[amsat-bb] Re: Polarization for ISS and Weather Satellites
AJ9N at aol.com
AJ9N at aol.com
Sat Oct 27 16:34:07 PDT 2012
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.
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
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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