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It was back in 1947, and of course it didn't happen. But it was actually thought about - insuring that when you changed from an AM station to one on FM, the station you were listening to would be in the exact same position on both bands, so you could compare how each sounded.
It seems ridiculous now, but FM was just getting started and there were only a few who adopted the technology. Imagine if this had happened. So somehow CHUM would have been at 1050 while CHUM-FM would have been at - well, frankly I'm not sure, just so you could change from one to the other and hear the same thing.
Bizarre, but the article below shows at least someone was considering it a very long time ago.
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I was told by someone in the know at CFRB (in the 1970s) that the reason they chose 99.9 for CFRB-FM was the relative proximity of the dial positions.
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RadioWest's radiofan worked at CKNW 980 AM Vancouver, and shared that the owners/executive were of this same line of thinking when they successfully sought the 101.1 FM frequency in Vancouver for CFMI (FM One).
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Maybe this made sense when the AMs & the FMs simulcast part or all of their programming within the same company. Now, it seems completely unnecessary. Either way, it sounds so unwieldy, it could never really have worked, and they could not have predicted back then how crowded the once little used FM dial would become.