RTL-SDR guide · checked 23 October 2026
RTL-SDR software: using a dongle with FoxSDR
Written by the maker of FoxSDR, so read it with that in mind. What this page says about FoxSDR comes from its own source code and documentation. What it says about other programs comes from the SDR software comparison, whose facts were read from each program’s own pages on 26 September 2026 and are linked there. If something here is wrong or out of date, tell us and it will be corrected.
An RTL-SDR is a USB stick built around Realtek’s RTL2832U chip and a tuner chip. It was sold to watch digital television, and it became the cheapest way into software-defined radio because the chip will hand its raw samples to a computer. The dongle only delivers those samples. RTL-SDR software is the program that turns them into a spectrum, a waterfall, sound and decoded data.
FoxSDR is one of those programs. It opens an RTL-SDR with its own driver, written from the behaviour of the chips, with no librtlsdr, no libusb and no SoapySDR module in the path. It is free for noncommercial use and runs on Windows and Linux.
At a glance
| Tuners driven natively | R820T, R820T2 and R828D, which covers the RTL-SDR Blog V3 and V4 and most current dongles |
|---|---|
| Frequency range | 24 to 1766 MHz on an R820T or R820T2. Below 24 MHz through the Blog V4’s built-in upconverter, or by direct sampling on a dongle wired for it |
| Sample rates | The standard ladder, 250 kS/s to 3.2 MS/s |
| Gain | LNA, mixer and VGA set separately, the single TUNER gain other RTL-SDR programs offer, or the tuner’s automatic gain |
| Frequency correction | PPM correction in whole parts per million |
| Bias tee | Its own checkbox, off every time a dongle opens unless you turn it on, and remembered for each dongle by its serial |
| Over a network | A built-in rtl_tcp client |
| Windows | Bind the WinUSB driver once with Zadig. FoxSDR’s RADIO SETUP page says when a dongle still has the television driver |
| Linux | Nothing to unbind. FoxSDR detaches the kernel’s television driver itself |
| Price | Free for noncommercial use; a commercial licence for everything else |
Setting up an RTL-SDR on Windows
- Download FoxSDR and install it.
- Plug in the dongle. Windows usually gives it a digital television driver. While that driver holds the dongle, no SDR program can open it, FoxSDR included.
- Run Zadig. Tick Options, then List All Devices, select Bulk-In, Interface (Interface 0), choose WinUSB and click Replace Driver. This is done once per dongle.
- Start FoxSDR. Its RADIO SETUP page lists each radio it finds with the driver Windows gave it, and says plainly when that driver is the wrong one. After Zadig, press CHECK AGAIN and the dongle appears in the Source list.
On Linux and the Raspberry Pi
An RTL-SDR on Linux starts out bound to the kernel’s own television driver. You do not need to unbind or blacklist it: FoxSDR detaches it and claims the dongle itself, the same way other Linux SDR tools do. Your user does need permission to open the USB device, which one udev rule grants; the Linux notes give the rule and the three commands that install it.
Be aware: the Linux USB path is written and unit-tested, but it has not yet been confirmed against a real dongle. A 64-bit Raspberry Pi build is published, and no Raspberry Pi has run it yet either. A report either way, working or not, is exactly what closes that out.
HF on the RTL-SDR Blog V4
FoxSDR recognises the RTL-SDR Blog V4 as a V4 rather than as a generic R828D dongle. Below 28.8 MHz it tunes the upconverted frequency, switches the V4’s upconverter on, bypasses the tracking filter on that path and opens the notch filters inside the bands they would otherwise cut. Without that handling a V4 hears nothing below 24 MHz. On any other R820T or R828D dongle, tuning below 24 MHz switches to direct sampling instead, which is what the common HF modification connects an antenna to.
The bias tee
The Bias tee checkbox sits below the gain sliders and appears for every RTL-SDR FoxSDR opens itself. Tick it to power a mast-head LNA from a Blog V3 or V4, or from any dongle whose maker wired a bias tee to the chip’s first GPIO pin. It is off every time a dongle opens unless the dongle’s own memory says it is wired permanently on, because putting 4.5 V on somebody’s antenna is not a safe default. FoxSDR remembers your choice for that dongle by its serial number, and never applies it to another one.
Many dongles ship with the same serial, often 00000001. If you use more than one, give each its
own with rtl_eeprom -s so FoxSDR can tell them apart.
An RTL-SDR somewhere else: rtl_tcp
rtl_tcp is the small server that comes with the RTL-SDR tools. It holds a dongle on one machine, such as a Raspberry Pi in the loft, and streams its samples to another. FoxSDR has its own rtl_tcp client: choose rtl_tcp server (network) at the end of the Source list, type the server’s address and press Open. Gain, automatic gain, the bias tee and the frequency correction are sent to the remote dongle. Because the server does the driving, this also works for a dongle whose tuner FoxSDR’s own driver does not handle, such as an E4000; its gain is then shown as step numbers rather than decibels.
What you can decode with an RTL-SDR
Broadcast FM in stereo with RDS is built in, along with NFM, AM, SSB and CW. Decoders are plugins, installed from a catalogue inside the app. Within an RTL-SDR’s range that includes:
- Aircraft: ADS-B positions on 1090 MHz, drawn on a live map, and ACARS messages.
- Digital radio: DAB and DAB+ stations in Band III, at the 2.048 MS/s an RTL-SDR offers.
- Ships: AIS, on the same map.
- Packet and pagers: APRS, POCSAG and FLEX.
- Weather: NOAA APT satellite pictures and 433 MHz weather sensors.
- Around the house: ERT utility meters and 406 MHz distress beacons.
- On HF, with a V4 or direct sampling: Morse, RTTY, FT8, SSTV and weather fax.
How far each is proven differs, and the plugin catalogue says which: the aircraft decoder has been confirmed off the air and the DAB plugin has played stations off the air, while AIS, APRS, SSTV, Morse, RTTY and POCSAG have been tested against generated signals. Every decoder in this list has a Windows build and a Linux build.
When a dongle is not listed or will not open
- Windows, and the dongle is missing. It almost certainly still has the television driver. Open RADIO SETUP, which names the driver, and run Zadig as above.
- “No R820T or R828D tuner answered”. The dongle has an older tuner, such as an E4000, FC0012, FC0013 or FC2580, which FoxSDR’s own driver does not handle yet. Serve it with rtl_tcp, or reach it through SoapySDR with its RTL-SDR module installed.
- Two dongles that keep swapping settings. They share a serial. Give each its own with
rtl_eeprom -s.
Other RTL-SDR software
FoxSDR is not the only choice. As checked for the comparison on 26 September 2026:
- SDR# ships an RTL-SDR driver and runs on Windows.
- SDR++ has native RTL-SDR and rtl_tcp modules and runs on Windows, Linux, macOS and BSD.
- HDSDR reaches an RTL-SDR through a 32-bit ExtIO driver and runs on Windows.
- SDR Console supports RTL dongles and runs on Windows.
- Gqrx reaches an RTL-SDR through gr-osmosdr and runs on Linux and macOS.
- SDRangel has native plugins for most common radios and runs on Windows, Linux, macOS and Android.
The SDR software comparison sets them side by side, with licences, transmit support and release dates. RTL-SDR.com keeps a longer list of RTL-SDR software, including single-purpose decoders.