Good question, the obvious are fractions of the given freq. 1/2, 1/3, 1/4 etc. But it can be almost unlimited.
I'm nowhere near an expert but 2 frequencies can "work" together and generate another - intermod.
I've seen instances where a strong frequency at a repeater site interacted with a piece of metal, in this case a gutter, to create another that happened to be the input freq. for another repeater at the same site.
Will be watching for more replies.
HP-1, BC780, BCD996, Pro 2005, 2006, AT803,R5000
and other RF capture devices
-Remember Bill Cheek -