I am in Boston (Charlestown) MA.
My suggestion is to place a pair of pulleys in your tree. The first pulley
A is attached by tying it around a trunk or limb.
This is a permanent installation. The tree will grow over the rope, so tie it
loosely to avoid girdling the tree.
The second pulley B is tied to a lifting loop. The lifting loop is a loop
that runs from where it ties to B, through the sheave
of pulley A, down to ground level (where you can reach it) and back up to the
attachment to pulley B. By pulling on the appropriate
side of the loop, you can raise and lower pulley B from the ground. The
lifting loop can be secured to a cleat that is mounted on
the tree trunk. Every year or two you will need to unscrew the cleat and move
it to a slightly different location on the trunk.
Otherwise the tree will grow around the cleat and you will have to chisel out
the lifting loop.
Last, the antenna support rope from the end of your antenna now passes over
the sheave of pulley B and off to a counterweight or
tie-off point. If you do not have a counterweight on the antenna, I would
strongly recommend one.
Use Harken pulleys, available on the web (e.g., from West Marine or
Annapolis Performance Sailing) or a local boating supply
store. Harken pulleys are designed to spend their life outdoors. Other
pulleys that you might get from the hardware store will
corrode and the sheaves will stop turning.
The advantages of this system are:
1) The antenna support rope will chafe and rub as the tree moves in storms.
This is unavoidable, even with good quality pulleys.
But, with a counterweight and 2-pulley system like this, the rate of wear is
slow. The antenna support rope will not need to be
replaced for several years (depending on the quality of rope).
2) With the lifting loop, pulley B (and the antenna support rope) can be
lowered easily to the ground and inspected. The antenna
support rope can be replaced when needed. If the antenna support rope fails
suddenly, it can be replaced without climbing the tree.
Because the lifting loop moves through pulley A ONLY when raising and lowering
pulley B, there is essentially no wear on this rope.
3) A counterweight is highly recommended for any permanent attachment to a
tree. Without a counterweight, tree movement will put
sudden strain on the antenna wire and support ropes. The antenna itself will
flip and swing violently in a storm, causing the
feedline to thrash around and adding to the fatigue at the feedline-antenna
attachment. Most importantly, the tree will yank (with
substantial force) on whatever is supporting the distant end of the wire
antenna. If it's another tree, maybe you're not so
concerned, although two trees working against each other can easily snap the
wire or its support ropes. However, if the distant end
is attached to a tower or building, it is a guarantee that the tree will apply
forces against the structure which run all the way up
to the breaking point of the wire/support ropes. Think about it: would you
want something to yank on your building or tower with a
sudden force of half-ton or more?
4) The last advantage of a counterweight system comes in ice storms. The
extra weight of ice (and the added wind load it presents,
if there is a breeze) adds substantial loads to the anchoring structures
(trees, towers, buildings). With a counterweighted system,
as weight is added to the antenna and its supports, the counterweight rises...
allowing the antenna to sag and greatly reducing the
sideways stresses. At my old QTH on a mountain ridge top in Maryland, my 400
foot long dipole string (counterweighted, even though
it was strung between two towers) and 160m dipole (one end at the top of a
tower, the other supported by a tree) both survived many
ice storms. The worst was 1.5" radial ice (3" diameter of ice along the entire
length of the antennas) with winds above 60 mph.
Every piece of yagi aluminum was swept off the towers and many trees were
destroyed, but the counterweighted antennas survived and
were back at normal height when the ice melted. As another example, enormous
counterweights are used to support the two VLF
transmitting arrays at the US Navy's transmitted site in Cutler Maine: the last
line of defense against ice.
Last tip: If one end of the antenna is anchored to a tower or building, do
not simply tie the end of the rope to the structure.
When you do that, all of the load (largely sideways) is applied to the
structure. Structure stresses will be far lower if you place
a pulley at this point. Run the support rope over the sheave of the pulley and
down to the ground -- not straight down, but at an
angle so the anchor point is some distance PAST the structure (in the direction
opposite of the wire antenna being supported). If
you look at the force vectors, you'll see the structure has far less sideways
loading. The structure is now largely lifting the
support rope to the desired altitude, not attempting to restrain it sideways.
This reduces sideways shock loads in storms, and
added loads from ice. (And you can lower this end of the antenna for
maintenance without climbing the structure, and tension the
antenna up in the air while standing on the ground.)
-- Eric K3NA
-----Original Message-----
From: Eric Rosenberg [mailto:wd3q@erols.com]
Sent: 2003 September 10 Wednesday 23:10
To: eric@k3na.org
Subject: RE: [TowerTalk] A Better Rope?
Hi Eric...
The rope is simply draped over the tree limbs, holding the antenna on
one side and fixed to a spot on the ground on the other side.
btw, where are you these days?
Eric W3DQ
At 06:58 AM 9/8/03 -0400, you wrote:
> Can you describe a bit further how you are using the ropes in the
> trees; i.e., how your antenna is rigged?
>
>-----Original Message-----
>From: towertalk-bounces@contesting.com
>[mailto:towertalk-bounces@contesting.com]On Behalf Of Eric Rosenberg
>Sent: 2003 September 8 Monday 03:14
>To: Tower Talk Mailing List
>Subject: [TowerTalk] A Better Rope?
>
>
>My Synthetic Textiles dacron rope is losing its cover (the black
>sheath) from rubbing in the trees. While the first run lasted a
>couple
>of years, this time I got only 6 months use. Admittedy, the number of
>days of rain, high winds and otherwise miserable weather has been
>considerably worse this year than in the past.
>
>The trees are tall (70-100 ft), and it's impossible to get near where
>the ropes cross the branches.
>
>Can anyne on TT recommend a rope with a strong outer sheath?
>
>Thanks in advance,
>
>Eric W3DQ
>Washington, DC
>
>_______________________________________________
>
>See: http://www.mscomputer.com for "Self Supporting Towers",
>"Wireless Weather Stations", and lot's more. Call Toll Free,
>1-800-333-9041 with any questions and ask for Sherman, W2FLA.
>
>_______________________________________________
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>http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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