Anyone tried to make BIG dish at home?

[Channel Hopper]

mine is 0.8 ratio. thanks for the help.

Then the first set from this link should help

http://www.satellites.co.uk/forums/attachments/forum17/24434d1253178700-2194-back-pdf.att

 

[JanH]

Actually, offset dish is segment, cut out from plain primefocus dish. So, at least theoretically, it's possible to consolidate offset dishes, like flower petals, equip system with primefocus lnb, and check for results...

I do not think so that offset dish is a part of parabolic. It is a bit more complex shape.

 

[Satcom1]

JanH
Originally Posted by BombedOne
Actually, offset dish is segment, cut out from plain primefocus dish. So, at least theoretically, it's possible to consolidate offset dishes, like flower petals, equip system with primefocus lnb, and check for results...

I do not think so that offset dish is a part of parabolic. It is a bit more complex shape.

JanH-

It is said to be developed from PF dish, But actual measurements of Offset dish show that Horizontal section has been closed slightly by the design engineer.

So both of you are correct.

 

[JanH]

Right.
Another difference is that convertor doas not looking to parabolic focal point means focal point of complete virtual parabolic dish as theoreticaly shoud be. Looks a bit crazy.

We needs multibeam dishes now becouse receveing satelites 1W and 23E in same time and it is not practicle to use two dishes. I tested some multibeam dish and it provide less top gain but for larger angle.
Dish is more wide with fastening for 5 LNB.
What about ideas about multibeam dish?

 

[digihoe]

Hi, and thanks everybody for a really nice thread, what inspiration it has been to me.

Actually, offset dish is segment, cut out from plain primefocus dish. So, at least theoretically, it's possible to consolidate offset dishes, like flower petals, equip system with primefocus lnb, and check for results...

I really like this Idea using say 4 smaller offset dishes to make a bigger one, I would think that four dishes should be enough. The biggest problem I would think is focusing the signal from the dishes. First I was thinking about a second dish for refocusing, but now I'm thinking maybe a cantenna will be enough or even a C120 feedhorn.
I would think one should arrange the dishes on a X structure with perfect 90 degrees (and it's own inclination bracket) with the inclination bracket still attached to the dishes for easier installation.

 

[Satcom1]

Could work for analog signal but not DVB. 1 mm KU or 5 mm error and nothing will work. Besides you have to time the signals before you can combine them if using more then one LNBF.

So if idea is to use four offset dishes in X array, then one LNBF would be fed from offsets of these dishes. Maybe it would work.

 

[digihoe]

So if idea is to use four offset dishes in X array, then one LNBF would be fed from offsets of these dishes. Maybe it would work.

That is how I planned it in my head, the problem as I said would be the getting the angle right since the signal would come in at a ~40 degree angle. Maybe a feedhorn should be used. One should also be able to do a simple test with two dished one upside down and the other like proper offset on a pole, and just try vertical transponders and see if there is a gain in signal. But I still think one will need a feedhorn or a horn/cantenna of some sort to maximize the signal gain.

@Satcom1; Thank you for the inspiring work you have done with all these dishes/antennas.

 

[Satcom1]

If one would make two one meter prime focus dishes with long F/D (shallow dish) it would be interesting test. Adjacent satellite rejection would suffer it would seem. Very interesting subject digihoe.

Yes, two offset dishes with their elevations tipped inward and some experimentation with feed horn design. Or center reflector to redirect to normal LNBF.

 

[digihoe]

I really think this could work, at the moment I however only have one dish (second one got dented while moving) so I can't really try it myself. I do not really think there will be timing errors since in the correct angle the dishes should be at an equal distance from the signal source, not when using an X structure atleast, but I could be wrong... I like the subreflector, but I think it will be hard towork out how to make one that will work and in what angle to put the LNB, gregorian dishes uses a parabolid but catches the signale at the same angle as the incoming signal, so we can't use that here, therefor I suggest a straight horn. I'm not really sure how one can go about simulating this kind of systems, but I guess there must be some simulation software, does anyone know of such?

I hope someone out there have time and equipment to test this.

@Satcom1; Thank you for allowing me to through Ideas with you.

 

[digihoe]

I've found some paper where a dish with similar geometry to what I have proposed is discussed but it has an more intricate design. _http://www.cpdee.ufmg.br/~fernando/artigos/imoc03a.pdf But the subreflector they use might work with the application I proposed.

 

[Satcom1]

This is a picture of Galaxy 18 and shows parabolic reflectors and signal ray trace.

