There are several broadcast television systems in use in the world today. Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic An analogue television system includes several components: a set of technical parameters for the broadcast signal, a system for encoding color, and possibly a system for encoding multi-channel audio. Analog (or analogue) television encodes Television picture and sound information and transmits it as an Analog signal: one in which the An encoder is a device used to change a signal (such as a Bitstream) or Data into a Code. In digital television, all of these elements are combined in a single digital transmission system. Digital television (DTV is the sending and receiving of moving images and sound by discrete ( digital) signals in contrast to the analog signals used by
All but one analogue television system began life in monochrome. Each country, faced with local political, technical, and economic issues, adopted a color system which was effectively grafted onto an existing monochrome system, using gaps in the video spectrum (explained below) to allow the color information to fit in the channels allotted. In theory, any color system could be used with any monochrome video system, but in practice some of the original monochrome systems proved impractical to adapt to color and were abandoned when the switch to color broadcasting was made. All countries use one of three color systems: NTSC, PAL, or SECAM. NTSC ( National Television System Committee) is the Analog television system used in the United States, Canada, Japan, Mexico PAL, short for Phase Alternating Line, is a colour -encoding system used in Broadcast television systems in large parts of the world SECAM, also written SÉCAM ( Séquentiel couleur à mémoire, French for "Sequential Color with Memory" is an analog color television system
Ignoring color, all television systems work in essentially the same manner. The monochrome image seen by a camera (now, the luminance component of a color image) is divided into horizontal scan lines, some number of which make up a single image or frame. As applied to video signals luma represents the brightness in an image (the "black and white" or achromatic portion of the image A monochrome image is theoretically continuous, and thus unlimited in horizontal resolution, but to make television practical a limit had to be placed on the bandwidth of the television signal, which puts an ultimate limit on the horizontal resolution possible. When color was introduced, this limit of necessity became fixed. All analogue television systems are interlaced; that is to say, alternate rows of the frame are transmitted in sequence, followed by the remaining rows in their sequence. For the method of incrementally displaying Raster graphics, see Interlace (bitmaps. Each half of the frame is called a field, and the rate at which fields are transmitted is one of the fundamental parameters of a video system. Usually it is closely related to the frequency at which the electric power grid operates, to avoid the appearance of a flicker resulting from the beat between the television screen and nearby electric lights. Electricity distribution is the penultimate stage in the delivery (before retail) of Electricity to end users In Acoustics, a beat is an Interference between two Sounds of slightly different frequencies, perceived as periodic variations in volume whose Digital, or "fixed pixel", displays are all progressive scan and must deinterlace an interlaced source. Deinterlacing is the process of converting Interlaced video like common Analog television signals into a non-interlaced form Use of inexpensive deinterlacing hardware is a typical difference between lower- vs. higher-priced flat panel displays (PDP, LCD, etc. ).
All movies and other filmed material shot at 24 frames per second must be transferred to video frame rates in order to prevent severe motion jitter effects. Frame rate, or frame frequency, is the measurement of the Frequency (rate at which an imaging device produces unique consecutive images called frames The Typically, for 25 frame/s formats (countries with 50 Hz mains supply), the content is sped up, while a techniques known as "3:2 pulldown" is used for 30 frame/s formats (countries with 60 Hz mains supply) to match the film frames to the video frames without speeding up the play back. Telecine (ˈtɛləˌsɪni/ /ˌtɛləˈsɪni/ ˌtɛləˈsɪnə also /ˌtɛləˈsiːn/ — "tel-e-Sin-ee" "tel-e-Sin-a" as 'cine' is the same root as in 'cinema' (See Telecine. Telecine (ˈtɛləˌsɪni/ /ˌtɛləˈsɪni/ ˌtɛləˈsɪnə also /ˌtɛləˈsiːn/ — "tel-e-Sin-ee" "tel-e-Sin-a" as 'cine' is the same root as in 'cinema' )
Since television was originally implemented using cathode-ray tubes (CRT), the physics of these devices necessarily intrudes on the format of the video they can be used to display. The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or The image on a CRT is painted by a moving beam of electrons which hits a phosphor coating on the front of the tube. A phosphor is a substance that exhibits the phenomenon of Phosphorescence (sustained glowing after exposure to energized particles such as Electrons This electron beam is steered by a magnetic field generated by powerful electromagnets close to the source of the electron beam. An electromagnet is a type of Magnet in which the Magnetic field is produced by the flow of an electric current.
