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The person with reported Isotron experience is RFB, and he checks here a lot, so he’ll probably give the answer you’re looking for.
In the meantime I get to give an opinion, which may not be exactly correct.
I think the Isotron expects a standard 50-ohm input, but since they make special models for Part 15, there may be an exception. But here’s why that’s important.
The AMT5000 was very intelligently designed around the fact that Part 15 only allows a 3-meter antenna, whereas licensed AM more typically has 1/4-wave antennas.
The 50-ohm standard is designed around tall 1/4-wavelength antennas, but does not agree well with short antennas.
The AMT5000 provides an exact match to a short (3-meter) antenna, plus a good grounding system.
Even with all that, there could be a way to make the Isotron match.
Check to find out the impedance of the Part 15 Version of the Isotron. That is probably the key to everything.
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