In some cases, yes you can install an outside antenna to receive TV signals, but there are restrictions on the installation. 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.
Please see the diagrams link attached below to help you understand how to connect a preamp in your antenna system.