[MW1CFN] Kevlar Antenna Wire - Revised Perspective.

[MW1CFN via rec.radio.amateur.moderated Admin]

Real-World Amateur Radio

///////////////////////////////////////////
Kevlar Antenna Wire - Revised Perspective.

Posted: 02 Jul 2016 04:46 AM PDT
http://mw1cfnradio.blogspot.com/2016/07/kevlar-antenna-wire-revised-perspective.html

A couple of years ago, I wrote about the benefits of Kevlar-cored wire for
antennas.

I concluded at the time that the relatively high price of Kevlar was worth
it, principally due to it being three times lighter per unit length than
Flexweave.

It won't be too long before I have to replace my 20m delta loop wire
again. Despite the Kevlar core, the braid of tinned copper that is wrapped
around it eventually suffers metal fatigue, and an open circuit develops.

Kevlar-cored wire's strength is in tension, not lateral flexing. Millions
of movements over the years due to wind for a vertical delta made of this
wire leads to the aforementioned metal fatigue. So, I find that Kevlar
cored wire is best used in situations like dipoles, end-feds, verticals,
and so on.

Having recently re-wired the house with DC from a solar installation, I
came to thinking that, seeing as Flexweave may well actually outlast
Kevlar-cored wire in that it is less prone to fatigue (as suggested by my
17m delta, which is made of Flexweave), I ought to use some of the DC wire
(which is the same as medium speaker wire), which is also, of course PVC
coated.

Sticking two identical lengths of Kevlar-cored and DC wire on a kitchen
balance, I was surprised to find the DC wire was a full gram lighter than
the Kevlar wire. If you multiply this up to the full wave length of a 20m
vertical delta loop, that's a saving of 56 grams on the support. That's
much the same weight as two AA batteries - quite significant. The width of
both wires is the same, so there is no change in the wind-catching area.

There is also a big benefit to ditching Kevlar, because it's a pain to
solder and add lengths to. You need to remove the Kevlar fibres, otherwise
they absorb heat and contaminate the joint. This is important for repairs
in windy winter weather. You are also compelled to use spade or similar
connectors, because the copper braid of Kevlar-cored wire has no strength
at all. With DC wire, soldering is simple, clean and strong.

Price-wise, Kevlar wire in its standard diameter is selling (mid-2016) for
90p per metre on a 100m drum. The DC wire is selling for 52p per metre,
handily in 25m lengths (for a 14MHz antenna), almost half the price!

Once again, I'm happy to be saving you money, without any loss in
electrical or mechanical performance.