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Oh, and the 200 foot limit to a typical (whatever that is) radio is mentioned by the FCC in association with Part 15 FM broadcasting. It too is not in the rules per say, but a rule of thumb they suggest broadcasters use to determine if their FM station is legal.
And the kicker is that word ‘typical’. A better method is to listen to your station using a receiver with a known sensitivity and see what range you get with no obstructions between the antenna and the receiver.
As an example, Canada is allowed 4 times the field strength than that of the U.S. and while I won’t go through the calculations here (they’ve been enumerated many times in the past in this Forum), using a very sensitive car radio with a sensitivity of 1.5uv or maybe a bit worse, I can legally achieve something close to 1000 meters range (no obstructions – if there are any, that range goes down considerably).
So for the U.S., and a similar car radio (most aren’t as sensitive as that), you can expect to get about 250 meters range maximum, or less than 800 feet. If I consider a standard portable FM stereo blaster as ‘typical’, those tend to have sensitivities of 25uv or worse, and horrible selectivity, or adjacent channel rejection. You’d be lucky to hear your signal out 25 meters on those. So 200 feet for Part 15 FM is generous.