[Towertalk] Calculating guy distance for rotating towers

[Georgek5kg@aol.com]

In a message dated 10/10/2002 9:37:14 PM Greenwich Standard Time, 
kr7o@vhfdx.com writes:


> I am looking for a formula to determine in advance how far my guy anchors 
> need to be for a side mounted antenna at any given height to clear the 
> guys.  Example, a 75' rotating tower with guy wires attached at 75' and an 
> antenna with a turning radius of 25' at say 60'.  I'm sure I could graph it 
> 
> out, but I would prefer to know exactly before sinking anchors (I want to 
> do things once).
> 
> 

Robert,

I had to work out this very problem for myself a couple of weeks ago.  At one 
time I was good at trig, but when I tried to remember how to calculate the 
sides and angles of a right triangle, I was totally baffled.  Old age had set 
in!

I turned to my trusted friend, www.google.com, and came up with this clever 
trig site:

http://www.ies.co.jp/math/java/trig/sixtrigfn/sixtrigfn.html

After some playing around, I was able to use the trig function, tangent, to 
solve the problem.  

Here is your case as I understand from your statement above:

The turning radius of your side mounted antenna is 25'.  So, lets make the 
guy 26' from the tower at the 60' level to give a 1' distance from the 
antenna to the guy.

You have guys attached at 75'.  At 60 ft, you need for your guys to be 26' 
away from the tower.  This forms a right triangle, height 15' and base 26'.  
The "tangent" of the angle is the opposite side / adjacent side, or 1.73.  
Now go to the web site, click on "tan" and put your cursor on the red dot at 
the top of the triangle.  Move the dot until tan = 1.739.  (This is close as 
you will get to 1.73). Now, read the angle.  It is 60 degrees.

Now, imagine a triangle, the height of which is 75', the base is unknown and 
the angle at the top is 60 degrees.  Lets call the base "x"

Now, since Tan = opposite side / adjacent side, you can work out the distance 
your guy anchor must be from the tower.

Tan = opposite side / adjacent side

Tan = base "x" / 75' tower height

1.739 = x / 75'

Now, solve for x:

x = 1.739 * 75'

x = 130.125'

Soooooo, your guy anchor must be 130.125' from the base of the tower.  

Now, that seems pretty far away from the tower for my liking, but it will 
accomodate your side mounted antenna at 60'.  

Pse let me know if you have any questions or, worse yet, if you see anything 
wrong with my calcs.

73, Geo...

George I. Wagner, K5KG
Productivity Resources LLC
941-312-9450
941-312-9460 fax
201-415-6044 cell





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