Almost all network broadcast TV is now in digital format as well as the long existing analog format. Free over-the-air (OTA) digital TV from the ABC, NBC, CBS, FOX, and PBS network depends on you location relative to the broadcast towers. If you live close to the towers, an indoor TV antenna will work, but if you live more than 20 miles from the towers, you will need an outdoor antenna for optimum reception. The signal flow is antenna to digital (ATSC) tuner to TV.
To see what may be available in your area, enter your zip code or full address into www.antennaweb.org and when the results are displayed, click on the selection to show "digital" stations only.