In most cases, yes you can install an outside antenna to receive TV signals. The Federal Communications Commission (FCC) has adopted what is called the Over-the-Air Reception Devices (OTARD) rule, which governs restrictions on the installation of antennas specifically for TV viewing. The FCC has published a guide which explains the OTARD rules, which can be found at http://www.fcc.gov/guides/over-air-reception-devices-rule. You should review this document to make sure your installation is allowed under these rules.