[amsat-bb] Antenna Polarization Technical Question

[Thomas Doyle]

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