- Get the heading of my truck via GPS ( I know I need to be moving for that to work) I would like to feed NEMA data into the Arduino from an external GPS.
This can be done. You don't necessarily have to be moving, but you do have to have moved, in order to define a direction vector (there minus here).
- Get the direction the antenna is pointed RELATIVE TO THE TRUCK, need something attached to the antenna mast that can indicate rotary position and can be turned repeatedly.
A rotary encoder seems like just what you need.
- Calculate the direction of the transmitter.
The easiest part.
- Send info to Google Earth via the serial port.
What will be on the other end of the serial port? The serial port is not some magic device that can make data go anywhere. It is one end of a data transmission mechanism. There must be something on the other end, with a wired or wireless connection between the serial port devices.
If the Arduino is connected to a PC, and some application is running that forms the other end of the connection, that application can read the serial data and send it to google earth.