Anyone tried to make BIG dish at home?

[Satcom1]

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

In the attached photo you can just make out the egg shape of the parabola.

This method is best for casting round or square prime focus reflectors.

As you thought, cutting out an offset dish from a prime focus will give you the offset dish.

 

[sycron]

Hi all, I have been reading all the threads in this post for 2 weeks now. I made a dish myself based on all what I read here. I made it out of wooden parabola ribs, laid it up with 4mm plywood, then fibreglassed it.Then, to make it reflective, based on what I read here, I used the cold galvanizing spray cans (with zinc added) from Ace Hardware. I made a 1.4m dish, 14cm deep, focal point 87.5cm. Today I was finally done, but did not get any results... I would like someone to verify if this spray actually works as a reflector. I am contemplating to stick aluminum foil over it. Also, I have a universal lnbf, the distance (focal point) is 87.5cm from center of dish, the question is, is that from the center of dish to the white plastic cover of the lnbf or slightly more inwards (feedhorn)?
I will upload pictures later if y'all are interested. Thanks.

 

[BombedOne]

Attach some white paper at place of LNB, and align your dish to sunlight. Try to find correct focus distance in that way, but be careful of burns.

 

[Satcom1]

Attach some white paper at place of LNB, and align your dish to sunlight. Try to find correct focus distance in that way, but be careful of burns.

I use three little mirrors spaced around the dish which illuminate the center of the lnbf. Should be coin sized, if cloverleaf pattern then too close or too far.

 

[Satcom1]

Hi all, I have been reading all the threads in this post for 2 weeks now. I made a dish myself based on all what I read here. I made it out of wooden parabola ribs, laid it up with 4mm plywood, then fibreglassed it.Then, to make it reflective, based on what I read here, I used the cold galvanizing spray cans (with zinc added) from Ace Hardware. I made a 1.4m dish, 14cm deep, focal point 87.5cm. Today I was finally done, but did not get any results... I would like someone to verify if this spray actually works as a reflector. I am contemplating to stick aluminum foil over it. Also, I have a universal lnbf, the distance (focal point) is 87.5cm from center of dish, the question is, is that from the center of dish to the white plastic cover of the lnbf or slightly more inwards (feedhorn)?
I will upload pictures later if y'all are interested. Thanks.

I gave up on my Fresnel dish too soon. Thanks to a strong wind the dish was blown onto good alignment and I get C Band reception now.

The Paint I used said on the can 93% pure Zinc and was made by Rust-Oleum. Ace makes some very good paints but you should compare Zinc content to Rust-Oleum. If you can find the Rust-Oleum their, it might help to give your dish a topcoat with it.

Is this C Band or KU Band or both? What LNBF are you using?

 

[Satcom1]

Here are detail pictures of construction of water casting table. If you can find an old discarded table or a folding card table you could just use that.

 

[sycron]

I gave up on my Fresnel dish too soon. Thanks to a strong wind the dish was blown onto good alignment and I get C Band reception now.

The Paint I used said on the can 93% pure Zinc and was made by Rust-Oleum. Ace makes some very good paints but you should compare Zinc content to Rust-Oleum. If you can find the Rust-Oleum their, it might help to give your dish a topcoat with it.

Is this C Band or KU Band or both? What LNBF are you using?

Hi, it's actually Rust-Oleum that I used as well, the 93% zinc one, so you are saying that this has to work, right? I am using a universal dual lnbf Ku Band I imagine to pick up 110 and 119.

I will also try the lnbf focussing method with white paper or little mirrors. I am not getting any signal at all!

I love the jig that you made for the water mold!! I might tried that out, after I succeed with my current dish.

 

[Satcom1]

Hi, it's actually Rust-Oleum that I used as well, the 93% zinc one, so you are saying that this has to work, right? I am using a universal dual lnbf Ku Band I imagine to pick up 110 and 119.

You will need a Standard Circular lnbf for those satellites except for a few information channels or preview channels.

I will also try the lnbf focussing method with white paper or little mirrors. I am not getting any signal at all!

I love the jig that you made for the water mold!! I might tried that out, after I succeed with my current dish.

Do you use Parabola calculator to determine F/D?

It is very touchy to focus KU on large dish, With your lnbf on those satellites you won't have much luck.

 

[Satcom1]

I found a fabric that streches both directions easily. I will lay in the dish media and cover it with a 2 mil plastic sheet stapled down. I estimate about 35 liters of water

The fabric formed such a nice dish all by itself, anyone see a short cut here?:toke:

 

[sycron]

Do you use Parabola calculator to determine F/D?

