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[TowerTalk] stacking antennas & Rohn specs

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Subject: [TowerTalk] stacking antennas & Rohn specs
From: (Bruce Makas)
Date: Wed, 09 Jul 1997 08:04:43 -0400
I am installing several Rohn towers and want to stack antennas on the towers. 
Being a "good" amateur engineer, I intend to follow the specs in the Rohn 
catalog. My question is about the allowable projected area that is called out 
by Rohn. For example, if I were to put up 130 foot of Rohn 45G in a 90 mph area 
(coastal Maine), the book says that 12.3 sq ft of projected area of round 
elements is allowable (C870478R1). I assume that is at the top of the 130 foot 

Now, I want to stack antennas; say one at 60 feet, one at 100 feet and one at 
130 feet. How do I calculate what is the allowable sq footage? Is it as simple 
as summing the moment arms (height x sq ft of each antenna compared against 130 
ft x 12.3 sq ft) or is it more complicated?

For example, a 205CA specs out at 9 sq ft, I would hope that I could put at 
least three of these, and 3 155CA's (5.2 feet each) on the tower, but it 
doesn't look it. 

       ((60x9)+(100x9)+(130x9)) > (130x12.3) ........... for just the 205CA's 

If this is true, how can anyone stack more than 3 large antenna's per tower? 
Even a 55G installation only allows 14.8 sq ft @ 130 feet.

What am I doing wrong?

Thanks in advance for your ongoing support of my antenna project.  73,  Bruce



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