How Does an HD Antenna Work?

HD signals are sent primarily along the Ultra High Frequency, or UHF, band. These signals are line-of-sight from the broadcast tower to your antenna. The curvature of the Earth places limitations on the distance from the broadcast antennas to your antenna that's typically in the range of 60 to 75 miles. However, obstacles such as trees and buildings cause signal bounce known as "multipath," which causes the signal to reach your antenna more than once and at different times, causing cancellation. Orienting your antenna as high as possible helps to overcome these obstacles. Correctly installed HD antennas receive all channels broadcast by local antennas, including sub-channels. Known as "multicasting," this feature allows broadcasters to send a single HD channel alongside two or more digital channels that feature educational, weather and other special interest information stations.

Over-the-air HD broadcasts are free, just like analog broadcasts were for decades. The broadcast spectrum, although regulated by the Federal Communications Commission, is still owned by the general public -- you only need an HD antenna and an HDTV, though you can instead use converter boxes to convert the digital signals from your HD antenna to an older analog television. HD terrestrial broadcasts offer superior HD picture quality over subscription services, because those services must remove some digital data to squeeze multiple channels in a certain amount of bandwidth. Known as compression, this is needed due to the limited quantity and carrying capacity of orbiting satellites used by satellite and cable companies. Terrestrial HD antennas simply pull in the signal directly from local affiliates, removing the need to compress the signals, and thus offering cleaner, crisper images.

HD antenna types include the common mast-mounted, aluminum array antennas seen on many rooftops. Modern HD antennas are geared towards receiving primarily UHF signals, whereas older units were formatted for Very High Frequency, or VHF, signals. Other types include powered "V"-shaped units for equipment rack or tabletop mounting. These require a nearby AC outlet to work properly. Outdoor designs often feature square-shaped antennas that mount similarly to satellite dishes, offering a potentially more aesthetically pleasing option. It is important to select the right antenna based on your geographic location. The Consumer Electronics Association operates a free service at AntennaWeb.org, correlating color codes on antenna packaging to maps on the website (link in Resources). Use this site to ensure you've selected the right antenna prior to climbing on the roof and installing it.

HD antennas connect directly to HDTVs or decoder boxes using a type of cable called RG-6 coax. This cable features extensive shielding and sufficient wire gauge to carry and protect delicate digital signals from antenna to decoder. The screw-on type connector is familiar to anyone with an antenna, cable or satellite services. New HDTVs have built-in ATSC digital tuners, allowing a direct connection to the antenna. Alternately, satellite and cable HD boxes typically have inputs specifically to receive antenna feeds. Connections may be split or amplified as needed, accommodating multiple televisions and/or longer runs that may otherwise degrade the signal.