----- Original Message ----- From: "Graham Dillabough" gdillabough@nf.sympatico.ca To: amsat-bb@amsat.org Sent: Saturday, October 27, 2012 10:58 PM Subject: [amsat-bb] Polarization for ISS and Weather Satellites

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

Hi Graham, VE6KJ, VO1DZA

Since you are building Quadrifilar Helix Antennas please remember that for RHCP both loops of the antenna must be left wounded and for LHCP they must be right hand wounded as just the reverse of wath happens in a well know classic helix antenna of the type W8JK

The best way to work on weather satellite and ARISS contact using a Quadrifilar Helix Antenna is to switch between two antennas having one RHCP and the other one LHCP

The importance to switch between RHCP to LHCP depend on many factors related mainly to Faraday rotation of the signals into the ionosphere and the attitude of the satellite antenna with respect of position of your receiving and transmitting antennas.

BTW since I have made many experimentation in this field at 2400 MHz using AO40 I have written an article into the AMSAT-Journal May/June 2004 that can help you to designe,wound and connect both loops of a Quadrifilar antenna in order to get both RHCP and LHCP polarizations.

The title of the article is:

"Experimental investigation on Quadrifilat Helix Antennas for 2400 MHz"

In a separate email I have sent to you an attachement of this article in PDF format.

I hope this helps.

Best 73" de

i8CVS Domenico

The polar orbiting NOAA weather satellites have right hand circular helical antennas for the VHF APT service. Right hand circular polarization is recommended for NOAA APT receiving antennas.

http://www.noaasis.noaa.gov/NOAASIS/pubs/Users_Guide-Building_Receive_Statio ns_March_2009.pdf

See the section on ground station antennas, p. 45

Grant Zehr AA9LC

-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Graham Dillabough Sent: Saturday, October 27, 2012 3:58 PM To: amsat-bb@amsat.org Subject: [amsat-bb] Polarization for ISS and Weather Satellites

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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