From: k2av@qsl.net (Guy Olinger, K2AV)
To: towertalk@contesting.com
Hi Guy,
> Just exactly what I would have done. Dippers may be a pain, but they
> certainly can confirm the [octave, order of magnitude, general
> neighborhood, approximate value] of a capacitor or inductor. It *will* be
> around 9-12 pf. While that is a killer in the middle of an other wise
> resonant HF conductor, at the ends of a long section, it will move the
> resonant frequency a lot.
Measuring "big things" is always a royal pain. There is often as
much self-capacitance and stray capacitance as "across the
component" capacitance. It isn't like measuring a 10 pF ceramic
disc, or a chip cap.
In any event, I did the thing a third way today and calculated the C
based on surface area and spacing, allowing 5 for the dielectric
factor of ceramic.
Doing it by math results in about 4.6 pF. Of course that does not
include strays.
The real proof is in measuring the frequency shift of a real guyline
in a real situation. But this is the best I can do.
> Next time I model guywires, I'm going to use a single conductor on
> EZNEC and put a 12 pf load where the breaks go. That may explain a few
> things.
Maybe you can try both 5 and 12, one should be the low limit and
one the high.
My main concern is that the resonances at 10 and 15 meters get
pretty close to bands when longer guy sections are used. It
wouldn't take much to move the resonances in or close to the band.
I never worried about this until I started installing a rotating tower
where the yagis look through a maze of guylines. I might wind up
mixing fiberglass links and steel.
73, Tom W8JI
w8ji@contesting.com
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