes into the cable instead of bouncing back off the join. Halve the 300 rule and you have the number to remember:

Half-wave dipole, tip to tip, in metres = 150 ÷ frequency in MHz

Each of the two arms is half of that again, a quarter of a wavelength: 75 ÷ MHz in metres, or 7,500 ÷ MHz in centimetres.

That quarter-wave number is also the one to use with a single whip, like the telescopic one in our Nooelec bundle. A whip on its own is half a dipole: it uses the metal it stands on as its missing half, so it wants to be a quarter of a wavelength long. Set the whip to the “each arm” length, and stand the magnetic base on something metal, such as a baking tray, rather than on wood or plastic.

Worked example: an FM station on 98.5 MHz.

1. Wavelength: 300 ÷ 98.5 = 3.05 m.
2. Half-wave dipole: 150 ÷ 98.5 = 1.52 m tip to tip.
3. Each arm: 1.52 ÷ 2 = 76 cm. Pull each telescopic arm out to 76 cm and set them in a straight line. With a single whip, pull it out to 76 cm.

The lengths for the examples below

If a telescopic whip won’t reach the length in the table, pull it out fully. Nooelec doesn’t publish how long the telescopic whip in our bundle is, collapsed or extended: its bundle page, the NESDR SMArt v5 datasheet and the Amazon listing give no figure, and its support FAQ says only that the whip’s frequency range depends on how far you extend it (it rates the two fixed whips for 433 MHz and for 800 to 2,200 MHz). All checked 13/10/2026. So measure yours fully extended before you count on it reaching FM’s 75 cm; if it falls short, a length of wire will do the job.

How exact does it need to be?

Not very, for listening. In practice a dipole works best slightly shorter than the formula, by about 5%, because the signal behaves as if the ends of the wire were a little further out than they are. (Radio amateurs’ rule of thumb, 468 ÷ MHz in feet instead of the free-space 492, is that 5%: ARRL.) Within 10% of the right length, you’ll hardly see a difference on the waterfall. What does hurt is being wrong by a lot. Arms set at 17 cm for 433 MHz will pick up FM far more weakly, and no telescopic aerial is anywhere near long enough for 27 MHz.

The quickest check is the waterfall itself. Tune to a steady signal, slide the arms in and out a few centimetres, and stop where it is brightest.

Receiving is forgiving. Transmitting is not: a transmitter driving a badly matched aerial reflects power back into itself. An RTL-SDR never transmits, so all a wrong length costs you is signal.

When the right length won’t fit: coiling

The formula runs into practical limits fast. A quarter wave at 27 MHz is 2.8 m, and in the AM radio band it’s anywhere from about 50 to 140 m. Nobody puts that on a toy, a car or a kitchen radio. The usual answer is to coil the aerial.

A coil of wire stores energy in its magnetic field, which makes a short aerial behave electrically like a longer one. Wind part of the aerial into a coil, called a loading coil, and a whip a fraction of the full length can still resonate at the frequency you want. You see it everywhere once you know to look:

• The “rubber ducky” on a handheld radio is a wire wound into a tight spring inside a rubber sleeve. It resonates as a quarter wave at a fraction of the height.
• A 27 MHz CB whip on a car is usually around 0.6 to 1 m, not 2.8 m, with a coil at the base or the middle, or a wire wound along the length of a fibreglass rod (a “helical whip”). Australian maker GME’s range, for example, includes a 60 cm whip and a 1.04 m base-loaded fibreglass one.
• An AM radio’s aerial is a coil of fine wire around a ferrite rod a few centimetres long, inside the case. The ferrite concentrates the magnetic part of the wave so a tiny coil can stand in for an aerial hundreds of metres long.
• The stubby aerial on a modern car, and the shark fin on the roof, are coiled or electronically amplified versions of the 75 cm FM whip older cars had.

