[TowerTalk] How To Avoid Telescoping Mast Colapse

[Bob K6UJ]

Sounds like a very good installation to me. 
The only thing I would suggest is to break up the guy wires with egg insulators to make sure 
none of the wires would be resonant on 40 meters.  

Bob
K6UJ



On Nov 16, 2011, at 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
> _______________________________________________
> 
> 
> 
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk