Hi John,
It's easy to see pattern issues with using a Elecraft XG3 generator
https://www.dxengineering.com/parts/ect-xg3
to excite the antenna under test. Then use another antenna (almost any
horizontal antenna will work) 1000 feet away for the RX and then turn the
XG3 antenna. The pattern distortion was identified with the NEC model and
confirmed with the XG3 test.
If the VSWR varies as you rotate the antenna, that is a good indicator of
probable Preform interaction.
73
Tim K3LR
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
john@kk9a.com
Sent: Thursday, October 3, 2019 9:37 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] EHS leads for Phillystran
I am not sure how you know that the pattern was distorted but I think
this is a good practice Tim. My top homebrew 15m beam has a higher SWR
than the lower two - 1.4:1 vs 1.1:1. Just below the top antenna is a
Rohn 65 massive star guy bracket with six Phillystran Big Grips
directly attached. Perhaps insulating the guy would help.
John KK9A
Tim Duffy k3lr at k3lr.com
I had a problem with just Preforms attaching to the tower legs connection -
which caused distortion in the pattern of close mounted Yagi's. That is,
Yagi's that were mounted only a few feet above a guy connection point. The
VSWR of the affected Yagi would change with rotation and the effect of three
Preforms connected to the tower was confirmed with modeling. The solution
was to use a bent pin shackle and an insulator right at the tower
connection. You can see it in this view of the middle four element 40 meter
OWA Yagi stack at K3LR:
http://www.k3lr.com/2016/ring.jpg
Using insulators at the tower connection completely solved the pattern
distortion and VSWR changes with rotation.
73
Tim K3LR
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