 

[Satcom1]

This is a very simple inexpensive satellite dish to make.

 

[JanH]

Interesting, is it really parabolic?
In windy conditions could be a bit unstable but I can imagine to use oposit pressure one as perfect template.
What about Mylar Membrane. I do not know how to get it.

I am thinking about dish composed from more ordinary dishes but looks like for me that it is possible with two reflectors only. It is bad because big losses and it is complicated. Means dishes with normal face not special shape.

 

[franksanderdo]

Hi Folks,

I will try to gofor a 3m one.
As I was reading all the thread I am stunned by all the diferent aproaches. A bit confused which one might be best

At this moment I am thinking on a mixture of the "vacuum" and PU Foam.
to be excact I am thinking about presurising a plastik or rubber sheet fixed in a huge pipe.
on the back side then to apply the foam to bekome the dish in foam.
Only have to find a peace of pipe in the required diameter

The other way I can imagine is to build a sand/concrete tempalte and use PU foam again.

In any case I will keep you updated

See you around
Frank

 

[franksanderdo]

Hi JanH

The main Problem with using a combination of dishes is to get them aligned in a way that the reflection of one dish is not eliminating the reflection of the other.
Means the dishes have to have EXACTLY the same distance to the feed and the last but not least the EXACTLY the same alignment to the satellite.
2 times exactly is a little to much at the end.

I have made some trials on this here and finally figured that the dish shape needs to be specially made for that. Looking at it you are ending up with a segmented dish some how.

The "Vacuum" or "Pressure" Methos is giving you a perfect parabolic. To use it as a template does not really work at bigger sizes as only minimum force is pushing it out of shape. To create a template from it satcom1 has described a little earlier to use fabric and resign instead of the Mylar. In any case be careful with bigger sizes as the circle should be really a circle to get a perfect shape. I will run a test here with 3m and my biggest problem is to get the circle prepared

Never the less do not give up. I do not want to be the only one trying to work on some thing big

See you around
Frank

 

[JanH]

I think distance to LNB could be in wave multiple not only exactly same. It may enable chances to do somethink but it is probably unreal becouse complicated. I have some litle experience with 1,8 m segment commercial dish and it was a bit horrible. Not appropriate gain and more then one focal point. You are right it is about accuracy.

Yes I expected problems with small stability of "presure" model. I am thinking about sequence coating to make it more stabile. Other possible way could be big pressure and hard material for the model.

I thought or feel that for example sqare form of "presure" model could work too. I can not imagine.

 

[franksanderdo]

Hi,

looking at it a square one will work, but the "used" surface will only start some what inside.
Please be carefull with the material selection and the pressure. With the volumes we are talking about it gets dangerous very quickly.
A bursting membrane can easily do severe harm.

about the 1.8m segmented commercial: I have the same problem here. In fact I could proof that most of them available here do not even reach a 1m offset from the same shop. The shop owner was frustrated afterwards.

I have learned by now that 3m is a real difficult story. The pressure version is almost impossible as I can not find some "pipe" with 3m diameter blinded on one end. The water "natural" shape version is tricky as well. But at this moment it looks this will be the one I try. I am looking for materials right now.
I also have some Ideas about building a segmented Dish. Here the biggest issue is to create the template for my 36° segment.
Tomorrow and friday will give the decision. I will keep you updated.

see you around
Frank

 

[franksanderdo]

Hi and Hello,

I have spend today some money and replaced the 1.9m with a 2.4m dish. not yet self made as I wanted to find out first what the problem with this segmented dishes is. The result is not really good ;-)
In fact the new 2.4m is worse than the 1.9m.
Reason is the shape of the metal sheets in the "frame". I will do some more tests tomorrow, but I believe this nice dish will be used only as the support for my self made one.
What I found out so far: The steel frame seems to be very well shaped. I will do some detailed measuring on this. If it is ok, I will use it as a template to work from there ;-)

see you arround
Frank

 

[JanH]

Problem could be f/d of the dish. LNB or feedhorn must be correct for used dish shape. Sometimes sells together LNB which looks as old fashion one with big feedhorn.

I tried to checked my 75 cm classic dish with "special" technique. I point the dish to sun and to focal point I put metal plate. Then I can saw where exactly focus point is and if focus is right. BUT when I put to focal point piece of wood then flame immediately. The dish was from aluminium without painting.

 

[Low Profile]

Well done, you've created a death ray. All you need now is an optical lens, some fiber optic cable and a mirror for the other end of the fiber optic cable (to switch the death ray off).

Have fun............mate!