> 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?
Fiberglass and resin is highly prone to UV caused deterioration, however a
large rod would last a very long time.
> 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
That is definatly not a down side. The "stretch" so is much less than the
catenary and the associated give when using EHS that I'd give the nod to
Phillystrand is so light weight that the catenary is barely visible when you
are looking for it. Hence you do not have the "spring" or give associated
with the catenary of EHS.
> 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
The makers actualy tell you to use EHS from ground to well out of reach to
keep critters and vandals away.
> 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.
Fiberglass is easily sanded and not what I'd call abrasion resistant. "To
me" the main drawbacks for Phillystrand is the necessity for keeping it
sealed and water out. Although I retensioned mine once, it really could
have gone without.
> Another point -- Originally, I had the 21-foot fiberglass power pole
> insulators on the top guys of my tower, with grounded EHS for the
> 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.
With steel guys I break them up at varying intervals. The top section may
be only 6 or 8 feet, the next 12 feet with the next being maybe 14 feet.
> 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
> 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
I'd not think vibration dampers would be necessary, but my experience with
fiberglass would make me leary of unprotected fiberglass holding high loads
for years out in bright sunlight.
Roger Halstead (K8RI, EN73 & ARRL Life Member)
N833R, World's Oldest Debonair (S# CD-2)
> 73, Pete N4ZR
> Check out the World HF Contest Station Database
> Updated 9 Jan 04
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See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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