Coiling isn’t free. A shortened aerial has three costs (an engineer’s worked example of a shortened 28 MHz dipole shows all three):

1. It works over a narrower range. A full-size dipole is happy across most of the FM band. A coiled one is sharply tuned, so it is good on its design frequency and falls off quickly either side.
2. It catches less signal. A short aerial intercepts less of the wave, and some of what it catches is lost as heat in the coil’s wire.
3. It is tuned by trial, not by formula. How much wire a coil needs depends on its diameter and how tightly it is wound, so coiled aerials are adjusted until they resonate, not calculated from 150 ÷ MHz.

For an SDR on the low frequencies, where a full dipole won’t fit, the usual answer is the opposite of coiling: a long piece of wire strung out along a fence or through the roof space, joined to the dongle through a small matching transformer (a 9:1 unun or balun). Nooelec suggests exactly that for this dongle below 25 MHz. Length beats cleverness when the waves are tens of metres long.

Common aerial sizes, and why they are that size

Run the formula over everyday aerials and most of their sizes make sense. A quarter-wave whip on a metal roof or ground plane uses the metal as its missing half, so it is a quarter wavelength long, not a half.

The phone is the extreme case of the same trade-off: a dozen bands, no room at all, and engineers folding, coiling and printing aerials into whatever space is left. The telescopic dipole on your desk is the opposite: inefficient to carry, but adjustable to almost any frequency the dongle can hear.

Where to put it

Put the aerial at a window, then try the arms both upright and lying flat. Transmitters differ, and whichever way gives the brighter signal on the waterfall is the right one for that station. For TV, the far better answer is the roof antenna you already own; the TV tuner guide shows the adapters.

Example 1: FM radio — where everyone starts

FM is the best first signal because it is strong, it is everywhere, and you already know what it should sound like.

1. Tune SDR++ to the middle of the FM band, about 98 MHz, set the mode to WFM (wide FM), and look at the waterfall.
2. Each station is a bright vertical band about 200 kHz wide. In Australia most of them sit on frequencies ending in an odd number: 104.1, 105.7, 106.5. That is the ACMA’s channel plan: 88.1, 88.3 … 107.9 MHz.
3. Click on one and you hear it. If the station sends RDS and the signal is strong, turn on the RDS decoder and the station name appears, the same text a car radio shows (SDR++ manual).

In our use, FM comes in very well on the telescopic whip from our Nooelec bundle (our results, 13/10/2026). We still don’t know that whip’s extended length, so measure yours, as in the aerial section.

What makes FM a good teacher is what you can see once it is demodulated. An FM stereo signal is several signals stacked together: the mono sound, a quiet tone at 19 kHz called the pilot, the stereo difference signal centred on 38 kHz (ITU-R BS.450), and the RDS data at 57 kHz (ITU-R BS.643).

What you learn here: the waterfall, tuning, the WFM mode, gain, and that a radio station is a shape before it is a sound.

Example 2: DAB+ digital radio — many stations in one block

Drag the window up to around 200 MHz and something different appears: a few flat, solid blocks about 1.5 MHz wide, with sharp edges and no gaps. That is DAB+, and each block isn’t one station. It is a multiplex: typically a dozen to two dozen stations squeezed into one digital stream and broadcast together. (A block carries about 1.15 Mbit/s at the usual level of error protection, and DAB+ stations generally use 40 to 88 kbit/s each: ETSI EN 300 401, WorldDAB.)

Australia’s capital-city DAB+ sits on blocks in VHF Band III:

Sources: ACMA DAB block table and Digital Radio by Area Served, July 2026, checked 12/10/2026. Sydney, Melbourne and Brisbane use all three 9 blocks; Adelaide and Perth use 9B and 9C; Hobart and Darwin use 9A and 9C; Canberra uses 8D and 9C. In Sydney, 9A, 9B and 9C are broadcast from Artarmon and six smaller sites, from Sydney Tower to Bonnet Bay.

How many stations that adds up to keeps changing, because pop-up and seasonal stations come and go, and we couldn’t find a current official count for Sydney alone. The industry body Commercial Radio & Audio puts it at up to 30 DAB+-only stations in each mainland state capital, as reported by WorldDAB (page updated 05/03/2026, checked 13/10/2026). welle.io’s scan, below, will tell you exactly what is on air where you are.

