Searching on google I found various projects to get a digital compass with Arduino.
The sensor that is used is the HMC5883L or similar and have a negligible cost.
The idea would be to implement in the Satnogs software this sensor that should be mounted on the rotor, obtaining at the turning on of the rotor the pointing to the North, without having to search for it manually (especially when we are outdoor in portable). It works with I2C bus
I can do some tests but I’m not very good at C ++ code.
Here some links on how to get the digital compass