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Re: [TenTec] OMNI VI Chirp Report

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] OMNI VI Chirp Report
From: VE1BN <ve1bn@eastlink.ca>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sun, 17 Feb 2008 20:33:26 -0400
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
Paul -

What ur QRG ?
Don
----- Original Message ----- 
From: "Paul Christensen" <w9ac@arrl.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Sunday, February 17, 2008 7:57 PM
Subject: Re: [TenTec] OMNI VI Chirp Report


> Don,
>
>> I understand T-T changed the transmit audio/BFO board crystal frequency
>> adjustment from 9.000700 mHz to
>> 9.000400 mHz.  Apparently this was done as part of eliminating the small
>> chirp.
>
> First, not every Omni VI/VI+ exhibits the chirp phenomenon -- either 
> through
> evolutionary changes, or component tolerances that allowed some Omnis to
> sound just fine.
>
> Next, check your data as it is not correct.   The TX CW BFO frequency was
> originally 9,000.400 kHz.  It is possible that it was later changed up in
> frequency, but not down.   You state that it was changed downward.  Check
> your source and get back to us.
>
> The 2.4 kHz filter is centered at 9,001.500 kHz -- leaving a margin of 
> error
> of just 100 Hz.  Depending on filter tolerances, I believe this 
> contributed
> to much of the perceived chirp on most (but not all) Omni VI/VI+.  In 
> fact,
> it was myself who appealed to George, W2VJN to produce a 2.8 kHz @ 9 MHz
> filter for the sole purpose of ensuring that the CW BFO frequency had a 
> 100%
> probability of falling safely within the filter's passband.  But that was
> only part of the overall solution.  Some BFO crystals perform better than
> others and my original crystal performed poorly.  Add all this to the fact
> that the ALC circuit was modified in the VI+ generation and you have a
> transceiver that produced leading-edge clicks that exacerbate the chirp.
> Did the F/W fix some units?  Perhaps it did.  Was it 100% effective for
> everyone?  Absolutely not.  Again, the best approach is to look for the 
> root
> of the problem and solve it there rather than cutely masking it.
>
>> Moving the F/W chips around did the job for me even if you think moving
>> them
>> around is not the solution.
>
> I am not trying to provoke a fight, Don.  I just let the data speak for
> itself.  If you have a an Omni VI/VI+ without any clicks or chirps, then
> goody gum drops for you.  If you have done nothing to the ALC circuit, I
> would be highly suspect of the click situation, unless TT had made an
> affirmative hardware change that I am not aware of.   The ALC design 
> change
> was so aggressive that I would find it difficult to believe that it was
> solved solely in F/W.
>
>> I don't have clicks or chirps.  Want to check with me?
>
> I'm on 40M right now.  Give me a frequency and I'll be happy to give it a
> listen.  If you have no chirp or click problems, I will give you an honest
> report.  But if you, I'll be equally honest.
>
> 73,
>
> Paul, W9AC
>
>
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