[TowerTalk] guy placement questions
k1uo at uninets.net
Mon Apr 10 16:12:42 EDT 2006
I had 2 sections of 45G above the last guyed point on a 145ft rotating
tower. It had a beefed up 402 40M yagi along with a 4 ele 20M on a 35ft
boom side mounted on the Rohn 45. Both were above the last set of guys
with the 40M yagi being at the 19ft level above the last guy point. Never
had any problems even with extensive ice loading with that configuraton. In
fact the entire tower had 9 HD monobanders on it (4X4X4 on 10, 4X4 on 15,
4X4 on 20 and 2X2 on 40) with no problems being guyed at the 40,80 and 120ft
levels and anchors at 100ft away from the tower.
With the beefier 55g, you can easily go two sections above the last set of
guys and still use 5ft of mast above the last section for the 40M yagi with
Larry - K1UO
----- Original Message -----
From: "Dick Green WC1M" <wc1m at msn.com>
To: "Tower" <towertalk at contesting.com>; "YCCC" <yccc at yccc.org>
Sent: Monday, April 10, 2006 2:04 PM
Subject: [TowerTalk] guy placement questions
Background: I've got a permit for 100' of Rohn 55 that will support a
three-stack of 4-element SteppIR yagis and a 40-2CD. The 40-2CD will be on
the mast and all three SteppIRs will be on TIC rings. HFTA shows that
90'/60'/30' spacing is best for the stack from my location. Not too long
ago, a TowerTalk poster said models he did for SteppIR showed interaction
between the 40-2CD and the 4-el SteppIR on 15m (some) and 17m (significant.)
At least 15' of separation is needed to minimize the interaction. If the top
SteppIR is at 90', then the 40-2CD should be at least five feet up the mast
Question 1 - Guy elevations: Rohn specs call for guying at 33', 63' and 95'.
The stack models fine at 96'/64'/34', so this would be a reasonable choice.
In that case, the 40-2CD would be 10' up the mast, at 110'. In both cases,
the 40-2CD will be 15 feet above the top guy. Are there any structural
advantages/disadvantages between having 10 feet of tower and five feet of
mast above the top guy versus five feet of tower and 10 feet of mast above
the top guy?
Question 2 - Mast length: In the 90'/60'/30' case, I would put eight feet of
mast above the top section (40-2CD five feet up, boom struts three feet
higher.) In the 96'/64'/34' case, I would put 13 feet of mast above the top
section (40-2CD ten feet up, boom struts three feet higher.) At the two
proposed guy placements, how much of the mast should be inside the top
section (i.e., how far down should the rotor be?) Is it best to have the
rotor close to the top guy point? If so, I would need 20' of mast in both
Question 3 - Guy radius: The SteppIRs need at least 25' of turning radius
(24' plus one foot for the TIC ring.) The middle SteppIR will probably not
clear the top guy if the guy radius is at the Rohn nominal 80'. If I put the
guys 85' out (slightly over the spec of 80% plus or minus 5%), then I'll get
about 3 feet of clearance. If I put the guys 90' out, then I'll get about 5
feet of clearance. How do I compute the expected sag in the guy wires?
(Note: The plan is to use phillystran guys.) Does 3 feet leave enough
margin? Does 5 feet leave enough margin?
Thanks in advance for any learned answers to these questions!
73, Dick WC1M
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