(or '''analogue television''') encodes Television and transports the picture and sound information as an Analog Signal , that is, by varying the amplitude and/or Frequencies of the broadcast Signal . All systems preceding Digital Television , such as NTSC , PAL or SECAM are analog television systems.
Broadcasters using analog television systems encode their signal using NTSC , PAL or SECAM analog encoding and then modulate this signal onto a VHF or UHF carrier. An analog television picture is "drawn" on the screen an entire frame each time, in the manner of a motion picture (cinematograph) film, irrespective of the picture content.
Analog television, like all other motion picture systems, exploits the properties of the human eye to create the illusion of moving images. The human eye retains an image for a fraction of a second, which is called "persistence of vision." Due to the persistence of vision effect, a rapid sequence of images will be perceived as an integrated moving image. If the rate of frames is too low, such as 16 frames per second, the moving images will seem jumpy and jerky. Frame rates of 24 frames per second were used for motion pictures to create a smooth moving image. When NTSC television standards were developed, 30 Hz was chosen at the frame rate, and then later 29.97 Hz. The PAL system has a frame rate of 25 frames per second.
When onscreen images are bright, the persistence of vision effect does not last as long, which meant that more frames had to be projected per second. Motion picture projectors resolve this problem by using shutters. Since shutters cannot be used for televisions, television engineers increased the repetition rate to two "flashes" per frame by interlacing and scanning a single frame two times. These interlacing repeated frames do come at a cost, though; in some cases, the repeated frames cause aberrations such as serrations on the edge of moving objects, misalignment, interline flicker, or a shimmering effect.
In black and white television based on a cathode ray tube (CRT), a single electron beam scans a phosphor screen from left to right and then returns to the top. The electron beam is brightness-modulated to create intensity changes which cause the different shades of grey. Analogue television equipment has been manufactured using alternative forms of display, such as LCD, but the picture display is still updated a frame at a time in the same manner as the flying-spot CRT.
To support color signals contained in the broadcast, a color synchronization signal called a "color burst" is added to the basic black and white information. When color television was introduced, engineers ensured that black and white televisions would still be able to display signals that were broadcast in color. To do this, the original monochrome information is still transmitted in the color signal, and then the color difference information is added on top.
Three major standards for television are American NTSC (National Television Systems Committee) color television system, the European PAL (Phase Alternation Line rate) and the French-Former Soviet Union SECAM (Sequential Couleur avec Memoire) standard. The three systems have different numbers of vertical lines. NTSC uses 525 lines (interlaced). In contrast, PAL and SECAM use 625 lines. NTSC displays more frames per second than PAL and SECAM. PAL's color encoding is similar to the NTSC system's. SECAM, though, uses a different modulation approach than PAL or NTSC.
Many countries have, or have decided to, cease analog transmissions to switch to digital broadcasting.
- The Netherlands moved to digital broadcasting on 11 December 2006 . The switch-off was helped greatly by the fact that about 90% of the households have cable that continues to use analog distribution.
- Sweden began the switch-off in late 2005 , region by region. By January 2007 half of the analogue transmitters had been switched off. The switch-off is expected to be completed by 1 February 2008 .
- Germany started the switch-off at different times in different regions. The first was the Berlin area, where the switch-off began on 1 November 2002 and was completed on 4 August 2003 . Most other regions have followed, and in most populous areas the switch-off is completed, but a number of regions have not yet started. The switch-off is planned to be completed by the end of 2008 .
- In format since 1999 (the first in the world). Cable Television Networks are already being broadcasted in simulcast since 2004 and analogue cable services were switched-off in April 2007 .
- Belgium will switch to digital broadcasting completely in 2008 . It will happen gradually.
- In Brazil , the free-to-air digital transmissions will start on July 2008 at São Paulo , but broadcasting companies must beam signals in both analogue and digital formats until 2016 .
- In Canada , the main FTA broadcasters ( CBC , CTV , and Global ) have launched HD streams of their programming. Currently, analogue and digital broadcasts co-exist, with virtually the only way to receive digital TV via cable or satellite TV. However, in some urban areas like Toronto , it's also possible to pick up DTV. Canadian broadcasters must switch to digital over-the air signals by 31 August 2011 , although exceptions may be made where analog transmissions will not cause interference (e.g. remote areas). 1
- In China , the switch-off is scheduled to be in 2015 .
- In Denmark , digital transmission has started and the analogue net will be closed at the end of October 2009 .
- In Ireland DVB-T trials are being held but the digital switch-over, which was intended to begin in 2008 has been postponed indefinitely.
- In Japan , analogue transmissions will be terminated nationwide in July 2011 .
- In Malaysia , Information Ministry was planning to shut down the country's analogue television system in phases beginning from 2009 and set to convert to full digital TV in 2015 .
- In Norway , the switch-off will start in late 2007 and finish by 2009 .
- In the United Kingdom , the switch-off of all analogue terrestrial TV broadcasts is scheduled to begin on 17 October 2007 with Whitehaven in Cumbria and proceed region by region. The last regions will be switched off in 2012 . There is a free-to-air Digital Terrestrial replacement called Freeview that complies with the DVB-T standard. A set-top box can be bought to enable analogue television sets to receive Freeview .
- In the United States by no later than February 17 , 2009 , all U.S. television broadcasts will be exclusively digital, by order of the Federal Communications Commission, with legislation setting this deadline signed into law in early 2006.Section 3002 of the Deficit Reduction Act Of 2005 , Pub. L. No. 109-171, 120 Stat. 4 (February 8, 2006), amending the Communications Act Of 1934 , section 309(j)(14), codified at . Furthermore, starting March 1 , 2007 , new television sets that receive signals over-the-air, including pocket sized portable televisions, must include digital or HDTV tuners for digital broadcasts. Currently, most U.S. broadcasters are beaming their signals in both analog and digital formats; a few are digital-only. Citing the bandwidth efficiency of digital TV, after the analog switch-off the FCC will auction off channels 52–59 (the lower half of the 700 MHz band) for other communications traffic2, completing the reallocation of broadcast channels 52–69 that began in the late 1990s. The analog switch-off ruling, which so far has met little opposition from consumers or manufacturers, would render all non-digital televisions dark and obsolete within 2 years. The FCC has determined that an external tuning device can simply be added to non-digital televisions to lengthen their useful lifespan. (However, as of March 2007, external tuning devices are not widely available, are relatively expensive, and require bulky AC power supplies.) Currently, even the earliest televisions continue to work with present broadcast standards. This mandate was designed to help provide a painless transition to the new standards.
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