[TowerTalk] sorry for multiple mails, but had another

[Roger (K8RI)]

Its from Onion wrote:
> When thinking about antenna design one should look at the people who have a working, COMMERCIAL, money making system that works.  Go look at a AM broadcast tower in your area.  Ask for a tour from an ENGINEER there.
>
> Almost guarantee you will find a tower that is pin mounted.   Why, you ask?  That is the way towers are made to be installed.  (IMHO of course) This is the only way a tower can twist and flex, and believe it or not a tower must move to be strong.  Climb a tower past the 500 foot mark and feel how much it moves in a bit of wind.
>
> Granted, its EASIER to stob a section in the ground and climb, stand and hang your antenna creations on.  Yet know this, anything in the wind oscillates.  From bridges to skyscrapers. It is measurable less stress on the tower when it can twist and move in the wind.
>
> For ya'll that need some fancy words, try these: dynamic torque loading of the antenna, K-factor computations for overpowering horizontal load vector limits.
>
> Also read Electronics Industry Association Structural Standards for Steel Antenna Tower and Antenna Supporting Structures - EIA/TIA-222-E.
>
> ALL I'M SAYING IS don't disregard pin mounted tower because you don't or wont understand them.  Once you have it installed, it really is the best way.  Never have to worry about the legs filling with water and bursting again to boot
>   
Yes, I understand the reasons for using the pier pin mounting, but, if 
putting up a 40-50' foot (give or take) tower  with only a tri-bander or 
small array or lightly loaded tower its unlikely to be of any advantage. 
There I'd most likely forget the concrete and just go with the old "dirt 
base".

Mine was put up when they were still listing a base section to be 
mounted in concrete. At 100 feet in 20 MPH plus winds and that large 
array the top of the tower is rock steady. Admittedly were I to do it 
over again I'd now use a pin base, but there is a point of diminishing 
returns.

However I beg to differ with never having to worry about water in the 
tower legs freezing and bursting.  I've seen tower legs many feet off 
the ground that have frozen and split.  There was even one top section 
that split about 4 or 5 feet down from the top. IOW spiders built a web 
in the legs, moisture collected, froze, more collected, froze, and 
eventually the leg split leaving the top and antenna at a bit of an 
angle.  I think the main thing that save his antenna was the rotator was 
down in the tower far enough that the mast through the sleeve at the top 
kept things held together.

Here in the north country, freezing water in tower legs can be a problem 
regardless of how the tower is mounted unless it has solid legs and 
those little web spinning critters can get into some mighty small spaces.

73

Roger (K8RI)
> de KE4VYN
> Lee
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