At 03:38 AM 4/17/2006, you wrote:
>I don't know if this question has been brought up on the reflector
>or not, but here it is:
>
>I have a small lot (73' x 122') and want to install a 60' Rohn
>25G. Because of how the house is set and other structures, I am
>having problems placing the tower where I can get the specified 80%
>guy length (48'). I am pretty close to getting it but come up just
>short on two of the legs. On the third one I can get 48' without
>any trouble. On the other two, I am about 4' short (73% instead of 80%).
>
>I definitely plan on constructing and loading the tower to Rohn
>guidelines and would like to know if this would be a problem. Would
>it be possible to add 2 additional guys to each leg off center of
>the normal guy placement at equal angles in order to supplement it
>at it's slightly shorter length? Does anyone know of any books,
>reports or other information where I can find the necessary
>equations to perform the calculations? Thanks for the help.
>
>73 es gud DX,
>
>Jon, N7XW
Jon,
Let me try to answer your question with a brief comment. The 80%
spacing of guy
wires is not required, nor is it even "recommended". It is just the
spacing for which
Rohn has worked out the compression and tension loads on the tower and guys
and provided a safety factor and an antenna load factor. Other
angles will work
if you 1) do the engineering and/or 2) are conservative in your
antenna loading.
Example of guys at other than 80% are the Rohn foldover designs for
Rohn 25 and 45.
This clearly shows that Rohn 25 can be used with other than 80% guying.
Rohn builds into their designs a significant safety factor as
demonstrated by all of the
Rohn towers that have been severely overloaded and have survived for
many years.
Since your guy points are pretty close to being per the Rohn designs you can
PROBABLY load the tower per the Rohn specifications by giving up some of the
safety (overdesign) factor. Or you can derate your antenna loading somewhat
to maintain the same safety factor.
Just remember  Free Advice is worth every penny you pay for it! But I have
installed a lot of towers for many government agencies in environments from
the arctic to the tropics and never had one fail. And a lot of them were not
exactly "by the book" due to local conditions forcing the designs to be
modified from the Rohn 80% guy factor.
73 John W0UN
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