Anyone tried to make BIG dish at home?

[selvam]

Hello

can any one guide me to get calculations for arriving the offset dish of size 10 and 12 ft.

vkumar

Dear All,
I also want the calculations for making offset dish size of 6 and 8ft can any one guide me.

Selvam

 

[selvam]

Do you need offset dish calculation formulas? I have excell preset somewhere...

Dear BombedOne,
Yes I need offset dish calculation formula.

 

[gatojojoi]

Did anyone mentioned the Nelson Parabolic manual? I build a 10' fiberglass dish in 1980 when I lived in upstate New York. I now live in Puerto Rico but just got a farm in Colombia South America and will need a couple of dishes there. The problem is that no one knows anything about them down there. No one sells them either. I still have the manual but have better ideas of how to make the mold. I just don't have much time to work on it now but once I move to Colombia I will make the mold and a couple of dishes from it. I will gradually take pics and when finish I will post them.

 

[BombedOne]

Great...

Should be very interesting.

 

[Satcom1]

I just returned from four months in my winter home. Ran a scan of Galaxy 17C satellite and came up with a good signal on this dish. I was never able to get a signal in prior tests. Winter winds may have blown the dish onto the correct position. Notice it is a spiritual channel.

I agree with Divbi about surface precision.

To that extent, I am working on building a "Casting Table" that uses a liquid to form a perfect parabola. I will make a 1.2 Meter dish and replace the Fresnel dish for testing.

 

[kamaleon]

ghetto dish ... beautiful

 

[Satcom1]

This experiment shows how to make a perfect parabola using water, plastic sheet, resin wetted fabric and a pot.

 

[kamaleon]

Fantastic mate, truely fantastic :-worship

 

[divibi]

This experiment shows how to make a perfect parabola

Hi Satcom1,

Wow, this is amazing!!! So far I only thought such tricks were possible using mercury and done by some serious scientists. I didn't know it could be made homebrew - friendly. How did you find out about this method? I can't wait for more details. All I can say is thank you for sharing and reviving this topic.:-worship

 

[kamaleon]

say, can you get a lot of C band stuff with that small offset dish on your avatar and the ghetto one? or are you using it for Ku as it seems to be a dual band one?

 

[Satcom1]

say, can you get a lot of C band stuff with that small offset dish on your avatar and the ghetto one? or are you using it for Ku as it seems to be a dual band one?

The Avatar dish is a Primestar 1 X .7 Meter elliptical and has a dual lnbf for C Band and KU Band. These dishes need an elliptical Scalar Ring to fully illuminate them. However, I get a few C Band channels and several KU Band satellites. A Conical Scalar Ring works OK but there is no elliptical scalar ring made for C Band, so performance is degraded. You see alot of these dishes used for multiple KU lnbf applications. The problem with that is that those lnbf's are using conical scalar rings for offset dishes and will only illuminate a .7 meter area of the dish. The dual lnbf is a trade off for C and KU. I do not find them to be acceptable for either band. a center mounted C Band lnbf with a side mounted KU lnbf works the best.

The Ghetto dish is a 1.2 Meter Prime Focus dish that works better then a 1 Meter dish. I am experimenting with it for C Band mostly. In USA there are strong zoning restrications against BUD's. Big Ugly Dish.
I use the BSC-621 lnbf because it has a large soft spot to make tunning easy but is not as sensitive as a BSC-421 13 Degree K.

 

[Satcom1]

Hi Satcom1,

Wow, this is amazing!!! So far I only thought such tricks were possible using mercury and done by some serious scientists. I didn't know it could be made homebrew - friendly. How did you find out about this method? I can't wait for more details. All I can say is thank you for sharing and reviving this topic.:-worship

I have done a lot of research into simple methods and found two that work best.

1- Water method, forms a perfectly smooth parabola when a uniformally elastic membrane is used.

2- Bow method, formed by stringing a length of plastic pipe to form a bow. This is used as a template to form aluminum tubes to the required parabolic reflector shape. This reflector is then used for UHF high gain TV dishes.

I will be posting more detail about both of these methods.

 

[BombedOne]

take any big cylinder, sealed from one side. Cover one side of it with thin rubber sheet, make it airtight.

Suck out air from cylinder, untill you'll receive 10-15cm depth parabola in the rubber.

Use some silver spray paint on...

you've done

 

[kamaleon]

The Avatar dish (...) The Ghetto dish (...)

Satcom1 in da house! Respek!!! :-worship

 

[Satcom1]

take any big cylinder, sealed from one side. Cover one side of it with thin rubber sheet, make it airtight.

Suck out air from cylinder, untill you'll receive 10-15cm depth parabola in the rubber.

Use some silver spray paint on...

you've done

Yes, This will work just fine. Here, it is easier and cheaper to get a 3 mil. plastic drop cloth for under $2 and works just as well.

If you add fine wire mesh like window screen it will be pulled into shape and stay there.

You don't have to suck out the air, just press down on the membrane and the air squirts out around the edges and the atmosphere forms the parabola. I have done this and it works.

I will be posting some pics. of fiberglas dish I made using the water method.

 

[Satcom1]

I made a small fiberglas dish using the water casting method. I then used a parabola calculator program to layout a template.
Then the template was placed inside the dish.
Perfect fit.

Proof to me that this method makes a perfect parabola.

 

[kamaleon]

do you think you could cut an offset of the parabola afterwards? to get an offset dish?

 

[BombedOne]

I've made 50cm parabola dish out of fiberglass and epoxy. Still no free time to test it...

 

[Satcom1]

do you think you could cut an offset of the parabola afterwards? to get an offset dish?

I have not tried it yet, but you just tip the pot 24 degrees and what you get is an offset dish.

When I get a chance, i'll do an experiment and post photo.

 

[kamaleon]

my point exactly