Not too many years ago I lived outside of Washington on a 5.5 acre lot in
the Virginia countryside. I had huge oak trees around such that you could
not see the 5 towers I had unless you were literally in the driveway. I
used a CAROLINA WINDOM II as one of the wire antennas between two of the
towers. The support rope was strung between two of the towers at 150ft.
Something to note: No matter what you do, even with NO weight on the nylon
or dacron rope it is going to sag. You can put enough pulling power on it
that it breaks and it's still going to have some sag before it does. But
here is what I did to get the antenna flat. I used the screw eye on top of
the center insulator ( or off center insulator if you will )and raised the
center insulator as high as I could get it....I put as much strain on it as
I dared. The insulator was still about 15 ft or so lower than the top of the
tower as I recall. You have to remember that you are not only raising that
insulator but the 450ohm or 300ohm feed line AND the matching transformer
AND the coax that is going to feed the whole thing. With all that wire,
insulators, coax, etc the entire affair weighs quite a bit. Anyway, when
the strain is applied to the center insulator and you have it up as high as
you can, you will have created the fixed height for the antenna. At that
point I raised the ends of the dipole to a point on each of the two towers
where the dipole was/is as flat as possible. As far as the nylon or dacron
or whatever I was using...I cannot remember. But I will tell you this, that
the nylon gets very, very tight. It looks like fat dental floss and I dare
say that it might get a little wet but in mid air and that tight I don't
think it is going to hold much moisture. The cord is just too tight I think
to hold much. I wish I had the space to put something like that up here in
Florida. Palms don't get that high here or lightning has something to say
about it. Good luck with your installation.-- Mike K4CVL
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com]On Behalf Of wa3afs@inav.net
Sent: Wednesday, October 11, 2006 11:43 AM
To: Eugene Hertz; TowerTalk@contesting.com
Subject: Re: [TowerTalk] Stringing dipoles?
Hmmm,
I think that an additional rope would work ok AS LONG AS the rope remained
dry. Most antennas prefer to be away
from conductive surfaces. Water and ice/snow tend to have some conductive
properties until totally distilled and I
have never seen any distilled stuff falling from the sky!
Also you would be putting additional stress on the center insulator thingy
(especially when the rope was wet). Water
starts to get heavy when maintained in absorbant materials like rope!
Antennas in trees are always subject to a lot of variable stresses. I just
'live' with it (I use coaxial inverted Ls in my
trees and plan on replacing them every couple of years with the ones that
cross multiple trees (160M) being the
ones that have the shortest life expectancy. I also use a bungy cord at one
end to take up some of the slack when
the wind blows...but I find that the bungy cords also have a short life so I
try to inspect them every couple of weeks.
The coaxial inverted Ls do not seem to mind being close to the trees. I see
not differences when the trees are wet
or when the leaves are on or off.
I have a pair of 160M, a pair of 75M, a 4-square on 40M and on 20M. These
have only been up a maximum of 6
months at this QTH, but experience at other QTHs with this type of antenna
gives me a good idea of the effects of
stress.
73 and good luck
-- Bruce, WA3AFS
On 11 Oct 2006 at 14:15, Eugene Hertz wrote:
> Ok, this may be the simplest question I will ever ask here so here goes.
>
> During my research for OCF dipoles, I have read about some horror stories
of dipoles breaking or coming apart due to the stress of wind, weight and
other factors. Especially I've heard that the carolina windoms, with their
extra weight in the center caused by the matching unit, the isolator, and
the length of feedline can cause a big sag at the feedpoint. Several folks
I've corresponded with indicated that they attempted to "lift up" the
feedpoint as high as possible by putting more tension on the wires (legs) to
hoist it higher. This was for people that did not have a convenient center
mounting location like a tower or tree or house.
>
> In thinking about this, it seems that these antennas have lots of phyiscal
stress on them from both gravity as well as tension on the ends of the wires
in the horizontal plane to try to counteract gavity.
>
> My thought was this: By using one rope (dacron etc) to connect leg1 to a
tree and another rope to connect to leg2 to a tree (with pulleys and
weights, of course), this is putting lots of "horizontal" stress on these
wires and the center matching conductor/insulator thingy. This force is
always trying to pull apart the antenna.
>
> Why not take one very long rope, thread it through the leg1 insulator, the
center insulator/matching unit and then the leg2 insulator? Surely the two
ends of the wires would have to be attached somewhat taught to the rope, but
this could be done with some black wire-ties along the length of each wire.
Or tie some knots in the rope somehow to hold the insulators in place.
>
> My thought was, this would all but eliminate any horizonatal stress
normally put onto these wires and we would be left only with the stress of
gravity vertically. I would imagine too, that this would help keep the
center up a big better than nothing going through the center point.
>
> Any thoughts? Could this work? What am I missing?
> Eugene
>
>
>
>
> _______________________________________________
>
>
>
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>
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