What are my requirements as a licensed Amateur Radio operator in the US to keep to a single frequency? How much drift can I have during transmission and still be within my license? Does it depend on the mode or band? Note that I'm not asking about the band plan, simply the FCC rules.
I'm asking in relation to making transmitters. I'm sure a crystal (20ppm) is more than sufficient, but should I decide to make a simpler oscillator, how much error is permissable?
If you want to add how much error is preferable for a given activity (DX, contests, rag chewing, etc) then that's fine, but please note that I'm primarily interested in what my license permits, rather than what other operators might prefer (at this time, anyway).