"Richard Clark" wrote in message
...
On Tue, 22 Mar 2005 22:06:24 GMT, "Dale Parfitt"
wrote:

Depending on surface size, that may be correct. An offset dish and an
0.7F/D
horn would avoid that problem. Without doing the math, the now defunct-
and
available fro free, Primestar 1M offset dishes may be an excellent
solution.
Then again, if he only needs 10dB, a small loop yagi could serve with a
lot
less surface area.

Hi Dale,

But this does not answer the problem of the horn design.

As I see it, a simple waveguide (no flared horn) itself will run
something like 6" x 12". About the size of a shoe box. Adding the
flare will probably quadruple that area. Now, to build an offset dish
will force a rather more difficult reflector design project. The
irony is that simply turning the horn around and using it would
probably do just as well, but unfortunately be more cumbersome to
construct and use than the simple design already linked to.

As for the Primestar dish, that is undoubtedly a Point Locus Parabolic
Reflector design that would clash with the geometry of its 10 times
larger intended application. This does not bode well when the appeal
is efficiency based.

Even the style of the classic pringles-can-array is probably simpler
to achieve than horns combined with offset dishes. [However, probably
closer to Crisco Can sized weighing in at several pounds.]

Quick Moral, The first 6 to 10 dB is the easiest gain to achieve.

73's
Richard Clark, KB7QHC

At least on the last paragraph- agreed.
On the Primestar, I have sued this on 10GHz with a feed designed for high
F/D with very good efficienvy. Being offset, the feed does not eclipse any
portion of the dish.
There are a couple of new designs for feeds out- one is a square guide
that does not require a scalar for choking off edge currents. My version at
1296 has an inside dimension of 5.75" and would then be 1/2 this for 2.4
GHz- or about 6 " SQ inches of occupied space. A 1M dish would have approx
1200 SQ", so even in a prime focus configuration, the feed blockage is a
non- issue.
In the final analysis though, I'd go with a parasitic design- bogner or
loop yagi. Too high a gain can also be a pointing issue problem.

Dale W4OP