[TenTec] off frequency omni VI+

[Bob McGraw K4TAX]

The digital displays are merely indicated values and ARE NOT frequency measurements. 

Most ham radios are reasonably accurate but resolving less than 100 Hz is based on many variables and assumptions.  Even the number of digits in the software calculations are truncated. 

If you need to know the exact frequency you will need an external frequency counter with an external GPSDO reference. 

The ARRL Frequency Measuring test is this month.  Try your hand, if you believe your radio is really accurate.  

Bob, K4TAX


Sent from my iPhone

> On Nov 2, 2019, at 1:31 PM, Ken Brown <kenradiobrown at gmail.com> wrote:
> 
> 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 at 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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