K3MH continued:
>In my extensive conversations with Mike Mertel, parasitic and reflector
>lengths are not so critical as a result of small dielectric constant
>difference and unlikely makes any significant impact on ACTUAL performance.
>I would focus attention on re-adjusting the driver to SWR, which is what I
>did with a quite a great deal of precision. Once readjusted, it worked like
>a charm
I can't recall the exact shifts reported for which bands,
but changing the reflector of a 3-el model on 20m at 15m
by 1.5% (I think it was in that neighborhood), the F/B
changes more towards the 1 dB that might be ignored
above 2 dB instead of the 1 dB below it. That's the better
part of the way to 3 dB.
A 1.5% change to the reflector on a 2-el should be a
bit more noticeable.
Mix tubes & maybe throw in a version of firmware with
one-of-numerous iterations of lengths & then operate
towards the end of a segment without tracking - an
entirely plausible scenario & added together could be
a bit more than 1.5%.
After the driver, I would guess new tubes are best used
on a director (if a 3-el).
Just something to bear in mind, as I think all of us
will replace the tubes should they fail as they fail & not
all in one go. The firmware doesn't understand a mix of
tube vintages, though it is easy to deal with for the driver.
I must admit to only glance at the SWR meter from time
to time, but spend a lot of time making something of the
directivity of my tribander. After all, that is why we have
them. That 2+ dB better F/R could be the 2+ dB better
C/N+I that makes or beaks LP from here, where swinging
towards the north on 20 usually comes with S3-5 noise,
bleeps, blurps, spus, intermods, etc.
With only the dipole, I envy the consistency of pattern
possible with variable parasitic element lengths. Instead
of best SWR, I jump between band segments in order to
keep a GU74B happy when I switch to it from my tribander
(well cool). Wish it were as easy to change the lengths of
the carefully cut insulated wire the tribander is made of, as
the one thing it lacks is good F/R across the entire band.
So enjoy all that dynamic elements can offer by putting
new tubes on an old SteppIR driver first & keep in mind
tube vintage when changing firmware versions (and not
needing every bit of F/R if you're so lucky ;^).
73, VR2BrettGraham
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