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Re: PJ8 Sint Maarten



In a message dated 3/6/00 8:02:06 AM Mountain Standard Time, 
bruninga@nadn.navy.mil writes:

> Also, the Arrow uplink and downlink are cross polarized, so although I
>  think we have a tendancy to align for the best downlink, this actually
>  tends to make your uplink be in the wrong polarization.  You might
>  consider aligning for the best down link and then rotating about 45
>  degrees.  This only drops your donwlink a few dB while making sure that
>  your uplink is not in the crosspolarized null...
>  

My emailer shows all of this text with lines through it.  I've noticed that 
with many of Frank's postings.  Not sure what's going on there.

As for the Arrow being cross polarized, it does not mean that an optimal 
downlink signal will automatically produce a minimum uplink signa.  This is 
because of the differences in Faraday rotation of the signals.  In the case 
of AO27, even though the antennas on the satellite have the same polarization 
at the bird, the amount of Faraday rotation for each band is different so 
they are unlikely to be aligned on the ground.  Also, the alignment will 
change as the distance between the ground station and the satellite changes.  
With a dual band yagi antenna, it is sometimes necessary to rotate the 
antenna while transmitting and compromise the downlink signal strength to be 
able to capture the bird more reliably while transmitting.    I have heard 
reports that nulls in transmitting were even more common when both sets of 
elements were of the same polarization.

Lee Devlin, KØLEE  (K0LEE)
Greeley, CO
http://members.aol.com/lee810/ham.html
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