Cfox33:
Thank you Emeritus I'll check them out as well! Also I'm not sure if this helps. aprsdroid/ at master · ge0rg/aprsdroid · GitHub
Here is the APRS droid on github I have no idea what I'm looking at though and not sure if it is C, or C++ or some prehistoric alien language of the lizzard people of hollow Earth....
Your stated goal was to make it run on an Arduino, so you will need to thoroughly understand it.
Paul