sdr

327 Articles

ESP-SDR Can Now Transmit

October 13, 2026 by 2 Comments

Well, that was fast! Last week, we reported on two apparently simultaneous hacks using the 2.4 GHz radio inside many ESP32 variants that enabled raw access to the radio samples, turning it into a listen-only software defined radio (SDR) platform. Listen only? That’s only half of the SDR story.

Last weekend, [Murmel] got started fixing that, and released an early early version of ESP32 firmware that can also transmit, and got it working with gqrx. He demos it by communicating using a Hellschrieber mode of his own devising between an S3 and a C6. And he didn’t stop there, either. He’s working on 802.15.4 modulation at the moment, which means that maybe soon your ESP32 will speak ZigBee.

This is all in the roughly 2.4 GHz band, but Espressif’s API suggests that the radios will tune down as low as 100 MHz, although we can hardly imagine that the filters are tuned to make that particularly effective. Still, it’s clear that the boundaries on the ESP-SDR are just starting to get pushed.

If the early hacks on the RTL-SDR set off a wave of hacker SDR radio experimentation, and we can only hope that this is the beginning of the ESP-SDR era. Thanks then to [Murmel] – aka [Marble] – and the original hacks coming from the Espargos team for kicking this all off!

WiFi Router Does Software-Defined Radio

October 12, 2026 by 3 Comments

Perhaps the most famous of software-defined radios is the RTL-SDR, which is very cheap because it’s a digital TV receiver that’s been pressed into service delivering raw I and Q data streams. But the RTL-SDR is certainly not the only chipset that can do this, and today we have a new one.

The MediaTek MT7996 radio chip in the Gemtek W1700K WiFi 7 router can serve as a very competent SDR receiver, and here’s [h0m3us3r] with the code to make it stream over Ethernet to a Linux machine with a web server, through the device’s SoC.

The radio works on the 2.4, 5, and 6 GHz bands, depending upon which version of the device — and thus which radio chip — you have. These may not be entirely useful to many who use lower bands, and given that a similar hack has been found for ESP32 radios on 2.4 GHz it’s likely a demand will arise for a receive up-converter. Until then, you can look at WiFi packets in a waterfall view to your heart’s content.

Since more and more devices now incorporate a radio, we hope that more such undocumented raw streaming modes will be found, and that we’ll see some other new SDRs. Something to look forward to.

The ESP32, An SDR In Itself

October 3, 2026 by 38 Comments

Perhaps the most famous of all the software-defined radio (SDR) receivers is the RTL-SDR, a digital TV receiver on which an undocumented feature was found. Perhaps other radio-enabled chips also have the same undocumented feature? It seems in the case of some members of the ESP32 family, they do. It’s a discovery made independently in two places, by Espargos, and a Reddit user by the name of h0m3us3r.

What’s happening is that the undocumented mode taps the I/Q stream off before the WiFi modem, and this can be read and processed by SDR software on an external computer. The undocumented mode can be found on ESP32 chips with the earlier Tensilica hardware onwards, so the low power Bluetooth only chips or the non-radio-equipped P4 won’t work. Sadly it’s also only possible with the receive side, with both 2.4 and 5 GHz bands being supported depending on the microcontroller in question.

This isn’t quite the general purpose SDR we got with the RTL-SDR, but there are still plenty of uses to which it can be put. We’re curious as to whether someone can implement the software side of an SDR on the same chip, but we are guessing that might be beyond their capabilities. Either way, we’re looking forward to what the community does with this new-found knowledge.

SDR– Lets You Patch Together Your Setup

October 1, 2026 by 15 Comments

It is often helpful to think of a radio as a series of interconnected functional blocks—hence the use of block diagrams to convey how a given radio operates. [Julian Haag] has brought this ethos to SDR–, a software-defined radio program where you can patch together your setup.

There are many software defined radio tools out there, with various interfaces and methods of configuration. [Julian] wanted to keep things intuitive and simple, and so built SDR– with an interface similar to that of a modular synth. You drop in blocks, like a radio, a demodulator, or a speaker, and then you link them together with patch cables to route the signals where they need to go.

