Hi there,
this is my first post here, hope not being off topic
I was asking myself if there were resources over the net that cover the
development of a cassegrain antenna [from the design up to the building]
in a homebrew fashion.

Thank you for paying attention towards this mail

Bye bye

Emanuele Colucci


PS. I already posted this message to rec.radio.amateur.homebrew, but a
user suggested to me to post it here too.

well, searching for "cassegrain antenna" with google only gives 60,400
links, searching for "cassegrain antenna design and construction" narrows it
down to about 4000.

"Emanuele Colucci" wrote in message
. ..
Hi there,
this is my first post here, hope not being off topic
I was asking myself if there were resources over the net that cover the
development of a cassegrain antenna [from the design up to the building]
in a homebrew fashion.

Thank you for paying attention towards this mail

Bye bye

Emanuele Colucci


PS. I already posted this message to rec.radio.amateur.homebrew, but a
user suggested to me to post it here too.

Dave ha scritto:
well, searching for "cassegrain antenna" with google only gives 60,400
links, searching for "cassegrain antenna design and construction"
narrows it down to about 4000.

It's April, 9th, 2009. By this date I still wonder why there are persons
so arrogant to think that who asks for advices never looked at google.

Have a nice day.

Emanuele Colucci

In article , Emanuele
Colucci wrote:

Hi there,
this is my first post here, hope not being off topic
I was asking myself if there were resources over the net that cover the
development of a cassegrain antenna [from the design up to the building]
in a homebrew fashion.

Thank you for paying attention towards this mail

Bye bye

Emanuele Colucci


PS. I already posted this message to rec.radio.amateur.homebrew, but a
user suggested to me to post it here too.

Hello, and while I can't point you to any specific sources I would ask why
you feel you need to use a Cassegranian feed. This complicates the design
in that you need both a parabolic main dish and a hyperbolic reflector.
Have you worked out the antenna's frequency band and required radiation
pattern/gain? Would a non-Cassegrainian feed (e.g. placing the main
radiating/receiving element on a support at the focal point of the
reflector) be viable? Sincerely, and 73s from N4GGO,

John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337

"Emanuele Colucci" wrote in message
.. .
Dave ha scritto:
well, searching for "cassegrain antenna" with google only gives 60,400
links, searching for "cassegrain antenna design and construction" narrows
it down to about 4000.

It's April, 9th, 2009. By this date I still wonder why there are persons
so arrogant to think that who asks for advices never looked at google.

Have a nice day.

Emanuele Colucci


because there are those who have never searched with google or any other
engine and just want someone to feed them the answers.

On Thu, 09 Apr 2009 10:01:32 +0200, Emanuele Colucci
wrote:

well, searching for "cassegrain antenna" with google only gives 60,400
links, searching for "cassegrain antenna design and construction"
narrows it down to about 4000.

It's April, 9th, 2009. By this date I still wonder why there are persons
so arrogant to think that who asks for advices never looked at google.

Hi Emanuele,

This is probably due to the way the question was offered. You want a
complete solution to an unknown problem. When such "wish lists" are
posted here, they obtain one of several results:
1. An exhaustive reply that is complete to the question asked, but we
then have the luxury of reading from the original poster that "that
specific solution won't work because...."
2. The beginning of an exhaustive series of postings to draw the
specific issues out of the original poster. That has already begun by
another poster in this thread.
3. The fire hose is opened (much as above) which is another form of
(2) in that you imply you have done a google search, but you haven't
expressed what your search terms were - which would, of course, reduce
those 60,400 links to something more tractable. You don't offer
anything like this in your response except outrage.

Each of these possible outcomes inevitable returns to you, and
something you could have done first instead of last: What is your
problem, why do you think this (a "cassegrain antenna") is the
solution, and some fundamental design issues such as
1. Frequency;
2. Bandwidth;
3. Match;
4. Gain;
5. Budget (time and/or money);
6. Specific issues (phase control?);
7. Application issues (EME?).

When such things are asked for, students coming here to complete an
homework assignment are usually stunned. If you are not a student,
then an engineer is always prepared to submit the characteristics
required. If you are not a student, nor an engineer, then almost any
quick answer could lead you down the path to lost time. You are lucky
no one supplied that quick answer, because we have enough miracle
antenna designers who come here to do just that.

73's
Richard Clark, KB7QHC

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.

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!).


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.

6. Specific issues (phase control?);

Nothing special: I would like an output signal proportional to the power
of the radiation picked up.

7. Application issues (EME?).

Amateur radioastronomy.

Well, that's all by the moment.

Greetings,

Emanuele Colucci

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

Hi Richard. Thank you for the answers
Richard Clark ha scritto:
That is plenty of money. Do you have any time constraints?

Yep. I can only use Sundays... But on the other side I have no deadline.

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.

Great! I'll surely look for his messages!

Many thanks again.

Greetings,

Emanuele Colucci

On Apr 13, 2:08*am, Emanuele Colucci wrote:



Greetings,

Emanuele Colucci


W1GHZ has a website on amateur microwave stuff that might be useful
(construction practices, etc.)

If you have access to a university library or online equivalent, there
was a set of articles in the IEEE Antennas and Propagation Magazine
(not the transactions on A&P) a few years back covering design of
various reflector antennas.

The Cassegrain is popular for the reasons you give: low noise from
behind the antenna, especially if the secondary reflector is
underilluminated. And, it lets you put the electronics right at the
feed without having to worry about putting them out at the prime
focus.

You might also look at the Gregorian or Dragonian configurations,
which are offset feed schemes. The Allen Telescope Array is using a
form of Gregorian.

After that, it's mostly a matter of paper and pencil and working out
the curvatures. The biggest challenge is in figuring out what the
effect of your construction tolerances is.