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AO-40 S2 link




   Although it may have been addressed here at some point, I do not
   recall seeing much on this subject in this forum.  I am fairly
   new to microwaves so I have been doing a lot of experimenting
   with antenna systems for S2 downlink that you don't need to
   pour money into.  I have a decent signal with my 30 turn helix
   so far, but have been wondering about DSS dishes.  I have found
   1 project documented on the net so far about using a small direct
   TV type dish.  The G6LVB project.  The more common dish in the
   US is the 18" round dish such as made my RCA, SONY, HUGES, etc...
   Quick calcs show that this dish should have approx 18.6dbi gain,
   with a 19.4 degree 3db beamwidth.  Better than the helix.
   Now, although it would be simple to feed this dish with a 2+ turn
   helix, are there advantages/disadvantages to feeding it with
   a horn?  Since a horn would be approx 4" dia it would shade the
   dish a bit too much if it were a straight feed, but these being offset
   fed dishes, I would think you might be ok.  Since this dish
   has an f/d ratio of .64 it seems a natural.  Also the f/d' comes out
   at around .7 so illumination seems ok as well.  Has anyone got
   comments/suggestions on this?  Much thanks in advance!

   -James  KI0KN
   james@colostate.edu
   ki0kn@amsat.org
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