Radio World wrote earlier this year about efforts at KPFK(FM), Los Angeles, to build a small AM radio network using low-power license-free AM (“LPAM”) transmitters for a Spanish-language feed. (See the article at tinyurl.com/rwlpam.)
According to the story, “LPAM broadcasts are limited to an effective service range of approximately 200 feet.” Pay no attention to that statement. A big technical loophole in the license-free rules permits these stations to often cover a range of a mile or more daytime. Consider, for example, a “Part 15 legal” low-power AM transmitter mounted onto and coupled into a tall metal light pole — the pole acts as a big antenna.
The FCC in Washington is sound asleep when it comes to license-free AMs.
What the commission needs to adopt is a simple field strength rule for licensee-free AM stations. Either an LPAM passes the test or it does not. Anyone with a calibrated hand-held field strength meter could make the pass/fail determination on short order — even FCC inspectors who have no convenient way to deal with the current complex rules.
President, Communications General Corp.
Consulting Radio Engineers