Hi Barry,
Unlike many PLL based radios, not all of the oscillators are locked to one
common frequency reference in a Ten-Tec Omni VI. The band selecting
oscillators and the VFO are locked to the 20 MHz reference (at least when
it is working right), but the BFO is a stand alone crystal oscillator with
a few crystals and several adjustments. The manual for the Omni VI explains
how to adjust the 20 MHz reference and the BFO at all the different
frequencies it needs to operate at for different modes, LSB, CW, USB, RTTY
mark and space. You really should RTFM.
You need some way to measure the BFO frequencies, independent of just
listening to WWV on 10 MHz. If you were to attempt adjusting the 20 MHz
reference oscillator to get WWV zero beat at 10.0000 MHz readout setting,
without first getting the BFO correct, you could misadjust the 20 MHz
reference. And if you were to adjust the BFO without having the 20 MHz
reference correct, you would then get the BFO wrong.
I suggest you get access to a good frequency counter, or a communications
monitor such as an IFR 1000 to measure the BFO frequencies and the 20 MHz
reference. If you cannot get your hands on one of those devices I have a
suggestion that in concept could work, but it won't be easy and it will not
get all of the BFO frequencies right.
You will need another receiver that can monitor 10 MHz WWV. Then you can
find a sample of the 10 MHz signal inside the Omni VI that is a product of
the 20 MHz reference oscillator. If you can get enough of that signal into
the receiver monitoring WWV you could adjust the 20 MHz reference for zero
beat with WWV. If you can get the 20 MHz reference on frequency by this
method with a high degree of confidence, only then could you adjust the
BFOs in the Omni VI while listening to WWV on the Omni VI and adjusting for
zero beat of the WWV 10 MHz carrier. This will only get the BFOs set for
LSB and USB, and they could still be off for CW and RTTY modes.
Ultimately you will get frustrated until you have found the right gear to
do the adjustments by the book.
Good luck,
73 DE N6KB
On Fri, Apr 19, 2019 at 2:30 PM Barry Simpson <vk2bj@optusnet.com.au> wrote:
> I have recently acquired an Omni VI Option 3 which is working but needs
> some TLC to bring it up to par both physically and electronically.
>
> One thing I need to do is to correct the frequency calibration as on 10mHz
> WWV it is off by around 100Hz on USB and LSB and about 120Hz on CW.
>
> I thought I would have a preliminary go at it and I have been trying to
> follow KG7KDX's instructions on the Ten Tec Wiki. I located what I believe
> to be C31 on the logic board but adjusting that trimmer makes absolutely no
> difference to the frequency so I don't know what it is I have been
> adjusting or how I do actually adjust the calibration.
>
> Going on from there, I have downloaded both the Omni VI and Omni VI+
> manuals from the TenTec website but I believe that the Omni VI+ manual is
> incorrect as all the circuit boards have exactly the same numbers and
> circuits as the Omni VI whereas my rig has some boards with numbers that do
> not appear in either manual or the addendum.
>
> Can anyone help me please with:
> 1. A copy of the correct Omni VI+ manual
> 2. The correct calibration instructions for using 10mHz WWV. What is it
> exactly that I adjust ???
>
> Thanks in advance for your help.
>
> Barry Simpson VK2BJ
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> TenTec@contesting.com
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>
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