Topband: T Top Verticals and yagis

[donovanf at starpower.net]

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 at earthlink.net> 
To: topband at 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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