A diplexer is not a splitter - think of it as a "combiner" in a way. It combines the satellite feed from the dish along with RF from cable TV or an off-air antenna and allows both signals to travel (either way) on one
coaxial cable -- very handy devices. They will
not split one satellite signal for two receivers. Nothing will. You must run two separate cables directly to the dish and connect them to a dual output LNB.
kat