I am only moving my finger a fraction of an inch and my hand not at all
when this happens .The feed lines are disconnected when this is going on
.There is no dc continuity between the antenna and any mounting hardware or
th>>>>
You have the very high impedance part of the antenna near the post. This is
part of the reason I always use large hats, which self-resonate the antenna
near 3.6 MHz. With no hat and a 30 ft vertical above the loading, the
antenna has an almost triangular current distribution, so voltage gets
pretty high. You didn't say (or I missed) the length of the post, but
impedance problems like that are also aggravated by post height. If the post
was 8 feet above ground, that would be a substantial fraction of element
length.
Not using a hat on a short vertical is just generally a bad idea. Not using
a hat makes the antenna behave more and more like a mobile whip as you go
down in frequency. It's a good design esthetically, but a bad design
electrically.
Insulate the element like you have 50 kV at every point (even though you
don't) and it will start to stabilize with moisture and other stray effects.
This includes insulation of the entrance to the box containing the loading
coil. As long as the coil is inside a dry large metal box and stable
mechanically (low temperature coefficient), it won't detune with weather.
Things are a whole lot better and easier electrically with the element self
resonant at 80 meters or lower by virtue of element length and a hat.
e post .I disconnected the base loading and put the analyzer on it and it
is resonant at about 8 mhz and touching the post causes no change with
this setup . There are eight 30 foot radials laying on the ground and a 2
inch wide copper strap about 3 foot long in the hole that the 4x4 is in .
What is going on here and should I make an effort to limit the coupling
between the 4x4 and the antenna?
On 8 MHz the base impedance is low. That makes the impedance low, and
altering the electric field near the low impedance point has minimal effect.
Almost any insulation or dielectric is good enough. On 16 MHz, you could be
back to the same problem you have on 160, because base impedance would be
high again (assuming a thin element).
73 Tom
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Topband Reflector
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