I tried a 45' tall flattop vertical with a 72' long by 5' wide flattop
all hung in oak trees. It worked OK when it was below freezing temps
outside and decent when the temperature went below zero degrees in the
winter. At any temps above freezing, it made a good dummy load. The
trees have no effect on my TX loops like Laurence found out =-O
Later,
--
Mike
WE0H
WD2XGI
Laurence KL1X wrote:
....well Cottonwood/Pine trees were certainly an affect that reduced
my effectiveness in producing a strong into USA/world signal from
Alaska - ok the distance was more to the nearest receivers but I was
using a pretty large vertical and good top loading, and extensive
earth radial system probably close to "commercial" standards - I just
was in a small cut out the middle of a deep dark dense damp dank
forest - and used trees to suspend additional top loading wires but
didnt get the insulators closer than 20ft from the support braches. As
you say it was always difficult to ascertain the loss/gains on
additional top loading versus loss C due to proximity.
Working on what we have here in OK with this 380ft circum lazy tx
loop, the same tx power as was etc and from extensive local field
meaurements, Im up about 12dB (or more) compared with my poorer 110
ft vertical and extensive top loading! - Its got to be these high Z
verticals, trees and the associated lossy C, compared with the Low Z
loop, that doesnt seem to mind rubbing up and down tree trunks, slung
without insultors over branches, and which birds sit and "cheep" on
with close to 35A of aerial current running thru it (and no
connections to earth per se!)
However if I lived on a farm, with say 20 acres and a 110 ft tower and
a few trees Id probably go for a vertical....then perhaps not!
ps I used dry cedar to support the vaccum cap which has a few Kv
across it and now cooking/burning smells as of yet...
Cheers
Laurence KL1X/5
ps conditions are %&^$#!!, but daytime enhancement over a 1500Kms are
up quite a few dBs at the momemt.
From: "Vernall" <z>
Reply-To: [email protected]
To: <[email protected]>
Subject: LF: Re: Re: Wood formers
Date: Fri, 12 Nov 2004 09:26:37 +1300
Hi all,
Some interesting comments on wood and plunging Q of LF coils. It
also made
me think about "live wood" and that definitely does have sap. It
strongly
suggests that a transmitting antenna should be well clear of trees.
For a
vertical, the up-wire is where the current is maximum, and that
situation is
similar to a one turn inductor as far as magnetic induction is
concerned.
If the wood is also a lossy dielectric, then the top loading wires and
electric fields could also be contributing to losses with trees in the
antenna environment.
In terms of efforts made to maximise radiated power on LF, it would be
unbalanced to focus only on loading coil loss, even if that is more
directly
under the control of those making the coil. It would be interesting
to find
out for top loading that is tied off to a tree (with suitable
insulation,
and in a situation where there are no other practical choices for
suspending
the top loading) if there is an optimum spacing of the insulator from
the
tree. It may be better to accept moderately lower capacitance for top
loading if the net losses are lower.
73, Bob ZL2CA
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