RememberWHEN said:
The home page of Schurz Communications, parent company of Sunny 101.5, states that in May, 1943, WSBT signed on an experimental FM station (W71SB) which is currently known as Sunny. I believe back then FM spectrum was not 88 - 108 but somewhere in the 40 - 50 mHz range. If I am correct in that, I believe the station went silent when the government moved the FM broadcast spectrum to present 88 - 108. Seems to me I remember WSBT signing on there FM station sometime in the early 1960's along with WNDU-FM (U-93). You might contact Schurz and ask for clarification.
Regards,
RememberWHEN
W71SB wouldn't have been an experimental station - it would have been a regularly licensed FM station. At the time, the FM band was 42-50MHz. The 71 meant the station was on 47.1MHz; the SB, as you may have guessed, stood for "South Bend". Other FM calls of the time included W75NY (47.5MHz, New York City) and W55M (45.5MHz, Milwaukee).
They went to the current four-letter call system (already in use on AM) near the end of the war. At that time they also established the current 88-108MHz band. (actually, they originally reserved 106-108 for **fax** broadcasting!) It took a few years to get everyone moved up from 42-50, in part because the move obsoleted all the existing FM radios & threatened to decimate the FM industry...