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A Shock-Absorber for a Wire Antenna
21 October 2011 | by Of the three support-points for my wire antenna, one of them has caused me some concern. The end of the longest span of my New Carolina Windom is attached to a rigid, unguyed 12 foot steel mast by a very short length of rope — not nearly long enough to stretch and absorb the shock that a wind-whipped wire might induce in a good storm. Furthermore, this 12 foot mast is set in a small 3′ tripod without any reinforcement below the roof. Obviously this isn’t good enough for a heavy load, but I’m hoping it will suffice to support one end of a 42′ wire. As a precaution, I’ve built a shock-absorber into the system:
This is a spring that I bought at the local hardware store. I didn’t do any calculations to select the thing. I just went through the drawers and handled all the likely-looking springs they had. This one felt about right when I pulled on it. I tied it into the 3/32″ braided dacron/nylon rope with a loop long enough to match the length of the spring when fully extended. The electrical tape is to prevent chafing for as long as it stays on.
The spring is strong enough that on a calm day it doesn’t stretch at all, but it still has plenty of give if the wire gets to whipping around. Will it help this antenna-system weather the storms we get out here in western Minnesota? Time will tell!
5 Responses to “A Shock-Absorber for a Wire Antenna”
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Except for the fact that those types of springs turn rusty ugly fast, they work for years. I find them to be much more servicable than a pulley and weight which is usually suggested for this use. Spring steel surface rusts fast but then doesn’t get worse for a long time.
Of course, in my case, it still doesn’t prevent a tree falling throught the path of the antenna from taking it down! (I am starting to hate wire antennas)
Fred W0FMS
Hm, I dunno about the spring. Seems like a lot of force to put on one point, which can work harden the wire and make it brittle? I think a pulley/weight would be a better long-term solution.
Thanks for the comment, Michael. We’ll see how it stands up over time. Your concern is warranted — that’s why I chose to tie the spring in parallel with the dacron/nylon line instead of in series. If the wire fails, the fabric is still there to keep me on the air until I can replace the spring.
I’ve had good luck with using “bungee cords” for shock absorption on the corners of my loop antenna. They seem to last 3-5 years or more and I replace them only if the squirrels chew on them. I’ve found that spraying them with insect spray that has a bad smell seems to keep the little critters away, hi hi. Just a matter of pick the length and firmness of the respective cord needed for a given installation.
At one time I tried slender weights for shock absorption but the wind kept banging them against the tree causing damage so I went with other approaches.
Thanks for the idea, Evan. I’m at a new QTH now and am once again contemplating my options for hanging an antenna from trees. Bungee cords are now on the list of options. 73