Kazu AG6NS and I have been working on a couple of trackers. One is a dual band 2/20 m APRS/WSPR with other modes coming. It is based on an ATMega1284 processor, which is a 328 (used currently) with more memory and and running at 10 MHz, the safe limit for 3.3 V operation. Kazu has come up with code for it and I need to catch up with a revised PCB.
The other is a Raspberry Pi Pico based tracker. This is a longer range project. It will use the same Si5351 based modulator and filters for 2/20 m. The Picos are attractive as they have a dual core ARM Cortex-M0+ @133MHz which is far more powerful than the ATMegas.
The RP2040 chip has instructions for DIYing a board but I went the Raspberry Pi as it was the easiest path to start working on a design.
Due to the chip shortage, I may need to use through hole components for the output filters.
We are looking at a lot of fun things that can be done – SSTV data and cam, voice ID over VHF, crossband repeaters, and latex floaters. If you’re interested in helping out out or at least join in please get on our chatter list.