[TenTec] Omni VI Mystery

[Steve Hunt]

Jim,

The VI+ results look close to what you would expect, but the VI shift is 
far too small and confirms this is where the fault lies.

The only thing that surprised me is that you couldn't hear the VI BFO 
with the 706 set to 8999.700 kHz USB or thereabouts. That suggests the 
VI BFO is also off frequency on LSB Rx. Can you confirm that you can't 
hear any tone with the 706 tuned to (say) 8999.500 kHz and the Omni VI 
set to Rx LSB?

I know you are reluctant to "dabble", but I don't think there's anything 
to lose at this stage by adjusting the BFO trimmers; they get a bit 
"scratchy" with age, and moving them could be all that is needed. 
Because we are fault-finding at this stage - rather than looking for 1Hz 
accuracy - you could try this:

1) Set the 706 to 8999.600 kHz USB
2) Set the Omni to Rx LSB and adjust trimmer C10 for a 400Hz audio tone. 
Don't be afraid to turn the trimmers back and forth a few times if they 
are "scratchy"
3) Set the 706 to 9002.600 kHz USB
4) Set the Omni to Rx USB and adjust trimmer C12 for a 400Hz tone
5) Set the 706 to 9000.000 kHz USB
6) Set the Omni to TUNE and adjust trimmer C16 for a 400Hz tone

I can understand if you prefer not to "dabble", but at least you've now 
localised the fault to one small area.

Steve G3TXQ








On 30/07/2014 21:07, Jim Allen wrote:
> Fascinating!
>
> I am here out in the shack with the radios, and have performed the test you
> outlined.
>
> I tuned the 706 with a pick up lead to 9.000.040 to hear the Omni BFO, It
> was not heard with the 706 in USB but was heard in CW mode.  I then tuned
> in a 400 hz note.  I verified this by using the VI+ sidetone, matching the
> tones exactly. Omni is in LSB with dummy load.  When I put it in tune, the
> tone raised, to 460 hz, again measured using the sidetone in the Omni VI+
> (not the VI).  The sidetone varies in 10 Hz steps.
>
> I also have a tuner in my iPhone for tuning up band instruments which shows
> the pitch of tones in notes and in Hz.  The tone was 401 in LSB and in tune
> 466 Hz.  I tried repeatedly to set the 706 to exactly 400 Hz tone, before
> realizing that the 706 tunes in 10 Hz steps, so it was either 402 Hz or 392
> Hz!
>
> The sidetone setting on the VI is 700 Hz.
>
> This was so much fun I put the top back on the VI and took the top off the
> VI+, same set up other wise.  The tone beat to 400Hz was much lower in
> frequency, 8999.700 on the 706 to get a 400 Hz tone.  When I went to tune,
> the tone jumped to 768 Hz on the instrument tuner.
>
> The sidetone setting on the VI+ is 700 Hz also.
>
> So on the VI, the tone increased ~60 Hz.  On the VI+ the tone increased 368
> Hz.
>
> This seems to confirm your "guess," Steve.
>
> What do we do next?
>
> Many thanks BTW.
>
> 73 de W6OGC  Jim Allen
>
>
>