Back in 2025, a project called ESPARGOS built a phased array of many patch antennas, each connected to an ESP32 WiFi microcontroller. The idea was to figure out where WiFi signals were coming from and build a live heatmap that showed signal strength in real time. Now the ESPARGOS team has found something far stranger: several ESP32 chips can capture raw radio signals at will, even though the chips are meant for WiFi and Bluetooth.
The discovery is documented in a post titled “Various Projects Find Hidden SDR Capabilities in ESP32 Microcontrollers.” The post describes how the ESP32 firmware can bypass its usual duties and record baseband samples instead, letting the chips act as software-defined radios (SDRs). Several ESP32 models can cover 2.2–2.7 GHz, while the ESP32-C5 extends that to 4.8–6.0 GHz. Sample rates top out at 80 million samples per second, with analog bandwidth ranging from 13 to 54 megahertz depending on the chip.
But there is a catch. For general-purpose use, the output bandwidth is too small to stream continuous data to a PC. That means the SDR works only as a spectrum analyzer, not as a device that can decode radio signals in real time. The exception is the new ESP32-S31, which streams up to 16 million samples per second over its Gigabit Ethernet interface. A SoapySDR driver for GNU Radio and gqrx is coming soon.
“The output bandwidth is insufficient, so only snapshots of data can be exported to a PC.”
What ESPARGOS Found
ESPARGOS originally used the ESP32 to track WiFi and Bluetooth signals. The new discovery changes that. Phase-coherent IQ sample capture is now possible, meaning the hardware can lock onto any signal in the 2.4 GHz band, not just WiFi and Bluetooth. The team says coherent transmissions would be possible too, but they are not building them because they could be misused.
The team also notes that at least two other projects found the same or similar features around the same time, each solving a different problem. One is on Reddit, the other on GitHub. Both teams arrived at the discovery independently.
The Reddit Discovery
On Reddit, user /u/h0m3us3r posted about finding the same feature and uploaded it to GitHub on Sept 26. They recorded a video showing an ESP32-S3 working as an SDR with an FPGA used as a USB3 front end. Unlike ESPARGOS, this setup streams raw IQ data to a PC continuously rather than in snapshots. That should allow full demodulation and decoding on the PC.
There is a hitch. The current prototype clocks the ESP32 through the FPGA, which causes poor phase noise. Fixing that would let an ESP32 combined with an FPGA become a standard general-purpose SDR, like the RTL-SDR, but with a wider frequency range and higher bandwidth.
C5VRX and the FPV Receiver
Another project, C5VRX, uses a similar finding for a very different purpose. First uploaded to GitHub on Aug 13, it turns an ESP32-C5 into a 5.8 GHz real-time FPV video receiver. The project captures FPV signals using an undocumented IQ data stream, demodulates them onboard, and outputs analog composite video through a simple resistor DAC.
The mechanism looks different from the others, but the result is similar: an ESP32 recording radio signals at will. The project is still a work in progress and does not yet work reliably at range.
What This Means for SDRs
The ESP32 was never marketed as an SDR platform. It was designed for WiFi and Bluetooth, and its hidden capabilities were apparently unknown to anyone outside the ESPARGOS team until now. That makes the discovery unusual.
The fact that three separate teams found the same or similar features independently is the real story. Each team approached the problem from a different angle — direction finding, continuous streaming, and FPV video reception — and each found the same underlying capability in the chip.
The implications for hobbyists and makers are significant. An ESP32 running at 80 million samples per second costs far less than a dedicated SDR, and the ability to stream data to a PC opens up real-time processing. The phase-coherent capture also means direction-finding applications, like ESPARGOS’s original heatmap, are now within reach.
For serious users, the snapshot limitation is a real barrier. Continuous streaming requires the Ethernet-capable ESP32-S31, which is a newer model and not available everywhere. The FPGA workaround on Reddit shows promise, but the phase-noise issue means it is not ready for production use yet.
The Road Ahead
The SoapySDR driver for GNU Radio and gqrx on the ESP32-S31 is coming soon. That will make the streaming version of the SDR usable with standard open-source software. The ESP-WebSDR page lets users flash the firmware to most ESP32 dev boards directly from their browser, which lowers the barrier to entry considerably.
The C5VRX project remains a work in progress. Its analog composite output is a clever hack, but the unreliability at range means it is not a production-ready solution yet.
The Reddit project’s FPGA approach is the most promising path forward. Once the phase-noise issue is resolved, an ESP32 combined with an FPGA could indeed become a standard general-purpose SDR.
Why This Matters
The discovery is notable because it shows how deeply a single chip can be understood. The ESP32 has been around for years, and its undocumented capabilities remained hidden until now. The fact that multiple teams found them independently supports the claim that the feature is real.
The broader lesson is that hardware often contains more than its advertised purpose. The ESP32 was designed for WiFi and Bluetooth, but it also happens to be capable of radio signal capture. The teams that found this capability did so because they looked for it, not because it was obvious.
The post documents something genuinely surprising. A WiFi chip, used for decades for its intended purpose, quietly turned out to be capable of something entirely different. That is the kind of discovery that rarely happens in mature technology, and it is worth celebrating.
The ESP32-S31’s Ethernet streaming is the future of this work. The FPGA approach is the present. The snapshot limitation is the current constraint. All three paths are worth watching, and all three point to the same conclusion: the ESP32 is not just a WiFi chip anymore.
Source material: “Various Projects Find Hidden SDR Capabilities in ESP32 Microcontrollers,” rtl-sdr.com.
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