Perhaps I should have worded my question differently. I understand the concept of circular polarization and the reasons for it. What I should have asked was "Is one direction preferred over the other for working the satellites?". Thanks for all the excellent info and I think what I've learned is that the ability to switch between directions of polarization is best but RHCP is preferred if only one direction is available.
Domenico, thanks for the attachments. Good stuff which I had not seen before!
Tom - K0TW
If I'm building an antenna of circular polarization for use with the birds what determines if it should be LHCP or RHCP? I've read the ARRL Satellite Handbook and "sort of" searched the AMSAT-BB archives but found nothing about this question.
Thanks. Tom - K0TW
Hi Tom, K0TW
If a satellite transmit RHCP and your antenna is LHCP then you loose almost 20 db on receiving !
As an example VO-52 transmit LHCP on 2 meters toward the ground and if your antenna is only RHCP polarized your received signal will be very weak.
In addition during the orbit the satellite is tumbling and the sense of polarization changes many time between RHCP to LHCP during an orbit.
More over the sense of polarization changes by the Faraday rotation as the wave passes through the ionospefere.
This is why switching between RHCP to LHCP on receiving and transmitting is strongly recommended particularly using LEO satellites that are not three axis stabilized and the antennas are not constantly pointed toward the earth.
By the way if you use linear polarization on receiving in any condition you will loose a maximum of 3 dB suffering more fading instead of loosing about 20 dB using the wrong or reversed circular polarization.
73" de
i8CVS Domenico.
----- Original Message ----- From: "Tom" k0tw@cox.net To: amsat-bb@amsat.org Sent: Thursday, October 07, 2010 12:42 AM Subject: [amsat-bb] Re: LHCP or RHCP?
Perhaps I should have worded my question differently. I understand the concept of circular polarization and the reasons for it. What I should
have
asked was "Is one direction preferred over the other for working the satellites?". Thanks for all the excellent info and I think what I've learned is that the ability to switch between directions of polarization
is
best but RHCP is preferred if only one direction is available.
Domenico, thanks for the attachments. Good stuff which I had not seen before!
Tom - K0TW
If I'm building an antenna of circular polarization for use with the
birds
what determines if it should be LHCP or RHCP? I've read the ARRL
Satellite
Handbook and "sort of" searched the AMSAT-BB archives but found nothing about this question.
Thanks. Tom - K0TW
Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
participants (2)
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i8cvs -
Tom