Hello all,
On Tuesday, Sept. 15, a thunderstorm with very high winds
rolled through the northern IL area, where my QTH is lo-
cated. Our neighbors to the west of us lost 2 mature oak
trees in their front yard - they were about 12" diameter and
just snapped off above the base. Our yard was filled with
debris, including large branches from one of our larger ma-
ple trees.
After the storm subsided, I glanced up at the stack of yagi
antennas on the top of a 76' high Rohn 55G tower. The
antennas lloked like they were still in place so I didn't pay
any more attention to them, until the next day, when I
happened to notice that the top antenna had half of its
driven element broken.
The damaged antenna was a home-made copy of a KLM
3-el. 30 meter yagi and the insulator that held the element
on the boom had broken. My wife came home later and
as I was out in the "back woods" unloading a pick-up
truck full of storm debris, she came by and I told her that
my antenna had a broken element.
She looked at the stack of antennas from where we were
standing and said that she didn't see any broken antenna,
so we walked into the middle of the back yard so that she
could get a look from a different angle. She then saw that
the element was broken and as she was looking at the
antennas and tower, she said to me that the whole tower
appeared to be bent.
I took a closer look myself and sure enough, the tower did
appear to be bent! I then walked to the guy wire anchor in
the back yard and found that the 2 sets of guy wires were
very loose. Neither of the turnbuckles had loosened up and
all of the Big Grips looked normal. So I am assuming that
the 1/4" EHS guy wires stretched under the load from the
high winds.
I had originally installed the tower for the previous home-
owner about 10 years ago. We put it up as a 100' tower,
with the guy anchors 80 feet out from the base; all of the
guy anchors and the tower base installed according to the
specs in the Rohn catalog, complete with the re-bar
assemblies in all anchors and the tower base.
I had taken his antennas and tower down for him before
we realized that my wife and I were going to be buying
the house from him and his wife. After we moved in, I
decided that I'd only go up 76' (with 4' of tower in the
concrete base). I installed 7 sections of 55G on top of
the section coming out of the concrete and used Rohn
1/4" EHS guy wire, Big Grips and forged, galvanized
1/2"-11 x 12" turnbuckles.
I had 3 antennas on the top of the tower, using an "IIX"
ladder mast. Just above the top plate of the tower was a
HyGain TH7 for 10, 15 & 20 meters. 5-1/2' above that
was a little 3-el. CushCraft A3-WS yagi for 12 & 17
meters and 5-1/2' above the A3-WS was the home-made
copy of the KLM 30M-3 yagi, a 3-el. monoband yagi for
30 meters.
A couple days after the storm, I took a 24" long brass-
bound mahogany contractor's level and checked the
tower at various points, to see how far it was now out of
plumb. At the section coming out of the concrete, it was
off approx. 1/16" (in 24"), just above the lower set of
guy wires, it was off about 3/16" and just above the top
set of guy wires, it was off about 1/4".
So now I have a bent 76' high Rohn 55G tower with an
antenna that is in need of repair. I am going to replace
the top set of guy wires with 5/16" EHS and I will replace
the turnbuckles for that set of guy wires with forged,
galvanized 5/8"-11 x 12" ones. I am not going to use Big
Grips on the new guy wires; I'll use 2 forged wire rope
clips (Crosby Clips) per turn-back and serve the 7 in-
dividual strands, as the Rohn catalog suggests. I'll also
replace the lower set of guy wires with new 1/4" EHS
material.
In the past, I had never worried too much about high
winds; I figured that nothing short of a direct hit from a
tornado would cause any significant damage to my
towers. Boy, was I WRONG! Live & learn, I guess...
73 de Brad, N9EN
@ (Storm-Damaged) Radio Free Roscoe (IL) [tm]...
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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