On Tue, 16 Oct 2018, Spike wrote:

On 16/10/2018 09:14, Jeff wrote:

A common way of generating both usb and lsb was to have 2 switched
crystals with frequencies just above and below 9MHz in the oscillator,
feeding a balanced mixer, before the xtal filter, and switch depending
on which sideband you required.

Is there a mathematician on here that can explain the maths of sideband
inversion/retention?

No inversion is required with this method.

If you feed a ~9MHz signal and audio into a balanced mixer the output
will be both sidebands plus a suppressed carrier.

Your xtal filter is ~2.4kHz wide centred on 9MHz, so if you move the
frequency of the ~9Mhz signal (switch a crystal) going into the balanced
mixer either above or below 9MHz you can select which side band goes
through your filter.

Simples.

Wasn't a similar system used in the Yaesu FT-200 (9MHz IF, 5 MHz VFO)?

IIRC the set had a NORM/INV sideband switch.

That wasn't uncommon, the conversion scheme allowing for the "default"
sideband to be one switch position, so the only time you needed to switch
sidebands was if you needed the "wrong" sideband".

Michael