[amsat-bb] L/S helix feed

Hello Questions on my current L/S helix feed. I am building a dual L/S concentric helix feed for a 48x54 inch primestar dish. The reflector is cut for L band does that cause a problem with S band? Where can I find a good design for a notch filter for S band to reduce desense? Where does the focal point want to be on the helicies? Or is it pretty forgiving. Any other information is appreciated. 73 Bob W7LRD Seattle