[TowerTalk] stacking antennas & Rohn specs

[Bruce Makas]

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 tower. 


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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