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Author Topic: Loop Insulation Questions  (Read 240 times)
N8RDT
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Posts: 3




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« on: August 21, 2004, 11:00:10 AM »

Hi, I am going to put up a big loop, about 540', around several trees in my yard.  I was wondering if I needed to insulate the wire from the trees or not.  I would expect that I do since the tree would essentially ground the antenna, especially when wet.  Aside from that, what suggestions does anyone have for rigging the wire to the tree at 60ft up and insulating it.  I do not have a ladder or a climber, just a slingshot!  Thanks.

Larry, N8RDT
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AC5E
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Posts: 3585




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« Reply #1 on: August 21, 2004, 12:16:31 PM »

You should use insulated wire for your big loop. And do remember that trees sway with the wind, each tree sways a different amount and at a different time, so you should arrange some sort of tension reliever at each attachment point. Otherwise your loop will be in pieces sooner rather than later.

The time honored line over a limb attached to a bucket of concrete works, but the swinging bucket can be a hazard - so make sure you restain the bucket! While this will eventually damage the limb, if you can change limbs every few years bark will grow back over the wound with little damage to the tree.


Personally, I climb the tree and install pulleys, and use replacement garage door springs from the local Home Depot to provide tension. They are attached by lag bolts and fender (large) washers to the tree at step ladder height above the ground to keep small and curious fingers that might be trapped between the coils of the spring away.

73  Pete Allen  AC5E

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K1CJS
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Posts: 6045




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« Reply #2 on: August 21, 2004, 04:48:11 PM »

Yes, the wire should be insulated from the tree.  Another option for tension and strain relief are plain, simple bungee cords.  Not the black rubber kind, but the fabric covered type.  Use a loop of rope around the limb, hook the cord to the rope and close the hook with pliers (you need a bungee with metal hooks to do this--not plastic hooks).  Use the other end to hold the wire directly or use an egg type ceramic insulator between the hook and wire.

Of course you have to put some tension on the wire to stretch the bungee cords a little, but this system works well, even over time.

Good luck!
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W8MW
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Posts: 326




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« Reply #3 on: August 21, 2004, 06:04:17 PM »

That's right Larry, you don't want the antenna wire to come in direct contact with the trees.  Best to have the loop supported by some good quality rope. I'm using 3 trees plus a tower to keep my loop in the air.  There is plenty of tree movement in the wind and I don't have a lot of tension on the ropes, allowing the antenna to sway.  Suggest you consider copperweld which is steel wire with a copper coating.  I've had ropes break, trees fall, feedpoint connections fail, but never a failure with copperweld.  My present loop has been up 3+ years thru some nasty winds.  It's made of #14 solid copperweld.

73 Mike
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VA7CPC
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Posts: 2393




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« Reply #4 on: August 22, 2004, 12:48:42 AM »

Just an idea for using weights and pulleys . . .

To each corner of the loop, tie a long line (Line A). Run it through (around the wheel of) a pulley.  Attach a weight to the end of line A (far from the loop).

To each pulley's frame, attach an even longer line (line B).

Use the slingshot to throw Line B over the top of the tree (you may need lightweight "messenger lines" for this), and tie it to the bottom of the tree on the side _opposite_ from the loop.

Pull on Line B from the ground, to raise the pulley, and the loop, into the air, and tie Line B off to the bottom of the tree.  

Adjust the length of Line A so that the weight is in the air, not on the ground.

This should let Line B take a fairly fixed position in the tree.   The weight on Line A gives constant tension to the loop antenna as the tree (and the pulley) moves in the wind.


[This is typical of what happens when sailors take up ham radio!<g>  I suspect it's in the "RadioWorks" instructions, somewhere.]
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N3BIF
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Posts: 1190




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« Reply #5 on: August 23, 2004, 12:01:16 PM »

     MY 3 year old 80m loop is more or less a 75 x 60 foot rectangle, it is made of insulated 12 ga stranded ($12.00/500 foot roll).  Two corners are secured by "chalkline like" cord which go over the very top of the respective trees and pull the wire towards the trees. This allows for a lot of springlike action from the trees branch tips and twigs, easily 5-10 feet of sway at each corner during windy times, but at rest the antenna is reasonably taut. The rest of the antenna finds its way over, under, through,around, etc at least 30 other trees and is secure  passively by its path.  In other words it just lays there at an average height of 45 feet. It did take many shots with my homebrew slingshot for me to get it to its current resting place but not a problem since. i have used this technique on many wire installations with very few failures.  In simplest terms, I stand outside the trees canopy and shoot Over the entire tree so that the lead comes down on the far side so that it rest on the limbs tips never a main branch.  I then attach my line to the fishing lead, reel it in, attach my antenna and up it goes no insulation other then the support line. the free end then gets tied off to whatever is convenient , be it the tree's trunk, a second tree, fence post, deck railing etc.
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WB6BYU
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Posts: 13336




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« Reply #6 on: August 23, 2004, 08:10:39 PM »

Generally using insulated wire gives enough insulation
from tree branches, but even occasional branches or
leaves rubbing against a bare wire probably won't
disturb the antenna: the impedance of a branch is
usually lower than that of the antenna, so most current
will stay in the wire.

There are many different ways to install the loop,
depending on what trees you have available and how
dense the branches are.  My favorite is to use black
plastic egg insulators sold for electric fences - these
are similar to the standard ceramic ones but have open
ends so they can be slipped over the middle of a wire
instead of being threaded onto the end.  I lay the wire
on the ground in the approximate location, identify
the support points, and slip an insulator over the
wire at each of them.  Then I tie a rope to each
insulator and toss it over a convenient branch.  (A
better method is to pass this rope though a pulley and
use a second rope tossed over the branch to raise a
pulley, but most of my installations are "temporary",
even if they stay up several years!)

The important thing is to have some way to raise and
lower the wire for repairs and modifications.  Two or
more of the ropes can be secured to counterweights to
avoid overstressing the wire when the trees blow in
the wind - an old window sash weight hanging in a
length of ABS pipe will keep it from swinging.  Tying
the rope to the end of a springy branch can provide
a similar effect.

In thick forest this isn't practical, and you probably
will have to resort to threading it through the tree
branches as you work your way around the perimeter.
Don't worry too much about the exact length, shape, or
height of the wire - just get it up as best you can and
use it.
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