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Hole in a helix reflector?

Can someone with the appropriate software, model the effect of having a 
hole in the middle of a reflector on a helix. I say this because I have 
made a helix to a design seen somewhere ( I can't find it again ). This 
uses a 4" square piece of tinplate or PCB with a 40mm hole in the middle, a 
piece of 40mm external diameter PVC plumbing pipe is passed through the 
hole. It is held in place by 2  wires at 90 degrees that go through the 
tube and are soldered to the tinplate. The helix is wound one side of the 
reflector, with an N-type socket at the feed point, at the correct 
positioning to mount the down convertor ( a Drake ) with an N-type back to 
back. It is a short helix to feed a dish. Would using a cupped reflector 
reduce the side lobes if used in this configuration.

I have also seen a design that used just a single shorted turn as a 
reflector, are these effective?

Thanks in advance


      G4DMF  QTHR   IO93HA
      Amsat-UK Member 5372

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