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Re: "Trash Can" or steel drum dish antennas



So far there are two votes for "high performance dishes".  Those votes
are correct!
BUT...the shrouding is accomplished by a "drum" or cylindrical surface
that is covered in *microwave absorbing material*.
At 2GHz this stuff is *heavy*.  Not impossible but a bit tricky.
As to performance, it both 1. reduces spillover from the feed and 2.
edge diffraction from the rim of the reflector.  Resultant antennas meet
FCC Part 101 "category A" requirements for radiation pattern.  This is
something like -50dB sidelobes and a front-to-back of more than 65dB
(not sure of the precise numbers, but they are ridiculously small!).
So...for satellite work they would be the cat's meow; Tsys nearly just
that of cold sky and the receive preamp.  Just a bit bulky (and not sure
where one would get the microwave absorbing material; Cuming Corp. used
to/still does(?) make a product called EccoSorb which is what you'd
want).

As an aside, anyone ever heard of a "cornucopia" antenna?  Some of the
old long-haul analog microwave sites run by the old AT&T still have some
up.  They are generally a cone pointing up with an "elbow" opening that
opens to the horizon.  Those have even better sidelobe/backlobe
performance.  I have some pictures in old textbooks; they appear to be
one of the original radio astronomy antennas.  And now they're all dark;
someone needs to pull one down and fire it up!!

Douglas Cole wrote:
> 
> On Monday 03 December 2001 13:48, T5z4@aol.com wrote:
> > In a message dated 12/3/01 4:04:10 PM Eastern Standard Time,
> > RMckni8527@aol.com writes:
> >
> > <<  They do actually look like a trash can, or maybe more
> >  closely resemble a tub used for icing down a beer keg.  >>
> >
> > I wonder if a steel drum like those in the islands could be fashioned to
> > work well without the hammered out musically tuned zones on it's surface.
> 
> Well what I see described fits what we call a "hi-performance" dish shroud
> for most of our 6GHz ( actually 5.6 to 5.8 ) paths ( ds3 radios running
> telephone and public safety traffic ) , and ours are 2 and 3m dishes so I can
> tell you  from experience that those shrouds ( trash can sides ) are pretty
> large and heavy , but they work very well when you have local paths that are
> not in the same line as your path , but are close enough nearby ( proximity )
> to be a problem without the shroud and are required with some licenses .
> 
> With that said the only thing I can think that a shroud would do for us round
> dish owners on S-band would be to reduce the terrestrial noise ( microwave
> ovens etc ) , anyone know better on this please correct me , since I have
> been thinking about building my own "hi-performance" shroud for my 60cm dish
> to see how it would help my local noise .......
> 
> What do the "experts" have to say ?
> 
> --
> Douglas Cole N7BFS
> AMSAT#26182
> http://www.users.qwest.net/~cdoug3
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