[TowerTalk] Base Insulators for Rohn 25

[John Brosnahan]

At 11:49 AM 8/24/97 -0500, you wrote:
>I need several sets of base insulators for Rohn 25 tower.
>Rohn's pricing on these items is prohibitive.
>Any ideas, sources, suggestions appreciated.
>
>(((73)))
>Phil, K5PC

Phil, here is my response to someone else with a similar requirement.
Should work for you as well--actually I added a few words to make
my original answer a little more detailed.

73  John  W0UN

------------------

You can make your own insulated Rohn 25 section quite
easily.  Take a regular section and remove 4 inches from
each leg exactly half way between the any set of horizontal
"steps" or braces.  I chose the center set for mine, but you
can do this modification anywhere along a section of tower as
long as you make the cut BETWEEN steps.  Of course you'll
have to remove the diagonal braces.  Bolt cutters do it easily.
Take 12 inch pieces of G-10 fiberglass rod and insert 4 inches
into each half of the tower, leaving 4 inches as the gap  (removing
the 4 inches from the leg allows the "steps" to stay at the same
spacing.  I used four 1/4" bolts spaced 1 inch to bolt the insulators
into position on each side of the gap.   This gave me more
cross sectional area than the normal 1/4 inch plus 5/16 inch 
bolts that Rohn uses between sections.  And a 1/4 hole
removes less material material from the G-10 than does a 5/16.

For my installation I bought G-10 rod equal to the diameter of the
outside of the legs and turned it down for four inches on each
end to allow it to smoothly slide into the legs.  This was done
on four towers and N0RR also did it on four towers.  We both 
have years of experience with no failures and Ron's old
place often got 120+ mph winds--a bluff in the mountains.  He
has winds as high as 150 on occasion!  AA0RS (G3SZA) has
also built his 160 4-square this way but just bought rod that
would slip inside the legs without turning it down.  It is a bit of
a sloppy fit but has been up for a couple of years now with no
problems.  If the fit is snug then just make sure you drill small
"weep" holes into the leg just above the insulators so moisture 
cannot accumulate and then freeze.

Takes a little bit of work but doesn't cost all that much.  I covered
my insulators with Scotch 88 tape to keep the UV away from the
G-10.

BTW  I cut my legs with a pipe cutter, making for very clean and
square cuts but a hack saw will work.


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