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Sky hd satellite cable splitter.
Another answer and a method relatively overlooked here in the uk this could be done would be using a smart splitter and an scr single cable router compatible lnb or satellite multi switch amplifier and scr enables satellite receiver the majority of new sky hd boxes come equipped with this facility accessed within the hidden installer menu.
If you are looking at extending the wires from your satellite dish to your sky box then a sky extension cable is what you need to get the job done quickly and easily.
A seperate cable from the lnb is the only sensible option you should have two spare outputs if you only have one sky sky hd box.
A switch will connect one or the other and not both at once.
If you look the splitter passes dc back from both outputs to the input.
Unless both connected boxes are outputting the same controls 12 18v dc 22khz on off.