FM Radio Finds its Niche

by

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.