[TenTec] Omni VI calibration...

John Clifford johnclif@ix.netcom.com
Wed, 25 Sep 2002 14:15:35 -0700


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