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Frequency modulation (FM) a means of radio broadcasting, utilizing the band between 88 and 108 megahertz; FM signals are marked by high levels of clarity, but rarely travel more than eighty miles from the site of their transmission
amplitude modulation (AM) a means of radio broadcasting, utilizing the band between 540 and 1,700 megahertz; AM signals are prone to frequent static interference, but their high- powered signals allow them to travel great distances, especially at night
Despite public controversies over payola and over the airing of rock n' roll music, the growth of radio formats continued, based on the targeting of certain age groups and musical tastes. One factor that encouraged the changing of radio to include longer songs and the expansion of the number of station choices was the development of FM radio—which stands for frequency modulation—an invention of Columbia University engineer Edwin Armstrong during the 1930s. From the start, leading radio executives realized that the static-free sound of FM was far superior to the sound produced by the AM (amplitude modulation) technology upon which existing radio transmitters and sets were based. But for technical reasons, the FM technology could not simply be used to improve AM radio. FM would have to either replace AM or co-exist with it. Broadcasters worried that their huge investment in AM would be threatened if they developed FM as a substitute. They also worried that the development of a whole new set of FM stations would reduce their profits by dividing both audiences and advertising money. For these reasons, radio executives tried hard to influence the FCC to derail the development of FM radio. At the same time, however, they protected their business interests by getting FM licenses and simply duplicating on FM stations what they were airing on AM—just in case FM caught on. The debate was so strong and so ugly that FM's inventor, Edwin Armstrong, became deeply depressed over what he saw as the radio industry's attempts to derail his invention, and committed suicide.
FM radio did emerge, though years later than its supporters wanted. By the 1960s, the FCC was not handing out new AM licenses, and the amount of money needed to buy an existing AM station was soaring. In the face of these developments, new business interests saw opportunities in FM radio and pressured the FCC to encourage the growth of FM by passing a nonduplication rule. The FCC passed this rule in 1965, stating that an owner of both an AM and an FM station could not play the same material on both stations more than 50 percent of the time. The rule had the effect the supporters of FM wanted. FM stations, looking for things to play and not having many commercials, developed formats that played long cuts or even entire albums, an approach that AM stations resisted. Many listeners migrated to FM; they liked the music and the static-free sound. FM radio began an astounding rise in popularity. Ir. 1972, FM had 28 percent of the radio audience in the top 40 radio markets, with AV taking 72 percent. By 1990, these figures were reversed.
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