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Re: Cross Boom (Not as Long)



Dom,

     The environment inside a waveguide does not resemble the Yagi.  You can
do all sorts of strange things with waveguide and coax that will not work
with Yagi antennas.  It is a simple matter to bolt together a piece of
waveguide with a couple of right angle turns.  This won't effect your signal
at all.  Next try putting a couple of right angle turns in your Yagi.  I
think it will have some impact.

73,
Joe
ka0yos@amsat.org


----- Original Message -----
From: "i8cvs" <domenico.i8cvs@tin.it>
To: "Gary "Joe" Mayfield" <gary_mayfield@hotmail.com>
Cc: "AMSAT-BB" <amsat-bb@AMSAT.Org>
Sent: Saturday, March 08, 2003 4:03 AM
Subject: R: [amsat-bb] Cross Boom (Long)


> Joe,
>
> Look please at a circularly polarized microwave feed horn for EME
> type W2IMU or VE4MA
>
> They are made using a lenght of circular waveguide wich is closed at
> one end and is open to the other end.
>
> Two probes mounted at 90 degrees one to the other are fitted in the
> same plane near the close end of  waveguide.
>
> Each probe is supplied with the same amount of power and with the
> same phase.
>
> To produce the necessary delay of 90 degrees in one of the linearly
> polarized wave travelling inside the guide a set of metallic screw
> is diametrically fitted at 45 degrees in front of  probes to produce CP in
> the far field at the open end of  the guide thereby demonstrating that
metal
> posts are producing an effect to the electric and magnetic field inside
the
> tube where the electromagnetic wave is travelling.
>
> Metal of the above posts is not a dissipating material and since the
energy
> cannot be destroyed it is reflected producing the above effect.
>
> Going back to yagi the probes replaces dipoles at X position and posts are
> repacing the metallic boom in some extent obviously.
>
> Even dielectric material produces similar effects if immersed in to
electro
> magnetic field and infact teflon plates are fitted at 45 degrees to the
> probes in to a waveguide feed horn to act as polarizer and produce the
> necessary 90 degrees delay in one of the linearly polarized wave to get CP
> in the far field outside the tube.
>
> 73" de i8CVS Domenico
----
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