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Re: [TowerTalk] Plumbing a tower

To: Jim Lux <jimlux@earthlink.net>
Subject: Re: [TowerTalk] Plumbing a tower
From: David Gilbert <xdavid@cis-broadband.com>
Date: Tue, 22 Jan 2008 11:02:03 -0700
List-post: <mailto:towertalk@contesting.com>

Not that I know of.  I've never seen any deflection spec on the AN 
Wireless website, nor in the documentation I got for the tower.  I 
bought the HD-70 model, though, and it is rated at 62 sq ft at 70 mph 
(28 sq ft at 80 mph) so it is pretty sturdy.  I generally don't place 
much faith in eHam product reviews, but there are some comments there 
from experienced tower installers who say it feels solid under their 
feet even in a stiff wind.

The combined wind loading of the antennas I plan to install on the tower 
is less than 25 sq ft, but they will be on a mast of course and I have 
personally measured wind gusts here on this mountain hillside in excess 
of 80 mph so I decided to be cautious when I chose the tower.

73,
Dave   AB7E



Jim Lux wrote:
> David Gilbert wrote:
>   
>> Hi, Pete.
>>
>> I'm kind of sorry I even wrote my post now for the confusion it has 
>> apparently created, but just to clarify ... I was putting up a 70 foot 
>> AN Wireless self-supporting tower (model HD-70).  It's basically a 
>> heavier version of the popular Trylon towers, and both have the same 
>> issue.  You encase the base in concrete before you ever add the rest of 
>> the tower, and the eventual "plumbness" of the finished tower is a 
>> function almost solely of how accurately you plumb the relatively short 
>> base (five feet in my case) before the concrete is poured.  My tower 
>> tapers from 48 inches on a face at the base to about 22 inches at the 
>> top, which calculates out to a leg angle right at 89.0 degrees.  Every 
>> 0.1 degree of error therefore gives about two inches of offset at the 
>> top, and obviously anything beyond a full degree of error (pretty easy 
>> to get with many alternate methods) would put, in my case, a 2,000 pound 
>> tower partially leaning out over one of the legs ... with no guy wires 
>> to help support it.
>>     
>
>
> Out of curiosity, does the spec sheet or engineering drawings say how 
> much deflection of the top one would expect at rated wind load?  It 
> might actually be more than a few inches.  I've been at the top of some 
> unguyed poles in the 50-100 ft range, and it's seemed to me that they 
> swayed a fair amount.
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