I had a actual qso on FO-29 the other day and during the contact circular polarization switching was discussed. The station I was talking with described a very large change in received signal strength when switching between LHCP and RHCP. I have heard other people mention this and I recall some change when using AO-10 with my switchable KLM's back in the good old days.
I have been trying to figure out why there would be such a big change. Here is a collection of theories/questions. I would appreciate comments on any or all of them. This is a bit complex so a direct reply is probably best.
- In a perfect world if the satellite antenna is linearly polarized LH-RH switching would not make any difference.
- In a real world it is unlikely that the ground station receive antenna is truly circular. It is somewhat elliptical.
Question: if the receive antenna has an elliptical pattern does the angle of the major axis change when switching LH - RH. This is a complex question related to the nature of what caused the elliptical distortion in the pattern. Perhaps someone has measured this. If the angle of the major axis receive antenna pattern changes when switching between LH and RH and the satellite antenna is linearly polarized this could account for some change in received signal strength. Other than that I am at a loss to explain why switching LH-RH on a receive antenna would cause a large change in the strength of a signal received from a linear antenna.
tnx & 73 W9KE Tom Doyle
Hi Thomas, W9KE
In a separate email I have sent to you a very compreensive article explaining why during an orbit of a LEO satellite like FO-29 the changes in polarization is generated.
73" de
i8CVS Domenico
----- Original Message ----- From: "Thomas Doyle" tomdoyle1948@gmail.com To: AMSAT-BB@amsat.org Sent: Saturday, August 04, 2012 4:46 PM Subject: [amsat-bb] Antenna Polarization Technical Question
I had a actual qso on FO-29 the other day and during the contact circular polarization switching was discussed. The station I was talking with described a very large change in received signal strength when switching between LHCP and RHCP. I have heard other people mention this and I recall some change when using AO-10 with my switchable KLM's back in the good old days.
I have been trying to figure out why there would be such a big change. Here is a collection of theories/questions. I would appreciate comments on any or all of them. This is a bit complex so a direct reply is probably best.
- In a perfect world if the satellite antenna is linearly polarized
LH-RH switching would not make any difference.
- In a real world it is unlikely that the ground station receive
antenna is truly circular. It is somewhat elliptical.
Question: if the receive antenna has an elliptical pattern does the angle of the major axis change when switching LH - RH. This is a complex question related to the nature of what caused the elliptical distortion in the pattern. Perhaps someone has measured this. If the angle of the major axis receive antenna pattern changes when switching between LH and RH and the satellite antenna is linearly polarized this could account for some change in received signal strength. Other than that I am at a loss to explain why switching LH-RH on a receive antenna would cause a large change in the strength of a signal received from a linear antenna.
tnx & 73 W9KE Tom Doyle _______________________________________________ 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
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Thomas Doyle