From what I read its not a bitx20 or 40, so the math shown appleis to a single conversioon receiver.
The microbitx ubitx is very different as its DUAL CONVERSION. So any math shown is just plain
wrong to a degree. Yes you can flip the 3rd oscillator for sideband change or the second of for
that fact is the oscillator can do it the first!
First all signals are converted to the 45mhz first IF, makes no different if its 1.8mhz or 144mhz save for the
1st LO is going to be above the IF or below it. The second mixer and associated 2nd LO are being switched from
45MH-12mhz=~33 or 45+12mhz=~57mhz and can be used to switch what sideband is in use just as easily as
flipping the 11.9978(give or take) and 12.500(also give or take). The trick is if you take 45-33 your get -12
(the minus means inversion in frequency in this case) or its 45-57 or 12 note the sign is positive or no inversion.
Also the fact that the first IF filter is 45mhz means images are not an issue all the way up to 432/450mhz or higher
as the image frequency is 90mhz away and easily filtered. So with a decent RF (LNA) and appropriate filters
VHF and UHF are possible with the same basic design though the Local osc the 1st may requires a multiplier
stage to reach UHF. Its an positive artifact of using a high IF so the radio can tune the whole HF range without
switching filters other than the required low pass output filters. Its a simplification of what most commercial
(YaIcKen) HF radios do.
YaIcKen is Yaesu/Icom/Kenwood.