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The Isotron will work with the AMT5000 with one caution. Coax can’t be used between the TX and the antenna. Instead, a relatively short wire (no more than maybe 2 ft. tops) should be connected from the TX antenna terminal to the center pin of the coax connector on the antenna. The TX ground terminal should be connected with a separate wire to the bottom end plate on the antenna. The AMT5000 has a jumper option to bypass internal tuning. This jumper plug must be installed.
In general the MW version of the Isotron is really a base-loaded vertical. The loading coil can be seen near the bottom. Also, there is a capacitance top hat (top end plate) and an adjustable tuning rod at the top for fine tuning. The bottom end plate could possibly be considered a rudimentary elevated ground plane, except it is too small to have that effect. There are no taps on the coil, so it will tune only within a fairly narrow range of the frequency you specify when ordering. Since the tuning rod is near the top, you should consider that access to it will be needed when installed in its final location on the roof. You can’t tune it on the ground first because the tuning conditions will be different on the roof.
Here are two links from the Isotron site you should study to gain understanding.
INSTRUCTION MANUAL 160C MODIFIED ALSO AM BROADCAST BAND MODELS
Particularly, you should read the sections in the manual that discuss grounding. They recommend grounding the bottom of the mast. If that is not done, then they say the ground will be through the coax shield to the transmitter ground. In, your case, you should connect a heavy-gauge ground wire from the bottom of the mast on the roof, down the outside of the building, to earth ground. This will improve performance and provide that all important safety ground.