[TowerTalk] Shadowing of small antennas by larger ones?

[Pete Smith]

At 05:13 AM 2/2/01 +0000, Steve wrote:
>Good point Tom, I purchased EZNEC to see if metal guy cables would effect
>the radiation pattern for a 3 stack for 20m on a 150 ft. tower. I modeled a
>single beam then a beam with a boom touching the elements and one not
>touching. The model showed radiation from the boom. I then modeled the stack
>with a tower and there was more radiation from the tower. I then modeled the
>tower with the guy wires insulated from the tower and there was radiation
>from the guy wires. The radiation from the guy wires were about the same as
>from the tower so I decided to go with steel guy wires insulated from the
>tower. The question is how much will the extra metal in the near field and
>not so near field effect the antenna and how much do you want to spend to
>create a perfect environment for antennas

I don't know about perfect... but I modeled my entire station, including
guys insulated from the tower and grounded at their outer ends, and a
2-high stack with the bottom antenna inside the first set of conductive
guys.  It showed heavy interaction and a badly distorted pattern when
running the lower antenna alone, and a smaller but definite effect on the
stack.  That seemed scary enough that I replaced my top guys with
Phillystran.  Both antennas in the stack show comparable patterns in my
crude on-the-air tests, and the stack definitely works well.  An added
benefit was a noticeable improvement in performance of the 40-meter yagi
above the top tribander.  

73, Pete N4ZR
Contesting is!

The World Contest Station Database 
is waiting for your input at
http://www.qsl.net/n4zr 



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