ESP32 SDR Firmware: Turn a Dev Board Into a Radio Scanner

The humble ESP32 has a hidden talent. In early October 2026, the ESPARGOS team released ESP-SDR, open-source firmware that uses an undocumented feature of Espressif chips to capture raw radio samples, turning a common ESP32 dev board into a software-defined radio spectrum analyzer. CNX Software and RTL-SDR.com both covered the discovery, and the tools are free to try today.

• Coverage: roughly 2.2 to 2.7 GHz, plus 4.8 to 6.0 GHz on the ESP32-C5.
• Speed: up to 80 MSa/s sampling with about 13 to 54 MHz of bandwidth, depending on the chip.
• Chips: ESP32, ESP32-C3, C5, C6, C61, S2 and S3, with the ESP32-S31 in preview.
• Software: ESP-WebSDR flashes the firmware from Chrome or Edge and shows a live spectrum and waterfall; the code is GPL-3.0.

How Does ESP32 SDR Firmware Work?

Normally, the radio inside an ESP32 is locked to Wi-Fi and Bluetooth. Florian Euchner and Zoltan Doczi of the ESPARGOS project found debug registers that let firmware bypass the Wi-Fi modem and read the raw I/Q baseband samples straight from the chip's signal chain. CNX Software reports that the team used large language models to help reverse-engineer parts of Espressif's RF test library. The samples land in internal memory and are passed to a computer over USB or UART.

RTL-SDR.com notes the discovery was made independently more than once. A developer known as h0m3us3r posted a similar ESP32-S3 project to GitHub on September 26, and another project used the ESP32-C5 for 5.8 GHz FPV video reception.

What Can You Do With an ESP32 Spectrum Analyzer?

The easiest starting point is ESP-WebSDR. You plug in a supported board, flash it from the browser, and watch the 2.4 GHz band light up as Wi-Fi, Bluetooth and other devices transmit. That makes it a cheap way to find a quiet Wi-Fi channel, troubleshoot interference in a smart home or teach radio basics in a classroom. On the dual-band ESP32-C5, you can see the 5 GHz band too, and the ESP32-C61 reaches far enough to see LTE Band 7.

What Are the Limits of ESP-SDR?

Bandwidth out of the chip is the catch. USB and UART cannot keep up with the full sample stream, so most boards capture short snapshots. That works well for a spectrum view but can miss brief signals and rules out continuous decoding. The exception is the ESP32-S31, which can stream about 16 MSa/s over Gigabit Ethernet. A SoapySDR driver for GNU Radio and Gqrx is in development for it.

Why This Is Great News for Makers

Most makers already own an ESP32 or two, and this unlocks a new hobby with hardware they have on hand. If you need a dual-band board to try it, the Waveshare ESP32-C5 Touch LCD kit is one option; for a far more serious RF rig, see the QuadRF Raspberry Pi 5 SDR camera. Follow more microcontroller news in our mini computers section.

Sources: CNX Software — October 4, 2026; RTL-SDR.com — October 1, 2026.