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Belden 9913 & Aluminum towers

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Subject: Belden 9913 & Aluminum towers
From: (Robert Chudek)
Date: Tue, 11 Feb 1997 04:11:30 +0000
Hello Ed Sleight & reflectorites...

   Two topics in this post...

   I have connected Belden 9913 directly to my antennas for a number
of years (over 4, less than 6).  The coax comes up a tower leg and
makes a gradual turn into a 'coil' of 4 or 5 turns about a foot in
diameter.  The coax gradually turns toward the mast where it is
attached and continues to the antenna.  I have NOT had any problem
with this, even when the temperature turns sub-zero (of course a
rotor turns MIGHTY slow when it's -20 degrees F).  A second ham
in town has also successfully used this 'coil' technique.

   Next flame topic...  Aluminum towers.

   During the past 20 years I have used numerous self supporting
aluminum towers.  The last 7 years my 90 foot Universal tower has
survived where other towers have failed.  In January of 1996, the
Minneapolis / St. Paul area was devastated with an ice storm and
accompanying 50+ mph winds that took many installations down.  I
credit the tower survival (with nearly an inch of radial ice) to
not overloading it and the antenna not 'slipping' in the mast plate.
(It's a 24' Mosley, with large cast aluminum saddle blocks.)  I
personally know of 3 (major manufacturer name deleted) antennas
that turned from horizontal elements to nearly vertical elements
in this storm.

   In one instance, two antennas slipped and caused a tremendous
increase in wind load on the 80 foot Trylon tower.  The tower took a
visual 'set' to the SE.  It was too dangerous to climb this tower
because of the slick coating of ice, the wind, and the temperature.
The temperature remained near 0 degrees F for weeks afterward.  Even
though there were some sunny days, the ice remained 'welded' to
everything; towers, antennas, power lines, trees, siding, pavement,
etc.  A real nightmare.

   In an 'act of God', the following week the winds picked up again.
This proved too much stress for the tower and it folded over about
12 feet from the top.  (Pictures at 10.)  It was a helpless feeling
during the previous week, knowing something needed to be done, but
too dangerous to attempt anything.  Luckily the homeowners insurance
covered this loss.

   Back to my aluminum tower accolades...  Yes, I had TWO legs split
on my tower.  It is true regarding the upper legs sliding inside the
lower legs, a real water trap.  Also a poor engineering decision, in my
opinion.  The lower 4 feet of my tower sat in compacted snow.  This did
not allow the tower legs to drain during the freeze/thaw cycle. I am
convinced this is what caused the damage.

   I discovered the split legs in the spring.  We had a severe wind
storm that broke several 70 foot ironwood trees and flattened my fence.
(Nothing touched the tower, which remained standing with split legs.)
When I was inspecting the house for damage, I grabbed one of the tower
legs and felt something sharp in the palm of my hand.

   Upon careful examination I saw a vertical fracture starting about
5 feet from the bottom and going up another 18 inches.  I inspected the
other legs and discovered the second split, about the same position and
length as the first.  A quick call to Universal and they asked about
drainage out the bottom during the winter.  I now routinely clear any
snow during the winter and have not had this problem.  Bummer taking
everything down then putting it all back up again!  It's much easier to
shovel snow.

   I like the clean installation my self supporting tower provides.  I
don't have to worry about the de-tuning of my yagi from guy wires. I don't
have to contend with guy wire anchors, insulators, Loos tension gauges,
elevated supports, tramming antennas up and down, anchoring into a swamp,
etc, etc, etc.  However, I concede it is not the least expensive way to
put 15 square feet of antennas up 90 feet and be able to sleep at night.
A 30" section cost more than $500. There are 4 of these.  The next two 26"
sections cost more than $350 each.  (Am I nuts?... I could have bought a
new Icom 756 with all that money!)

   I have two of these aluminum towers.  BUT, I also have 170 feet of
Rohn 25 waiting to be put to use.  (I guess I'll be ordering a Loos gauge
after all!)

   So there you have it.  Three distinct items to flame me about...

   1) Rotating 'hardline',
   2) Aluminum towers, and
   3) Mosley antennas.

   If we were playing hockey, it would be a 'hat trick'!

   73 de Bob - K0RC

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