Scott wrote:
Actually, I think the convention is LSB below 9 MHz and USB above 9 MHz.
That comes from the fact that most old rigs used 9 MHz as the I.F.
Doesn't really matter though since our voice bands are 40M and 20M (CW
only on 30M), so by convention, we use LSB on 40M and below and USB on
20M and above. However, one can reverse this if one desires. It will
just confuse new people when they try to tune you in and wonder why they
can't get you tuned in...

Yeah, and more than once I've scratched my head about what type of voice
encryption someone was using in the middle of 20 meters before it dawned
on me to try listening on LSBgrin!

The 10MHz figure is somewhat arbitrary since indeed there are no amateur
voice frequencies between 7.3 and 14.1MHz - and commercial services
don't follow our LSB/USB convention.

As I understood it, the decision to use different sidebands in the two
spectrum areas came from the design of some early SSB equipment. If you
used a 9MHz IF and a 5.0-5.5MHz VFO, you could cover both 80 and 20
meters without having to mess with heterodyne oscillators. But since
you'd be using addition on 20 vs. subtraction on 80, the sidebands would
flip.

(there's GOT to be a better way to say that but it's too darned early in
the morning!)

At the time either there wasn't a phone band yet on 40 or phone
privileges there were very new & SSBers didn't care that much about it.
15 was also very new or non-existant, and I suspect most SSBers didn't
believe anyone had a receiver stable enough to receive SSB on 28MHz!
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com