In order to reorient this magnetic steering mechanism, a certain amount of time is required due to the inductance of the magnets; the greater the change, the greater the time it takes for the electron beam to settle in the new spot. In Electrical circuits, any Electric current i produces a Magnetic field and hence generates a total Magnetic flux \Phi acting
For this reason, it is necessary to shut off the electron beam (corresponding to a video signal of zero luminance) during the time it takes to reorient the beam from the end of one line to the beginning of the next (horizontal retrace) and from the bottom of the screen to the top (vertical retrace or vertical blanking interval). The vertical blanking interval (VBI also known as the vertical interval or VBLANK, is the time difference between the last line of one frame or field of a Raster The horizontal retrace is accounted for in the time allotted to each scan line, but the vertical retrace is accounted for as phantom lines which are never displayed but which are included in the number of lines per frame defined for each video system. Since the electron beam must be turned off in any case, the result is gaps in the television signal, which can be used to transmit other information, such as test signals or color identification signals.
The temporal gaps translate into a comb-like frequency spectrum for the signal, where the teeth are spaced at line frequency and concentrate most of the energy; the space between the teeth can be used to insert a color subcarrier. Familiar concepts associated with a Frequency are colors musical notes radio/TV channels and even the regular rotation of the earth
Television images are unique in that they must incorporate regions of the picture with reasonable-quality content, that will never be seen by some viewers.
For more information, see overscan in television. Overscan is extra image area around the four edges of a Video image that is not normally seen by the viewer This concept is analogous to producing widescreen content that will be cropped for some viewers who do not have widescreen.
In the PAL standard the odd (upper) field is drawn first and the even (lower) field second. For the method of incrementally displaying Raster graphics, see Interlace (bitmaps. PAL, short for Phase Alternating Line, is a colour -encoding system used in Broadcast television systems in large parts of the world In the NTSC standard, the even (lower) field is drawn first and the odd (upper) field second opposite to PAL. NTSC ( National Television System Committee) is the Analog television system used in the United States, Canada, Japan, Mexico
Another parameter of analogue television systems, minor by comparison, is the choice of whether vision modulation is positive or negative. In positive modulation, the maximum luminance value is represented by the maximum electrical signal; in negative modulation, the maximum luminance value is represented by a zero electrical signal. In Telecommunications, modulation is the process of varying a periodic Waveform, i Most video systems were defined to use negative modulation to reduce the appearance of noise, on the theory that dark spots in the image would be less noticeable than bright white spots in the image, given a particularly common sort of noise.
Given all of these parameters, the result is a mostly-continuous analogue signal which can be modulated onto a radio-frequency carrier and transmitted through an antenna. All analogue television systems use vestigial sideband modulation, a form of amplitude modulation in which one sideband is partially removed. Single-sideband modulation ( SSB) is a refinement of Amplitude modulation that more efficiently uses electrical power and bandwidth. Amplitude modulation ( AM) is a technique used in electronic communication most commonly for transmitting information via a Radio Carrier wave This reduces the bandwidth of the transmitted signal, enabling narrower channels to be used.
