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[TowerTalk] stacking antennas & Rohn specs

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Subject: [TowerTalk] stacking antennas & Rohn specs
From: (
Date: Tue, 15 Jul 1997 02:45:21 +0000
To: <>
> Date:          Sun, 13 Jul 1997 02:09:57 -0700 (PDT)
> To:            Bruce Makas <>
> From: (Stan Griffiths)
> Subject:       Re: [TowerTalk] stacking antennas & Rohn specs
> Cc:  

> >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
> --
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Since I have addressed this before I will be brief:  on a 190ft rohn 
45 i have 2 5 ele 20m - 44 ft boom es 3 4 ele on 26 ft booms; on a 
rohn 25 180 ft i have 2  6 ele on 40 ft booms and 6 4 ele on 22 ft
on 10m i have 4 6 ele on 26 ft booms- on 40m full size 3 ele over
a klm 4 ele on a rohn 45 up 170 ft--- my point is simply to say 
these towers will hold up much much much more than you would expect 
with proper guying... no engineering-- i just keep adding antennas

73 es have some fun

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