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

i8cvs domenico.i8cvs at tin.it
Sat Oct 27 17:05:11 PDT 2012

----- Original Message -----
From: "Graham Dillabough" <gdillabough at nf.sympatico.ca>
To: <amsat-bb at 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

I hope this helps.

Best 73" de

i8CVS Domenico

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