Rigging wire antennas in
trees
Trees present a ready opportunity to support wire antennas. This
article describes a method for rigging an antenna for short term or
long term use, providing convenient access to the antenna system for
maintenance, and without damaging the tree.
Tree Saver
The Tree Saver is a synthetic strap that can be rigged over a tree
branch from the ground, providing a large bearing area on the branch so
that it does not cut into the bark, or get jammed in the crotch of the
branch. A halyard is rigged through rings on the tree saver, so the
running rigging is relatively free.
Fig 1:
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Above is a Tree Saver made from a length of 25mm synthetic webbing and
two rings.
- The two rings are welded stainless steel and smooth so that rope
can run freely without tearing or abrading. The rings must be different
sizes as will become evident, in this case 40mm (ID) x 5mm and 35mm x
5mm.
- A 1400mm length of webbing is cut and ends sealed sealed to
prevent fraying gives a final strap length of 1000mm eye to eye.
Place a ring on one end of the tape, turn back 200mm of tape against
the standing part and tie a tape knot. Work the tape not down close to
the ring and pull it tight. Do the same at the other end with the
remaining ring.
You will need a Tree Saver for each tree attachment, typically two
for a dipole.
Throw weight and line
Another piece of equipment is a throw weight and line.
Fig 1:
|
Above is a commercial throw weight of about 300g (used by
arborists), and 3mm PE
monofilament throw line (orange for visibility). The throw weight is a
small streamlined bag of lead shot, and importantly, a ring that will
not pass through the small ring on the Tree Saver.
Placing the Tree Saver
- Use appropriate Personal Protective Equipment (hard hat) and
clear the area of other people. Keep a keen lookout for falling
branches or rigging equipment.
- Test the stopper that will be used in retreival (see retrieval
instructions).
- Choose a target branch. It should be relatively clear, strong
live wood, provide a clear path below of retreival, and adequate
height. With practice, you should be able to throw reasonalby
accurately to better than 20m in height.
- Secure the end of the throwline to the ground, and place the
throw line into a weighted bucket so that it can pay out freely without
fouling.
- Attach the free end of the throw line to the throw weight, a
bowline is a good knot, easy to tie and can be undone easily.
- Throw the weight over the target branch and let it fall to the
ground. Remember which direction the throw weight crossed the branch,
it is important.
- Untie the throw weight and pass the free end of the line through
the smaller ring on the Tree Saver and tie it again to the throw
weight. Make sure that the Tree Saver is not twisted.
- Untie the secured end of the throw line and pass it through the
larger ring of the Tree Saver and resecure. Pull the surplus line
through the larger ring so that the Tree Saver is ready to be raised.
- Haul down on the throw line to raise the throw weight. This will
draw the Tree
Saver up behind the throw weight. When the throw weight reaches the
branch, give the line a sharp pull to flick it over the branch and
immediately let it fall freely to the ground. You should now have the
Tree Saver rigged over the branch and the throw line passing through
both rings underneath the branch.
- Untie the throw weight and attach a halyard. Pull the halyard
back through the Tree Saver to the ground.
- Making a closed loop of halyard is a good safety measure, but
include a heavy ring or the like in the loop so that the wind does not
blow the whole halyard up into the tree.
Needless to say, if you let go of the free end of cordage at some
stages of this process, you may fail. Exercise common sense in securing
cordage and suspended objects.
Rigging the antenna
Use the halyard installed to raise the antenna, and tie of the end
securely. Allow enough slack for tree movement under wind etc. The
halyard does not run sufficiently freely to use a weight to hold
constant tension on the antenna, allow sufficient slack.
Retrieving the Tree Saver
- Use appropriate Personal Protective Equipment (hard hat) and
clear the area of other people. Keep a keen lookout for falling
branches or rigging equipment.
- Tie a stopper on to the end of the halyard on the side of the
branch where the throw weight fell to the ground during placement (open
the loop if you have make a loop). The stopper MUST pass freely through
the larger Tree Saver ring, but NOT pass through the smaller Tree Saver
ring.
- Tie the throw line to the same end of the halyard. Don't skip
this step, tempting as it might be, because it provides protection for
a mistake in Step 1.
- Haul down on the other side of the halyard so that the stopper is
pulled up to the Tree saver, and through the larger ring.. Continue
hauling so that the Tree Saver is pulled over the branch. When the Tree
Saver is clear of the branch, the throw line can be released, and the
halyard used to pull the Tree Saver down, then to retrieve the throw
line.
Warning
Do not use this Tree Saver to climb
a tree, it is not sufficiently strong for that purpose. If you get your
gear stuck up in the tree, find some other way to retrieve it.
Costs
At the time of writing:
- Stainless steel rings are about A$1 each (Ebay);
- Webbing is about $0.80/m (Ebay);
- Commercial throw weight is about A$25;
- Throw line is about A$0.20/m.
So, about A$35 for throw weight and throw line, and A$4 per Tree Saver
that you make.
© Copyright:
Owen Duffy 1995, 2021. All rights reserved. Disclaimer.