Turning A Wi-Fi Adapter Into An SDR

Since the invention of an undocumented I/Q sampling characteristic in ESP32 chips about two weeks in the past, there’s been a flood of comparable options being present in different wi-fi chips, together with LoRa and Wi-Fi chipsets. The newest chip to affix their ranks is the MediaTek MT7921AU, usually utilized in Wi-Fi adapters, with two totally different tasks creating unbiased SDR drivers for it in the previous few days.

The first was BirriaSDR, which found that the chip exposes uncooked I/Q samples for debugging and calibration; BirriaSDR as a substitute streams these to the host at 40 Msps in 14-bit decision, with the choice to tune from 2156 to 2610 MHz. BirriaSDR makes use of libusb to instantly talk with the Wi-Fi adapter and entry its registers; it doesn’t make any everlasting firmware modifications, so the Wi-Fi adapter goes again to its authentic state after getting used as an SDR. BirriaSDR implements an API just like the RTL-SDR’s.

Mtk79ICAP, against this, exposes the MT7921AU’s sampling options over a typical SoapySDR interface. Unlike BirriaSDR, it applies some firmware modifications to the chip, and it requires a modified driver to work. However, it might attain a most bandwidth of 80 MHz and tune to the 5 GHz bands. The Wi-Fi adapter in use may also concurrently work in monitor mode and stream SDR information, although this solely works when automated acquire management is enabled.

This is the second MediaTek chip we’ve seen repurposed for SDR work, after the earlier MT7996. Conveniently, Wi-Fi adapters usually have exterior antennas, which ought to make it simpler to attach a frequency mixer circuit. These adapters aren’t fairly there but, however some hackers have already used the ESP32 to transmit arbitrary signals.