It is very touchy to focus KU on large dish, With your lnbf on those satellites you won't have much luck.

Yes. I used the parabola calculator. The focal distance is 87.5cm
I am not sure if that 87.5cm should hit the white cap edge. Or should I like make the lnbf distance 86.5cm for instance. So I know that the beams actually enter the feedhorn. Or is just touching the lnbf cover alone?

I am still not sure about the cold galvanize spraypaint to use as metal shield. I tried to measure resistance over the dish surface. Did not measure any conductivity. Isn't it supposed to be? I was searching on google for RF microwave shield materials. There is conductive paint for instance.

 

[sycron]

I found a fabric that streches both directions easily. I will lay in the dish media and cover it with a 2 mil plastic sheet stapled down. I estimate about 35 liters of water

The fabric formed such a nice dish all by itself, anyone see a short cut here?:toke:

I would spray Castin Craft Resin Spray over the fabric so it becomes hard and then lay it up with fibreglass. It comes in cans.

 

[Satcom1]

I would spray Castin Craft Resin Spray over the fabric so it becomes hard and then lay it up with fibreglass. It comes in cans.

:-worship


The focal point for best signal is typically just inside the LNBF. The front section of a KU lnbf has a conical Scalar ring and so the opening to the lnbf wave guide is beyond that. Roughly 1/2" to 3/4" inside lens cap.

Your suggestion about the Resin Spray seems perfect. Also flipping the dish over and laying up Fiberglas for strength.

If the paint does not work for you, then your idea of aluminum foil will creat a solar reflective surface as well and make focusing your lnbf easier. I also like Aluminum window screen whch you can by 4' X 4' at ACE. You would have to match the suns elevation and be very careful not to burn your lnbf. If you have an empty tomato paste can you can replace the lnbf with it If you go to the NOAA Solar Calculater website you can get all the info. This will also set your True South. You can always spray paint the foil after tunning. Good Luck

 

[BombedOne]

Regarding oval scalar ring
You can try to heat existing circular one quite heavily, and then carefully deform it...

 

[Satcom1]

In the early morning with my cup of Java, I have my insperations.

No water needed!:-worship

I flipped the table upside down on a sheet of plastic and rolled on a 20 Ounce coat of polyester resin fully catalyzed.

Then flipped the table right side up to form a perfect parabola.

Here are some pictures;

Pic1- Notice bar of parafin to coat casting table.
Pic4- Sheet of plastic for floor.
Pic5- Ready to roll on Resin.
Pic6- Upright table and leveled legs. A thing of beauty.

 

[Satcom1]

This is what I got with the amount of slack I left in the fabric.

((Click on thumbnail to open, left click on picture to get new windoe cursor turns to magnifer, click on picture to get high resolution, readable picture.))

 

[Satcom1]

Calculates to be 32.786 dBi for C band.

If you are interested in the KU performance, please go to the link.

++_http://my.athenet.net/~multiplx/cgi-bin/parabolic.main.cgi

((Click on thumbnail to open, left click on picture to get new windoe cursor turns to magnifer, click on picture to get high resolution, readable picture.))

 

[Satcom1]

Here are pictures of todays work.

Pic1 - Mesh laid over dish and marked for cutting to allow it to conform to dish surface.

Pic2 - Foil lined dish with plastic barrier and water.

Pic3 & 4 - Dish standing up, front and rear.

 

[BombedOne]

Your approach is trully amazing. Wish you success!

 

[casser]

Here are pictures of todays work.

Pic1 - Mesh laid over dish and marked for cutting to allow it to conform to dish surface.

Pic2 - Foil lined dish with plastic barrier and water.

Pic3 & 4 - Dish standing up, front and rear.

I´m still trying to understand how you got that perfect shape..great work!!

After you finish the antenna and test it, can you create a tutorial?

I prefer to use HDL_ANT to calculate focal point´s/gain/etc and it also create templates ready to print for any dish size...use Corel Draw to read the template files that HDL_ANT generate (it create *.PS files, corel draw read those files 100% and you can test it for 15/30days )

 

[Satcom1]

Your approach is trully amazing. Wish you success!

I like your idea of using a cylinder closed at one end and applying vacuum.

I will try that this summer. I will make a 1.2 meter circle out of 3/4" plywood and attach it to a cylinder made of 1/4" Luan plywood about 6" deep. Then cover the open end with Jersy fabric and wet it with resin. Then I will cover that with plastic drop cloth and apply vacuum to get shape. This whole thing becomes the finished dish. The plywood can have the dish bracket attached to it. The reflector is protected by the structure.