The only advice I would add is to not use Phillystran through a pulley.
Kevlar is not very fatigue resistant and the wind will work the support
line back and forth through the pulley. The black dacron braid is
plenty strong enough in 3/16" and a better choice.
Grant KZ1W
On 11/16/2011 9:04 AM, Wayne Willenberg wrote:
> Hello,
>
>
>
> I am in the planning stages of a new antenna project. It is going to be a
> simple, center fed, 40-Meter dipole (using a 1:1 DX Engineering Maxi-Core
> balun) connected to RG213. (My county has a maximum wind speed of 100mph.)
>
>
>
> The supports I intend to use at each end are Rohn H50 telescoping masts,
> raised to their maximum, about 44. I am following Steve’s (K7LXC) first
> rule – follow the manufacturer’s directions. So, the stays I am using are
> 25 guage-galvanized wire sold by Rohn and the radius of the anchors for the
> stays will be per Rohn’s specs.
>
>
>
> Steve’s second rule, “don’t do something the manufacturer doesn’t tell
> you,” creates several issues. First, the instructions for the Rohn masts
> don’t indicate the length or type of the anchors that should be used. So,
> I plan to use the recommendations from the ARRL Antenna handbook. I plan
> to use 1” OD galvanized pipe driven 4 feet into the ground. QUESTION 1:
> Are these anchors sufficient?
>
>
>
> The second embellishment I plan to use is ¼ inch galvanized thimbles at the
> anchors and at the collars of each section of the mast. It seems to me it
> is better to have the guy wires wrapped around a thimble rather than going
> through the rough edges of the collars and anchors. QUESTION 2: Is this a
> good idea?
>
>
>
> At each point where a guy wire goes through a thimble, I plan to use a
> series of 3 -- 3/8 galvanized wire clamps (i.e., the type that has a U-bolt
> that goes around the two cables. Each end of the U-bolt is threaded. The
> U-bolt extends through a flat part, and nuts are tightened on the threaded
> ends of the U-bolt and thereby clamp the wires together.) QUESTION 3: Is
> this form of attachment correct?
>
>
>
> The ends of the dipole opposite the antenna wire from each feedpoint will
> be connected to H1200 Phillystran. The Phillystran will go through a small
> marine-grade stainless steel pulley at the top of the mast and then
> continue to the bottom of the mast. The center of the dipole is heavy
> because of the DXEngineering balun (rated at 2,000 W) and the RG213
> connected to the balun. My reason for using Phillystran for the dipole
> halyards is the strength vs weight ratio. I know I can’t make the dipole
> horizontal to the ground, but I hope to avoid an acute angle on each side
> of the feedpoint by exerting significant horizontal force on the halyards.
>
>
>
> I plan to tension 3 of the sets of guy wires just enough to take the slack
> out and to make the masts plumb. However, the fourth set of guy wires
> opposite the each end of the dipole will have turnbuckles for adjusting the
> pull in a direction opposite the dipole wire. I intend to have the guys
> exert significant force to try to take some of the droop out of the dipole.
> I know some of this force will be directed downward through the mast and
> try to buckle the mast. QUESTION 4: Is this additional force on the fourth
> set of guy wires a problem?
>
>
>
>
>
> My final general question: What is the primary reason for causing
> telescoping masts to fail? Am I setting up a failure situation by planning
> to have more force in the guys opposite the dipole wires?
>
>
>
> Thanks for your help.
>
>
>
> Wayne KK6BT
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>
>
>
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