On 9/24/2014 9:21 PM, W2RU - Bud Hippisley wrote:
Don't forget that those guying forces plus are transferred to the base
of the tower (roof) when the tower is self supporting. A guyed tower
spreads the force over a wide area and the forces add algebraically
between the guys.
All of that force is transferred to the base anchor with a self
supporting tower, so the roof will need to be much stronger than for a
guyed tower.
We've used mounts of roofs before, but under all that crushed rock was a
membrane. Temporary towers were mounted on wide wood platforms. I'm not
sure how the present UHF and digital systems are anchored.
73
Roger (K8RI)
You didn’t specify the wind loading of the DSTAR repeater antenna you intend to
put atop this tower, but I have three comments:
1. Depending on the antenna wind load in combination with the zoning requirements and
wind speed category of your county, three sections of Rohn 45 _might_ be
self-supporting in this application — with no guy wires required.
2. Instead of your system of a secondary “guy wire” to pull the “real” guy wire around the
offending obstruction, why not just move the guy anchor point inboard enough to clear the obstruction? (The only reason I can
think of is that it’s a flat roof with no obvious or easy way of creating guy anchors except at the exterior walls.
But then I will ask how you intend to create a suitably strong guy anchor out there at the edges.) The problem with the
system in your drawing is that it causes the upper part of the “difficult" guy wires to come off the top of the
tower at the same steep angle as they would if you simply located the guy anchors inboard.
3. If your only source of guy anchor points is on the perimeter of the roof, and you
(or your PE) insist on guying the tower, consider attaching the guy wires lower on the
tower. I’d be surprised if any available repeater antenna mounted 10 or 15
feet above the guy wire attachment point would stress Rohn 45.
Bottom line: If it were my problem, I’d hire a professional engineer to determine
whether I needed any guy wires at all. Assuming your DSTAR repeater antenna has a
substantially smaller wind load than, say, a 4-element 15-meter monobander, I’d put
all my effort into a secure, strong roof mount for the Rohn 45 sections, and make the whole
thing free-standing. But to repeat, I have no idea how much wind loading your antenna
represents.
Bud, W2RU
On Sep 24, 2014, at 8:26 19PM, tsharar@comcast.net wrote:
Many thanks to VE4XT.
The Dropbox link to the diagram I mentioned in my message below is:
https://www.dropbox.com/s/045eg6clpclbk3k/Tower%20Guying.png?dl=0
73 de Terry Sharar W3EDS
----- Original Message -----
From: tsharar@comcast.net
To: towertalk@contesting.com
Sent: Monday, September 22, 2014 9:58:48 PM
Subject: [TowerTalk] Alternative Method of Tower Guying
Towertalkians,
We are planning to erect a tower for our club's DSTAR repeater antenna. This
tower will consist [of] three ten foot Rohn 45G tower sections on the flat roof
of a multistory building. The problem we have is that two of the three guy
anchor points are under an adjacent structure roof overhang and will not allow
us to guy the tower at or near the top. One of our club members has proposed a
novel idea for deviating the guys around the roof overhang - please see the
diagram below. Has anyone ever tried something like this before? Does this look
like a good idea or not?
Please note that this diagram is not to scale.
73 de Terry Sharar W3EDS
Chair, Repeater Committee
Montgomery Amateur Radio Club
Rockville, MD
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73
Roger (K8RI)
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