The prospect of additional radio service using frequency modulation (FM) was hardly discussed until the late 1930s. Until then, all radio transmissions were based on amplitude modulation (AM). FM service might have died for lack of support had it not been for the tenacious determination of Armstrong, who began work to eliminate static in 1923. Ten years later, Armstrong received five patents for frequency modulation. He showed his invention to David Sarnoff, then president of RCA and NBC. Although Sarnoff recognized the superior sound quality of FM broadcasting, he did not want to support the system because RCA was developing television. FM was considered a competitor to AM radio; it would divert the attention of scientists and the government away from television.
Armstrong didn’t give up. He built an experimental FM station in Alpine, New Jersey , in 1939, provided funding for FM receivers, and petitioned the FCC for FM stations. Although the service was authorized in 1940, by the beginning of World War II there were fewer than 400,000 receivers in the hands of the public . By contrast, twenty-nine million households could listen to AM radio at that time. FM service might have grown after World War II had the FCC not changed the assigned frequency range. When FM moved from 42-50 MHz to 88-108 MHz, all the receivers produced before the frequency change suddenly became obsolete.
Local radio evolves
Between 1946 and 1948, more than fifty million AM receivers were produced. As the price of radios fell, the multifamily household developed. Radios spread from the living room to the kitchen and into the bedroom. The growth of television attracted radio programs and audiences, but radio survived by adopting an all-music format and an emphasis on daytime listening. Radio became a local advertising medium.
One of the most popular music formats used by local radio stations in the 1950s was the Top 40 format. This format was the result of the independent work of four AM station owners: Todd Storz, Gordon McLendon, Gerald Bartell, and Harold Krelstein. In trying to develop a new approach to radio station programming, all four of these men contributed significantly to the development of the Top 40 format, which succeeded in creating a new identity for radio. One of the best explanations for the forty-song radio format came from Storz, who said he observed people playing the same songs over and over in the jukebox and concluded that listeners most wanted to hear the hits over and over again.
The decline of AM radio and the rise of FM radio
The Top 40 format helped change the position of radio, but it also created a group of stations with a similar sound. AM radio stations broadcast similar music and jingles, played loud and long commercials, and tended to have poor playback quality (i.e., sound quality). Thus, in the 1960s, attention shifted to FM radio. In addition to the obvious availability of FM channels, operators began to recognize other benefits of FM. FM provided 24-hour service with the same power levels and coverage areas. The width of the FM channel meant superior sound, including stereo, and less interference.
While the Top 40 AM formula did not suggest playing songs longer than three minutes, FM’s approach was to play an album version of ten minutes. Rock music, which grew out of the anti-Vietnamese “flower children” and “make love, not war” movements, provided much of the content for FM stations’ programming. The music industry has also contributed to the growth of FM radio. Top 40 AM stations’ playlists were tightly controlled, and new songs or new bands had few opportunities to play on the airwaves. Many FM stations would play almost anything, so record companies used FM radio to introduce new artists and styles of music. By 1971, nearly half of all radios sold included FM tuners. In the fall of 1978, the national share of FM listeners exceeded that of AM listeners; 50.698 percent of listeners tuned into FM stations.de facto was the standard for most music radio listeners, causing many AM stations to switch to talk radio formats in the 1980s.