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At one time the FCC considered allowing LPFM stations with radiated powers of 1 to 10 watts, giving a useful coverage radius of about 1.5 miles. But then in their 6th Report and Order (https://www.fcc.gov/document/lpfm-fifth-order-reconsideration-and-sixth-report-and-order) they eliminated that class per their reasoning on pp 76-77 of that document. Here is a quote of that section:
A number of LPFM proponents urge us to retain the LP10 class of service, arguing that it
is needed to ensure that LPFM opportunities are available in urban areas. 517 Other commenters advocate eliminating the LP10 class. 518 They point out that, from an engineering standpoint, the LP10 class is spectrally inefficient. 519 We agree that the existing LP10 class is an inefficient utilization of spectrum. LP10 stations offer more limited service but are more susceptible to interference than LP100 stations. Given the increasingly crowded nature of the FM band, we find it appropriate to take this into account. 520 We also are concerned that the reach of LP10 stations would be too small for the stations to be economically viable. As the Media Bureau recently noted, even higher-powered LP100 stations have small service areas and are constrained in “their ability to gain listeners” and “appeal to potential underwriters.” 521 Because we find that licensing LP10 stations would be an inefficient use of available spectrum and are concerned that LP10 stations would have an even higher failure rate than LP100 stations, we eliminate the LP10 station class.
From what I’m reading of the views of posters on Part 15 websites, it appears that this coverage radius of about 1.5 miles is approximately what they want from a Part 15 FM setup. But it seems unlikely that the FCC would permit that for unlicensed FM transmit systems when they didn’t permit that for licensed stations — where they would have control of the frequencies and powers they permitted.
The FCC considers all uses of the FM spectrum in its actions, and the potential for mutual interference among them. Whether or not such spectrum use is licensed makes no difference to the interference such setups can produce.
Maybe ALPB members and/or “FM Manifesto” supporters could discuss this, to see if it gives them perspective on their best course of action.