But remember, Clark, that the "carrier" is the BFO frequency. We can
adjust that to be about anything we want within reason.
Changing the center frequency changes the position of the sidebands.
In a SSB rig, we actually change that to get the best response for the sidebands
from the filter. The filter itself doesn't change. How it is constructed will determine
the bandwidth, but not the actual frequencies that go through it. The position of
the BFO does that.
It also means that if a given filter allows the USB through, shifting the BFO will
allow the LSB through. BUT the position of the frequencies will be reversed
(inverted). So the LSB will come out "upside down". But that doesn't matter as
the transmitted frequency is determined by the mixer, not the BFO. And
the other receiver's mixer determines what is extracted -- it can extract that
"inverted" signal and set it "right side up" in its own crystal filter. So the
other side hears a regular audio signal.
That also means that any carrier that gets out of the mixer can go through the
filter if the BFO is positioned right. Ordinarily in SSB, any suppressed carrier
that gets out of the mixer is cut off by the filter. The sides of the filter are
designed to do this -- but one could, if one wanted, unbalance the mixer,
center the BFO on the mixer signal, and get a form of CW through the filter.
The result is indistinguishable from a true A1 CW signal.
So it's all about the BFO and the shape of the filter...
john
AD5YE
