Another thing to look out for is enthusiastic Painters painting the Antenna.Saw it recently after a Check.Cleaned the paint off and the system worked fine.
I don't know if you should check the resistance of the Antenna.I would leave that to the Shoppie's.Smith's make a test set for checking the VSWR of line's and passive Antennae but I don't know if you would be able to check a non passive antenna with this box.