Is it possible to increase the size of an offset dish?

DishDick

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Dear All,

I know you can add petals to prime focus dishes to increase their reception area, but is it possible to add petals to an offset dish to increase their reception area? I ask as I would like to try and attempt to get some of the missing vertical transponders. I am lucky that one of my neighbours used to have an engineering company and would welcome a challenge.

I thought that adding 30 cm all round (making dish 3.6 x 3.3m) could be done by using a section of the current outer 30 cm to make the mould, then making 8 petals that clipped onto the side of the dish. Thus the curve of the dish would be maintained.

Thoughts please.
 

Analoguesat

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You would be wasting your time - the lnb focal length is engineered to illuminate the manufactured dish size. You can add as much metalwork as you liked - the lnb wouldnt see any more.
 

Zorba

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What if you moved the lnb out more in proportion to the area expansion?
 

rolfw

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I you moved the LNB out, you would lose focus on the original part of the dish.
 

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If the dish were bigger, and the focal point the same as it is now, as AS says the standard LNB would not see the extensions, without a different feedhorn, with a lower F/D.

However, I think the biggest problem would be to get the extentions the right shape, making a mold from part of the existing dish wouldn't work, the offset dish is part of a hypothetical very much larger prime focus dish.
 

Telia

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I tried this once on a 90cm dish, i added CDs all around the dish rim, i actually got about 0.5dB more signal.
 

Topper

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Telia said:
I tried this once on a 90cm dish, i added CDs all around the dish rim, i actually got about 0.5dB more signal.

Well that was lucky....... but i'll bet your your dish ended up looking a bit like a pansy or should that be a daisy
 

T_G

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Making all the moulds, and then attaching them in such an accurare manner that they all focus to the correct point, and then fiddling with the LNB is more or less doomed. It will cost a lot of time and materials, and most likely the first samples will have to be remade until you learn from it. I have done a lot of work oncarbon fibre and glass fibre moulding - it never works out the first time.

If you have the time and money and the engineering possibilities, why don't you go and build a completely new large dish, that would probably have a better chance. we got a good thread about this here.
 

JanH

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I perfectly agree that it is wasting time to make ready use offset dish biger. Another problem is that offset dish is not quite parabolic and dish should be exact round millimeters.

What do you think about other idea.
Next to original dish put second similar dish. To focal point of the second one could be fasten reflector instead LNB which is pointed to midle of first dish.
Signal phase could be set up by dishes distance.
 

essao

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Well that was lucky....... but i'll bet your your dish ended up looking a bit like a pansy or should that be a daisy
hi...do you have pictures of this experiment?
 

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hi...do you have pictures of this experiment?
Not for an offset only a prime focus dish
 
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