[TowerTalk] Guys - how many?

[KI7WX@aol.com]

In a message dated 12/24/99 13:27:29, you wrote:

>Is the tower 25G or 45G? I don't think I'd do it for 25G - the legs 
>don't have the leg capacity to take 67% more guy tension preload. This is my 
>'non-engineer' perspective. 

I'm not sure that's quite right Steve.  For a 190' 25G tower my 1992 Rohn 
catalog shows six guys per leg.  If the bottom section of a 190 foot tower 
can support  six guy lines plus the additional weight of an extra 90 feet of 
tower weight it's hard to see why 5 guys on 100 feet would be a problem.

What additional guywires gains us in additional capacity/safety would be nice 
to know.  I've considered guying my (planned) 100 footer in four places and 
using 1/4" EHS instead of the suggested 3/16".  My logic is that the 
additional guywire will help the tower resist twisting and the thicker 
guywire is less elastic which whould help control bending.  The added cost is 
a fraction of a 100' tower project so it seems a good idea.  None of this 
will stop a hurricane wind, but's it is a bit of over engineering which seems 
helpful.

I'd be interested on additional input to this whole line of thought.  
Particularly from people that could model some hypothetical towers and show 
why different things are good or bad.  A good example (well for me...) would 
be to compare a 100' 25G tower built to Rohn specs vs the same height tower 
guyed at the top with four equally spaced guy wires of 1/4" EHS.  I'd also be 
interested in the difference between the suggested 80% anchor to tower 
distance compared to 85 or 90%.  Logic suggests that an additional guywire 
per leg (4 vs 3), heavier wire and additional tower-anchor spacing would all 
be good ideas.  

In anycase it's a real shame that the "data" we all have to work with is 
either the not always applicable Rohn Catalog specs or anecdotal evidence 
from other projects.  We have easy access to great tools like NEC for 
modelling antennas and horrible tools for figuring out how to hold them up in 
the air!

Cheers,

Mark

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