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If I can play devil’s advocate here, I don’t believe that anywhere in the rules does it talk about ‘radiating grounds’.
The rule states that the total length of the feedline + antenna + ground wire have to be less than 3 meters in length.
The intent of the rule may be to limit radiating grounds, but that’s not what is written. Actually, I believe the intent is to limit range, period.
All that goes to show is that it is the FCC inspector who passes judgement on your installation. There have been elevated installs with long ground wires that have been OK’ed. Also ones that have a short ground wire attached to a metal structure that have also been approved. And many others that have not. The FCC inspector has the final say.
This has all been talked and argued out many times. The least risky installation is ground mounting. I don’t know if an FCC inspector has ever rejected radials, but I suspect that that is within the realms of possibility, particularly if the inspectee is uncooperative. Elevated mounts are the most risky, even if you don’t hook up a specific ground wire, because it is entirely possible for an audio or power feed to act as a ground if none other is available.
Overall, if use Part 15.219 on AM, it’s much more difficult to know if you’re compliant in the eyes of an FCC field inspector than for FM. FM is cut and dry by comparison – if you meet the field strength limits, then you’re likely compliant.