I have never modeled the two driven element configuration so this is 
interesting data Rick. I am not sure how important F/B is in TX. I 
suggested a simple alternative of feeding only one vertical. As a 
reference my stack of 2el 40m beams has only 10dB f/b and I am happy 
with its performance. Many contest records have been set using a simple 
parasitic vertical array. In 2000 I had the world high 40m score in the 
ARRL DX Phone contest using a vertical with a parasitic reflector so the 
configuration is effective.
John KK9A
Subject:         Re: [TowerTalk] Phased verticals one direction
 From:   "Rick Karlquist" <richard@karlquist.com>
Date:    Wed, 2 May 2012 11:24:56 -0700
john@kk9a.com wrote:
> It would be easier to just feed one vertical with a random length of 
> 50
> ohm coax and make the other vertical a parasitic reflector.
>
> John KK9A
>
There are 2 disadvantages to that.
1.  The front to back will be 10 dB at best, whereas with a driven
array you can easily get 20 or 30 dB.  For receiving purposes, a
driven 2 element array is as good as a parasitic 3 element array.
2.  The bandwidth of a parasitic array is considerably less than
a driven array.
Rick N6RK
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