On Wed, Jan 22, 2014 at 1:00 AM, Richard (Rick) Karlquist <
richard@karlquist.com> wrote:
> About 30 years ago, I had a 55 foot tower with a feedpoint at the
> top. It fed a horizontal wire 55 feet high and 130 feet long against
> the tower. The base of the tower was grounded, but no radials.
> It loaded up fine, but was nothing great in terms of getting out.
>
That jibes with models showing the basic pattern you describe. The feed Z
is wildly dependent on the nature of the tower ground plus capacitance to
miscellaneous conductors on the tower for its specifics.
That the tower was grounded, with or without radials, would completely
alter the pattern from that of a center fed L with bottom of a vertical
wire insulated. The current distribution changes in two ways: 1) the
current on the vertical conductor has its maximum at the ground instead of
at the feedpoint. 2) this makes the impedance of the vertical conductor go
high at the feed, The load presented to the feedline is severely
unbalanced, probably beyond the abilities of any "balun" device. Diminished
balun function or lack of balun then turns the feedline into a primary
radiator.
Even if the tower was insulated, if there was a feedline or rotator cable
on the tower, it would alter the pattern. If the bend of an end-insulated
insulated wire L is supported by a tower, that will also unfavorably alter
the pattern.
73, Guy.
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