[TenTec] Omni VI calibration...

n4lq@iglou.com n4lq@iglou.com
Sat, 28 Sep 2002 08:52:44 -0400

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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