[TenTec] SSB receive audio?

[Ken Brown]

Barry Gross wrote:

>pure conjecture on my part - only one of the two oscillators (either
>USB or LSB) should effect cw, and the effect would probably be to
>shift the cw offset/sidetone, but I don't honestly know.  I no longer
>own the Omni VI, and don't even have access to the owner's manual.
>  
>
I do own an Omni VI and a manual for it, so I can answer this question.

The Omni VI has a single BFO. Only one oscillator circuit for the BFO. 
The frequency it operates on is controlled by SELECTING one of two 
crystals and one of three trimmer capacitors. There are a couple of 
other trimmers that are always in the circuit. I emphasis the word 
"select" because there is no variable control of the BFO frequencies 
from outside the oscillator circuit. What the crystals and the trimmer 
capacitors are set to work at is what you get, with no variable external 
control. The rest of the radio has no control over it other than just to 
select one of the five possible frequencies. The rest of the radio also 
has no "knowledge" of what frequency trhe BFO is actually generating. 
The control and logic circuitry that controls the VFO and bandswitching 
oscillators "assumes" that the BFO is running at the correct specified 
frequency for the particular mode the radio is in. Therefore if you 
adjust your BFO frequency incorrectly, your operating frequency display 
will be incorrect. Also the CW sidetone generation assumes correct BFO 
frequency, so if you adjusted the BFO frequency for LSB (which is used 
for LSB RX, LSB TX and CW RX) your sidetone would no longer be an 
accurate representation of where your CW TX frequency is relative to 
other signals in your receive bandpass.

The other oscillators in the Omni VI differ, in that the bandswitching 
oscillators have analog control  via a DC correction voltage. So the 
control system keeps it exactly where it needs to be. The VFO of course 
is under control of the logic board. Both the VFO and the bandswitching 
oscillators accuracies are dependant on the reference oscillator on the 
logic board.

The 15.3 MHz VCXO on the bandpass tuning board is added to and then 
later subtracted from the RX IF so its net effect on frequency 
calibration is zero.

To sum it up:

If you adust C16 on the BFO board in order to change your LSB TX and RX 
BFO frequency relative to the 9 MHz IF filter bandpass, you will make 
your frequency display incorrect in LSB TX, LSB RX and CW RX, and the CW 
sidetone will no longer be accurate.

If you adjust C12 in order to change your USB TX and RX BFO, you will 
only mess up the frequency display for USB TX and USB RX. You would also 
have to readjust C13 and C18 if you care about your FSK TX frequencies.

By the way, there are a couple of errors in the BFO schematic in both of 
my Omni VI manuals, showing C12 connected across Y1 instead of across 
Y2. And D11 should be connecting C16 to Y1 instead of to Y2.

I hope this helps you make the right decision.

DE N6KB

"I before E except after C, and when sounded as A, as in neighbor and 
weigh"