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## [TowerTalk] stacking antennas & Rohn specs

 To: [TowerTalk] stacking antennas & Rohn specs w7ni@teleport.com (Stan Griffiths) Sun, 13 Jul 1997 02:09:57 -0700 (PDT)
 ```>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 Hi Bruce, I have yet to meet the guy on this reflector who will admit he knows how to properly answer your question. Rohn can answer it for you but it will cost you lots of money, somewhere in the thousands of dollars. It takes an experienced structural engineer to really engineer a project of the kind you are describing. But, you say, you know other hams who have put up such installations. How did they determine they were safe? I'll bet they didn't. Most of them have looked at similar installation that have been up a long time so they used them as good examples. They have also studied all the data they could get on failures so they would know what to avoid doing. You either have to step up to a large engineering bill or take some risk. Studying what has worked what hasn't will minimize your risk. Good luck. Stan w7ni@teleport.com -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com Search: http://www.contesting.com/km9p/search ```
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