Use a standard Rohn flat plate with three of these between the concrete and
the baseplate:
http://www.ebay.com/itm/CERAMIC-INSULATOR-w-BRASS-END-PLATES-UNKNOWN-MANUFACTURER-/350574235757?pt=LH_DefaultDomain_0&hash=item519fda506d
73
Jim W7RY
-----Original Message-----
From: David Robbins
Sent: Wednesday, August 01, 2012 6:08 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] base insulators
be careful with repurposing old insulators, or even in applying new
insulators in cases that they haven't been designed for. I bought 4 big
porcelain insulators for my elevated radial 80m 4-square array. the plan
was for using a roofplate and 10' section of rohn 25, then an insulator,
then 65' of rohn 25 above that. The insulator was sandwiched between two
plates made for the purpose... you can see the construction here:
http://www.k1ttt.net/2007towerwork.html#80m4square The insulators and
plates were sold for this purpose... but obviously not for exactly the
design that i was using. one small factor was missed. While the insulators
obviously had plenty of compression strength they did not have enough
resistance to off center or bending forces as i broke 2 of them the first
winter. this resulted in adding fiberglass support to reduce the side
forces:
http://wiki.k1ttt.net/2008%20Maintenance%20and%20Upgrade%20Blog.ashx#80mverticalmod
. The small factor that was missed was tha
t i was not putting a concrete base and tensioned guy cables holding the
towers rigidly vertical, mine are just sitting on roof plates on the ground
and are guyed with polyester rope, so there is a bit of movement in them...
too much for the insulators obviously. by the way, since those pictures
were taken i doubled up the angle fiberglass on each leg. the V bolts are
from Tessco, the fiberglass from Grainger or McMaster-Carr, i forget which
right now. If i were to do it again i would probably go with machined
fiberglass inserts in each leg, or use the two plates with a much shorter
piece of fiberglass or lexan between them plus the angle fiberglass
reinforcement.
Aug 1, 2012 08:53:15 AM, km1r@comcast.net wrote:
Years ago I managed to scrounge a few large insulators from the railroad.
(they used them either on top of electric cars or for hanging the overheads
along the right of way). Seems that if they were chipped, they could/would
not use them. They worked very well, and typically were about 1 foot high by
about 8 inches in diameter with heavy steel end plates.
That was years ago, times probably have changed. Or maybe ask some of the
electric utility guys what they do with "removals" from HT lines... worth a
shot.
I have long since gone to shunt fed verticals...
Good DX, epecially on T/B
73,
Mike KM1R / HS0ZAI
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