Hi Dale,
The Omni VI frequency calibration is dependent on a 20 MHz reference
oscillator and the BFO oscillators.
The BFO operates at several different frequencies depending on mode of
operation and whether in transmit or receive. The manual explains how to
adjust the BFO frequencies in a specific order. There is some interaction
between the BFO frequency adjustments and it is necessary to repeat the
procedure in order to get them all correct. The BFO operates
independently of any PLL system. It is not locked to the 20 MHz reference
or to anything else.
The band select crystal oscillators should not need adjustment since they
are supposed to lock to the 20 MHz reference. If they have been improperly
adjusted or if there is a component fault (aged crystal perhaps) it may be
necessary to adjust the slug tuned inductors to get the band select crystal
oscillators to lock to the 20 MHz reference. This is somewhat tricky. I
don't recommend going there unless you are really certain it needs to be
done. In that case you should have a good oscilloscope to monitor the PLL
for the adjustment. I have damaged the ferrite slug in at least one of mine.
The VFO is locked to the 20 MHz reference and therefore it's accuracy is
directly dependent on the 20 MHz reference accuracy.
I suggest you check your frequency calibration error on multiple bands. I
suspect you will find it is different on every band.
My experience with the Omni VI is that even after very carefully adjusting
the BFO frequencies and the 20 MHz reference the final digital readout
versus actual zero beat receive frequency is off by several Hertz to tens
of Hertz depending on the band in use. It does meet the manufacturers
specification, but it is not exact and not as near zero beat as the
oscillator adjustments have been set to. In other words if I have the BFO
set to less than 1 Hz error from correct and the 20 MHz reference to less
than 1 Hz error the final receive frequency readout will be off my many
Hertz and it is not the same on every band, nor is the error proportional
to the operating frequency.
Cheers DE N6KB
On Sat, Nov 2, 2019 at 3:57 AM dale via TenTec <tentec@contesting.com>
wrote:
>
> My VI+ is of frequency by .22, Several guys got back and the answers
> for calibration.of the rig were from easy to do to look in the manual. My
> manual says nothing about the problem, that I can find. or how to correct
> it. I was told the rig had a txco and all was adjustable with a single
> adjustment. Can anyone tell me the correct
> oprocedure is to correct the problem. Have a very limited bench anymore,
> if that is required.
> thanks for any help
> 73
>
> dale wt4t
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