A low-profile version of full-featured software radio based on Raspberry Pi Pico (fully open source + detailed explanation)

With just a Raspberry Pi Pico, an analog switch and an op amp, you can build a powerful SDR receiver covering the LW, MW and SW bands. Capable of receiving signals from halfway around the world. This design uses a Raspberry Pi Pico to handle almost all functions of the radio. The RF oscillator is driven by one of the Pico's programmable I/O (PIO)
pins, taking some of the load off the processor. For AM and SSB, you also need to control the amplitude, generate a PWM signal on another PIO, and then use an analog multiplexer to mix with the RF oscillator. The design also includes a microphone with a preamp that can be fed to a third PIO or it can
receive audio from a computer via a USB interface. More processor resources are required when generating phase-modulated signals such as RF, but Pico is still able to accomplish all of these tasks without incurring jitter larger than the clock cycle. Design Features: 0 - 30MHz Coverage 250kHz Bandwidth SDR Receiver CW/SSB/AM/FM Receiver OLED Display Simple Spectrum Range Headphones/Speakers 500 Universal Memory Uses 3 AAA Batteries Powered by Current Consumption Less than 50mA