Developers uncovered an undocumented mode in multiple ESP32 variants that lets firmware bypass built-in WiFi/Bluetooth and output raw IQ baseband samples. Supported frequency ranges include about 2.2-2.7 GHz on many chips and 4.8-6.0 GHz on the ESP32-C5, with sample rates up to 80 MS/s and analog bandwidths roughly 13-54 MHz depending on the silicon. Most chips can only export short snapshots, making them useful as spectrum analyzers but not for continuous demodulation; the ESP32-S31 is an exception, capable of sustained streaming up to 16 MS/s over Gigabit Ethernet with an impending SoapySDR driver. ESP-WebSDR firmware enables flashing dev boards from a browser for live spectrum and waterfall views. With phase-coherent IQ capture now possible on ESPARGOS hardware, direction finding across the 2.4 GHz band becomes viable, and coherent transmit would be feasible though intentionally unimplemented due to misuse risks.
Two independent projects applied similar discoveries to different ends. A hobbyist integrated an ESP32-S3 with an FPGA USB3 front end to stream continuous IQ to a PC, enabling full demodulation but suffering poor phase noise because the FPGA currently clocks the ESP32; correcting clocking could produce a low-cost general-purpose SDR covering ~2.2-2.8 GHz with up to 80 MHz bandwidth. Another project, C5VRX, uses the ESP32-C5’s undocumented IQ stream as a 5.8 GHz FPV receiver, demodulating onboard and outputting composite video via a resistor DAC, though range and reliability remain works-in-progress.
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