Machine for making wooden offset dishes of various focal lengths

[polgyver]

For some time I was thinking about making own dish of certain focal length. For one project, needed f= 80 cm.
For another, f=150 cm. As there is no way to buy such a dish, the only solution is to make it. I used wood, but certain styrofoam, utilized for bicycle helmets, probably would be better. Aluminum paint or foil will be used for
satellite reception.
I did not finish the dish today, but it looks promising.
Pictures follow;

 

[. Raine]

Awesome! Can't wait to see the finished product!

 

[Wescopc]

Wow - what sort of curve accuracy do you think you will be able to hold?
Bob

 

[armadillo_115]

That's the first Satellite dish I ever saw that may need routine termite treatment.Don't let them holes get too big or it'll only work on C band. lol.

Good luck...that's a lot of tedious work!

 

[jorgek]

How are you going to keep the woodpeckers away?
Another interesting and excellent project!

 

[polgyver]

Wow - what sort of curve accuracy do you think you will be able to hold?
Bob

Hopefully, below 1 mm, and it is said that it should be below 10 % of wavelength, - for Ku, the wavelength is around 25 mm, so, it should be OK.
A few more pictures:


Many years ago, Marinus Bosma was able to make aluminum panels with accuracy below 5 microns, in his machine was used 14 ton block of granite.

http://www.mmsonline.com/articles/down-to-the-micron-up-to-the-stars

 

[polgyver]

Re: termites and woodpeckers ; they rather prefer solid wood, not plywood full of glue.

 

[pacificrim]

Please keep us up-to-date on your progress

 

[polgyver]

I finished cutting (milling?) the dish, painted it with aluminum paint, leaving the rough wood surface deliberately, to check if there will be any improvement in Q - after the dish will be later sanded.
Tried it - unsuccessfully - with Hispasat, on my porch.
Later decided to add wooden plank and a standard post bracket.
Four small mirrors showed that the dish's focus is not as small as expected.
A LNBF bar will be added next, as a temporary help (the real purpose for this dish is to be installed on a balcony, without LNBF bar...)

 

[Cosmo Blatz]

Are you sure the dish surface is conductive? I would think it would take a very thick coating because of the extremely porous material. Looks like it has potential. Hang in there!

 

[lost_mesa]

Yes, maybe paint a piece of cardboard with the aluminum paint, hold it in front of the LNBF of your functioning dish, and see if it completely blocks the signal?

If you have a longer than normal focal length, do you have a feed that will properly illuminate the dish, so you don't pick up ground noise?

 

[polgyver]

Are you sure the dish surface is conductive? I

Yes, maybe paint a piece of cardboard with the aluminum paint, hold it in front of the LNBF of your functioning dish, and see if it completely blocks the signal?

You, gents, are real pro's.
The alum. paint is COMPLETELY non-conductive - as checked with ohmmeter on megaohm scale.
Thick coat of alum. paint on a thin piece of plywood, only partially attenuates the signal.
Therefore, aluminum paint is useless for this experiment.
Now, alum. foil is a must (got to think about proper glue... )

 

[FaT Air]

contact cement. Try some quality mylar. If it's good, could place a sheet of it across the face then introduce a vacuum to the void to pull it into the dish. may need some heat (hair dryer) to the front(???) Just thinking with my fingers.

 

[Cosmo Blatz]

Good ideas FAT Air! Maybe smooth the reflector surface first with a coat of the plastic type plaster patch or drywall mud? One of those shiny Mylar balloons could be a source for the Mylar. (I hear those balloons short out power lines.) Saw a post where a guy used one of those silver emergency sleeping bags on a satellite project.

 

[waylew]

posted this one before;

 

[bpalone]

Just a thought here, but how about double sided tape? Would allow easy replacement, during the experimentation phase. Wouldn't think of it for the final, but initial testing... Just thought about this. How about that metalized duct tape?

 

[Jason S]

3M spray on headliner adhesive may work for a more permanent mounting.

 

[Titanium]

For testing, I would use a wide roll of aluminum foil wrap and press it into place. No adhesive should be necessary until it needs to be permanently attached.

 

[jorgek]

For testing, I would use a wide roll of aluminum foil wrap and press it into place. No adhesive should be necessary until it needs to be permanently attached.

In case the foil lifts then some thumb tacks or even a small stapler could hold the foil tight against the wood.

 

[. Raine]

When I made the 30'' fiberglass dish, I used just regular aluminum foil and it worked good, but it began to tear before I sealed up the back side. I patched it up with the aluminum duct tape and that worked good.

I don't know if it's a viable test or not, but a while back I covered a metal dish with aluminum tape and painted it, [painted only because it was blinding in the sun at the right angle] then compared the signal to when the dish was uncovered, it was about the same. Did that cause I'm planning on making another fiberglass dish using the aluminum duct tape rather than aluminum foil.