OTHER Question about LNB position

jessica6

Member
Nov 21, 2021
13
5
Tucson, AZ
While mounting my LNB, I noticed it seems a bit low by visual inspection. But after looking at various pictures of other dishes, this seems to be normal (see attached picture, of where I thought the LNB should be (red focus lines) compared to reality (the pictured LNB, well below the intersection)). Can anyone explain why this is so low down? Is the dish not really parabolic?
dishLNBposition.jpg
 

primestar31

SatelliteGuys Master
Lifetime Supporter
Mar 15, 2005
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Beta Omicron Delta III
The small dishes are "Offset dishes", which means the lnb is mounted much lower like the photo above. That's to help keep it from shadowing the signal. It "looks" much higher up for signal than you'd think, and then it bounces down to the lnb.

It IS a parabolic dish, but a 'section cut' of one, so the lnb is where it would belong, IF the dish was a true "prime focus" (like old school large C-band dishes)

 
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Titanium

AI6US
Lifetime Supporter
May 23, 2013
7,346
8,443
Meadow Vista, Northern California
The reflector is an offset design. This is a section of a parabolic and the look angle of the dish is not in line with the surface of the reflector as in your photo, but rather, the actual look angle is roughly 22-30 degrees higher (depending on the model).

30-deg-elevation-dish.gif
 
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a33

SatelliteGuys Pro
Feb 4, 2015
593
392
netherlands europe
And to add, still:
You'll notice that the deepest point (measured along the vertical mid plane of the dish) of an offset dish is not at the center, but below the center.
Even on the drawing in the post by Titanium, that can be seen.

(With a prime focus dishes, the deepest point is at the center.)

greetz,
A33
 
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