[Julian] has populated the tool with plenty of useful decoders, too, so you can have lots of fun from the get go. You can play with things like ADS-B, POCSAG, SSTV, DAB, and RDS right out of the box. There’s also some fun passive radar and direction finding tools there too if you want to dive in. Files are on GitHub for the curious.

We’ve featured lots of neat SDR hacks over the years, like this neat real-time beamforming setup. Meanwhile, if you’re cooking up your own radio experiments in the homelab, don’t hesitate to let us know on the tipsline.

Handheld Scanner Is A Radio Multi-tool

September 24, 2026 by 3 Comments

These days, it’s possible to cram a whole lot of radio functionality into a very compact device. A great example of that is the LakeShark scanner from [SAMS0N1TE].

The LakeShark is based on the LilyGO T-Display P4—which combines an ESP32-P4 microcontroller with a 4.1 inch AMOLED touchscreen display. It comes with an onboard SX1262 LoRa radio module as well as GPS and a nine-axis Inertial Measurement Unit to boot. [SAMS0N1TE] then set it up to also hook up to an RTL-SDR Blog V3 or V4, providing all kinds of extra software-defined radio functionality.

It can scan everything from P25 Phase 1 trunking transmissions, to ADS-B, POCSAG, and even good old FM broadcast radio. If you want to listen in on what’s on the air, or see a minimap with tracks of the planes flying overhead, you can do it all with this rig. You can even investigate various bands with waterfall displays or try and look for activity from nearby nRF24 devices.

Ultimately, it’s a bit of a Swiss Army knife for radio fun—able to do all kinds of neat things, and it fits right in your pocket. We’ve featured some other great SDR hacks recently, too, like this $50 build with an impressive 20 MHz of bandwidth. If you’re cooking up your own gear for the ham shack and beyond, let us know on the tipsline.

A laptop is shown set up on a desk next to a spectrum analyser, an SDR, and two antennas. The antennas are aimed toward assorted electronics, including headphones and a phone handset.

Reviving TEMPEST Attacks With An Injected Signal

September 20, 2026 by 3 Comments

TEMPEST attacks are often the most effective way to break air-gapped security: rather than directly accessing a computer, the attacker records the system’s unintended radio emissions and uses them to reconstruct its internal operations. This kind of attack was much more effective in the days of noisy, high-voltage CRT displays, and has gradually become less effective as electronics migrate to quieter, less powerful components. A group of researchers, however, has found that even modern electronics can become effective TEMPEST transmitters when irradiated with an RF signal.

The RF a device emits depends on the unintentional antennas in its internal structure. These are difficult to eliminate, and it’s usually not worth the effort; they’re usually small enough that they only effectively radiate at much higher frequencies than the electronics carry. The researchers’ technique, called InjectEave, radiated these electronics with a radio frequency tuned to their internal antennas, injecting that frequency into the circuit. Nonlinear electronic components, such as amplifiers, then mix the injected frequency with the internal signal, creating RF sidebands. This mixed signal then radiates out of the device and can be picked up and demodulated to recover the device’s internal signal.

Continue reading “Reviving TEMPEST Attacks With An Injected Signal” →

It’s GNU Radio Companion, But In The Browser

September 9, 2026 by 15 Comments

The progression of the web browser from a tool for simple static information browsing into a do-everything computing environment has been inexorable, with package after package making the jump. Today it’s the turn of GNU Radio Companion, lowering the barrier to software defined radio considerably. It’s the work of [Marc Lichtman], who’s name you may recall if you have ever used pysdr.org.

Loading it up gives you a very familiar window if you’re used to GNU Radio Companion, and it comes with a set of example flowgraphs that cover a large range of applications. It supports a collection of software-defined radios (SDRs) including the well-known RTL-SDR, and if that’s not enough it can also use your sound card. There is even a set of recorded off-air captures to experiment with.

We’ve spent a while here playing with it, and it does everything we’re used to from the version outside the browser. The only thing we’re told it won’t do is work with a networked SDR, but that’s no deal breaker.

Thanks [Marcus Müller] for the tip.