[TowerTalk] Unconventional Tower Installation

[n4kg@juno.com]

Rohn 45 can be safely guyed every 40 ft. using 1/4 inch
guy wire.  A GOOD solution for a 78 ft tower would be
to place one set of 1/4 inch guys at 39 ft and the other
at 78 ft.  This would be SAFE and COST EFFECTIVE.

What kind of engineer would space heavy guys on 78 ft 
of R45 at 22, 44, and 66 ft, leaving 12 ft unsupported?
This arrangement GUARANTEES that you will NOT
be able to utilize the tower to it's full ratings.

If you only have one antenna on top, and it is not very big,
you are probably safe, but it is a very inefficient design.

If you have a long mast and multiple antennas on top,
you will very likely have an excessive bending moment
on the unsupported tower, at / just above the top guy 
under high wind conditions.  

One of our local hams had the top of a R45 tower rip
off with just such an installation.  He had a 6L20 placed
14 ft up on a mast with a 2L40 / 2L80 at the top of his
R45 tower which had the top set of guys 10 -12 ft below
the top of the tower.

IMHO, every tower owner should have a basic understanding
of STATICS to comprehend the forces applied to a loaded
tower.  Yes, I know that a multiple loaded, multiple guyed
tower is EXTREMELY complex to analyze, but there seems
to be a lack of understanding about the more fundamental
basics of bending moments applied to the top of towers 
when guyed well below the load(s).

de  Tom  N4KG  (an EE who had a course in Statics)


On Fri, 2 Jun 2000 06:20:14 -0600 tony_brock-fisher@agilent.com writes:
> 
> I have just such an installation. I had a ham/engineer work out the 
> details.
> My case:
> 
> 78 feet of Rohn 45; three sets of guys (overkill) at 22, 44, and 66 
> feet.
> Two sets are anchored 56 feet from the base; the third set is only 
> 30 feet.
> The 56 foot guys are 1/4 inch; the 30 foot guy is 5/16" EHS. all 
> base sizes
> were increased to the 4B spec. One of the 56 foot anchors is on a 
> down
> slope, about 10 feet lower in grade than the other. The anchor was 
> placed so
> as to keep the angle on the middle guy wire at nominal.
> 
> My guess is that your proposed installation is possible, but that 
> like
> myself you will have to spend some $$$ with an engineer to get plans 
> that a
> building inspector will accept.
> 
> -Tony, K1KP

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