PLEASE SEE THE WIKI FOR SIGNIFICANTLY MORE DETAILED INFORMATION.

click here to download the pre-compiled firmware (original version)

click here to download the pre-compiled firmware of the new, multi-band version. (see wiki for info for Overclocking if using bands other than 20M)

Summary

Extremely low-cost Raspberry Pi Pico based WSPR beacon for tracking GPS position and other telemetry from High Altitude Balloons (HAB), specifically "pico balloons".

Tracker uses the RP2040 microntoller in the Raspberry Pi to directly generate a 20mW RF signal using software trickery. No RF oscillator, TCXO, transmitter or amplifier is needed.

Only two common, readily available and cheap components are needed to implement: A Raspberry Pi Pico, and a tiny GPS module (ATGM336H, or a uBlox clone). Two resistors and some bits of wire and solder hold it together.

Instead of using a TCXO, the extremely precise frequency base needed for the WSPR protocol is obtained by continually "disciplining" the standard crystal oscillator onboard the Pico with the PPS pulses from the GPS module.

The WIKI has more information, instructions and schematics etc. The project also includes gerber files to make a custom PCB version of the tracker, that is lighter but uses the same firmware as the Pi Pico version.