In analogue television, the sound portion of a broadcast is invariably modulated separately from the video. Most commonly, the audio and video are combined at the transmitter before being presented to the antenna, but in some cases separate aural and visual antennas can be used. In almost all cases, standard wideband frequency modulation is used for the standard monaural audio; the exception is systems used by France, which are AM. Monaural (often shortened to mono) sound reproduction is single-channel Stereo, or more generally multi-channel, audio is encoded using a number of schemes which (except in the French systems) are independent of the video system. The principal systems are NICAM, which uses a digital audio encoding; double-FM (known under a variety of names, notably Zweikanalton, A2 Stereo, West German Stereo, German Stereo or IGR Stereo), in which case each audio channel is separately modulated in FM and added to the broadcast signal; and BTSC (also known as MTS), which multiplexes additional audio channels on the existing FM audio carrier. NICAM stands for Near Instantaneous Companded Audio Multiplex. Zweikanalton ("two channel sound" A2 Stereo is a Television sound transmission system used in Germany and other countries Multichannel television sound, better known as MTS (often still as BTSC, for the Broadcast Television Systems Committee that created it is the method Multichannel television sound, better known as MTS (often still as BTSC, for the Broadcast Television Systems Committee that created it is the method All three systems are compatible with monaural FM audio, but only NICAM may be used with the French AM audio systems. NICAM stands for Near Instantaneous Companded Audio Multiplex.
For historical reasons, many countries use a different video system on UHF than they do on the VHF bands. Very high frequency (VHF is the Radio frequency range from 30 MHz to 300 MHz. In a few countries, most notably the United Kingdom, television broadcasting on VHF has been entirely shut down. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Note that the British System A, unlike all the other systems, suppressed the upper sideband rather than the lower—befitting its status as the oldest operating television system to survive into the color era. The 405-line Monochrome analogue Television broadcasting system was the first fully electronic television system to be used in regular broadcasting System A was tested with all three color systems, and production equipment was designed and ready to be built; System A might have survived, as NTSC-A, had the British government not decided to harmonize with the rest of Europe on a 625-line video standard, implemented in Britain as PAL-I on UHF only.
The French System E was a post-war effort to advance France's standing in television technology. Historically the term high-definition television was first used to refer to television standards developed in the 1930s to replace early experimental systems with as few as 12 lines This article is about the country For a topic outline on this subject see List of basic France topics. Its 819 scan lines were almost high definition even by today's standards. Like the British system A, it was VHF only and remained black & white until its shutdown in the 1980s. It was tested with SECAM in the early stages, but later the decision was made to adopt color in 625 lines. Thus France adopted system L on UHF only and abandoned system E.
In some urban areas of Germany, notably in and around Berlin and some other major cities, all analogue TV broadcasting has been shut down in 2003–2005 in favor of reallocating the frequencies to digital broadcasting in the DVB-T standard. Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. Berlin is the capital city and one of sixteen states of Germany. DVB-T is an abbreviation for Digital Video Broadcasting – Terrestrial; it is the DVB European-based consortium standard for the broadcast transmission of See http://www.ueberallfernsehen.de/ for a map of coverage areas and near-future switchovers. Analogue signals are still on air in the non-colored areas of the map. The rest of the country is scheduled to follow suit by 2010. Many other countries are planning a shutdown of analogue broadcasting, and as of 2007 a few smaller countries have already done so. (See "Analogue switch-off" in the digital television article for more information. Digital television (DTV is the sending and receiving of moving images and sound by discrete ( digital) signals in contrast to the analog signals used by Digital television (DTV is the sending and receiving of moving images and sound by discrete ( digital) signals in contrast to the analog signals used by )
A number of experimental and broadcast pre WW2 systems were tested. A number of experimental and broadcast pre World War II Television systems were tested The first ones were mechanical based and of very low resolution, some times with no sound. Latter TV systems were electronic.
On an international conference in Stockholm in 1961, the International Telecommunications Union has defined an identification scheme for broadcast television systems. ('stɔkhɔlm is Sweden 's Capital and its largest City. It is the site of the national Swedish government, the parliament, and the Each monochrome system is assigned a letter designation (A-M); in combination with a color system (NTSC, PAL, SECAM), this completely specifies all of the monaural analogue television systems in the world (for example, PAL-B, NTSC-M, etc).
