Aluminium Tin foil reflector for Ku band ?

[koansrc]

Is thin aluminium foil sufficient to reflect KU band signals ? I've seen some home grown dishes made from cardboard and tin foil that claim to receive signals ... ... but is it true ? Can a single layer of aluminum tin foil reflect signals ?

 

[PSB]

Sure can! In fact some dish antenna manufacturers use a plastic dish and paint them with a thin coating of Aluminum metallic paint to reflect the microwave signals into the LNBF!

This dish is made JUST with a thin film of Aluminum..........

[tube]-Srz4ToqzIY[/tube]

 

[Robbo]

The most difficult bit would be getting the parabolic shape correct.

 

[koansrc]

The most difficult bit would be getting the parabolic shape correct.

It's funny you should say that Robbo71 .. .. ..

I migth post some pictures late on .. .. .. when I actually receive .. .. something ;)

 

[Robbo]

It's funny you should say that Robbo71 .. .. ..

I migth post some pictures late on .. .. .. when I actually receive .. .. something ;)

What is funny is the attempt I made once. I carefully calculated a parabola using Excel, stuck lots of pieces of paper together to get a big printout. Used this as a template to make a frame, then cellotaped some aluminium foil to it. It was rubbish, and picked up nothing.
My construction skills are not up to much though.

I take it that it will be a prime focus?, come on post a picture now, it might give me a better idea how to build another one.

 

[HB13DISH]

What is funny is the attempt I made once. I carefully calculated a parabola using Excel, stuck lots of pieces of paper together to get a big printout. Used this as a template to make a frame, then cellotaped some aluminium foil to it. It was rubbish, and picked up nothing.
My construction skills are not up to much though.

I take it that it will be a prime focus?, come on post a picture now, it might give me a better idea how to build another one.

Did you try using a dish to make a template?
It already has the correct shape and all you need to do is make the prototype using a not-so-flexible metal sheet (Aluminum, Gold, Silver, copper).
Haven't tried this myself, as I have ran out of gold sheets.

 

[Robbo]

At the time I only had the one dish, it was very small, but I needed it up on the wall. Using an existing dish is a good idea though , but cheating a bit,
I'll give it a go..

 

[koansrc]

ok, here's the attempt ... at creating a subreflector for the 3.0m CM ...

drew the parabola using the string technique, made a mold from a piece of wood, copied the mold to a series of softwood pieces, used cardboard to form the dish petals, covered in silver foil, adjusted lnb to calculated focal point, hooked up to meter and received ... nothing. I was hoping I could blame the thin foil, but I guess not

 

[Robbo]

Excellent job!!

Shame it doesn't work, it deserves to.

 

[Channel Hopper]

Ah, you have suggested the 3m CM requires a subreflector, which it doesn't.

Any alteration from the original design would only lose efficiency.

 

[johnsattuk]

ok, here's the attempt ... at creating a subreflector for the 3.0m CM ...

drew the parabola using the string technique, made a mold from a piece of wood, copied the mold to a series of softwood pieces, used cardboard to form the dish petals, covered in silver foil, adjusted lnb to calculated focal point, hooked up to meter and received ... nothing. I was hoping I could blame the thin foil, but I guess not

Very ingenious construction :-worship

I think that a slight design flaw may not have helped the performance, sub-reflectors are not parabolic, they are spheroidal. The main dish is parabolic to collect parallel rays and focus them to a point, this gives a conical beam with a focal point in front of the sub-reflector. The sub -reflector then refocusses this divergent conical beam to a focal point at the LNB.

It would be interesting to see if a similarly constructed spherical mirror gave better results

 

[johnsattuk]

Just had a shave in my bathroom wall mounted concave mirror U-zzz

It's about 200 mm dia. and has a focal length of about 500 mm, maybe one of these sort of mirrors would be worth a try. Available quite easily and cheaply, also convex ones, which could be used on the reverse surface, so that you were not passing through the glass substrate

Just had a quick look on Ebay, interesting selection some very cheap.

