Hi Ed,
Your conclusions based on your modelling are completely consistent
with my practical experience and modelling.
The most likely degradation is a T-top between 60 and 75 feet long
degrading the front-to-back ratio, pattern and gain of a 40 meter
Yagi when its main beam points into a T-top that's roughly parallel
to the 40 meter Yagi elements.
Only the 40 meter Yagi is affected, especially if the Yagi is within
about 400 feet of a 160 meter T-vertical with a 60-75 foot T-top.
The 160M T-vertical is not affected.
How to avoid degradation of a 40 meter Yagi?
- avoid T-tops between 50 and 75 feet long, or
- use an inverted-L rather then a T-vertical
All of the above is based on actual degradation of my 3 element 40M
Yagi by a 160M T-vertical 40 years ago. Changing the T-vertical to an
inverted-L returned the 40M Yagi to its prior excellent performance
tks
73
Frank
W3LPL
----- Original Message -----
From: "Ed Sawyer" <sawyered@earthlink.net>
To: topband@contesting.com
Sent: Friday, February 28, 2020 2:47:34 AM
Subject: Topband: T Top Verticals and yagis
Frank had brought up the interaction of certain T top loading wires and the
possible interaction with yagis. I played around with modelling on this and
found that just as Frank said, there is interaction of T top wires and
yagis. One thing I found was that if the wire is in the front pattern of
the yagi it is much more influenced if the wire is the front 1/3 portion
rather than the sides and back of the yagi. I didn't find meaningful
distortion in the back area 200 ft away but closer than that and approaching
the front, and there was definite distortion.
Interesting topic Frank.
Ed N1UR
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