On June 12, 2009 the United States converted from analog to digital television broadcasting.
"The switch from analog to digital broadcast television is referred to as the digital TV (DTV) transition. In 1996, the U.S. Congress authorized the distribution of an additional broadcast channel to each broadcast TV station so that they could start a digital broadcast channel while simultaneously continuing their analog broadcast channel. Later, Congress set June 12, 2009 as the final date that full power television stations can broadcast analog signals. As of June 13, 2009, full power television stations will only broadcast digital, over-the-air signals. Your local broadcasters may make the transition before then, and some already have.
"The digital transition is underway. Prepare now! On Feb. 17, some full-power broadcast television stations in the United States may stop broadcasting on analog airwaves and begin broadcasting only in digital. The remaining stations may stop broadcasting analog sometime between April 16 and June 12. June 12 is the final deadline for terminating analog broadcasts under legislation passed by Congress.
"Why are we switching to DTV?
"An important benefit of the switch to all-digital broadcasting is that it will free up parts of the valuable broadcast spectrum for public safety communications (such as police, fire departments, and rescue squads). Also, some of the spectrum will be auctioned to companies that will be able to provide consumers with more advanced wireless services (such as wireless broadband).
"Consumers also benefit because digital broadcasting allows stations to offer improved picture and sound quality, and digital is much more efficient than analog. For example, rather than being limited to providing one analog program, a broadcaster is able to offer a super sharp “high definition” (HD) digital program or multiple “standard definition” (SD) digital programs simultaneously through a process called “multicasting.” Multicasting allows broadcast stations to offer several channels of digital programming at the same time, using the same amount of spectrum required for one analog program. So, for example, while a station broadcasting in analog on channel 7 is only able to offer viewers one program, a station broadcasting in digital on channel 7 can offer viewers one digital program on channel 7-1, a second digital program on channel 7-2, a third digital program on channel 7-3, and so on. This means more programming choices for viewers. Further, DTV can provide interactive video and data services that are not possible with analog technology" (http://dtv.gov/whatisdtv.html, accessed 06-12-2009).