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I’d bet that 30 ft off the ground at 3 meters, the reading would still be the same as on the ground at 3 meters, or very very close. In any case, it wouldn’t be anywhere near 600 times more to take an example from the other threads.
Considering actual commercial type approved part15 FM transmitters aren’t all that expensive, it’s not impractical to consider using several to cover a small neighborhood if they’re spaced far enough apart that the overlap definitely wouldn’t exceed the 250uV level.. Since FM has “capture effect” and any slight differences in frequency wouldn’t result in heterodyne (which you can’t hear on FM), for a very small town or a neighborhood, it could be done.
The “approx 200 ft range” is actually quite usable for a lot of things.. Think of inside a church so the hearing impaired could hear the sermon without having a PA system (which would cost considerably more).. Or on the regular community level, say the local stations no longer cover little league games and you like baseball.. get permission to set up in the middle of the stands and 250 feet would allow you to “play old time radio announcer at the ballgame” for a lot of people at the event who might miss that sort of thing. Or for other news coverage events, set up the transmitter where the people are and cover it via something like cell phone or a FRS walkie talkie (if you live in an area where there are usually channels open).. FRS wouldn’t have the sound quality for music, but for just voice for a special event it would probably do if one didn’t want to risk something like a cell phone.
The antenna for FM is small and easilly made portable. A natural for such things. But even for a fixed station, if you want to cover your yard and near neighbors, it can do it. Depending on how far away the neighbors are.
While there’s a limit in the part15 rules to how many homebrew devices a person can have on the air at once, I don’t think there are any for approved units? So yeah, it should be possible to cover a very small town or a stretch of road by using a number of legal part15 FM devices.. For a single transmitter station, the answer to better range while staying inside the law would be in getting better receivers to your listeners.
But yeah, I think you might have an idea there, Rev Chrysafis. Solar cells charging a small battery should be able to power part15 FM devices easy enough. I noted that the measurement of RF leakage via the AC line was “not applicable” in the case of the “003” because it’s made to use batteries. So something like solar cells might be preferable to power supplies since hooking it up to a wall wart might be using some part15 FM devices designed for battery use outside their test prams. Maybe use something like a zener diode and a current limiting resisitor with a small solar panel and a rechargeable battery to make sure the power supplied isn’t above whatever sort of battery the unit was designed for?
But the main tricky bit would be making sure the fringes didn’t overlap enough to exceed the allowed levels at the given distance from *any* antenna in the system.
Just “thinking out loud” with all that.