Jon Dawson's Pi Pico Rx Is a Low-Cost, Breadboard-Friendly Raspberry Pi PIco Software-Defined Radio
Housed in a 3D-printed case and built for standalone use, this clever yet simple radio is designed for low cost.
Maker Jon Dawson has designed a self-contained software-defined radio (SDR), which can be assembled at a very low cost — thanks to the use of a Raspberry Pi Pico as its controller and a breadboarded layout that dodges the need for a custom-built printed circuit board.
"A couple of years ago, I built a basic yet capable radio receiver using a [Raspberry] Pi Pico," Dawson writes, "and while I originally designed a custom PCB for it, this time I’m building an even simpler and cheaper version that can be built on a breadboard using (mostly) through-hole components. I wanted to build a very minimal (but useful) design that I could use as a platform for experiments, tweaks, and upgrades."
Dawson's original design, dubbed the Pi Pico Rx, combined the RP2040-powered Raspberry Pi Pico microcontroller development board with an analog switch and op-amps to create a receive-only software-defined radio capable of covering up to 30MHz with 250kHz of bandwidth and continuous-wave (CW), single sideband (SSB), amplitude modulation (AM), and frequency modulation (FM) modes.
"The design uses a 'Tayloe' Quadrature Sampling Detector (QSD) popularized by Dan Tayloe […] and used in many HF [High-Frequency] SDR radio designs," Dawson explains. "This simple, design allows a high-quality mixer to be implemented using an inexpensive analog switch. A quadrature oscillator is generated using the PIO [Programmable Input/Output] feature of the RP2040. This eliminates the need to use an external programmable oscillator."
Where the original Pi Pico Rx was built on a custom-designed printed circuit board, the new variant is instead put together on a breadboard to help bring down the cost. Despite this, a 3D-printed case with OLED display gives it a slick finish — and the design includes a handful of enhancements over the original including capacitors to prevent saturation of the op-amps, better frequency accuracy, and a lower-cost op-amp.
The full build guide, including schematics, is available on Dawson's website, with source code and design files on GitHub under the permissive MIT license.