"Richard Clark" wrote in message
...
On Mon, 21 Mar 2005 18:58:07 GMT, Nigel M wrote:
All parabolas have the same formula, simply different constants

Yes, but what is the difference (in gain terms) between one that looks
flat and one that looks pointy?

????????

They all look the same: Parabolas.

73's
Richard Clark, KB7QHC

Not even close. Prime focus parabolas ( and offset fed) are defined by their
F/D ( focal length to diameter ratio). A "deep " dish would have an F/D of
0.3 or less. Shallow dishes 0.6 or greater. The real problem here becomes
the ability to properly illuminate the dish with a feedhorn. Typical scalar
feeds will be efficient from 0.3 to 0.5 or so. Under illumination can mean
better G/T but you are likely not using the all the surface. Over
illumination results in seeing warm earth noise and degrading G/T.
Do a Google search of W1GHZ site- an excellent tutorial on passive
reflectors and feeds.

Dale W4OP