[amsat-bb] Re: Antenna Polarization Technical Question

i8cvs domenico.i8cvs at tin.it
Sat Aug 4 19:41:41 PDT 2012

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 at gmail.com>
To: <AMSAT-BB at 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
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