On 10/13/2014 10:42 AM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message
...
On 10/13/2014 10:12 AM, Ralph Mowery wrote:
"Lostgallifreyan" wrote in message
Rohn towers specifies about 10 % for their guy cables. That is for the
4000
breaking of 3/16 cable they recommend 400 pounds of tension on the guy
cables.


That is STATIC tension - that is, when no wind is blowing. Tension
increases significantly when there is a wind. Rohn tower specs are
designed to withstand winds of 85mph, IIRC (I last did commercial tower
work in 1972 or so, so I don't remember the exact specs). At that wind
they have maybe a 50% safety margin. Still significant for new cable,
but when your guys are 25 years old, the tower should still withstand
that wind.

And yes, some of the towers I put up over 40 years ago are still
standing. But I'm sure they've had some maintenance since that time.


Yes, static tension. I was thinking along the same line for the wire
antenna. YOu only want to put a fraction of the breaking tension on the
wire to allow for the wind and if on a swaying support like a tree.

Rohn 25g is specified for several differant wind speeds. Probably with
difffrant ammounts of antenna surface area. Sometimes either more or larger
guy wires are used.
I put a 60 foot tower up for myself about 10 years ago and it is still up.
Don't think we had any 75 mph winds, but could have during the gusts. I
tried to meet their specs or beter when I put it up. I know a couple of
local hams that over the years did not put them up to what I would have
thought was to specs and then came down.



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When I was doing it, we were putting up 150' towers. These towers were
guyed eery 35'. The biggest job was the concrete for the baseplate and
anchors - it would take use 2-3 days to dig those, depending on how hard
the ground was. But once those were in, it took us two days to put up
the tower, install the antenna (typically VHF Hi-band; this was the
early 70's, after all) and run the coax.

These towers were typically on high hills, often leased land from a
farmer. In Iowa, it's not at all unusual to get 75mph winds in the
summer thunderstorms on top of the hills. But they stayed up.

I was smart and got out of it in one piece. The first guy I worked for
fell from 60' up and broke his back on a guy wire. He was paralyzed
from the waist down. The second guy I worked for was working on a
platform at 425' and got pulled over the side while trying to lower a
beacon light (those things are heavy). Unfortunately, that day his wife
was the ground crew.

I enjoyed the work - you can't imagine the view from 1800' up a TV
tower. But I'm glad I'm not doing it any more.

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