Bob,
Thanks for the reply. A student of mine once told me that if someone tells you something is easy - it is not. Even though this is not only easy but "very easy" I still need a slight clarification. I think it boils down to the orientation of the satellite relative to the center of the earth.
If the satellite was a clock and the face of the clock was oriented toward the center of the earth the I believe the clock would appear to rotate CW on both ends of the pass. If the side of the clock rather than the face of the clock was oriented toward the center of the earth it would appear to rotate one way at the start of the pass and the other way at the end of the pass because we would be looking at the clock from the other side. I believe this is the basis of the "very easy" explanation you offered.
Not sure why anyone would want to maintain the orientation of the satellite in such a way that would cause the direction of circular polarization to change during the path. Perhaps people selling antenna circularity switches would like it but other than that I do not understand why it would be done. I am most likely missing something important.
tnx & 73 W9KE Tom Doyle
On Sat, Aug 4, 2012 at 2:47 PM, Bob Bruninga bruninga@usna.edu wrote:
I believe that is true but that does not explain why the optimum polarity setting on the receive end would change during a pass.
That's easy. The circularity on a pair of crossed dipoles (about all you can get on a spacecraft) May be designed for Right hand circularity when viewed from the prime direction. But by definition, that save waveform will be LHC when viewed from the opposite direction.
And since the geometry to any one observer is constantly changing by almost 180 degrees during an overhead pass, that is why it is very easy to see, complete change in circularity.
Bob, WB4APR