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Re: helix location vs focus

I've been experimenting with the focus location as well.  The length
of the can does make a difference and I have yet to determine just how
long the edges of the can should be.  When a helix is used, two inches
seems about right.  When a patch is used, then an inch and a half seems
better as the patch is so much closer to the ground plane.  The helix
phase center does seem to be one turn in from the end closest to the
reflector, while the patch appears to be at the surface of the patch.
     Scott and Greg, what F/D are you using and are your dishes center
fed or offset fed?  The goal of this is to obtain the minimum amount of
terrestrial interference which in my view is the limitation of mode S.
Cliff K7RR
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