SDR++ can show you a DAB+ block but can’t turn it into sound. For that, install welle.io (welle.io), which is free for Windows and Linux (the Mac version is no longer maintained; see On a Mac):

1. Close SDR++ (only one program can use the dongle at a time).
2. Open welle.io and let it scan. It steps through the blocks and lists every station it can decode.
3. Pick a station. Alongside the sound you get the station name, the song title and often a slideshow of artwork.

What you learn here: a digital signal looks nothing like an analogue one, a block of spectrum can carry many stations, and the 2.4 MHz window is just wide enough for one DAB+ block.

Example 3: Radio control — and the remotes all around you

Remote controls are where an SDR starts to feel like a superpower, because you can see signals that are normally completely invisible.

Toy and hobby radio control. Older and cheaper radio-controlled toys and models sit in the low VHF bands, mostly around 27 MHz (26.957 to 27.283 MHz, between the CB channels) and 40 MHz (40.66 to 41 MHz). Those, and most other low-power remotes, are covered by the ACMA’s low-interference-potential devices class licence. Higher-power hobby gear has its own radio-controlled models class licence, which covers just two bands: 29.72 to 30 MHz, and 36 to 36.6 MHz for model aircraft and boats on a 20 kHz channel grid (36.010, 36.030 MHz and so on; aircraft may also use the frequencies in between). Tune to the model’s frequency (it is often printed on the transmitter or its crystal), set the mode to AM or NFM, press the stick on the controller, and watch the bursts appear on the waterfall each time. Sources: ACMA LIPD Class Licence 2025 (F2025L01047) and Radio-controlled Models Class Licence 2025 (F2025L00971), both in force from 01/10/2025, checked 12/10/2026.

Modern drones and hobby transmitters use 2.4 GHz, also under the LIPD licence, which is above what an RTL-SDR can reach. That is a useful lesson in itself: every receiver has a range, and part of learning SDR is learning where yours stops.

433 MHz: the remotes that aren’t toys. Set the window on 433.92 MHz and wait. In most suburbs, short bursts arrive every minute or so: a neighbour’s wireless weather station, a doorbell, a garage remote, the tyre-pressure sensors in passing cars. These low-power devices need no licence of their own: the ACMA’s low-interference-potential devices class licence covers them, at up to 25 mW on 433.05 to 434.79 MHz.

The free command-line program rtl_433 (github.com/merbanan/rtl_433) decodes these devices and prints what they say (Getting set up shows how to install it on your computer). It is built mainly for 433.92 MHz and the other licence-free bands such sensors use around the world (315, 345, 868 and 915 MHz), and its README lists 380 device protocols, 44 of them switched off by default (checked 13/10/2026): weather stations, temperature and humidity sensors, tyre-pressure sensors, doorbells, remote controls and switches, energy monitors, smoke and water-leak detectors, security sensors, soil-moisture probes and even meat thermometers. In practice that is often the temperature and humidity from a weather station three houses away.

What you learn here: short digital bursts, on–off keying, and how much of the “wireless” world is nothing more than a signal on a frequency anyone can hear.

Example 4: Digital TV — the signal that doesn’t fit

Slide the window to an Australian TV channel, somewhere between 174 and 230 MHz on VHF (channels 6 to 12) or 526 to 694 MHz on UHF (channels 28 to 51), depending on where you live (ACMA channel table). The Australian Government’s mySwitch site shows the channels and transmitter for your address.

You’ll see the strangest shape yet: the whole waterfall turns into a flat plateau, edge to edge, with no structure in it at all. You are looking through a 2.4 MHz window at a signal 7 MHz wide, so all you see is the middle third of it. Australian digital TV uses DVB-T, which spreads one network’s channels across thousands of carriers (1,705 or 6,817, depending on the mode) in a 7 MHz block.

In SDR mode, that is as far as it goes. The stick can’t capture a whole TV channel as raw samples, so no SDR program can turn it into a picture.

