Radio Hacks

1508 Articles

ESP-SDR Can Now Transmit

October 13, 2026 by 25 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, [marble] got started fixing that, and released an early early version of ESP32 firmware that can also transmit, and got it working with gqrx. The demo communicates between an S3 and a C6 using a Hellschreiber mode, something that’s certainly out of the WiFi spec. And it didn’t stop there, either. [marble] is 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 [marble] suggests that it might be good down to 1.8 GHz. (Editor’s note: previously, we said 100 MHz, but that was incorrect.) So there is still some uncharted terrain, and 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 [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 5 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.

Keep That Old Radio Alive With An ESP32

October 7, 2026 by 11 Comments

As the legacy AM broadcast bands fade away, what happens to the millions of devices built to receive them? Many of them will go into e-waste, but with a century of radios to choose from, some of them are collector’s items. Vintage tube radios like the ones [GarethDaviesLondon] has would go silent, so he’s made a small AM transmitter to keep them alive.

At its heart is an ESP32-S3, which takes an online radio stream and transmits it through RF generated with a pulse chain on a GPIO. Generating analogue signals from radio to video with a microcontroller is nothing new, but perhaps the more interesting part of this one comes in how he radiates enough from that pin. There’s a 3D printed box with stand-offs designed to take a widely spaced wire coil, which is enough for the vintage electronics to pick up. He makes the point that it may not be legal, but at that power we doubt anyone will notice.

The output on this one is 200kHz for the European long wave band, but we’re guessing a higher medium wave frequency could also be generated. Meanwhile if you are curious about AM, we’ve featured someone having a closer look at it.

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.

A drone is shown, carrying underneath it a white plastic box. On the side of the box are two patch antennas. A camera extends from one end of the box, and a large GPS antenna from the other end.

Synthetic Aperture Radar Drone Gets Interferometric Imaging

September 28, 2026 by 10 Comments

It’s been more than a year since [Henrik Forstén] built the first iteration of his synthetic-aperture radar (SAR) imaging drone, and he’s certainly been productive in the meantime. Not only did he develop a much more powerful autofocus algorithm to clean up the radar images, but he also extended the software to create high-resolution interferometric images.

The main limitation of the original radar system was the GPS, which only had a resolution of about one meter; the autofocus algorithm owed much of its improved clarity to an improved estimation of the drone’s position. A simpler, though more expensive, solution was to add an RTK-capable GPS receiver. RTK (Real-Time Kinematic) receivers use a fixed ground station to constantly transmit a correction signal, letting them reach a couple centimeters of accuracy. Since the drone doesn’t actually need to know its position in real time, it can also use PPK (Post-Processing Kinematic) positioning, which compares recorded GPS signals after the flight to obtain similarly accurate positions.

[Henrik] also implemented a few other hardware improvements, including stabilizing the phase-locked loop used to generate the radar’s frequency sweep. The controller FPGA’s SD card interface had too low a bandwidth to record data in real time, so [Henrik] also implemented a simple, fast compression algorithm to speed that up. Most significantly, he also developed a program for interferometric imaging. The drone flies the same path twice at different altitudes; by comparing phase information from different passes, it’s possible to detect a target’s elevation. Normally, the radar program assumes constant elevation, making tall objects seem to lean toward the radar source; an interferogram, on the other hand, allowed [Henrik] to generate a detailed elevation map.

[Henrik] is no stranger to synthetic aperture radar; we’ve previously covered a bike-mounted iteration and a budget SAR system. If the concepts behind this are still a bit fuzzy, we’ve also covered a guide to making your own SAR setup.

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.