More than likely, you will need an antenna. Either one already on top of your house or an indoor antenna.RCA ANT121R Fine Tuning AntennaSuperSonic HDTV Digital Indoor Antenna
These are just a couple of examples (not necessarily recommendations). What I would do is go to AntennaWeb.Org
and see what kind of reception you can expect given your location and situation and then decide how much you want to spend on an antenna. Keep in mind, you shouldn't need to spend more than $20-$25 for an indoor antenna.