FM
From dKosopedia
Abbreviation for Frequency Modulation, a technical means for transmitting audio using radio waves. The FM band is home to most National Public Radio stations and stations on the much smaller Pacifica Radio network.
At one time, AM radio was the medium of choice for most popular music formats. These stations began moving to FM in the 1970s, and by the mid 1980s the move was complete. This left far too many AM stations looking for new formats, and station managers were all too eager to populate their lineups with raving right-wing lunatics like Rush Limbaugh.
FM, meanwhile, has always been the medium of choice for noncommercial broadcasting, usually found at the left end of the dial below 92 MHz. National Public Radio is by far the largest of these networks. Some say NPR is too conservative.
The much smaller Pacifica Radio network only owns 5 stations but their news programs are carried on many more public radio stations. Pacifica is unabashedly left-wing and progressive. Their flagship program these days is called Democracy Now.
Small community radio stations exist in a number of cities. These stations are usually independent and most of them have liberal or progressive leanings.
Unfortunately the non-commercial end of the FM dial is also heavily populated with fundamentalist Christian religious broadcasters.