Digital television

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Digital television (DTV) is a new technology for transmitting and receiving broadcast television signals. The digital television format is also known as ATSC (which is actually the name of the agency responsible for developing digital television standards, the Advanced Television Systems Committee; the conventional North American analog TV format is NTSC, for National Television Systems Committee).

DTV provides clearer resolution and improved sound quality, albeit a somewhat shorter signal range. Older televisions which receive only NTSC (analog) signals will need a digital converter box to receive over the air digital television signals. These converter boxes will work with existing antennas.

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Mandated switch to digital

In the United States, Congress has mandated a switch to digital television as of June 12, 2009. As of that date, traditional analog television broadcasting will cease, except for some low-powered stations and translators.[1]

Sub-channels

Digital television allows for sub-channels in addition to the main channel. For example, on the ION television network (formerly PAX television network), the digital signal from their broadcast stations includes the main channel, the Qubo cartoon channel, ION Life (a lifestyle, food, and exercise channel), and the Worship Channel. Thus, the digital broadcast signal from the local ION affiliate carries four channels instead of one. Other stations are doing likewise and carrying additional sub-channels, such as weather-only and movie-only programming, making the availability and quality of digital television programming available free over the air potentially comparable to that of cable television.

Effects of interference

A common belief used to promote this previously unheard of and unproven technology is the idea that DTV is somehow magically immune to the notorious effects of electromagnetic interference, such as ghosting (duplicate images and outlines of objects appearing on the screen), static, audio noise, and loss of color. In reality, DTV, both satellite, digital cable, and digital terrestrial television face equally serious problems of their own.

Effects of Inteference on digital terrestrial television

Effect Cause Solution
Complete loss of signal Improper antenna position, loose connection, TV transmitter located too far away Re position antenna, shift to different directions, use on screen signal meter, often located on TV menu or set top box, use better quality antenna
Picture freezes, audio cuts out or stutters Improper antenna position, loose connection, TV transmitter located too far away, presence of atmospheric interference, lightning, or improperly shielded electrical equipment Re position antenna, shift to different directions, use on screen signal meter, often located on TV menu or set top box, use better quality antenna, determine the location of power transformers, overhead lines, or electrical panels, avoid those locations.

In addition, being below average terrain, underground, or on the opposite side of a large bank of mountains and/or hills, such as areas east of Los Angeles have been known to prevent the reliable reception of over the air DTV entirely without a more substantial and costly rooftop tower antenna setup. In lower signal strength areas, indoor antennas don't as often provide satisfactory results (more than three or so channels). Analog signals fade and degrade much more gradually than DTV. With DTV, you either get perfect reception, acceptably good reception, or none at all.

Frequencies

Since the mandated government DTV transitions from 2009 to 2011 in the United States and Canada, the actual channels that TV stations broadcast over the air has been almost exclusively UHF (ultra high frequency} channels. Most TV stations broadcasting on channels 2 to 12 are only using those numbers as their virtual channels. In other words; VHF dipole antennas (rabbit ears) will likely receive extremely limited channels. This is because the frequencies that actually carry the data are located on the UHF spectrum, which have always had extremely limited compatibility with VHF dipole antennae. VHF frequencies are in the process of being auctioned off by the FCC to expand mobile phone, two way radio or civil defense communication availabilities.

References and notes

  1. http://www.dtv.gov/
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