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Re: F/D cal of offset dish


Unless I'm completely missing the point... The F/D ratio of a dish is just
another way of describing the max angle of the rim when looking from the
feed point. So selecting a feed for a particular F/D ratio, is just defining
the beamwidth of the feed.
With an offset dish, if viewed from the feed point, it appears completly
circular. So for an offset dish, the angle from the feed will be measured
from the centre of the corcle (where the feed will point) and the edge of
this circle.
I suppose you could calclate/measuer this angle, and calculate the F/D
required to give the same angle for a prime focus round dish? This is what I
did for my 80cm offset and the result seems to be confirmed by the data that
I sebsequently foung on the net.

If I'm wrong here, please enlighten me.

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