The following table gives the principal characteristics of each system. Most values are measured in MHz.
|System||Lines||Frame rate||Channel bandwidth (in MHz)||Visual bandwidth (in MHz)||Sound offset||Vestigial sideband||Vision mod. The following tables show the frequencies assigned to broadcast Television channels in various regions of the world along with the ITU letter designator for the system used||Sound mod.|
|(A)||405||25||5||3||−3. The 405-line Monochrome analogue Television broadcasting system was the first fully electronic television system to be used in regular broadcasting The 405-line Monochrome analogue Television broadcasting system was the first fully electronic television system to be used in regular broadcasting 5||0. 75||Pos.||AM|
|B||625||25||7||5||+5. 5||0. 75||Neg.||FM|
|(C)||625||25||7||5||+5. 5||0. 75||Pos.||AM|
|D||625||25||8||6||+6. 5||0. 75||Neg.||FM|
|(E)||819||25||14||10||±11. Historically the term high-definition television was first used to refer to television standards developed in the 1930s to replace early experimental systems with as few as 12 lines Historically the term high-definition television was first used to refer to television standards developed in the 1930s to replace early experimental systems with as few as 12 lines 15||2. 00||Pos.||AM|
|(F)||819||25||7||5||+5. Historically the term high-definition television was first used to refer to television standards developed in the 1930s to replace early experimental systems with as few as 12 lines Historically the term high-definition television was first used to refer to television standards developed in the 1930s to replace early experimental systems with as few as 12 lines 5||0. 75||Pos.||AM|
|G||625||25||8||5||+5. 5||0. 75||Neg.||FM|
|H||625||25||8||5||+5. 5||1. 25||Neg.||FM|
|I||625||25||8||5. 5||+5. 9996||1. 25||Neg.||FM|
|J||525||29. 97||6||4. 2||+4. 5||0. 75||Neg.||FM|
|K||625||25||8||6||+6. 5||0. 75||Neg.||FM|
|K'||625||25||8||6||+6. 5||1. 25||Neg.||FM|
|L||625||25||8||6||+6. 5||1. 25||Pos.||AM|
|M||525||29. 97||6||4. 2||+4. 5||0. 75||Neg.||FM|
|N||625||25||6||4. 2||+4. 5||0. 75||Neg.||FM|
Obsolete TV systems are shown in grey text, with the ITU designation in brackets.
Notes by system:
Converting between different numbers of lines and different frequencies of fields/frames in video pictures is not an easy task. Television standards conversion is the process of changing one type of TV system to another Perhaps the most technically challenging conversion to make is from any of the 625-line, 25-frame/s systems to system M, which has 525 lines at 29. 97 frames per second.
Aside from the line count being different, it's easy to see that generating 60 fields every second from a format that has only 50 fields might pose some interesting problems. Every second, an additional 10 fields must be generated seemingly from nothing. The converter has to create new frames (from the existing input) in real time.
There are several methods used to do this, depending on the desired cost and conversion quality. The simplest possible converters simply drop 100 evenly-spaced lines from every frame, and then duplicate some of those frames to make up the difference in frame rate. More complex systems include inter-field interpolation, adaptive interpolation, and phase correlation.
The situation with worldwide digital television is much simpler by comparison. Most current digital television systems are based on the MPEG-2 multiplexed data stream standard, and use the MPEG-2 video codec. MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information" A codec is a device or program capable of encoding and/or decoding a Digital Data stream or signal. They differ significantly in the details of how the MPEG stream is converted into a broadcast signal, in the video format prior to encoding (or alternately, after decoding), and in the audio format. The Moving Picture Experts Group, commonly referred to as simply MPEG, is a Working group of ISO / IEC charged with the development of video and This has not prevented the creation of an international standard that includes both major systems, even though they are incompatible in almost every respect.
