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
|