At one point in history, my DirecTV satellite dish required two coaxial cables running from the set top box to the dish. I think this was for a brief period in DirecTV history. I don't think you need that any more, and I don't think you needed it when DirecTV first came out.

It had something to do with the LNB polarization on the dish in relation to the transponders on the satellites. There was a way you could work around the two-cable need with some sort of in-between multiplexing box, but I never got the box, I just ran both cables.