The two principal digital broadcasting systems are ATSC, developed by the Advanced Television Systems Committee and adopted as a standard in the United States and Canada, and DVB-T, the Digital Video Broadcast — Terrestrial system used in most of the rest of the world. The Advanced Television Systems Committee (ATSC is the group established in 1982 that developed the eponymous ATSC Standards for Digital television in the The United States of America —commonly referred to as the Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page DVB-T is an abbreviation for Digital Video Broadcasting – Terrestrial; it is the DVB European-based consortium standard for the broadcast transmission of DVB-T was designed for format compatibility with existing direct broadcast satellite services in Europe (which use the DVB-S standard, and also sees some use in direct-to-home satellite dish providers in North America), and there is also a DVB-C version for cable television. DVB-T is an abbreviation for Digital Video Broadcasting – Terrestrial; it is the DVB European-based consortium standard for the broadcast transmission of Direct broadcast satellite (DBS is a term used to refer to Satellite television broadcasts intended for home reception also referred to more broadly as direct-to-home DVB-S is the original Digital Video Broadcasting forward error coding and modulation standard for Satellite television and dates from 1995 DVB-C stands for Digital Video Broadcasting - Cable and it is the DVB European consortium standard for the broadcast transmission of Digital television While the ATSC standard also includes support for satellite and cable television systems, operators of those systems have chosen other technologies (principally DVB-S for satellite and OpenCable for cable). OpenCable is a set of hardware and software specifications under development in the United States by CableLabs to "define the next-generation digital consumer Japan uses a third system, closely related to DVB-T, called ISDB-T, which is compatible with Brazil's SBTVD. Integrated Services Digital Broadcasting (ISDB is a Japanese standard for Digital television (DTV and Digital radio used by the country's radio |utc_offset = -2 to -4 |time_zone_DST = BRST |utc_offset_DST = -2 to -5 |cctld SBTVD, short for Sistema Brasileiro de Televisão Digital (Brazilian Digital Television System or SBTVD-T (Sistema Brasileiro de Televisão Digital Terrestre The People's Republic of China has developed a fourth system, named DMB-T/H. Talk People's Republic of China) PEOPLE'S REPUBLIC OF CHINA ARTICLE GUIDELINES DMB-T/H or DTMB ( GB 20600-2006 is the Digital terrestrial television standard applied in the People's Republic of China (PRC including
The ATSC system uses a Zenith-developed modulation called 8-VSB; as the name implies, it is a vestigial sideband technique. Zenith Electronics Corporation is a former American manufacturer of Televisions headquartered in Lincolnshire Illinois 8VSB is the 8-level Vestigial sideband modulation method adopted for terrestrial broadcast of the ATSC digital television standard in the United States, Essentially, analogue VSB is to regular amplitude modulation as 8-VSB is to eight-way quadrature amplitude modulation. This system was chosen specifically to provide for maximum spectral compatibility between existing analogue TV and new digital stations in the United States' already-crowded television allocations system. After demodulation and error-correction, the 8-VSB modulation supports a digital data stream of about 19. 2 Mbit/s, enough for one high-definition video stream or several "standard-definition" services.
