It depends on the focal length of the dish and the position of the offset satellite relative to the focal one.
As a rough guide, this is what I use, and then adjust accurately with a meter.
Let L= dish focal length
Let a = azimuth angular difference between offset sat and focal one.
Let d = spacing of LNB (from centres)
Equation:-
d= L x tan(a)
N.B, if the focal length is unkown, just measure the distance between the LNB and the centre of the dish as a rough guide.
This method will aslo work for obtaining a rough estimate of the height difference required also, but this is not as difficult, as it will normally be a lot smaller.
Robbo
