Impact of the transition

Digital TV uses a more efficient transmission technology that allows broadcast stations to offer improved picture and sound quality, as well as offer more programming options through multiple broadcast streams (multicasting). Television stations have been preparing for the transition from analog to DTV since the late 1990s, when they began building digital facilities and airing digital channels alongside regular analog broadcasts. Today, 1,609 out of 1,745 full power television stations nationwide offer digital programming, however, most of the smaller, low-power broadcasters, for whom switching to digital would be cost prohibitive, will still be permitted to transmit in analog for several years to come. [9] Since the majority of US viewership is no longer using over-the-air antennae to receive signals, but has switched to cable and satellite, the impact will be much smaller on current NTSC receivers which will continue to use NTSC content and devices after the cut-off date. Set-top boxes will enable existing over-the-air NTSC only receivers to watch over-the-air ATSC signals.




A major concern is that the broadcast technology used to transmit ATSC signals called 8VSB has problems receiving signal inside buildings and in urban areas, largely due to multipath reception issues which cause annoying ghosting and fading on analog images, but can lead to intermittent signal or no reception at all on ATSC programs.[10]. DTV broadcasts exhibit a digital cliff effect, by which viewers will receive either a perfect signal or no signal at all with little or no middle ground. Digital transmissions do contain additional data bits to provide error correction for a finite number of bit errors; once signal quality degrades beyond that point, recovery of the original digital signal becomes impossible.

The maximum power for DTV broadcast classes is also substantially lower; one-fifth of the legal limits for the former full-power analog services. A hundred-kW analog station on channel 2-6 would therefore be faced with the choice of either lowering its power by 80% (to the twenty kilowatt limit of low-VHF DTV) or abandoning a channel which it occupied since the 1950s in order to transmit more signal power on the less-crowded UHF TV band. Unfortunately, the higher frequencies perform poorly in areas where signals must travel great distances and encounter significant terrestrial obstacles.

The Consumer Electronics Association has set up a website called Antenna Web[11] to identify means to provide the correct signal reception to over-the-air viewers. The TV Fool website[12] provides geographic mapping and signal data to allow viewers to estimate the number of channels which will be gained or lost as a result of digital transition; while it estimates that marginally more stations will be gained than lost by viewers, this varies widely with viewers of low-VHF analog signals in distant-fringe areas among the most adversely affected. An estimated 1.8 million people will lose the ability to access over-the-air TV entirely as a result of the digital transition.

US markets which have presented unique problems for digital transition include:

* New York City-Newark - one of the early US terrestrial digital television pioneers with state-of-the-art ATSC facilities installed atop the World Trade Center as early as 1998, currently lacks one single point of sufficient height from which to cover the entire region without severe multipath interference issues in downtown Manhattan, New York. The 1776-foot Freedom Tower, proposed to replace the former World Trade Center, will not be completed in time for 2009's DTV transition, requiring the use of multiple booster transmitters to fill gaps in coverage from the Empire State Building. The Metropolitan TV Alliance, a group of eleven rival New York and New Jersey broadcasters, proposes to deploy twenty transmitters across the city to provide adequate quality signal.
* New Orleans, Louisiana and portions of Mississippi were operating some digital transmitters from temporary locations or from towers belonging to other stations due to damage done during Hurricane Katrina and Hurricane Rita in 2005. While stations are now back on-air, the coverage area often does not match that specified on the station licences due to the change in antenna locations.
* Denver, Colorado faces unique multipath interference problems largely due to its mountainous location; its antennas on Lookout Mountain will need to increase in height to overcome obstacles to digital reception, but attempts to get local zoning approval have met with strong opposition.