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Self-supporting tower questions

To: <>
Subject: Self-supporting tower questions
From: (Michael Tope)
Date: Wed, 11 Sep 1996 22:16:45 -0400
At 09:54 PM 9/10/96 -0500, you wrote:
>Hi Guys!
>Well, my quest for a self-supporting tower continues!  At last weekend's
>W9DXCC I got a lead on a self-supporting 80 foot "Pyrod" tower in use at a
>vet clinic.  It is holding up some vertical antenna that used to be used
>for paging, but isn't anymore.
>I looked at the tower, and it seems OK (as much as I can tell).  I got some
>documentation on the tower (the original schematic drawing from UNR-ROHN -
>it turns out that it is about a 13 year old Rohn SSV tower.  It appears to
>be only the smallest 4 sections (the weakest ones) that you can get.  Here
>is some info from the drawings that maybe will make sense to someone:
>Wind load = 20 P.S.F. w/I (rest of sentence got cut off)
>20 P.S.F. E.I.A.
>tower height = 80 ft w/ITT
>top section: ITT tapered top assembly, 1W, 18ft
>next: 2W, 20ft
>next: 2WST, 20ft
>bottom: 3WN, 20ft
>So, what have I got here?  Any clue as to how I could find out how much
>concrete to put in the ground and how big of an antenna can I put on this
>thing (wind load??)  I'd like to put a big tribander (TH6/TH7) and a 402-CD
>up there.  Can it handle that? (I doubt it!) And what does ITT mean?
>73 Scott KA9FOX
>INTERNET SOLUTIONS - Affordable web page design and storage
>Scott Neader (608)788-1234 / FAX (608)787-0100 /
>Internet Solutions web:   Ham web:

Hey Scott,

My Rohn catalog, dated February 96, includes some pretty thorough
documentation of the SSV tower line. What I read of it pretty much jives
with what you mentioned, except for the ITT part and the 2WST section. They
specify an eighty foot SSV tower which is composed of the following:

   top 20': 1W
  next 20': 2W
  next 20': 3WN
bottom 20': 4N

The base they call out for this baby is what they call a "MAT" base, which
appears to be a 8'W X 8'W X 4' Deep rectangle (that's 9.5 cubic yards of
concrete!!). The 20 P.S.F. specification refers to a mean wind speed of 70
MPH per EIA-222-E, but doesn't really tell you anything about the maximum
antenna load. The Rohn specs I have here indicate that an 80' SSV tower
composed of the aformentioned sections can handle an round member antenna
with a projected area of 6.7 square feet @70MPH - a little less than a
Hy-Gain TH5. The following page of my catalog gives loading specs for the
same antenna in 80MPH winds. For this design they call out a maximum load of
3.3 square feet - not even a Cushcraft A3. One would be inclined to think
that your tower might not be as strong since it has the 2WST/3WN in place of
the 3WN/4N combination.  Kinda looks like this thing was designed to support
relatively small antennas. 

I am pretty much a neophyte when it comes to this tower stuff so you may
want to give Rohn a call @ (309)697 - 4400. You can order one of their
catalogs for $10 U.S. This includes a $10 coupon towards the purchase of any
Rohn products. If you call, ask for Dana Lemmerman. Also, consider getting a
copy of "Physical Design of Yagi Antennas" by Dave Leeson, W6QHS. Dave does
a great job of explaining all this EIA wind speed/PSF, etc... stuff. Good Luck!

73 de Mike, AD4VH................  
Michael Tope, AD4VH (ex KD8NS)      
200 Easy Street                             
Melbourne, FL 32934                         
Phone: (407) 259-7494
"It is the empty space inside the vessel that makes it useful" - Lao Tzu

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