[TenTec] Omni VI calibration...

Robert & Linda McGraw K4TAX RMcGraw@Blomand.Net
Sat, 28 Sep 2002 09:17:57 -0500

The best I can determine using a Stamford Research counter the drift on my
Omni VI+ is less than 10 Hz over an hour of extended operation either PSK or
RTTY.  I've never observed more than this.  Even running RTTY at 50 watts
out for extended periods, there's no more than 10Hz.  Actual frequency
readout error may be slightly greater than 10 Hz but certainly not more than
20 Hz.  Of course last digit resolution is limited to 10Hz.  I don't see how
one could expect to be closer than that with the given hardware.

As to PSK operation, use the software AFC and don't lock the TX freq.
Problem solved.  And then, how does one know that the other station isn't

As to using another rig, most today don't have frequency readouts closer
than 10Hz.  Folks this is ham radio.......it's a hobby.  The Stamford
Research counter that I have costs more than 3 Omni VI+ 's combined.  It
easily reads to better than 0.01 Hz all the way to 1 GHz.  Also the Rhode
Schwartz receiver that I use for professional work is far superior to all
ham receivers.  It concurs with my findings.

Most rigs I've measured have at least the same or more drift than the Omni.
In many cases however, the drift characteristics are different.  As to using
the IC-706, the 2 that I've measured, I best not comment on the accuracy or
drift characteristics.  At the same time, the 706 is a good economical


P.S.  For what it's worth, I repair radios.......... as a hobby of course.

----- Original Message -----
From: <n4lq@iglou.com>
To: "John Clifford" <johnclif@ix.netcom.com>; <tentec@contesting.com>
Sent: Saturday, September 28, 2002 7:52 AM
Subject: Re: [TenTec] Omni VI calibration...

> All TenTec rigs drift some. The newer one's, Pegasus and Jupiter are less
> likey to drift. On one Omni VI, I removed the speaker and installed a
> small fan. That helped reduce the drift caused by transmitting. I think
> some heat is conducted via the chassis from the final amp to either the
> xtal osc. or bfo. The best way to zero beat the rig is to use another rig
> of know accuracy setting next to your's and adjust the trimmers on the TX
> OSC board as per instructions in the manual. What I do is set them up as
> if I were in a cw qso and adjust for exactly the same pitch in both rigs.
> I use an IC-706 to do this. For PSK-31, I would use another rig. A drift
> of just 20hz will drive you nuts!
> -----Original Message-----
> From: "John Clifford" <johnclif@ix.netcom.com>
> To: <tentec@contesting.com>
> Date: Wed, 25 Sep 2002 14:15:35 -0700
> Subject: [TenTec] Omni VI calibration...
> > Greetings,
> >
> > I'm sure that many of you have read the article on frequency
> > calibration in
> > the latest QST.  I decided to verify the calibration of my two main
> > rigs
> > (Omni VI, Elecraft K2) to WWV and see how accurate they really were.
> >
> > Using the USB/LSB/zero beat method and MixW's spectrum display to
> > ensure
> > both sidebands were at the same frequency, the K2 is within 20 hz
> > (actually
> > 20hz above).  The Omni VI is off by 10hz (above).
> >
> > But... I've noticed that, with the Omni VI, something is drifting
> > during HF
> > digital mode QSOs.  If I get into a PSK31 ragchew, I start sliding down
> > in
> > frequency.  What happens is that I select the other ham's signal,
> > transmit
> > to him, and then when he comes back his signal is lower in frequency
> > than
> > mine.  I have learned to 'lock' my transmit frequency in MixW so that
> > only
> > my receive frequency will automatically tune to the other ham's
> > signal...
> > hopefully this keeps my transmit signal on the same frequency.
> > However,
> > even after locking my transmit frequency, the other ham's signal
> > invariably
> > slides lower and lower down the band -- the split diamond tuning
> > indicator
> > ends up having the top of the diamond moving further and further to the
> > left.  My rig, an Omni VI/Option 1, has the crystal oven, and this
> > happens
> > even if my rig has been on for an hour and I have had several QSOs to
> > 'heat
> > things up.'
> >
> > Anyone else ever seen this?  Anyone have any ideas as to how this can
> > be
> > corrected?  Here's another question:  how certain can I be that my
> > transmit
> > freq is exactly the same as my receive freq?  I have a frequency
> > counter...
> > I've thought of using my K2 as a reference, zerobeating my Omni to its
> > signal and measuring the K2's signal on the counter, and then measuring
> > the
> > Omni's transmit signal on the counter.  This should let me determine if
> > I
> > have a discrepancy between receive and transmit frequencies... right?
> > Anyone have a better method?
> >
> >  - jgc
> >
> > John Clifford KD7KGX
> >
> > Heathkit HW-9 WARC/HFT-9/HM-9
> > Elecraft K2 #1678 /KSB2/KIO2/KBT2/KAT2/KNB2/KAF2/KPA100
> > Ten-Tec Omni VI/Opt1
> >
> > email: kd7kgx@arrl.net
> >
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> >
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