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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