The most important reason to make the switch to a digital signal is because it will free up valuable portions of the broadcast spectrum, which can then be used for other purposes, such as advanced wireless services and for public and safety services.

2009

1998

Digital television technology emerged to public view in the 1990s. In the United States professional action was spurred by a demonstration in 1987 of a new analog high-definition television (HDTV) system by NHK, Japan’s public television network.

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ATSC standards

There are four basic display sizes for ATSC, generally known by referring to the number of lines of the picture height. NTSC and PAL image sizes are smallest, with a width of 720 (or 704) and a height of 480 or 576 lines. The third size is HDTV images that have 720 scan lines in height and are 1280 pixels wide.

Congress passed the Telecommunications Act of 1996 with the original transition date of December 31, 2006. However, the transition to digital television was set back three times: first to December 31, 2008, then to February 17, 2009, and then finally to June 12, 2009.

Table 1. 4:3 aspect ratio ATSC picture formats Active H-samples Active lines Scanning mode Frame rate (Hz)* 640 480 Progressive 60(60/M), 30(30/M), 24(24/M) Interlaced 30(30/M) 704 480 Progressive 60(60/M), 30(30/M), 24(24/M) Interlaced 30(30/M) * M=1.001 is a frame rate divisor for NTSC-friendly systems.

HDTV (High-Definition Television), a very high quality digital broadcast television standard, is the long-awaited, next-generation solution to replace analogue TV formats like NTSC and PAL.

Analog signals use less bandwidth than digital signals. Analog signals provide a more accurate representation of changes in physical phenomena, such as sound, light, temperature, position, or pressure. Analog communication systems are less sensitive in terms of electrical tolerance.

Full power analog TV broadcasts officially ended on June 12, 2009. The transition not only affected analog TVs but VCRs and pre-2009 DVD recorders that had built-in tuners designed to receive programming via an over-the-air antenna. Cable or satellite TV subscribers may, or may not, be affected (more on this below).

NTSC is generally used to refer to the old analog signal which was first adopted in the USA in the 1940s. It has largely been phased out in favor of digital ATSC broadcasting. NTSC is inferior to ATSC, as it is doesn’t deliver HDTV picture quality, or the widescreen format.

NTSC as an over the air broadcast format has basically ended in the USA, except in small broadcast markets. But NTSC is still alive an well as a standard for DVDs, satellite and cable transmission method.

PAL stands for Phase Alternating Line and is a standard for analog video. PAL delivers 625 scan lines per image, 25 frames per second and has a 50-Hz grid frequency. PAL is used primarily in Europe, Australia, part of South America and some areas of Africa. NTSC stands for National Television Standards Committee.

Analog TVs can receive digital television (DTV) signals by using a “Digital-to-Analog Converter Box” that can be purchased at retail stores.

Aerials that were installed long before digital TV was created, are still capable of getting Freeview, as long as they are in range of a Freeview transmitter. Freeview, as well as analogue TV, is transmitted in the band 21 to 65 UHF, which can be received by standard TV aerials.