I have decided not to take the risk of spoiling the pattern of my antennas
on my planned tower with steel guy wires. Looking for non conductive
materials for at least the upper 20m section of the guy wires I came across
Dyneema that is sold here in boating/sailing shop at a price (USD 4-5 per
meter) of about Kevlar of equal breaking strength.
How does Dyneema (called and manufactured as Spectra in US) compare to
Kevlar?
Can anybody give me a reason why Dyneema should not be used for guy wires
instead of Kevlar?
Kevlar, containing Carbon, does conduct electricity to some extent? But I
assume it is really negligible in RF when it is used for guy wires?? Thus
Dyneema is even better dielectric?
For 45m high rotating tower with 2x3 el at 40m and 4 tribanders I planned
6mm steel wire of 3000 kg breaking strength, thus about 8mm Dyneema of the
same strength would do fine?? It's a strong tower and will be guyed from two
heights only : c.a. 40 and 17 meters. 3000 kg is not an overkill really, is
it??
I have found out that:
Dyneema vs Kevlar:
Dyneema is stronger (higher breaking load)
Dyneema lasts longer
Dyneema weights less
Dyneema resists much better to UV light
Dyneema has lower dielectric constant (about 2.2 vs 3.8 for Kevlar)
Dyneema has excellent abrasion resistance, low moisture absorption, very low
elongation, excellent flex fatigue resistance
Two negative aspects are:
Dyneema has lower melting point (c.a. 150 degrees C vs 400 for Kevlar)! How
important is it??
Dyneema exhibits something called CREEP -non-recoverable elongation when
constant load is applied for long time...but for late models and thicker
ropes this is almost nonexistent effect??
Dyneema is UHMWPE that stands for Ultra High Molecular Weight Polyethylene.
Fibers are made from this material by AlliedSignal (Spectra®), DSM
(Dyneema®), Tenfor (Snia®), and Mitsui (Tekmilon®). The molecular formula
for this polymer is the same as common polyethylene, but is significantly
different because of the very high molecular weight, from 10 to 100 times
higher than commercial polyethylene molding resin.
________________________________________________________________________
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same place that pays for the hosting of this list: The eHam Store.
Order online at http://store.eham.net.
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