On Fri, 10 Apr 2009 12:34:34 +0200, Emanuele Colucci
wrote:

Hi to everyone and thanks for answering to my message.

Richard Clark ha scritto:
Hi Emanuele,

This is probably due to the way the question was offered. You want a
complete solution to an unknown problem.

You and Dave were right. I originally posted the message in the homebrew
newsgroup because I was looking for a complete guide to design a cas in
order to build a little radiometer working in the "water hole" (1420 ~
1640 MHz) for an hobbystic aim.
The book I used at university to study antennas - Antennas and Radiowave
Propagation [by Robert E. Collin] - simply doesn't cover in depth this
argument. It just cites the Cassegrain feed system as an alternative to
prime focus paraboloidal reflector antennas, because the cassegrain feed
does't receive the thermal noise from the ground.

Hi Emanuele,

I have that book and I can see your source material. If it is your
choice, that is fine. Other correspondents here can respond to your
desire to eliminate thermal noise from the ground in alternative
designs. You may have to repeat your query to get their attention as
this is not a topic that many have experience with (repetition is for
the occasion when they check in on an irregular basis). An
alternative is to search this group, specifically, at
groups.google.com.

I was looking for a complete resource to study the system, and this is
why I wrote he to find someone with good advices.

Now, the thing I have now understood is that I haven't to be so
synthetic while writing a message.

So, I would like to study (and eventually build) a radiometer who
listens to 1420 ~ 1640 MHz, with a passing bandwidth of 8 MHz, in order
to receive a minumum density flux of 240-260 Jy (a Jansky is 10^-26 W /
[m^2 * Hz]). I need low antenna temperature (but not as cryogenics ones!).

You can get a lot of practical ideas here (construction materials and
feed issues); and you can use Collin for the math to simply scale the
structure to your frequency band. The design is rather more simple
than building it.

5. Budget (time and/or money);

I can't answer this question yet. Surely, I haven't more than 5-600
euros to spend in the building/buying of the antenna.

That is plenty of money. Do you have any time constraints?

7. Application issues (EME?).

Amateur radioastronomy.

We have a contributor who has been teaching that for 40 years at a
major university, and he studied under the pioneers of that specialty.
Search groups.google.com for posts by "Mac N8TT" or use "J.
McLaughlin; Michigan, USA" as search terms.

Well, that's all by the moment.

Greetings,

Emanuele Colucci


73's
Richard Clark, KB7QHC