[amsat-bb] Re: Polarization for ISS and Weather Satellites

[AJ9N at aol.com]

The antennas on the ISS are ground plane type antennas for 2m and  70cm.  
So one could just say that the antennas are vertically  polarized.  However, 
the ISS superstructure has gotten so big that it does  actually block or 
reflect the signal between the ISS and the ground  station.  So we recommend 
that a circular polarized beam be used as the  polarity changes throughout the 
pass.  I think most of the ARISS schools  have used RHCP but there have 
been a few where switching to LHCP during the pass  did help.
 
As a side note, the ARISS schools are to have a backup radio with an  
antenna that has no moving parts.  Usually that means a 1/4 wave  vertical.  I 
use a vertical and an Eggbeater for my school contacts with an  antenna switch 
between the two.  You might want to do the same thing with a  Quadrifilar 
and a vertical.  I always tell the backup radio operator to  switch between 
the two during the pass and go with whichever has the greater  signal 
strength.  They are usually stunned by the change in signal strength  between the 
two as the pass progresses.  The signal with the beam is much  more stable 
and stronger as expected.
 
Hope this helps.
 
73,
Charlie Sufana AJ9N
One of the ARISS mentors
 
 
 
In a message dated 10/27/2012 2:31:27 P.M. Pacific Daylight Time,  
gdillabough at nf.sympatico.ca writes:

I  haven't posted here in a very long time.  I hope this works.

I am  building two Quadrifilar Helix antennas (from QST, August 1996); 
one for  weather satellite experimentation, and one as a backup 
antenna for an  upcoming ARISS contact.

I haven't found anything in the ARRL antenna  book, or on the web, 
that specifically says that one mode (RHCP or LHCP)  of circular 
polarization is better than the other for either of the two  
applications noted above.

Any insight or experience with  polarization issues with the ISS and 
weather satellites are  appreciated.  The last time I did an ARISS 
contact, I was plagued  with very deep fades, and want to do better this  
time.

Thanks,
Graham

Graham Dillabough, VE6KJ,  VO1DZA

Albert Einstein, when asked to describe radio,  replied:

"You see, wire telegraph is a kind of a very, very long cat.  You pull his
tail in New York and his head is meowing in Los Angeles. Do  you understand
this? And radio operates exactly the same way: you send  signals here, they
receive them there. The only difference is that there is  no cat."
Albert Einstein (1879-1955)  

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