[4] In May 1940, the Federal Communications Commission (FCC) announced the establishment, effective January 1, 1941, of an FM band operating on 40 channels spanning 42–50 MHz.
[9] The station call letters became WTMJ-FM on December 1, 1945, and it was reported that "the change was made in anticipation of eventual duplication of programs on WTMJ".
On September 18, WTMJ-FM began regular operation of what was described as the first superpower station on the new band, from a new site located atop Richfield Hill, about 21 miles (34 km) northwest of downtown Milwaukee.
A 50 kw transmitter, fed into an eight-element antenna located atop a 550-foot (168m) Blaw-Knox tower, resulted in an effective radiated power (ERP) of 349 kilowatts.
[14] In early 1948, Walter J. Damm, vice president of the Journal Company, had predicted that "FM will replace AM as the American system of broadcasting.
The radio listeners in Wisconsin have not seen fit to invest in a sufficient number of FM receivers to make the continued operation of WTMJ-FM and WSAU-FM a worthwhile undertaking".