FM Radio Finds its Niche
R. J. Reiman, Historian
World War II research had raised issues of interference from sky waves in the 42 to 50MHz band
which had been previously assigned. The catalyst for the dispute over this allocation and an advocate
to move the range to higher frequencies was an FCC engineer, Kenneth Norton. During the war, he
served in a capacity which made him knowledgeable of the experimental programs in the sky-wave
propogation of VHF signals. He combined the War Department results with data obtained from the
Bureau of Standards, and from measurements obtained on a commercial FM station, WGTR in
Paxton, Massachusettes, to develop new predictions of VHF sky-wave transmission. He calculated
the amount of co-channel interference in the 42 to 50MHz band. He concluded that objectional
interference would occur, especially in rural areas, at the extreme end of the broadcast range.
The FCC took his report seriously, held a hearing in late 1944, and resisted the arguments of the
industry, especially those with established stations. Also at risk were 400,000 receivers in public
hands which would become obsolete. Norton assumed that the broadcast signal must be ten times as
strong as the interfering signal, and Howard Armstrong countered that a 2 to 1 ratio was more
appropriate as wideband FM had a unique ability to override interference. FM industry did not
challenge this assumption strongly and Norton's calculations were then not challenged.
On May 9, 1945, the FCC issued an order to raise the band for FM to 84 to 102MHz frequency
range. Just two days earlier, the War Production Board announced the plan to permit the
manufacturing of radio receivers. The manufacturers of the 42 to 50MHz equipment. owners of sets,
and in particular Zenith, a leader in the band, had lost a profitable edge, and owned obsolete
equipment. The FCC ruling also included specifications on channel widths, power, antenna height and
frequency assignments. Three classes of stations were established, local stations with maximum
radiated power of 50KW, regional with 50, and 100KW.