Nice front surface concave mirror with micro adjustments :-worship

 

[HB13DISH]

Went back to basics and looked up the electrical resistivities of several metals just to get a quantitative idea about which metal is best to make a dish.
The property is called Electrical Resistivity in ohm-m. the smaller the better:
Aluminum 99.9% 29.000E-9
Aluminum Alloys 45.000E-9
Copper 99.9% 17.000E-9
Brass 62.000E-9
Silver 18.000E9
Steel 1020 169.000E-9
Iron 98.000E-9
Gold 22.000E-9

There is also another property called Conductivity.

Anyway, it looks like a good metal to use would be copper with 17.000E-9
compared to Aluminum with 29.000E-9
I thought gold was better than copper, but it looks like this is not true.

I don't know what type of Aluminum was used in your experiments, but I doubt if they are anything near a pure type.
If you want to experiment, then your best choice would be a DIY dish made of copper.
As you have strong satellites in your area, then perhaps a small dish of 45cm made of copper or copper sheets might give you some signal.
I think that with such a small dish the surface has to be quite smooth all over the dish, without any cuts, so that rules out the petals possibility.
Enjoy

 

[johnsattuk]

Went back to basics and looked up the electrical resistivities of several metals just to get a quantitative idea about which metal is best to make a dish.
The property is called Electrical Resistivity in ohm-m. the smaller the better:

Resistance (ohms) and Conductance (mhos) only have a meaning when allied to current (amps). The currents generated by the beams from the sat. are so small that I think the effect of different metals used in the constuction of a dish would be very difficult to ascertain. Also at these frequencies any currents/voltages generated travel about the surface (skin effect) with very little penetration.

 

[Turok]

looks.great
today,i begining to to digging the hole for cm 3.0

in thailand,i see this system,on a backside of a mesh antenna!
how many db you have won now?
what the signal meter says?
when the sun shines,directly,into the antenna,maybe it reflect to much,and lnb could be gone coz of the heatreflection!

 

[koansrc]

... sub-reflectors are not parabolic, they are spheroidal.

! well I guess that means I'm looking for something spherical again (!) to mold a dish from (great idea HB13DISH). But I figure it has to be 40cm in diameter with an f/d of either .4 or .6. Is the f/d calculation the same for spheres ???

To all those that claimed aluminium tin foil works for satellite dishes .... well it does. When I originally posted that it couldn't receive anything, I meant as a subreflector. I tried it as a plain dish today ( as suggested ) and aimed for 13o Hotbird. Easily locked on to various freqs. I suppose I ought to do a proper test and compare the aluminium foil dish to a proper one and benchmark it etc or even hook up a TV to see what exactly I'm getting, but ... I'm too busy looking out for something spherical about 40cm wide at present
Pictures from the tuning at 193o, 11770, H, 27500

 

[PSB]

THANKS for the pictures Koansrc, a wonderful project!

 

[HB13DISH]

Nice work koansrc.
Would be great if you can actually receive a TV channel using a DIY dish.
Why do you think that the tin foil dish in your experiment gave you a signal?
Was it because of the reflectivity of aluminum or because it is metal?

 

[koansrc]

Nice work koansrc.
Would be great if you can actually receive a TV channel using a DIY dish.

I might try to hook it up to my digibox and telly. Who knows might even tempt me into getting the motor working on the 3m CM. Will be a pain to check many channels on a digibox though.

Why do you think that the tin foil dish in your experiment gave you a signal?
Was it because of the reflectivity of aluminum or because it is metal?

I have no idea, but I realize now that I have used various terms to describe the covering and this may be causing confusion. The dish has a cardboard backing covered in "standard kitchen foil bought as a roll from the supermarket " with the more shiny side facing the satellite. ( FWIW ).

 

[steffan_st]

Just want you to know that I'm one of those who encourage you in this project.

Obviously I'm not the only homebrewer in this forum,thank god!