Well, it wouldn't be the first time that a manufacturer or vendor gives wrong specs.
And I don't understand the reasoning tek2000 gives:
"With reference to the diagram below, the correct focal length is the distance from p to the parabola vertex v. It is NOT the distance from p to the centre disc (which in all likelihood he was measuring). You have to add an additional 2 inches from the disc to the vertex."
Adding 2 inches also to the depth of 20 inches measured by
bpalone gives 22 inches, even gives a focal length of 39.22 inch. Nowhere near the claimed 48.5. So that reasoning doesn't add up.
If he meant substracting ('adding to the other side of the disc surface'?), that would give 47.94 as focal length; that would be nearer, but still not 48.5
But what is exactly the position and curvature of this central disc? Is it really very different from the normal parabolic form, as tek2000 claims? He doesn't give his own measurements.
So the reasoning in his post I cannot follow.... Something wrong with me or with my reasoning?
For now I believe the calculation of
bpalone, and the improvements he got by the alteration of the LNB position.
'Trust but verify'!
greetz,
A33