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[TenTec] Omni VI frequency error

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: [TenTec] Omni VI frequency error
From: Steve Hunt <steve@karinya.net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Thu, 04 Sep 2008 15:54:50 +0100
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
I can't remember if I've raised this problem before; if I have, I apologise!

My OmniVI frequency readout is consistently 130Hz high on all bands and 
all modes; in other words if I accurately tune in a station on 14,200KHz 
the frequency read out will be 14,200.130.

I've adjusted all the BFO settings and the TCXO setting as accurately as 
I can with a frequency meter whose calibration I checked against a DDS 
source zero-beated to WWV.

Here's what's puzzling me:

1) I'm reluctant to suspect the BFO frequencies - it's too much of a 
coincidence that USB, LSB and CW are all out by exactly the same amount 
in the same direction. In any case they are within 5 Hz as measured on 
the counter.

2) If the TCXO was out, I would expect the 5MHz VFO, the Xtal 
frequencies, and the final LO frequency all to be out by the same 
percentage. That would result in approximately 3 times the frequency 
error on 10m as on 160m; but I see the same on all bands.

3) Interestingly, I recently swapped the oven oscillator for the TCXO. 
The same 130Hz shift was there before and after the change. Again it 
seems too much of a coincidence that the two reference oscillators were 
out by exactly the same amount. I needed to make a very small adjustment 
to the TCXO to get it on 20 MHz, but that had no effect on the "offset".

I could always deliberately "misadjust" the BFO frequencies to 
compensate, but that seems a retrograde step and would likely alter the 
Tx audio characteristics by moving the carrier relative to the filter 
skirts.

I can't think of anything that would produce the same offsets on all 
bands and all modes. Am I missing something?

It's not a showstopper - just an annoyance.

73,
Steve G3TXQ

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