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@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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