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Daniel wrote: But I’d definitely agree that 200 *meters* is closer to the range to a car radio if some pains were taken in mounting the transmitter outdoors and reasonably high and in the clear.
Good post. Just to note in a helpful way that Part 15 FM rules do not specify anything that would mean that the transmitter would have to be installed physically close to the transmit antenna. That is just a physical reality that has been applied to Part 15 AM systems under 15.219, which specify the radiating length of the antenna system to include the “feedline.”
Part 15 FM limits the peak field radiated by the transmit antenna to 250 µV/m in any direction 3 meters away from it. It is silent about the feedline, the antenna gain, transmitter output power, and radiated power.
The Part 15 FM radiation limit can be met even when the FM transmitter is located several hundred feet from the antenna, as long as the output power of the transmitter, the loss in the coax transmission line to the antenna, matching loss, and peak antenna gain acting together produce the maximum legal field for Part 15 FM systems.
Evaluating all that can be a problem, granted. But probably in all practical cases it does not require an FM transmitter capable of 10 to 35 milliwatts (or more) of r-f output power to meet the FCC limit for Part 15 FM.