Digging around in the archives I learned it was Telrex that manufactured the
"Big Bertha" system in the 1950's ~ 70's. Rich, KE3Q, had a good write-up about
this company and their product line. This link should take you there:
http://lists.contesting.com/_towertalk/2005-03/msg00067.html
73 de Bob - K0RC in MN
----- Original Message -----
From: Robert Chudek - KØRC
To: towertalk@contesting.com
Sent: Thursday, August 31, 2006 12:29 PM
Subject: [TowerTalk] 10 inch tube 100ft wind load? NN7J
Dan,
You can put your numbers through the WD9P mast calculator and see what you
get, Here's the URL: http://www.math.niu.edu/KARC/mast/
I put your numbers into the calculator, just out of my own curiosity...
SF = 2
WL = 0.004
MS = 60,000
OD = 10
ID = 9.732
TL = 100
HAS = 100
Ant1 = 1 + Area = 1
Ant2 = 0 + Area = 0
Ant3 = 0 + Area = 0
It told me this:
Survival velocity = 38.9 mph
Failure velocity = 55.1 mph
Mast Weight = 1,415.29 lbs
But if you used 1/2 inch wall, 10 inch diameter steel,
Survival velocity = 71.2 mph
Failure velocity = 100.6 mph
Mast Weight = 5,085.03 lbs
And if you used 1 inch wall, 10 inch diameter steel,
Survival velocity = 93.2 mph
Failure velocity = 131.9 mph
Mast Weight = 9,634.80 lbs
Of course if you are serious about installing something like this, a
qualified design engineer should be your first step. The calculator can give
you an idea of what kind of forces you are dealing with but as it warns, it is
for instructional use only.
Note, these figures were with a 1 sq ft two-meter vertical at the top, not
even a small yagi! You can plug in 8 to 20 sq feet of area for Antenna 1 and
see what happens. The results surprised me (assuming the calculator is working
correctly).
Free standing rotating tower systems like this have been engineered by HyGain
(I think) and were called "Big Berthas". I knew of 3 installations in
Minnesota, but nothing more. I'm sure other TT members can jump in with facts,
figures, and stories about these types of installations.
73 de Bob - K0RC in MN
Message: 7
Date: Thu, 31 Aug 2006 06:34:26 -0700 (PDT)
From: Dan D <yaesu4u@yahoo.com>
Subject: [TowerTalk] 10 inch tube 100ft wind load? NN7J
To: towertalk@contesting.com
Message-ID: <20060831133426.27075.qmail@web58303.mail.re3.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1
How do you calculate how much load a steel tube 10 inch with .134 wall can
handle with no guys 100 ft tall.
Dan NN7J.
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