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Re: [TowerTalk] Phillystran questions

To: "Pete Smith N4ZR" <n4zr@contesting.com>, <towertalk@contesting.com>
Subject: Re: [TowerTalk] Phillystran questions
From: "Patrick Greenlee" <patrick_g@windstream.net>
Date: Sat, 22 Dec 2012 09:21:29 -0600
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Thanks for your thoughts.

The Hy-Tower is a design from the 50's and the engineering information from the current producer, by no fault of their own, is unfortunately in poor condition, i.e. a copy of a copy of... and is virtually unusable and worthless. I didn't elect to risk a $1000 + antenna installation on a whim. I have good personal friends who graciously consented to sanity check my design/modifications as well as offer hands-on assistance. Their credentials are quite good. Mark and John... with Mark as a ham who has a BSEE plus about 35 years of antenna design experience and John with a masters in mechanical engineering and 35 plus years of hands-on experience. John flew in from California for a week and lent his experience (ANNUAL TREK NOT JUST AN ANTENNA PARTY). Mark came up from Texas for 3 nights over Thanksgiving plus we have email and telephone. I tend to overbuild, especially if I'm not quite sure. I am confident that any of my design ideas that make it past Mark and John have a terrific chance of success.

One of the failure modes is failure of one or more insulators at the base. My 4 point guys will reduce their bending moment which tries to take them out of column while increasing the columnar load, a compressive load well within their capability. Note: I am not tensioning the guys nearly as much as a "standard" tower guy job.

In addition to John's hands-on practical experience, his analytical skills and mathematic modeling ability is of the first order. He too opts for conservative designs (just not always as overkill as mine.) He "did the math" and we are confident the antenna installation will survive appreciably higher wind and gust loadings than the "stock" installation. We need higher wind survivability as the base of the tower section is 22 feet above ground level and the wind is faster there. We are confident that the weak point of the design is the telescoping 80 meter "nesting" aluminum tubes which should "crinkle" and fold over with no collateral damage other than possibly one or more of the stubs (40, 15, and or 10 meters.)

I originally intended to use a 3 point guy but John suggested a 4 point guy which will require sufficiently reduced tension and thereby less total down thrust (compressive force) on the tower.

Mine is not the first or only roof mounted Hy-Tower installation but I have no information whatsoever about the other such installations. Hy-gain lists a roof mounting kit with applicability to multiple models, including the Hy-tower. I have not seen this kit but the catalog info indicates the use of metallic guys which I wish to avoid for obvious reasons. That and I had already designed, fabricated, and installed the base mount on the roof before finding out about the Hy-gain kit. I recall the installation well as it was 112F in the shade but I was in full sun with a highly reflective roof under me and I was wearing welding leathers. The nuts I installed on the through bolts securing the mount to building structure got too hot to touch and had to be shaded for a while to cool (close quarters, couldn't use gloves.)

After the antenna was up as if on cue the winds piped up and we had gusts in the 50's as well as lots of 30+ and all is well. The upper sections of the 80 meter (pig stick) sure do flex over in an arc (I was only a little nervous) but everything was straight when the wind died down.

I'm willing to share details of the installation if anyone is interested but anyone using any of that information is on their own and accepts any liability. I'm not accepting liability in any form. Your mileage may vary. Extra-terrestrial influences could interfere, Mayan time keeping, coriolis effect, phlogiston, ether drag/drift...

I bill myself as an optimistic realist who hopes for the best and deals with reality.

73 Patrick AF5CK

-----Original Message----- From: Pete Smith N4ZR
Sent: Saturday, December 22, 2012 4:31 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Phillystran questions

Seems to me that something to consider  is that guying the Hy-tower will
alter the load distribution on the tower - I can't do the math, but in
principle it will replace some of the overturning force with compressive
load on the legs.  It might be a good idea to inquire whether anyone has
done this successfully in a high-wind environment - you could wind up
replacing one failure mode with another.

73, Pete N4ZR
Check out the Reverse Beacon Network at
http://reversebeacon.net,
blog at reversebeacon.blogspot.com.
For spots, please go to your favorite
ARC V6 or VE7CC DX cluster node.

On 12/21/2012 7:34 PM, K8RI wrote:
On 12/20/2012 3:31 PM, r miles wrote:

Today I lost my HyTower. 70+ MPH gust tore it loose & broke the 3 cone
shaped insulators. Antenna is in very gud shape as it fell onto very
soft wet soil. I have the old T base & it's a bit kinked but fixable.
The new solid triange base has different hole spacing  so I must go with
what I have. I'm thinking of guying  the HT after it's repaired. Cheaper
than going thru this again. Can I use the lightweight 1200 Lb
Phillystran guys the same  way as EHS.

Sure! If you aren't putting a lot of load on it.

73

Roger (K8RI)


 Nothing fancy just looped thru
insulators to guy posts. Can it be cable clamped? Guys I'm not guying a
monster tower with yagis. I just want the HT to stay up. I'm open to
suggestions. Can't use poly type rope here in the South. Sun does a fast
number on that stuff.  I need a non conductor guy that won't self
destruct in a year.

K9IL
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