Supporting a Beam from Trees

Our Field Day Group www.hsfdg.org∞ has been supporting beam antennas from trees for many years. We developed techniques of getting lines into the trees using Archery tackle, and later the Pneumatic Tennis Ball Antenna Launchers∞. This has proven to be a safe and effective method to support these antennas in the field. We have supported beams to 40 pounds this way from the TH3JR to the Steppir 2 element and xxx. The lifting setup has evolved to a 3:1 advantage system that allows safe and easy lifting of the beam antenna. Hardware store pulleys have been abandoned in favor of marine sailing gear. They cost more but are superior, with low friction ball bearings. Lifting a heavy beam can now be handled safely by a single person.

Warning - Lifting a 40 pound antenna up into the trees overhead poses a number of safety hazards. One year the pulley was not to be found and some enterprising soul decided to tie a loop in the top support line and run the beam lift line through the loop and pull the beam up without a pulley after the support line had been raised and tied off. The crossed lines sawed through almost immediately (it was poly line) when the load was lifted (good thing) and the beam fell a mere 8 feet to the ground. The person doing the lifting was standing in the middle of the beam during the lift, and the beam fell around him. Amazingly enough the only casualty was the cut line, and the embarassment of being in the story. THINK, PLAN, and BE SAFE. DON'T STAND OR WALK UNDER THE BEAM. We have never had a problem since, though one other time the wrong line was untied to lower the beam and it fell some distance before it was stopped, a near mishap for the beam but not a personnel safety issue. USE GOOD KNOTS. KNOW WHICH LINE YOU ARE WORKING WITH.

The Gear

The support lines have evolved over the years and we have settled on 3/16" Dacron. A pair of 500 foot spools are required. One is split into two equal lengths about 250 feet each and wound on two separate spools. These are the support lines. The third is kept full length on a third spool for lifting the beam.

Parts Required for Beam Lift System

• 2 500 foot spools of 3/16" Dacron line
• 3 Cord reels (100 foot extension cord reels)
• five carabiners
• one single pulley, loop head (Ronstan RF30101) (side pulley)
• one single pulley w/ becket, loop head (Ronstan RF30111) (beam pulley)
• one double pulley, 2 axis shackle (Ronstan RF30202) (top pulley)
• beam stabilization mast
• beam pointing line (nylon twine, 150 ft)

Other Equipment

• leather gloves
• safety glasses
• hard hats
• boots or good shoes
• pneumatic antenna line launching system
• nylon twine

Preparations

500 ft Dacron Spool #1

• cut two each 20 ft tree anchor lines
• split the remaining 460 ft into two 230 foot lines, each goes on a cord reel

500 ft Dacron Spool #2

• cut a 30 foot top line, one end gets a loop and carabiner with single pulley, the other gets a loop with carabiner and the double pulley
• cut a 10 foot beam tie line
• remaining 460 foot beam lifting line goes on cord reel #3

Knots
The Bolon

Where do all the lines go

The beam lift line goes up to the single pulley at one end of the top line, across through the double pulley, down to the beam pulley and through, back up to the double pulley and back down to the becket anchor on the beam pulley. When the beam is lifted the lift line is tied to a tree anchor line via a carabiner. The beam tie line attaches to the bottom loop on the beam pulley ties to the beam's main boom.

The tree anchor lines wrap around the trees at a convenient height, approximately 5 feet, and are used to anchor the support and lift lines.

The support lines go up over the treetop and to each end of the top line. They are tied to the anchor lines via carabiners.

Stabilizing and Pointing

The beam stabilization mast is a lightweight aluminum tube approximately 3 feet in length. It should be of a diameter that fits the beam's mast mounting hardware. This is extended above the beam and used to keep the beam level. A short beam tie line is fastened to the boom, and half-hitched at several points to the stabilization mast. Alternately a harness can be constructed of several lines to points on the boom and driven element to hang it from a point above the beam and maintain level.

The beam pointing line is tied to the end of the boom. It is used to point the antenna and is tied at a convenient place to hold the beam's orientation.

The Process

We choose a pair of trees that has sufficient space between them for the beam, but not too far apart. They must be sturdy enough to handle the load, but trees are a lot sturdier than they look so this has never been a problem. The trees we use are mostly fir, spruce or pine at the 5,000-9,000 foot level in California's Sierra range.

Minimizing Tree Damage

Threading the Lines

Getting the Support Lines into Position

Optional Inverted Vee Support Subsystem

• single pulley
• 1/8" line 200 feet (twice the length of the beam lift height)

Lifting the Beam
Coax
Pointing Line
Inverted vee lift line
Test Lift
Lifting Safety


AlanB