[Moon-net] Question about Dish optics

[Pat Barthelow]

Thanks Rasto!

Exactly a tool that I have wanted and can use.  You/and the Moon-net group 
are a wonderful resource!

73, DX, de Pat AA6EG aa6eg at hotmail.com;
                  Skype:  Sparky599

>From: Rastislav Galuscak <om6aa at yahoo.com>
>To: Pat Barthelow <aa6eg at hotmail.com>
>CC: Moon-net at list-serv.davidv.net
>Subject: Re: [Moon-net] Question about Dish optics
>Date: Mon, 11 Sep 2006 06:50:10 -0700 (PDT)
>
>Hello Pat,
>
>    most of your questions  can be solved by useing of I CARA software. You 
>can model Cassegrain antenna assemly with your own dimension, frequency 
>responce, directivity, pattern etc. Free download is available on web site 
>www.com.uvigo.es/ant/icara_english.htm
>
>       73, Rasto OM6AA

>Pat Barthelow <aa6eg at hotmail.com> wrote: I have some questions about large 
>parabolic Dishes,
>Anyone out there savvy on these?
>
>My question centers around
>frequency sensitivity of a secondary reflector, on a
>Cassegrain design dish.  If a secondary reflector, which I understand
>to have a hyperbolic surface, to distribute evenly the radiation from the
>base of the dish, to the main parabola surface,  is designed
>and dimensioned for, say 3 Ghz, it has some optimum  diameter
>in terms of wavelength to do its job  efficiently.  If you illuminate
>it with lower frequencies, its dimension becomes smaller in terms of
>wavelength, and may therefore be less efficient at illuminating the
>parabola.  Is there any such idea as a lower cutoff frequency for the
>secondary reflector?   The secondary reflector I am speaking
>of is one on an old Comsat Dish  (30 meter, Intelsat A model)
>See:
>http://groups.msn.com/towertrailers/shoebox.msnw?action=ShowPhoto&PhotoID=65
>I dont have dimensions  yet for the dish, but from photos,
>estimate the diameter of the secondary reflector  to be about
>10 feet, and is located about 60 ft above the bottom of the dish.
>In the photo, a sense of scale, is the individual panels
>whose outlines are visible, that comprise
>the dish appear to be 4 x 8 ft.  If the secondary reflector
>design frequency is in the vicinity of 3.5ghz, can it work reasonably
>well, illuminated  at, say 1.2 ghz, or 432mhz?
>Tnx,
>73, DX, de Pat AA6EG aa6eg at hotmail.com;
>                   Skype:  Sparky599
>
>
>
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