Re: [amsat-bb] Helix

[Al Lawler <alawler@xxxxxxxxxxxxx>]

  I've been wondering about this too, but Jerry Pixton 
seems to be having good luck with this.

  My guess is that since the general practice is to 
'underilluminate' dishes  for better noise figure,  
what you probably wind up with in the case of a helically
fed rectangular bbq dish is 

  1) A fully illuminated "short dimension" dish 
     (and an underilluminated long dimension) resulting in 
     a circular waveform  with  slightly degraded noise performance 
     in one  polarity,  

                                or
  2) A fully  illuminated dish in the long axis
     with substantial loss in the cross polarity due to 
     large spillover, but perhaps higher forward gain.

  Either way, the result is probably elipitcal (but  probably
still at least somewhat superior to linear polarization.)




hasan schiers wrote:
> 
> Perhaps someone could explain how circularity is maintained when about 1/3
> of the dish in the orthogonal direction is missing? Does that work? I
> understand how you can fill in the "slots" with wire cloth for a solid
> reflector, but when nearly 1/3 of the dish is missing in the "horizontal"
> direction, wouldn't this have a profound effect on circularity? (Depending
> on how you mount these BBQ dishes, either 1/3 of horizontal or 1/3 of
> vertical dish is "missing"). I would think this would cause a significant
> change in circularity, but maybe not.
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