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View Full Version : DIY dish contest?



jvvh5897
01-06-2014, 07:31 PM
It is winter and I figured folks have some time to kill. How about a contest to build satellite dishes in your living room?
No prize, but points for low cost, simplicity of building it and how well it works.

I figure couple of categories. C band and ku band. Structural--where you design all the elements. Casting--where you use existing elements in your design like taking a casting off of the front of a TV picture tube or big balloon or use spinning liquid to form parabolic shape--things like that. Stress dishes--see Katz's stress dish for an example of how to use bent beams, or read the pdf
http://ashokk_3.tripod.com/srinivasan.htm on making a sheet bend into a reflector (not that good a method though).

The structural methods might be interesting--maybe more like modern sculpture than anything else, but think of how computers tile surfaces now days and how one might apply that to making a modular dish (see the hexplanet demo
http://vickijoel.org/hexplanet/. Or how telescopes use many small mirrors rather than one big one.

Casting could be with fiberglass or paper mache--you could explore how to weather proof it with thinned out latex caulking or roofing paint like they do cardboard canoes. And how well can metallic paint act as reflector?

Maybe a found objects category. The other day I walked past an auto body repair shop and next to the recycle dumpster there was the hood off a car that looked an awful lot like it could work as a dish--maybe a few cables to pull it more into shape using the stress dish idea?

Cheap things like cardboard, AL foil, space blankets, using an old 18 inch dish as the basis of the dish but with longer LNB arm and big reflector. Do you do prime focus or offset, rectangular or circular or elliptical or spherical or...

jvvh5897
01-07-2014, 06:46 PM
How about making a dish out of snow or ice? Snow reflects RF and lots of us have some right now. You can use the offset dish idea in a horizontal way rather than a vertical like we usually do. Draw a parabolic arm to sweep the dish out suing the tangent method and cardboard maybe....

The tangent method has all drawn lines of equal size n the x axis projection using the method that I use--draw from 1/8 to first line intercept at 5/8, 1/4 to 3/4, 3/8 to 7/8 intercept in the example, but any fraction can be used. Pick f from 16^2/(4*6) (about 10 inches if the x of the graph is in inches too--f/D ratio is moderately deep--about 0.33 and about what is used with many offset dishes) or rework to the f, D and depth you want.

zelig
01-08-2014, 01:12 AM
spincasting concrete I think @6 rpm makes a perfect parabola but I never tried it.

jvvh5897
01-08-2014, 08:17 PM
There is a guy working on a degree in astronomy that is trying to spin mirrors from plastic using the method--if he can get halfway to optical quality with that then Ku band should be piece of cake. For Ku you should have curve smooth to about 1/10th of an inch--optical quality would be to 60 million'th of a meter--um, about 1 million'th of an inch I think.