Jaggy Taggy wrote:

Alas, a SSB station is only transmitting one of the sidebands! This by
convention is LSB on 40 and below and USB on 20 or above. If a station
WERE to xmt USB on 75 meters, for instance, you would have to use the
USB position and would not be able to detect it in LSB.

-Bill



Right Bill, but why. Could I not retune my receiver so that I would catch
the transmitted sideband with my "LSB window"?

I guess from experience the answer is no, and that is also what you said,
but what is the reason??

Uwe


Visualize a LSB signal as having the carrier frequency at 7000 kcs (or
more precisely, phantom carrier). The audio sidebands tune down to
6997. A USB signal on the same freq has the audio sidebands from 7000
to 7003.

To tune to an SSB signal (and have it intelligible) you have to tune to
the phantom carrier freq. You can't fool the rcvr by going 3kc hi or
low and switching sidebands. Yes, the signal is there - to wit you can
hear it - but you can't detect it.

Why? Think about how BFO injection works. Take a fixed freq BFO of
7000 in this case for simplicity. 7000 beating against an USB audio
sideband at 7001 gives you a bit of 1 kc audio information. Repeat the
same with an audio sideband at 7002...you get the 2kc audio information.
If you try to fool the radio by tuning to 7003 and selecting LSB, yes
you have duplicated the bandpass from 7003-7000 but all that audio
information is now inverted.

In most rigs nowadays there's a single filter of about 2-3kc width that
is used for both sidebands. When you select USB or LSB you're simply
moving the bfo freq from one edge to the other.

Thats all an oversimplification but does it make sense?

-Bill