The early SSB rigs that first moved from the phasing technique of
generating a suppressed sideband to crystal filtering all used an IF for
the crystal filter where the filter was easy to manufacture. That was
typically around 9 MHz. Not much has changed in 30 plus years. The
second IF in most transceivers today is around 8.2 MHz - the 1000MP is
but one example. Given where the mixers need to be, and to save an
additional oscillator, mixing above the IF produces one sideband and
mixing below the IF produces the other. Hence, we started with USB
above 9 MHz and LSB below.
The technology to produce either sideband on any band has long since
arrived - the convention to not do so lingers on without a technical
underpinning, except:
Anyone still running a Central Electronics 100V won't be able to work
USB on 40 - Hi, Hi.
73,
Hal
N4GG
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