Please explain this ...

[jenom]

I have come accross two dish pictures where a LNBF was replaced with a small subreflector, and then the LNBF was pointed towards the subreflector.
See the attached two pictures.One looks like factory made, another seems home made modifications.

Just wondering, what advantages this dish has ?
More gain ?
Less noise ?
What is the ideal size for the subreflector ?
How difficult to do this modifications ? (distance ?)

Any expert opinion will be appreciated ! Thanks !

 

[PSB]

Looks like someone has used a Gregorian WildBlue dish for FTA!

http://www.wildblue.com/aboutWildblue/equipment.jsp


Seems they are very efficient in gain, do a search under Gregorian Satellite dish for further details!

http://www.swe-dish.se/upload/_PDF/SWE-DISH DA150K Compact 2006.pdf

 

[TiminMb]

Read this article as well for some more details:

http://www.swe-dish.se/upload/_PDF/White papers/Dual Optics vs Prime Focus.pdf

 

[jenom]

Gregorian Dish

Thanks for the info !
From reading the article, it sounds like these so called "dual optics offset" dishes have about 20% more efficiency, so there gain is equivalent with a 32% larger area, or 15 % larger diameter dish.
So it looks like I will begin some experimenting by placing a dish onto ground level, and than start looking for a metal object with suitable size and shape to create a subreflector . (Maybe an ashtray + and modify it with a hammer hammer?)

 

[TiminMb]

Be sure to tell us if you get improved signal. Aluminum would be soft and easy to shape. It will be tricky to get the right focal length. Perhaps you could calculate a parabola and make a template to use to aid in shaping. Maybe a creative mind can find something ready made.

 

[jenom]

Creating a subdish

I have seen a documentary from Afghanistan, where the local handymans were cutting of the tops of the discarded military fuel supply metal drumms (used by Russian/US tanks ~40-50 Gals)) and than drawing concentric circles, and hammering the areas between the circles with different strenght !
By applying stronger and stronger hammering as they were going toward the center..........they created a parabolic reflector for a satellite dish

Heard lately a news from CUBA; where the goverment is cracking down on people with satellite dishes.......wondering, what method they use to make them ?
I bet, they were are also handmade from something !?

 

[PSB]

These kids make satellite dish from old tin cans!

 

[TiminMb]

In some of those countries artisty in metal is performed that is virtually unseen in this continent. Barefooted welders can build a jeep body from sheet metal entirely by hand. We're talking curved, hollow front window frame and all, perfectly formed into compound curves.

I assume light follows the same path a reflected radio waves. I'd polish the bare metal surface and use the sun to test the focal point and length. Once completed, it could be painted.

I have seen a documentary from Afghanistan, where the local handymans were cutting of the tops of the discarded military fuel supply metal drumms (used by Russian/US tanks ~40-50 Gals)) and than drawing concentric circles, and hammering the areas between the circles with different strenght !
By applying stronger and stronger hammering as they were going toward the center..........they created a parabolic reflector for a satellite dish

Heard lately a news from CUBA; where the goverment is cracking down on people with satellite dishes.......wondering, what method they use to make them ?
I bet, they were are also handmade from something !?