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Re: [TowerTalk] Fiber rods as guy insulators

Subject: Re: [TowerTalk] Fiber rods as guy insulators
From: Pete Smith <>
Date: Fri, 27 Feb 2004 16:00:11 -0500
List-post: <>
At 11:36 AM 2/27/04 -0500, KD4E wrote:
For what reasons might one select fiber rods & steel guys vs Phillystran? (Both eliminate the shunt-feed problem and the
resonance problem with nearby wire antennas.)

Any concern that the fiber rods may be more vulnerable to vibration
failure in a severely gusty storm?

K7NV has an analysis on his Yagistress web site (Google for the new server location) of the three materials -- fiberglass rod, phillystran and EHS steel. His analysis didn't assume the semi-rigid fiberglass power pole insulators (18-20 feet long), but rather the use of continuous "pultruded" fiberglass rod such as that made by Polygon. As I recall, the chief downsides of Philly are that it is about twice as elastic as steel, is prone to failure through abrasion, and can be easily cut or burned, which argues for a stretch of EHS at the bottom of each guy to put the Philly out of reach. The fiberglass, if I remember correctly, is only a little more elastic than steel, would be hard to cut, and is more abrasion-resistant.

Another point -- Originally, I had the 21-foot fiberglass power pole insulators on the top guys of my tower, with grounded EHS for the remainder of the length. A 40M yagi above the tower top maybe 6 feet was a mediocre performer. When I replaced the top guys with Phillystran, the 40M yagi suddenly "woke up." This said to me that 20 feet of insulator, even sloping away at 45 degrees, may not be enough to eliminate guy wire interaction with yagis, at least at 40m.... YMMV, needless to say.

Some local Polygon rod users invested in some vibration dampers for the material, thinking that would be a good idea. I';m not clear on whether it turned out to be necessary or not. I do know that another local just put up a 195-foot tower with stacked yagis using pultruded fiberglass without dampers. I think if he thought they were necessary he would have used them.

73, Pete N4ZR Check out the World HF Contest Station Database Updated 9 Jan 04


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