Raw IQ Capture with Espressif's ESP32 Chips
2 days ago
- ESP-SDR is a firmware for Espressif ESP32 chips that captures raw IQ baseband samples using an undocumented internal modem ADC signal chain, requiring no additional hardware.
- It works by utilizing special debug registers to bypass Wi-Fi modems and write raw IQ samples directly into chip SRAM, with a ring buffer mechanism for sample management.
- The firmware supports sample rates up to 80 MSa/s with a bandwidth of ~13–54 MHz, and operates in the 2.4 GHz band (and 5 GHz on ESP32-C5), with automatic or manual gain control.
- Users can test ESP-SDR in a browser via Web Serial, which displays a power spectrum and waterfall diagram, though at a low duty cycle due to data transfer limitations.
- The discovery originated from Espressif's librftest library and is now applied in ESPARGOS One for phase-coherent capture, enabling localization of arbitrary signals like Bluetooth and Zigbee.
- Limitations include low duty cycle for most models, but the ESP32-S31 supports continuous reception at lower sample rates with a SoapySDR driver for integration with GNU Radio and gqrx.
- Several ESP32 models are supported, and future developments include supporting additional chips and external mixers for frequency conversion, though transmitter implementation is withheld to prevent misuse.