The Earth's Curve

• An important factor in understanding how an HD television antenna works is understanding why one is necessary in the first place. Although the range of a standard television broadcast is vast, due to the curve of the Earth (which generally changes every 80 miles), a signal cannot be received without some kind of an antenna. The HD television antenna receives a television signal being broadcast. The antenna also converts that signal into audio and video information that is then used by your television to present to you whatever programming you're trying to watch.
  
  

Local Broadcasts

• Without some kind of cable service, an HD television antenna only receives local broadcasting. However, the vast majority of homes in the United States (upward of 80 percent) can pick up at least five local television stations with just an antenna. These are usually the major networks (NBC, ABC, CBS, Fox) with transmission sources in every large city around the country. Smaller networks (Comedy Central, TNT, TBS) can only be received via some kind of pay television service.
  
  

Image Quality

• Although it may not seem like it, an HD television antenna actually provides better image quality than a cable television service does. This is because of compression. In order to cheaply and efficiently transmit huge amounts of data directly into your house through a coaxial cable, your cable television provider has to compress that data. This results in a loss of image quality, although not a substantial one. Local stations broadcasting over the air send out a signal that is completely uncompressed, which means that the image is at its highest possible resolution and the picture is of the best possible quality.