One important reason for UHF for the Sup'R'Mod, instead of channel 3/4:
Some TVs at the time had a built-in VHF antenna, and no external connection for VHF! But, the UHF was a small loop or "bowtie" that connected to a pair of screw terminals on the back of the set.
For example, the 17"? 19"? portable Philco that my brother and I bought (and, our father chipped in the EXTRA COST for the model with UHF) I remember watching the cuban missile crisis on that set. And, seeing every light on Massachusetts Avenue ("embassy row") on all night.
By modulating to UHF (Channel 33), the Sup'R'Mod could connect to the UHF antenna terminals on TVs where there was no connector for external input of VHF.
Later TVs had external antenna VHF input, either screw terminals, or later, an F connector.
-- Grumpy Ol' Fred ci...@xenosoft.com
