I think what you are referring to is CATV balun. There is more to this then just plugging it in, the other end would require a like device (they are normally used in pairs) and connect to the CATV source (cable, etc.). There are limitations (length of cable on the higher channels and signal strength) to these devices. You should be able to purchase these through any high end structured cabling supplier (Anixter, Graybar, etc.) or on ebay at
refer to the item as a "CATV Balun"
Joseph Golan, RCDD