What is LPFM?
LPFM stands for Low Power FM radio broadcasting. In the United States, the lowest minimum wattage a licensed FM radio station may have is 100 watts. There are lower-power FM transmitters in use, though, by some stations who want to increase their coverage area by extending their signal. These are called translators or boosters.
While these may only have a wattage measured in a range from dozens to hundreds, they are not true broadcast stations by the FCC’s definitions – they do not originate their own programming. They rely on a “parent” station to provide what they air.
Ham (amateur) radio uses a similar system called a repeater; people don’t broadcast from it. They shoot a signal into it, and then it gets re-broadcast to an area larger than what ham operators might reach with their own gear. In a nutshell, translators and boosters are the repeaters of FM radio.
LPFM is the common term used to define an FM broadcast station that originates its own programming but has the power of a translator or booster. Under current FCC rules, operating such a station is simply not allowed. You may also see LPFM referred to by other terms – like “LPRS,” “microradio,” and “mini-FM,” but they all mean the same thing.