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Circular Polarization



From: Dave Cawley  
Cambridge  England
Timestep@dial.pipex.com
Tel.  +44 1440 820040
Fax. +44 1440 820281


Dear all


My original comment was that I did not understand a comment about a
satellite's orientation.  I now understand that a satellite due to poor
stabilization, can turn up-side-down, and have it's antennas pointing out
into space.  It was further suggested that when the antennas were pointing
into space, that the received signal would be of the opposite polarity than
normal, that is to say, pointing towards Earth RHCP and pointing to the
stars LHCP.

Various analogies were used and exchanged, and the flaws of using analogies
were exposed !

The difficult point to visualize, is the signal radiation out of the back
of an antenna, so just suppose for one moment you take a 8 turn helical
antenna, and remove the reflector.  Then instead of feeding it at the end,
feed it half way up, this is easier to visualize.  Now look into  what
would be the front and observe the polarity, then look into the back where
the reflector once was and observe the polarity.  The one in my garden; 
the polarity is the same.  Proving, in this illustration, that polarity is
truly intrinsic once the antenna has been made, and that the signal
received from a satellite with it's antennas pointing skyward is still RCHP
(assuming it was to start with).

Now, the good news is, that I'm nearly off to visit the Fort Lauderdale
Super Yacht Show, where amongst other things I will be exhibiting the
Worlds most expensive Quadafilar Helix Antenna.  So you can come and visit
me, and ponder on circularity, with a Bud or two ?  And those on the list
will find a sudden stop to this thread on Tuesday night ?


Regards

Dave G4IUG
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