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Re: [TowerTalk] No Explanation

To: "Bill" <>, <>
Subject: Re: [TowerTalk] No Explanation
From: Jim Lux <>
Date: Thu, 06 Apr 2006 10:55:15 -0700
List-post: <>
At 07:30 AM 4/6/2006, Bill wrote:
>Tor N4OGW Stated
>"Also note that the phasing for the cardioid array shown in that
>report is incorrect. You can't just add a "delay" line of 1/4 wavelength
>to get 90 degree phasing." and
>"Two verticals, 1/4 wave spacing, 90 degrees out of phase."
>withour any explanaiton.
>Please explain Tor.  It has worked for me.
>Bill W7VP

There's some examples of this in the ARRL antenna book, with lots of 
examples of what kind of pattern you get with "causually designed feed 
networks".  Forward gain isn't much affected, but the depth of the null is.

If you have two verticals a quarter wave apart, and you feed one with a 
transmission line that is 90 degrees longer than the other, you *might* get 
the right relative current phases and magnitudes and you might not.  The 
antennas are close enough that the mutual impedance is almost as big as the 
self impedance.  There IS a cookbook length for quarter wave spaced 
verticals that achieves the right phasing and magnitudes called the 
Christman phasing.  Using 50 ohm feedlines, one antenna gets a 84 degree 
long line and the other gets a 161 degree long line, they're joined at a 
T.  However, I suspect that if your antennas are non-ideal, it might not 
work as well.  For instance, if the loss is higher, the effect of the 
mutual coupling is less.



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