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.
LPFM Was Legal Once - The Class D Station Era
While the FCC recently (in 2000) began issuing licenses for LPFM stations, the idea is not exactly new.
LPFM had existed for more than three decades in the United States, in the form of a "Class D" station license, first given out by the FCC in 1948. Class D stations were originally licensed at 10 watts on the FM band, within the region of 88 to 92 MHz (known as the "educational band" of FM radio).
There's a specific reason for this: Class D stations were the FCC's first attempt to bring more schools and colleges onto the air - a way to give potential broadcasters an outlet for hands-on training while not breaking an institution's bank operating it (in radio, the more power you want, the more expensive it gets).
Eventually, Class D FM stations were allowed power levels between 1 and 100 watts. They were strictly non-commercial, and were only licensed to educational institutions. Major demand for Class D stations didn't happen - this is due in part to two specific reasons.
The Public Broadcasting Act of 1967
President Lyndon B. Johnson signed this Act into law, and in doing so, made federal funding available for non-commercial educational radio stations. It fundamentally changed the idea of what non-commercial educational stations should be.
The first goal of the Act was to establish a national "public radio" network. Three years later, National Public Radio was born, providing programming far above the level Class D stations were equipped to deliver on their own.
This was a very significant development, as it defined what's considered contemporary "public radio" today. The powers-that-be felt that "public radio" should provide a nationally-accessible educational service - kind of as a "school on the airwaves." Therefore, its outlet would be on educational stations.
Although many Class D stations were licensed to educational institutions, because of their small signal range they were often used as on-air radio laboratories - places where budding broadcasters and other students could experiment with radio (and make mistakes). As a result, the quality of the programming didn't measure up to the standards of National Public Radio.
An on-air broadcast
lab isn't always educational for a listener - but screwing up live is
a great way for future broadcasters to learn their lessons. Class
D stations were, in many ways, the perfect stepping stone to go from
classroom to career. However, such a situation was incompatible with