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R: modeling qha



Hello Wallace,KG4YUW

Look at a QHA standing vertical on the ground with its connector 
on bottom and the loops on top.
 
If the QHA is connected to radiate upward endfire /|\  i.e. in direction 
opposite to the feed point or connector than the presence of the ground 
should not  affect the pattern because the field in direction of 
the ground is cancelled out and this is why the QHA do not 
requires a reflector.

If the QHA is connected to radiate downward backfire  \|/ i.e
in direction of the feed point or connector than the field reflected
back by the ground will affect the pattern.

The small bifilar and the large bifilar end of the loops of a QHA can
be connected to the infinite balun in order to get a backfire or endfire
radiation and using the ground for modeling this difference should
be taken in to account.  

I have written an article on this matter for AMSAT Journal issue
of May/June 2004

73" de

i8CVS Domenico 
     
----- Original Message ----- 
From: Wallace Strom <kg4yuw@arrl.net>
To: <amsat-bb@AMSAT.Org>
Sent: Monday, April 19, 2004 4:22 AM
Subject: [amsat-bb] modeling qha


> Hello,
> 
> This might be off topic but...
> 
> I have been trying to model a Quadrifilar helix antenna with MMANA and
> EZNEC 3.0 demo without much luck.  The pattern breaks down when I model
> the antenna at 6 meters above ground.  I have modeled W3KH's antenna and
> Steve Blackmore's "Tall narrow QHA" - both have nulls at the lower 30
> degress(0-30 , 180-150).  Any help would be appreciated.
> 
> 
> 73,
> Wally
> KG4YUW
> 
> 
> 
> ----
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