But remember where the stick came from. The Realtek chip still has its original DVB-T decoder inside, and it handles the full 7 MHz channel in hardware. Switch the stick back to its TV driver and it is a TV tuner again. The companion guide shows how to watch it on a laptop or an iPad, no login required. For watching, plan on your TV antenna rather than the bundled whip: how the whip does depends on where you live, and in our use live TV was only good through the real antenna.

What you learn here: bandwidth is the limit that matters, and the same chip can do one job in software and another in hardware.

Listening, the law, and keys

Listening to broadcast radio and TV is what those transmissions are for. Receiving most other transmissions is generally permitted in Australia. Intercepting phone calls is not: the Telecommunications (Interception and Access) Act 1979 (section 7) makes it an offence to intercept a communication passing over a telecommunications system. Recording, passing on or acting on private communications you happen to hear can raise other legal problems too. Treat anything that isn’t a broadcast as none of your business. This is general information, not legal advice.

Transmitting is a different matter, and needs the right equipment and, for most bands, a licence. An RTL-SDR can’t transmit at all, which is one reason it is such a safe way to learn.

Car keys and garage remotes: most modern ones use rolling codes, and an RTL-SDR can’t transmit anyway. Watch the signal on the waterfall; leave it at that.

Where to go next

• Aircraft overhead. Planes broadcast their position on 1090 MHz, the ADS-B system CASA has adopted for Australia, and free software turns the dongle into a live flight map.
• Weather satellites. With a home-made aerial you can receive pictures from Russia’s Meteor-M weather satellites on 137 MHz as they pass overhead. (The American NOAA satellites that older guides describe were switched off in 2025.)
• A better aerial. Most improvements in SDR come from the aerial, not the dongle. Higher, outside and the right length beats any software setting.

Common questions

Sources

Laws, regulators and standards

• Radio and Television Broadcasting Stations, Internet Edition: General information (FM, DAB+ and TV standards, DAB block and TV channel tables). ACMA. link. July 2026 edition, checked 12/10/2026.
• Radio and Television Broadcasting Stations, Section 6: Digital Radio by Area Served. ACMA. link. July 2026 edition, checked 12/10/2026.
• Radiocommunications (Low Interference Potential Devices) Class Licence 2025, F2025L01047. Federal Register of Legislation. link. In force from 01/10/2025, checked 12/10/2026.
• Radiocommunications (Radio-controlled Models) Class Licence 2025, F2025L00971. Federal Register of Legislation. link. In force from 01/10/2025, checked 12/10/2026.
• Telecommunications (Interception and Access) Act 1979, sections 5 and 7. Federal Register of Legislation. link. Compilation No. 134, 27/08/2026, checked 12/10/2026.
• Recommendation ITU-R BS.450-4: Transmission standards for FM sound broadcasting at VHF. ITU. link. October 2019.
• Recommendation ITU-R BS.643-4: Radio data system (RDS). ITU. link. December 2022.
• ETSI EN 300 401 V2.1.1: Digital Audio Broadcasting (DAB) to mobile, portable and fixed receivers. ETSI. link. January 2017.
• Surveillance network and equipment (ADS-B, 1090 MHz). Civil Aviation Safety Authority. link. Checked 12/10/2026.
• mySwitch: digital TV reception by address. Australian Government. link. Checked 12/10/2026.
• POES Operational Status. NOAA Office of Satellite and Product Operations. link. Checked 12/10/2026.
• Meteor-M N2-4. WMO OSCAR satellite database. link. Checked 12/10/2026.

