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Hey, Signal Guy;
I came across that same blog about the “Unfair” transmitter; quite intriguing. And a friend in the UK has had very good success with a high-Q AM-band transmitting loop, albeit running some tens of watts into a loop of 30 feet in diameter!
It would seem that the Unfair transmitter does indeed conform to Part15 rules, as the total length of the copper pipe in the guy’s loop falls under the limit. A ground is of no material consequence in a magnetic loop, and any ‘feedline’ to the transmitter mounted at the base of the loop is only audio and power.
I don’t suppose a transmitting loop of those same dimensions, except made of plastic sprinkler pipe, and with several turns of heavy wire inside would still meet Part 15 restrictions, as the “total length” of the radiating element might be 50 feet with five turns inside the plastic pipe. Several turns would be easier to drive than a single turn, where lots of milliamps have to flow, and with more inductance and less capacitance to tune it, the Q might not be as restrictive.
I have seen articles on magnetic transmitting loops with far smaller dimension using ferrite bars, which claimed good results in 160-meter ham applications, just a bit above the broadcast band. I wonder if anyone has tried this? I’ve got a PDF of the original article, which I’d be happy to email if interested. Drop a private note.
Please keep us updated with any experiements, successful or otherwise.