How To Find Focal Point

[bel71281]

Find the focal point for any dish
All credit of this belongs to ZZZSparks.... he did all this great work and info..... kudos to ZZZ....txsgent
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I have been asked many times how and where to position the new LNB and support for a dish modification. The calculations are cumbersome, but if you attack the problem from the premise the manufacturer of the dish knew where the focal point belonged, and positioned the LNB of that dish correctly, we can use their knowledge without reinventing the wheel.

This process requires a straightedge like a yard stick or meter stick, a marking pen, cardboard with a straight (square face), and a pair of scissors. This will be an exercise of Physics at it basic elements. It doesn't matter what the support arm angle is, it doesn't matter if the dish is oval, elliptical, round, or even a rectangular dish.
The only thing you need is the original LNB....beg, borrow, or appropriate one for this short term project.

A picture is worth a thousand words...here is a little of both. My lines are not necessarily straight, but the concept should be evident without perfect corners.

Take your time, it will pay off in the end.



Once you have this template you have everything you need to cut off the support arm for adding a Y yoke, a single yoke, etc. Please remember if the mod needs to slide over the arm for attachment, leave the arm about an inch longer so you have something to mount or fasten the yoke(LNB holder).

The red mark is the center of the focal point that you want to hit the center of your new LNB.