Manufacturers and software

• NESDR SMArt v5 product page and bundle contents. Nooelec. link and bundle. Checked 12/10/2026; bundle page re-read 13/10/2026 (no whip lengths given).
• NESDR SMArt v5 datasheet, Revision 1, 04/10/2022. Nooelec. link. Checked 13/10/2026.
• RF Accessories (Balun, Antennas): frequency ranges of the antennas in the NESDR SMArt bundles. Nooelec support. link. Updated 30/06/2026, checked 13/10/2026.
• About RTL-SDR (history, tuner ranges, 8-bit converter, input impedance). RTL-SDR Blog. link. Checked 12/10/2026.
• RTL-SDR Quick Start Guide (Zadig steps, Zadig before SDR++ on Windows, no Mac driver, Linux driver blacklist command, sample rates; SDR# gain starts at zero, raise it until signals appear). RTL-SDR Blog. link. Checked 12/10/2026; re-read 13/10/2026.
• SDR++ website and user manual (platforms, RDS decoding; RTL-SDR drivers built in so Zadig “not needed”, Windows zip install, RTL-TCP source; setting the gain on a clear FM station, then on a weak one; RTL AGC and Tuner AGC). SDR++. site and manual. Checked 12/10/2026; driver, install and gain sections re-read 13/10/2026.
• SDR++ nightly builds (Windows zip, macOS Apple silicon and Intel builds, Debian and Ubuntu .deb packages). GitHub. link. Checked 13/10/2026.
• Gqrx releases (macOS arm64 and x86_64 .dmg, v2.17.7) and download page (Linux distribution packages, Flathub, Homebrew). releases and download. Checked 13/10/2026.
• gqrx-sdr and rtl-sdr packages (RTL-SDR support; rtl_tcp and rtl_test). Debian. gqrx-sdr and rtl-sdr. Checked 13/10/2026.
• rtl-sdr source: device rule (plugdev group), kernel-driver detach build option, rtl_tcp (I/Q server, port 1234, listens on 127.0.0.1 unless given -a). Osmocom. rtl-sdr.rules, CMakeLists.txt, rtl_tcp.c. Checked 13/10/2026.
• welle.io releases (2.4 is the last macOS build; Windows installer; Flathub recommended on Linux). GitHub. link. Checked 13/10/2026.
• CubicSDR releases (last macOS build 0.2.5, August 2018; 0.2.7 is source only). GitHub. link. Checked 13/10/2026.
• rtl_433 releases (Windows builds). GitHub. link. Checked 13/10/2026.
• Homebrew and the librtlsdr formula (Apple silicon builds; rtl_test, rtl_fm, rtl_tcp). Homebrew and formula. Checked 13/10/2026.
• If you need to install Rosetta on your Mac (Intel apps on Apple silicon; reduced from macOS 28). Apple Support. link. Checked 13/10/2026.
• Open a Mac app from an unknown developer (Privacy & Security, Open Anyway). Apple Support. link. Checked 13/10/2026.
• SDR# download. Airspy. link. Checked 12/10/2026.
• welle.io (DAB/DAB+ receiver, supported platforms). link. Checked 12/10/2026.
• rtl_433 (supported bands; README list of 380 device protocols, 44 disabled by default; Homebrew and apt install commands). GitHub. link. Checked 12/10/2026; device list and install section re-read 13/10/2026.
• Zadig USB driver installer. Akeo Consulting. link. Checked 12/10/2026.
• 27 MHz, UHF CB and marine VHF antenna product pages (AE312H, AE220, AE4002, AW364V, AW368V). GME. AE312H, AE220, AE4002, AW364V, AW368V. Checked 12/10/2026.
• GME 1.1 m UHF CB collinear (AE4703) listing. Bunnings. link. Checked 12/10/2026.

Antennas and background

• Antennas 101: The Basics (Ward Silver, N0AX). ARRL. link. 2013.
• Radio Lab Handbook, Unit 4: Transmitting and Receiving Devices (dipole length, 468 ÷ MHz). ARRL. link. Checked 12/10/2026.
• A short dipole for 28 MHz (Klaus Solbach, DK3BA). University of Duisburg-Essen. link. March 2024.
• DAB+ audio bit rates. WorldDAB. link. Checked 12/10/2026.
• Australia: current situation (Commercial Radio & Audio’s count of DAB+-only stations in the mainland capitals). WorldDAB. link. Updated 05/03/2026, checked 13/10/2026.
• RTL2832U based software defined radios (Alexandru Csete, OZ9AEC). link. 02/04/2012.