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Re: [TowerTalk] wind load

To: "Tower and HF antenna construction topics." <>
Subject: Re: [TowerTalk] wind load
From: "Dan Schaaf" <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Thu, 18 Feb 2010 16:07:50 -0500
List-post: <">>
Thanks. I don't know if I understand all of that But I will think about it.
My plan is to use a tiltover 22 ft tower to support a 25.7 ft tall vertical. 
The tower is actually part of the entire vertical antenna.
It will have a 60 meter trap at the 43 ft point and will also radiate on 
3.650 MHZ.
Along side the tower will be an aluminum tube with a 30 meter trap and a 
small stinger above it.
This will give me 30/40/60/80 meters in one assembly.
I have the traps already made.
Soon I will pour concrete and get this guy up in the air.
Depending on other things, I may put a switchable base loading coil in for 
160 meters.
My winds in SW FL rarely get above 50 mph gusts. then there is a dead band 
in speed until you get to hurricane force winds.
So, I am also including a base mounted hinged gin pole to tilt it over in 
really bad weather.

Dan Schaaf
"In the Beginning there was Spark Gap"
----- Original Message ----- 
From: "Gene Smar" <>
To: "Tower and HF antenna construction topics." <>
Sent: Thursday, February 18, 2010 3:47 PM
Subject: Re: [TowerTalk] wind load

> Dan:
>     For a RIGID vertical element (such as an antenna mast or a heavy
> vertical made of thick-walled or solid tube), the force (say, 12.54 psf)
> would be applied midway up the element, or at 11 feet above the ground or
> tower top.  (You can find the calculus for this in most introductory
> mechanics text books.)  The area this force is applied over is the 
> effective
> area of the mast or vertical antenna.  So assuming an effective antenna 
> area
> of 3.67 sqft (the actual shadow area of a 2 inch mast 22 feet long), the
> total force applied would be 12.54 X 3.67 = 46 pounds.  The force would be
> handlied as a force at 11 feet AGL or above the tower top.  We all must 
> take
> this additional force and area of the mast into consideration when
> calculating the total wind force applied to the tower system.
>     As for a real-world vertical that flexes in the wind, this will shed
> some of the wind loading leading to a reduction in total force applied to
> the vertical antenna.  The actual number depends on how far the antenna
> bends in the wind.  But by using the non-bending answer for a rigid tube 
> you
> will be taking the conservative (safer) approach.
> 73 de
> Gene Smar  AD3F
> ----- Original Message ----- 
> From: "Dan Schaaf" <>
> To: "Tower and HF antenna construction topics." <>
> Sent: Thursday, February 18, 2010 3:02 PM
> Subject: Re: [TowerTalk] wind load
>> How does this wind loading information apply to a bertical antenna which
>> is
>> rigidly mounted at the base and flexes in the wind?
>> In addition, if the vertical antenna is mounted on top of a 22 ft tower,
>> which is anchored in concrete, how does this info apply?
>> 22 ft tower is short in comparison and maybe can be considered 
>> non-movable
>> and then the vertical can be seen as the same as if it were mounted on 
>> the
>> ground.
>> Dan Schaaf
>> K3ZXL
>> "In the Beginning there was Spark Gap"
> /towertalk
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