[Fwd: [TowerTalk] Parting comments]

[Kurt Andress]

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YagiStress - The Ultimate Software for Yagi Mechanical Design
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Message-ID: <35CA8BF8.FA337507@yagistress.minden.nv.us>
Date: Thu, 06 Aug 1998 22:09:13 -0700
From: Kurt Andress <ni6w@yagistress.minden.nv.us>
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To: John Brosnahan <broz@csn.net>
Subject: Re: [TowerTalk] Parting comments
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John Brosnahan wrote:

> Kurt,
>
> I have never liked really heavy guys with lots of large insulators.  When
> pulled to 10% tension they still sag a LOT and that sag can come
> out under different loading conditions (I have especially worried about
> torque loading).  Much prefered the Philly guys since their weight
> per foot is much less and when tensioned properly they are straight as
> an arrow (well alomst--  <;-)   ---
>
> K0RF used to run a very heavy 40M Yagi on 200 ft of Rohn 45 with
> really saggy guys.  When the rotator started the antenna remained fixed
> (inertia) and the tower rotated about 45 degrees (maybe hyperbole) before
> the antenna started to move--at stop time there was lots of interesting
> oscillations.  A FUN tower to be on while testing the rotator!
>
> Gotta get back to work--on the day AND night shifts!
>
> 73  John  W0UN

Thanks John,I remember hearing similar comments in the past from you. This is an
excellent point.
The aramid cable stretches more than steel for a given size. But the negative
effect of excessive sag might offset the stretch. Have to do some head scratching
to figure out how to evaluate it. My initial thought is that the relationship
between sag and tension load remains fairly constant. Not necessarily linear. The
guy should still be able to exert a higher reacting lod on the tower, when still
bent in the catenary shape. The small amount of straightening will allow more
deflection.
Did Chuck's 40 meter tower have torque bars on it? I don't remember seeing many
torque bars when I was there, mid to late 80's. Have to go check the pictures.

73, Kurt

YagiStress - The Ultimate Software for Yagi Mechanical Design
Visit http://www.freeyellow.com/members3/yagistress



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