[TowerTalk] [Bulk] Re: The other end of Phillystran - connections to the tower

[Tim Duffy]

Thanks for the nudge George! 

 

Excellent idea - look for them to be in stock soon :-)

 

73

Tim K3LR

 

  _____  

From: George Dubovsky [mailto:n4ua.va at gmail.com] 
Sent: Saturday, March 19, 2016 12:38 PM
To: Grant Saviers
Cc: k3lr at k3lr.com; towertalk
Subject: Re: [Bulk] Re: [TowerTalk] The other end of Phillystran -
connections to the tower

 

Google Joslyn J372. Another fellow told me that they are available from
Hubbell Power Systems, but 50 is the minimum order. Some enterprising DX
type ham, perhaps with an ENGINEERING connection, might consider selling
them... ;-)

73,

geo - n4ua

 

On Sat, Mar 19, 2016 at 12:29 PM, Grant Saviers <grants2 at pacbell.net> wrote:

I'm curious what a "bent pin shackle" looks like.  I know there are bow, D,
chain, and sling shackles all with various types of straight pins, e.g.
threaded, pin, bolt.

Crosby is the top US maker, Chicago is another US brand at a cost savings.
Check rigging supply house near you for inventory or McMaster or
uscargocontrol.com

Thanks for the tip re 10m interaction with big grips, I think I have that
problem.

Grant KZ1W



On 3/19/2016 2:58 AM, George Dubovsky wrote:

But where do you get those shackles today? I have used Joslyn shackles in
the past, acquired from another ham, but when I went looking for more two
years ago, I couldn't find a vendor. I know it's utility hardware, but I
couldn't figure out how to buy any.

73,

geo - n4ua

On Sat, Mar 19, 2016 at 3:32 AM, Tim Duffy <k3lr at k3lr.com> wrote:

When installing the tower connection end of Phillystran guy cables, I
learned that a significant problem can happen with unintended Yagi guy grip
(Preform) antenna interaction.



The problem is this, if your guy grip tower terminations are close to your
antenna mounting position (right underneath), and the terminations (guy
grips) are electrically connected to the tower, they can (in many
installations) interact and cause antenna pattern/VSWR problems. This
problem is worse on the higher bands like10 and 15 meters.



For example at K3LR many Yagi's are side mounted on ring rotors.
Phillystran
or fiberglass guy attach to the tower right under each ring rotor. After an
installation several years ago of some 10 meter Yagi's I noticed that there
were three peaks and valleys in VSWR when rotating the antenna mounted on
the ring. Closer inspection and modeling the three short lengths of
"connected" guy grips revealed that in fact the Preform guy grips were long
enough (cumulative effect of 3 together) to impact the near field
environment of the Yagi. The problem is worse the more "horizontal" the guy
wire is relative to the Yagi (lower guy wire connection points heading to
ground mounted concrete guy dead men anchors) and the higher in frequency
the antenna is (Preform length is more "meaningful").



The solution is simple enough and easy at the time of installation. All of
my guy grip installations now include a "bent pin shackle" (tower side) and
a properly sized guy wire insulator - right at the guy attachment point on
the tower. The other side of the insulator contains the proper guy grip for
the Phillystran or Fiberglass guy material. This way the Preform is totally
insulated from the tower.



Once the insulators were installed at the tower connections, the VSWR and
directional pattern of the Yagi antenna remained constant and predictable
(as modeled) no matter where the antenna was pointed.



You can see the tower insulators installed on the K3LR 20 meter tower on
this W8WWV drone video at the 5:18 mark



https://www.youtube.com/watch?v=SA_NG-bVQuc





73

Tim K3LR





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