Antenna Issues. The first time you do a ship, which antenna is which can be quite a nuisance since transponder and dme antennas look the same. Consult the manuals. Wave the system near each antenna with the systems on to help find which. Coupling the antenna too far away or too close can lead to errors. Other aircraft, mules and hangar floors cause reflection of signals. If you have unexpected errors, try repositioning the test antenna just to see if that is an issue. Some test sets clamp directly over antennas and make this easier. Make sketches with your test set of what overall setups work with a certain aircraft for future use and use by others