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Re: UO-22 & KO-23



Hi Richard,

We notice the opposite here in the southern hemisphere...  poorer sigs as
the satellite moves north of us, towards the equator.  Uplinking on 2m is
harder too...  (120W into 9 elements helps a bit).

I believe the problem is due to the path betweeen satellite and observer
approaching the worst case situation with regard to Faraday rotation...
that is, the path is almost perpendicular to the Earth's magnetic field as
it approaches the equator.

I was hoping that there would be a relatively easy method of predicting the
absolute Faraday rotation at a given frequency and geometry with respect to
the Earth's magetic field...  not so easy though!  There was a good article
published in the Jan/Feb '98 AMSAT Journal by Bauregger & Law, which
provides some insight into the variability of the phenomenon....  take a
look at http://www-star.stanford.edu/~frankb/ee245p~1.doc for more detail.

Whilst the problem is quite noticeable on the 70cm downlink, remember that
the effect increases as the square of the wavelength, so it's about 9 times
worse on the 2m uplink!  

I'm also quite certain that other issues come into play...  Sporadic E
and/or tropospheric ducting 'abducting' the 2m uplink from time to time, etc
etc.  By the way, do you notice the problem to be more pronounced during
daylight hours?

73 Chris VK6KCH

At 07:20 16/05/98 GMT, you wrote:
>Hi Guys
>
>A tip, for what its worth:
>
>Do you find UO-22 weaker than usual at low angles in the southern part 
>of the sky (from the northern hemisphere) ?  I noticed this some weeks
>ago and found that switching polarization (usually RHCP) to LHCP brings 
>the signal up by a large amount until elevation gets to about 20 degrees
>when RHCP is, once again, better. This happens a few times every year but
>not usually for such a long time-scale. Some of that funny "propagation" 
>stuff I guess.
>
>BTW looks like KO-23 is in permanent sunlight again for a few weeks and
>the deviation has risen out of my usable Rx passband. Strange, I thought
>it only happened every five months but the last event was only a couple
>of months back. Seasonal ? your guess is as good as mine.
>
>73
>Richard W L Limebear G3RWL
>g3rwl@amsat.org
>FOC # 1188
>
>                    I've seen Deja Vu before
>
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