Tutorial: listen to your first signal

Hear a local FM radio station with an RTL-SDR and SDR++ or GQRX, in about 15 minutes. Your first real signal, start to finish.

Beginner · 5 min read · Updated September 27, 2026

In this tutorial you tune a software-defined radio (SDR) to a local FM broadcast station and hear it through your speakers. It is the “hello world” of radio: once it works, your radio, your lab, the display and the sound are all proven, and every other tool follows the same path.

Time: about 15 minutes, plus the first download of the toolbox.

What you need

  • RF Swift installed and rfswift doctor without red lines. If not: Install, then steps 1 to 3 of the Quick start.
  • An SDR receiver. A cheap RTL-SDR USB dongle is perfect. A HydraSDR, HackRF, Airspy or any other SDR supported by the tools works too.
  • An antenna. The small one that comes with most dongles is enough for strong FM stations. Near a window is better than in a basement.
  • Speakers or headphones.

Is this legal?

Listening to public FM broadcasts is fine almost everywhere. This tutorial only receives. Transmitting is a different matter: it needs the right licence or a lab setup such as a shielded enclosure, and RF Swift’s tools are meant for authorised work only.

Create a lab from the sdr_light toolbox

sdr_light contains the classic receiver tools, including SDR++ (sdrpp) and GQRX (gqrx).

bash
rfswift container create -i sdr_light -n fm

Already have a lab from the quick start? Enter it instead: rfswift container shell -c my_first_lab.

On a Mac, create the lab with rfswift --engine lima container create -i sdr_light -n fm: only the Lima engine can pass USB devices through on macOS.

Plug in the dongle and check that the lab sees it

Plug the dongle in. USB devices are shared with the lab by default; if you plugged it in after creating the lab, exit and enter again with rfswift container shell -c fm.

Inside the lab, test an RTL-SDR with:

bash
rtl_test -t

It should find your device and print its tuner. Other SDRs have their own test tools (for example hydrasdr_info for a HydraSDR, hackrf_info for a HackRF), or you can go straight to the next step.

Linux: the dongle is busy or not found?

Linux sometimes grabs RTL-SDR dongles for digital TV (DVB-T). Block that driver on your computer (not in the lab), then restart your computer:

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

Open a receiver

Start SDR++ from the lab’s shell:

bash
sdrpp

Its window opens on your desktop, even though it runs inside the lab. Prefer GQRX? Run gqrx instead; the steps below are the same idea.

Tune to an FM station

  1. Choose your device. In SDR++, open the Source section of the side menu and pick your SDR (for example RTL-SDR). GQRX shows a device dialog on first start: select your dongle there.
  2. Start the radio with the play button (top left in SDR++, the power button in GQRX’s toolbar). A live spectrum and a waterfall start scrolling.
  3. Set the frequency of a station you know, anywhere between 88 and 108 MHz (for example 98.5 MHz). Click the frequency digits at the top and type or scroll them. Broadcast stations show up as wide, bright bands in the waterfall.
  4. Select the demodulator WFM (wide FM). In SDR++ it is in the Radio section; in GQRX it is the Mode setting of the receiver options.
  5. Turn the volume up. You should hear the station. Click the centre of a bright band to fine-tune.

If the audio is noisy, adjust the gain in the source settings: too little and you hear hiss, too much and strong stations distort.

Keep your notes in the workspace

Everything saved in /workspace inside the lab lands in ~/rfswift-workspace/fm/ on your computer, and stays there even if you delete the lab:

bash
echo "Strong station at 98.5 MHz, clean audio with WFM" > /workspace/notes.txt

Point the record or save dialogs of SDR++ and GQRX to /workspace too, and your recordings will be waiting for you on your computer.

It doesn’t work?

No device found. On Linux, check the DVB-T note above; with rootless Podman, run rfswift host udev on your computer, log out and in, and re-plug the dongle. On Windows, run rfswift usb attach again. On a Mac, check that the lab was created with --engine lima and that the dongle is attached (rfswift usb vm-devices lists what the VM sees).

No sound. On Linux and macOS, run rfswift host audio enable on your computer (not in the lab); if pactl is missing it tells you which package to install. On Windows, sound goes through WSLg: if rfswift doctor cannot find the WSLg sockets, run wsl --update, then wsl --shutdown.

No window opens. On Linux, rfswift doctor checks the X11 display and xhost. On macOS, windows open through XQuartz, which must be installed. On any system, --desktop gives the lab a desktop in your web browser instead. More in FAQ & troubleshooting.

What’s next

You have proven the whole chain: radio, lab, display, sound and files. The same steps work for every other tool.

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