[TowerTalk] follow-up on 4-square conversion

[S. J. Blackwell]

The guy tension needed for keeping the antenna in column decreases as one 
goes up. I believe this should be considered. The lower guys are shorter and 
can be set up with more tension as the lower portion is larger dia and can 
tolerate more compression. The need for low stretch guys is not all that 
clear to me as the forces involved are relatively low and stretch is 
proportional to the tension. The decreasing diameter of the column also 
causes a decreasing wind load.Tension on the upper guys can also be a cause 
for failure in compression unless the upper guy anchors are absurdly 
distant. In any event it would seem to me that the guy tension should be the 
absolute minimum with tension decreasing as one goes up. Also implied is 
smaller dia guys as one ascends ergo less sag for a given amount of tension. 
  Any guy system will need checking for tension after installation as some 
creep will occur regardless. Nylon is a bummer in any event. Kevlar cored 
line may be hard to find in the small sizes needed for the upper guys. I 
have no idea as to how to save the system from falling tree limbs except 
acceptance or removal.
73,
Sam W5LU


>>Good point on the stretching of ropes.
>I had to learn that lesson also when developing the spiderbeam
>
>.  The purpose of guying is to keep the
> >aluminum tubing aligned in a column; this keeps downward forces (which 
>can
> >be substantial) from collapsing the column (column
> >failure).  To do this, any guy (rope or other material) needs to be
> >well-tensioned so that a sideways movement of the guy point
> >doesn't merely take up the slack in the guy.
> >
> >   The total amount of stretch in material increases as the material is 
>made
> >longer; i.e., elongation under a particular load add a
> >certain percent to the overall length.  Long pieces of rope (e.g., the 85
> >feet needed to guy to the 60 ft level at a 45? angle) will
> >therefore stretch more when the wind loads up the antenna (or a tree limb
> >falls on the guys).
> >
> >   Consider investing in low-stretch rope for at least the longest guys,
> >such as those with amarid fibers.  These are available at
> >marine supply stores or, e.g., from New England Rope company.  
>Low-stretch
> >ropes are quite strong, so you will be able to use a
> >smaller diameter rope.
> >
> >   The thinner the aluminum, the more important it is to have an adequate
> >number of low-stretch guys.
> >
> >   W1KM's approach to getting enough leverage to raise the antenna is an
> >excellent one.
>

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