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Re: rectangular "dish" illumination?



>So what is the rule of thumb when illuminating a not-round "dish"?

Hi Greg,

Far as I know 'rectangular' dishes are designed for use with linearly polarised feeds and
are nearly always BBQ or rods type of construction. Your screen mesh will allow use of CP
but I don't know how you would set up a CP feed to have a 'rectangular' pattern, there may
be a way. The LP feed for which the dish was designed would automatically have little or
no radiation/sensitivity in the direction of the short side of the rectangle. In which
case you would organise the feed to have a -10db (or so) pattern in the direction of the
long side of the rectangle. That usually amounted to a 2-element yagi type of feed,
perhaps with a co-linear reflector. Good luck with this one. Someone may come up with a
solution and it should make for an interesting thread. In a wider sense it's difficult to
see how one could make a rectangular dish perform anywhere near a circular dish with a CP
feed. Specially when you consider ground-noise from over illumination etc. I have one with
'slat' construction and a LP feed which was very carefully setup several years ago (when I
had access to instruments). It's not in the same street as my round dish with CP feed on
AO-40. Nor was it on AO-13 or Arsene. But they're cheap and plentiful so hang in there
Greg, I hope someone will tell of their successful setup which you may be able to
duplicate.

73, Bill...vk3jt
Milawa
Australia


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