I'd been looking for a way to provide continuous tension on a wire antenna, like a doublet or a dipole, that is supported on one or both ends by a tree. The idea is to run a line/rope from the end of the antenna, down through a pulley mounted high in the tree, and then to a weight hanging from the line; some people use springs to accomplish the same thing. When the wind blows and the tree moves, the weight would move up and down, keeping more or less constant tension, thus keeping the antenna from snapping. The ARRL Handbook and Antenna Book have had diagrams of doing stuff like this for decades...but finding a suitable weight can be an issue (besides getting the wire into the tree... that'll be another post...)
I've used a variety of things in the past including buckets full of dirt, cinder blocks, and even "no-weight" by just tying to the tree and hoping for the best, etc. but this time I wanted something that would minimize damage to the tree trunk should it swing into the tree and would be XYL friendly. Below is what I've constructed from two feet of 2" and 3" PVC pipe, concrete, 12" of rebar, and a lag screw with a loop.
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| PVC-Concrete Antenna Weight |
I mixed up the concrete in one of those plastic storage containers using a 60# bag of Sakrete High Strength mix (although any concrete should do) along with about 2 quarts of water. After taping off one of the ends of the PVC with duct tape, I filled the pipe up with concrete and then inserted the rebar into the center, leaving about 2" sticking out. (I had concrete leftover which I used for some driveway patching!)
Once it cured, my son welded the lag screws onto the end of the rebar. Done.
I haven't weighed them yet, but it feels like about 10 lbs for the 2" pipe and maybe 20 for the 3". Once I weigh them, I'll re-post my findings. There's nothing magic about the length and size here, although bigger antennas are going to require more weight to prevent excessive sag. And in my instance, the plan is to use a weight on just one end of the antenna.
73,
Rush, W4QA
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| Standard Wire Antenna Approach |
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| 2" PVC, Rebar, Lag Eye Bolt |
