The trick here: the dish is a 1.8m offset antenna (Kathrein CAS 180) so that I probably can afford a few dB loss due to the fact that the uplink feed is a bit off the focal point.
tnx for the interesting picture and experience.
I think you have a second trick: Your Helix is very close near the LNB, and, in your 1,8m dish the focus is further away from the mirror than the smaller dish diameters. The offset error becomes smaler, i think, you are still in a part of the main lobe...
Let´s wait and see the results from Thomas and Markus
73 de Robert