FM and AM Radio
Currently, U.S. radio stations are
almost evenly divided between two broadcast spectrums: amplitude
modulation (AM), which comprises the dial range from
540 to 1700
kilohertz (KHz); and frequency modulation (FM), from 88 to 108
megahertz (MHz). AM broadcasting, which allows a transmitter to have
greater geographical reach, consists mostly of talk programming,
including telephone
call-in shows, all-news formats, religious
evangelism, and sports coverage. FM, developed in the 1930s by Edwin
Howard Armstrong, has several advantages
over AM: It is nearly free of
static and can be broadcast in stereo—two simultaneous sound waves
that yield more realistic reproduction of music and
other sounds. From
Armstrong’s earliest demonstrations, it was obvious that FM offered a
richer, fuller sound than AM. But the millions of radio sets already
sold to the public could not receive FM broadcasts, so companies heavily
invested in AM technology suppressed FM for decades. FM did not reach a
large audience until the 1960s, when the public immediately embraced it.
Most FM stations are dedicated to presenting music. They tend to
establish specific, easily identifiable formats, such as rock, country,
rap, or other genres that appeal to particular audiences.
