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Re: UO-22 azimuth-only system



Hi John

>  Has anyone out there had experience using a modest cross yagi
>  for UO-22 receive?  I'm thinking about 5 or 6 elements,
>  switchable RHCP/LHCP with a good preamp, something on the
>  order of 60 degrees/3db beamwidth with a gain of 9-10 dBi.

My experience was with UO-14 but I think my comments are general.

There was an article by Martin Davidoff in Oscar News many years ago 
where he did an analysis of the average elevations of the 
UOSATs/PACSATs at a given latitude. His conclusions were somthing like 
90% of the passes would be below 40 degrees or something similar. So 
what I did was to put an azimuth only system together with a vertically 
polarised 9ele yagi for the uplink with a fixed elevation of 30 
degrees. This meant that the 3dB points of the yagi occured at the 
horizon and at 60 degrees of elevation. Please bear in mind that these 
figures are from memory. Downlink was a vertical 4ele yagi with the 
same elevation.

It worked very well. Apart from direct overhead passes, the system 
worked very well indeed. The only problem would be for you would be 
that with an Armstrong system, you'll have to spend a lot of time 
moving the antenna, compared to AO-40, the LEOs move quickly. AO-40 
lends itself to Armstrong (which is what I do also), LEOs do not. I 
built a trackbox and went automatic and it was even more fun then.

>  For transmit, I'm thinking 3 or 4 el. yagi, vertically
>  polarized, aimed about 30 degrees up.

I really wouldn't worry about circular polarisation, the LEOs tend to 
be linearly polarised with the antennas being monopoles sticking either 
above the satellite or below. When seen from the side they are 
vertically polarised.

>  I'd appreciate hearing your comments and/or suggestions.
>
>  Thanks, John
>
>
>  John Pfeifer - KLØWN - Kodiak, AK - www.johnpfeifer.com

Jonathan  HB9DRD/G4KLX
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