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Re: Has anybody heard AO-10 lately ?



>
> Various sidelobes, backlobe, etc of a CP antenna can have different
> polarization than the main lobe.  Some are right-hand and some are
> left-hand.  So if the spacecraft were rotating so that you move out of the
> main beam into a sidelobe, or from one sidelobe to another, or to the back
> lobe, you could experience the polarization changes you describe.  I think
> this is what is going on.
>

While at apogee, AO-10 moves very, very little (at least it appears so).  At
apogee, I have heard the signals rapidly change polarization several times
over a several minute period.  If my beam is fixed on an object that to me
is essentially not moving, I don't think it can be moving out of my main
lobe onto a sidelobe.

On the LEO birds, I could see this happening if you aren't tracking the bird
quick enough since they move so much faster.  However, I don't think the
beamwidth of most beams are that narrow.  And if you did move out of the
main lobe, you would move into a very deep null first, which would be your
indication you had fallen out of it.  And if you did move into an opositely
polarized side lobe on your antenna, you would still think you were in the
null since you are in the wrong polarization sense.

Now, if the spacecraft's antennas end up moving so that you are not in their
main lobe, then I definitely concur with you that this could occur.  And it
would be much easier for that to happen, particularly with a tumbling AO-10.
That is a good point and could well explain why we see the shifts we do.  I
think you were talking about the birds antennas, not the antennas at your
base, right?

73,

Jon
NA9D

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