http://www.aprs.org/
https://www.pi-in-the-sky.com/index.php?id=aprs-configuration  - Baloons and so ID,s configuration
inside baloon
https://roinspace.com/research/stratospheric-balloons/balloon4/
Arduino with LibAPRS + 1W DRA818v

Recommended:
https://github.com/DL7AD/pecanpico10/