Hi Stan,
I do indeed use 12x12x1 inch type LE phenolic (trade name: Garolite) plates on
my stacked 3 element 40M Yagis. However, since I use T-matched and not split
driven elements, I think your question is: how should I support the center of
a split 40 meter driven element?
You might inquire of K3LR about the mechanical design of his split 40 meter
full size driven elements. I doubt that he relies on a rod as the primary
source of mechanical strength. If I were to design a split full size 40 meter
element, I'd probably use a molded phenolic rod at the center, then mount the
entire assembly on a beefy aluminum channel, perhaps 3 feet long. There are a
variety of techniques to satisfactorily insulate and fasten the driven element
to the channel.
Phenolic and fiberglas rods are commonly manufactured by using a lathe on flat
plate stock. You can see the grain of the original flat plate if you examine
the surface of of phenolic or fiberglas rod. This type of rod is significantly
more susceptible to moisture intrusion and is significantly weaker than rods
that were originally molded into a rod shape. McMaster does not stock molded
rods, they must be purchased from a plastics supplier.
Molded phenolic rod has no visible grain on the outer surface, but you can see
the grain on the ends of the rod, it looks like the grain of a tree trunk.
Molded rod is highly resistant to moisture intrusion and just as strong as
phenolic plate (and much stronger and moisture resistant than rod manufactured
from plate).
73!
Frank
W3LPL
---- Original message ----
>Date: Mon, 4 Sep 2006 16:06:34 -0500
>From: Stan Stockton <k5go@cox.net>
>Subject: [TowerTalk] Garolite
>To: towertalk@contesting.com
>
>I am working on a 40M antenna project and want to split the driven element for
>sure and perhaps insulate all the elements from the boom.
>
>I noticed that W3LPL and others are using Garolite LE. According to the specs
>I read it has a tensile strength of 14,100 PSI lengthwise and 10,400 PSI
>crosswise. He mentioned several years ago that he did not use the Garolite
>for 40M elements because it was not strong enough.
>
>Looking at McMaster Carr Garolite Grade 11 is 58,600 PSI lengthwise and 41,900
>PSI crosswise - about 4 times stronger than LE.. It is about twice the price.
> GP03 Electrical Grade Fiberglass is about half the price of Garolite LE and
>seems to be about the same strength.
>
>If anyone has experience or knows the difference in all these materials and
>whether there are significant differences in how well they hold up in the
>environment, I would appreciate knowing.
>
>The other question is whether to insulate all elements or only the driven
>element. Anyone know the pros and cons?
>
>Thanks...Stan
>
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