On Sun, 27 Jul 2008 11:47:54 -0700, Ron D'Eau Claire wrote: >The counterweights need to be heavy enough to hold the antenna, but not >heavier than needed for that. When trees whip in the winds, the inertia >of the counterweights can produce shock loads many, many times greater >than the weights themselves for a brief moment until the weights begin >to move. The heavier the counterweight, the greater its inertia and the >shock load
Yes. I have a half dozen dipoles suspended in redwoods, a Douglas Fir, and a Madrone at roughly 100 ft. I'm at 2,000 ft, about 5 miles from the Pacific, about 250 ft below the top of the ridge on the ocean side. Without weights, every antenna I installed was on the ground after the first real storm. Since I've installed counterweights, all have weathered 75 MPH winds for a couple of days. These antennas are heavy -- typically 150-250 ft spans, #10 copper, most with parallel #12 fan elements (to cover additional bands), and fed with RG8 or RG11. My weights are roughly 90-95#, and are made by simply filling 6.5gal water jugs with dry sand (roughly 1.5x heavier than water). Others have had good success by recycling the counterweights from vintage wood frame windows. I chose the tension by experimentally determining what it took to achieve the acceptable degree of droop. Counterweighting, of course, is only part of the story. When an antenna must withstand these kinds of forces, every element of their construction becomes critical. For this reason, I find nearly all of the commonly available center insulators for dipoles to be seriously lacking. The absolute worst was the RadioWavz unit. I bought two and used them to build 6M dipoles. Both fell apart when I pulled on the LM240 that attached to them! 73, Jim K9YC _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
