Seeing the article on fiberglass coil forms in the October issue of
QST made me think that others might be interested in what I use as
standoff insulators on Rohn 25G tower. There will probably be
problems with using this technic on other types/brands of tower
without modifications.
I use standoff insulators in shunt feeding a tower as the driven
element of my four element parasitic vertical array on 160. I also
use them to support parallel skirt wire/tubing to serve as parasitics
on the higher frequency bands. Prior to my first shunt feeding the
driven element I used 4 foot fiberglass electric fence posts as
supports for my Beverage antennas. When it came time to come up
with supports for the tower skirt wires I thought of these fiberglass
posts. That sounded good--but how do I support them?
Looking at the Beverage post insulators that I used | \ |
(North Central Plastics Red Snap'r [they're yellow] | \ |
insulators #YRP25N) I came up with a novel way of | \ |
support. The groove on the insulators just fits the |______+|
25G diagonal supports. Put two of them on the diagonal |+ |
support just off both sides of a horizontal support. | \ |
They are now very loose and can easily fall. However, | \ |
when you put a post between the two there is tension | \ |
on them to keep them forced away from the direction | \ |
that they need to go to come loose. To come loose the
two need to rotate in opposite directions and the post + post
between them prevents that from happening. insulators
The shunt feed has been this way on my driven element
now for 5 years without problem. I have the posts every ten feet
on the tower. I have the upper support post "guyed" with nylon
rope to prevent the stress coming from only one direction on that
post from breaking the fiberglass post. The same insulators are
used to support the shunt wire (I wrap a single turn of wire
around each insulator to better divide the wire's weight).
The shunt wire can be spaced up to 2.5' away from the tower using
this method. A cable tie around the insulator and the vertical
tubing that its against might be nice if you don't like the minor
insulator wandering (I seldom use them).
I use copper tubing as a ground bus between elements and as
ground rods (that way the "ground rod" [copper tubing] can be
connected directly to the tower base without any breaks). Having
just put up a new parasitic element (replacing a shorter one) I
decided to increase the size of the skirt wire used. Having
found 1/4" OD copper tubing available for under $18 per 100'
I decided to try it. The same post insulators seem like they were
made for this tubing. The first skirt tubing is up and ready to
be tuned to the desired 80 meter frequencies.
All of the mentioned supplies can be purchased as most farm
supply stores. Anyway, this "note" is already too long and
detailed--but, I thought that I'd pass on my use of fiberglass...
73, Bill K0HA
-
---
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|