DMB-T/H is the digital television broadcasting standard of the People's Republic of China (including Hong Kong). DMB-T/H or DTMB ( GB 20600-2006 is the Digital terrestrial television standard applied in the People's Republic of China (PRC including Talk People's Republic of China) PEOPLE'S REPUBLIC OF CHINA ARTICLE GUIDELINES Hong Kong ( officially the Hong Kong Special Administrative Region, is a territory located on China 's south coast on the Pearl River Delta, and borders
DVB-T uses coded orthogonal frequency division multiplexing (COFDM), which uses as many as 8000 independent carriers, each transmitting data at a comparatively low rate. DVB-T is an abbreviation for Digital Video Broadcasting – Terrestrial; it is the DVB European-based consortium standard for the broadcast transmission of Orthogonal frequency-division multiplexing ( OFDM) — essentially identical to Coded OFDM ( COFDM) and Discrete multi-tone modulation ( This system was designed to provide superior immunity from multipath interference, and has a choice of system variants which allow data rates from 4 MBit/s up to 24 MBit/s. Multipath Interference is a phenomenon in the physics of Waves whereby a wave from a source travels to a detector via two or more paths and under the right condition One U. S. broadcaster, Sinclair Broadcasting, petitioned the Federal Communications Commission to permit the use of COFDM instead of 8-VSB, on the theory that this would improve prospects for digital TV reception by households without outside antennas (a majority in the U. The Sinclair Broadcast Group ( SBG) is the operator of the largest number of local Television stations in the United States with a total of 57 stations S. ), but this request was denied. (However, one U. S. digital station, WNYE-DT in New York, was temporarily converted to COFDM modulation on an emergency basis for datacasting information to emergency services personnel in lower Manhattan in the aftermath of the September 11 terrorist attacks. The City of New York Datacasting (data broadcasting is the Broadcasting of Data over a wide area via Radio waves It most often refers to supplemental Information Manhattan Island, in New York Harbor, is much the largest part of the Borough of Manhattan, one of the Five Boroughs which form the City of New York )
DVB-S is the original Digital Video Broadcasting forward error coding and modulation standard for satellite television and dates from 1995. For the chemical compound see Divinylbenzene. Digital Video Broadcasting ( DVB) is a suite of internationally accepted Satellite television is Television delivered by the means of Communications satellites as compared to conventional Terrestrial television and Cable It is used via satellites serving every continent of the world, this is even true in North America. DVB-S is used in both MCPC and SCPC modes for broadcast network feeds, as well as for direct broadcast satellite services like Sky Digital (UK & Ireland) via Astra in Europe, Dish Network in the U.S., and Bell ExpressVu in Canada. For multiplexing in electronics and signal processing see Multiplexer. Single channel per carrier ( SCPC) refers to using a single signal at a given Frequency and bandwidth. A broadcast network is an Organization, such as a Corporation or other association, that provides live or Recorded content such as Direct broadcast satellite (DBS is a term used to refer to Satellite television broadcasts intended for home reception also referred to more broadly as direct-to-home Sky Digital is the brand name for British Sky Broadcasting 's digital Satellite television service transmitted from SES Astra satellites located at 28 SES Astra SA, is a corporate Subsidiary of SES, based in Betzdorf, in eastern Luxembourg, that owns and operates the Astra Not be confused with Indian Service Dish TV DISH Network is a Direct broadcast satellite (DBS service that provides Satellite television The United States of America —commonly referred to as the Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page The transport stream delivered by DVB-S is mandated as MPEG-2. Transport stream ( TS, TP, MPEG-TS, or M2T) is a Communications protocol for audio, video, and data
DVB-C stands for Digital Video Broadcasting - Cable and it is the DVB European consortium standard for the broadcast transmission of digital television over cable. Digital television (DTV is the sending and receiving of moving images and sound by discrete ( digital) signals in contrast to the analog signals used by Coaxial cable is a cable consisting of an inner conductor surrounded by a tubular insulating layer typically made from a flexible material with a high Dielectric constant, all This system transmits an MPEG-2 family digital audio/video stream, using a QAM modulation with channel coding. MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information" In Computer science, a channel code is a broadly used term mostly referring to the Forward error correction code and Bit interleaving in communication and
The ISDB system differ mainly in the modulations used, due to the requirements of different frequency bands. Integrated Services Digital Broadcasting (ISDB is a Japanese standard for Digital television (DTV and Digital radio used by the country's radio The 12 GHz band ISDB-S uses PSK modulation, 2. 6 GHz band digital sound broadcasting uses CDM and ISDB-T (in VHF and/or UHF band) uses COFDM with PSK/QAM. It is used mainly in Japan.
Transmission technology standards
Defunct analogue systems
Analogue television systems
Analogue television system audio
Digital television systems