The Raspberry Pi Pico is a $4 microcontroller board. Recently radio amateur Luigi Cruz discovered that the ADC on the Pico could be used as a simple direct sampling software defined radio, with a bandwidth of 250 kHz. The idea is that the ADC data is made available to a PC connected to it’s USB port via emulated TCP/IP protocol. On the PC side, GNU Radio is then used to process the received ADC data, turning it into an SDR.
Applications of a direct sampling SDR with only 250 kHz are limited, as it’s only possible to receive up to the LF band, and there are not many signals that low in frequency. However, it is an interesting project that can be used to demonstrate a simple SDR. If you’re interested in trying it out, the code is available over on GitHub.