I have done lots of research on this site and on google and have been able to only find a partial solution. I have two Holland 5-2150MHz Diplexers. I have a DISH 500 with two cables going to the attic. Right now I only have one receiver and only one room I want the satellite in has the cable modem in it as well. The house is wired with RG-6 throughout so that's not a problem. When I hook a diplexer to both ends of the cable (ran from the attic to the room) the cable modem says there is no signal, yet regular cable tv works fine. Now I know this has to be an issue with the upstream of the cable. The ONLY solution I have found was that I need a bi-directional diplexer. Is this really what I need? Oh and another thing, If I don't hook the line going to the room from the attic to a diplexer and let it run straight from the cable to the room and then use a diplexer in the room, the cable modem works fine. It's only when I add the diplexer in the attic, the cable modem has a problem. The reason I bought the Hollands because they were supposed to work with the usual cable upstream from 5-40MHz or whatever its supposed to be. This thing has been bugging me for weeks. Does anyone know why this doesn't work?