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Re: R: modeling qha



Domenico,
Thanks for the reply.

I am a little confused - I can model the feed point at the top or the bottom.
Is the top -endfired and bottom  backfire ?

Other questions - should the second feed point be 90 degrees out of phase from
the first?  Should I model the antenna's at 40 ohms? (W2DU)  Should the SWR
for both feed points match?

Thanks
Wally
kg4yuw

i8cvs wrote:

> 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
> >
> >
> >
> > ----
> > Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> > Not an AMSAT member? Join now to support the amateur satellite program!
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>
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> Not an AMSAT member? Join now to support the amateur satellite program!
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