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RG6 cable should be fine. Your installation should include a ground block (near your electrical panel or some other grounded place) and than a splitter to your modem and TVs. The modem should be the first and only thing on it's leg of the splitter and the TVs on the remaining 1 or more legs. Get a splitter that can handle all your rooms - up to 7 with an 1:8 splitter (hopefully they all home run to the same point of origin outside).