Off-set V Prime focus Dish

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trigger

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Can any one offer any technical info on which is the better type of dish, or is it simlpy up to reflector size. I'm not looking for manufacturer specific info so assume they were both manufactured in the same material etc - which one would perform better?

Thanks
 
Llew

Llew

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Smaller dishes (say less than 1M) are usually off-set as the Lnb/holder doesn't shadow the dish so much, hence a greater efficiency in signal pickup.

Llew
 
enoc

enoc

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Talking always about the same size....just an example 2 meters dish...always off-set preform better the the prime focus.....

the reason is the lnb in the prime focus, this part make a shadow in the dish, so this part is useles..... but this factor you will see it better in fringe areas...
 
bignick

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I know the quoted statement SHOULD be right, but frankly out here in Cyprus it doesn't seem to be! Offset dishes have a finite size where they stop being effective of about 2.8m but I think after 1.8m a prime focus is the better option. They are less hassle to set up and more robust in use. The loss of the area caused by the shadow of the LNB is also made up by the fact that Prime focus dishes allow the use of C120 LNBs and feed horns better than Offsets.


With a bit of luck that put the cat amongst the pigeons ;)

Cheers

Nick

enoc said:
Talking always about the same size....just an example 2 meters dish...always off-set preform better the the prime focus.....

the reason is the lnb in the prime focus, this part make a shadow in the dish, so this part is useles..... but this factor you will see it better in fringe areas...
Click to expand...
 
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It's simple mechanics. Offset lnb doesn't "shadow" the dish, as correctly described above, and is always preferable, but above a certain dish size the antena arm gets too long, and can't guarantee the "millimeter accuracy" required for signal reception, hence 3 prong support instead.

It's also more difficult to manufacture the correct shape for large offset dishes, a parabola is easier to make!

But for performance, bigger is better, since you're collecting more signal.
 
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