[TenTec] UCW and LCW

[Ken Brown]

On Upper Sideband an audio note is heard when a signal is ABOVE the 
"effective BFO frequency" and in order to bring that note to zero beat, 
one must tune upward, lowering the pitch of the audio note until it is 
zero. If you continue tuning upward, past zero beat, the note will rise 
again as you are now detecting the signal in the lower sideband, if the 
BFO is inside the IF bandpass. Or in most modern receivers with fixed 
BFO frequencies that are on the edge of the IF bandpass, it will 
disappear having gone outside of the IF filter(s) bandpass.

On Lower Sideband an audio note is heard when a signal is BELOW the 
"effective BFO frequency" and in order to bring that note to zero beat, 
one must tune downward, lowering the pitch of the audio note until it is 
zero. If you continue tuning downward, past zero beat, the note will 
rise again as you are now detecting the signal in the upper sideband, if 
the BFO is inside the IF bandpass. Or in most modern receivers with 
fixed BFO frequencies that are on the edge of the IF bandpass, it will 
disappear having gone outside of the IF filter(s) bandpass.


By "effective BFO frequency" I mean the frequency at the antenna input 
that results in a zero beat. This is equal to the frequency of the one 
and only local oscillator in a direct conversion receiver. In multiple 
conversion receivers it is a combination of one or more local 
oscillators and the BFO. In some receivers, due to the conversion 
scheme, the input signal at the antenna is inverted so that USB at the 
antenna is LSB in the IF.

Some older receivers down convert from the input signal to the the IF on 
higher bands and up convert from the input signal to the IF on lower 
bands. In these receivers the direction you turn the main tuning knob to 
go up the band may be opposite on some bands. The common use of 9 MHz IF 
in early SSB rigs is what resulted in the amateur convention of using 
USB on 20 meters and up, and LSB on 40 meters and down. The BFO was set 
for USB operation, in the IF, and when up converting 40 and 80/75 meter 
signals to the IF they get inverted. I believe that early Drake 4 series 
rigs are an example of this, having dial markers going in both 
directions on the VFO, and a NOR / OPPOSITE sideband switch instead of 
LSB/USB.

I guess I went off on a bit of a tangent. The short answer is that in 
USB the audio note decreases as you tune upward.

DE N6KB



John B. Egger wrote:
> I'm a bit puzzled by these two O-2 modes. When UCW is selected, the 
> lower CW sideband is audible; that is, if zero-beat is 7020, to hear the 
> signal one tunes down to 7019 etc. When LCW is chosen, one must tune UP 
> from zero-beat to hear the signal.
>
> Isn't this the opposite of what LCW and UCW should mean?
>
>