Posted by
P.B. Christensen on
Dec 02, 2010; 5:09am
URL: http://elecraft.85.s1.nabble.com/Fwd-New-Sherwood-report-tp5793377p5794850.html
> The rise time by itself is not the important factor -- what is much more
> important are first and second order discontinuities, and even higher
> order discontinuities.
Evidence of this comes from our K3s. Some time back around F/W version 3.0,
the CW rise/fall time was accelerated. My K3 reaches full envelope power in
just 2 ms and yet it produces very little bandwidth due to: (1) the DSP
shape function; and (2) very well controlled ALC. The best DSP based
functions (e.g., raised cosine or Blackman-Harris), can be completely
destroyed by aggressive ALC action.
One of the best waveform controlled CW transmitters is the Ten Tec Omni VI.
One of the worst controlled CW transmitters is the Omni VI+. What happened?
In the upgrade process, the ALC time constants changed to the point where a
sharp, discontinuous waveform edge was produced. All the DSP shaping one
could try would not have helped. The ALC circuit took control of the
waveform and generated, among other anomalies, severe key clicks from the
abruptly fast leading edge of the CW waveform.
Regarding the FTdx-5000, my first suspicion is the ALC system as the culprit
and not the DSP generated waveform. When the ARRL tested the IC-7800, it
showed an aggressively fast rise time. However, the '7800 has a user
adjustable "Drive" control. With only slight ALC action, the '7800 produces
an excellent waveform and little keying bandwidth. If the FTdx-5000 has a
Drive control active in CW mode, it may be possible to reign-in bandwidth.
Paul, W9AC
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