Re: G/T for parabolic dishes


 

On Thu, 16 Jul 2020 at 10:41, Chris Bartram G4DGU <chris@...> wrote:
Hello John,

Analytically there isn't any real difference between Yagi-Uda antennas,
dishes (and optical telescopes ... look-up 'Airy Disc') when it comes to
optimising performance. They are simply different ways of focussing the
E-M energy towards a distant point. You get optimum 'gain' when the
first sidelobes are close to -17.5dB. Reducing the sidelobe levels is
possible, but at the expense of gain and although some of the amateur
antenna designers and manufacturers have been playing numbers games with
G/T ratio, but I can't see how they escape from the constraints of the
physics!

Chris,
what physics comes into play here? It's either something I never knew, or have forgotten. 

73

Chris G4DGU

Dave, G8WRB

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