[TowerTalk] Trig Question

[k6ll@juno.com]

On Sun, 20 Sep 1998 06:05:58 GMT "Rick Bullon" <kc5ajx@hotmail.com>
writes:
>
> I need some help doing some calculations for a tower. It has been 
>over 
>30 years since I took trig in school and I can't remember my formulas.
>  The tower is going to be 70 ft Rohn 25 guyed as per the Rohn book, 
>70 
>mph wind area guy  wires at 32' and 65' guyed at 56' from tower base 
>it 
>will right now have a TH 6 tribander on it.
>My questions are
> 1. With 2 of the guy points on the property line how far is it from 
>the 
>property line to the tower? ( I need this measurement so I can figure 
>the postion of the 3rd guy point to see if the proposed site is big 
>enough)

I'm on vacation, and I don't have the Rohn book with me, but
there is a drawing in there somewhere that shows how much real
estate you need for the various guying layouts. In your case
the distance from the property line is 28' (56cos60), or
1/2 of the guying baseline.


> 2. Will elevating the guy points make the guys wires longer or 
>shorter? 
>and if so by how much? ( XYL requires elevaterd guy points)

Shorter. For every foot of guy elevation, you can move the guy
point in by 0.8 foot to keep the same 80% guying angle. You can
then place your tower closer to the property line. 

For example, if the guys are elevated 8 feet, the baseline is
shortened by 6.4 feet, to 49.6', and the tower base can move to 
24.8' from the property line.


>  I seem to remember reading on here that "I" beams were stronger than 
>
>round pipe for elevated guy points right or wrong? 
>  Do I need to use an equlizer plate for this setup or is that over 
>kill? 

As I remember the discussion, the recommended method was to use an
I-beam, grind off one of the flanges near the guy attachment points,
and drill a separate hole for each guy. (Have all that done at a
machine shop.) You could probably also get both guys through one
larger hole, using two thimbles, or you could use an equalizer plate.


Dave Hachadorian, K6LL
San Diego, CA
K6LL@juno.com

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