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Re: [TowerTalk] Cage dipole revisited.

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Subject: Re: [TowerTalk] Cage dipole revisited.
From: Rick Stealey <rstealey@hotmail.com>
Date: Sun, 12 Apr 2009 01:53:04 +0000
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Today I did a little modeling with 4NEC2 on 80 meters.  First a regular dipole 
showed a bandwidth of 200 KHz at the SWR=2:1 points.
Then I decided to see how close to a real cage a pair of dipoles has to be to 
get the same benefit.  So I added another dipole, fan style, to it and got 320 
KHz bandwidth.  I varied the length of the second dipole all over the place.  I 
was modeling on 80 meters, and made the 2nd dipole small (like the length of a 
40 m dipole) and could see SWR dips in the 80m and 40m bands when I did a 
frequency sweep.  Then I lengthend the small dipole and watched the 2nd dip 
drop in frequency till it got close to the 80 m band and the bandwidth began 
increasing.  But I was never able to get a "double hump" inside the 80m band as 
I had hoped.
But 320 KHz bandwidth was easily obtained.
Now the question is, how different is a pair of dipoles (with 10-20 degrees 
angle between them)from a real cage dipole ?  So to do this I modeled three 
dipoles, parallel to each other and separated a few feet apart.  The bandwidth 
was the same as the fan, indicating to me that very likely a simple two dipole 
fan antenna (both elements can be the same length) will give good swr 
performance compared to a dipole and might be worth the effort.  Sure would be 
simple to build compared to a cage

Rick  K2XT

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