Broadcast television system
Encyclopedia
Broadcast television systems are encoding or formatting standards for the transmission and reception of terrestrial television
signals. There are three main analog television
systems in current use around the world: NTSC
, PAL
, and SECAM
. These systems have several components, including a set of technical parameters for the broadcasting
signal, a encoder
system for encoding color, and possibly a system for encoding multichannel television sound
(MTS).
In digital television
(DTV), all of these elements are combined in a single digital transmission system.
systems. Each country, faced with local political, technical, and economic issues, adopted a color television
system which was grafted onto an existing monochrome
system, using gaps in the video spectrum (explained below) to allow color transmission information to fit in the existing channels allotted. The grafting of the color transmission standards onto existing monochrome systems permitted existing monochrome television receivers predating the change over to color television to continue to be operate as monochrome television. Because of this compatibility requirement, color standards added a second signal to the basic monochrome signal, which carries the color information. The color information is called chrominance
or C for short, while the black and white information is called the luminance or Y for short. Monochrome television receivers only display the luminance, while color receivers process both signals. Though in theory any monochrome system could be adopted to a color system, 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 now use one of three color systems: NTSC
, PAL
, or SECAM
.
at which the electricity distribution
system operates, to avoid flicker resulting from the beat
between the television screen deflection system and nearby mains generated magnetic fields. All digital, or "fixed pixel", displays have progressive scan
ning and must deinterlace an interlaced source. Use of inexpensive deinterlacing hardware is a typical difference between lower- vs. higher-priced flat panel display
s (Plasma display
, LCD, etc.).
All film
s and other filmed material shot at 24 frames per second must be transferred to video frame rate
s using a telecine
in order to prevent severe motion jitter effects. Typically, for 25 frame/s formats (European among other countries with 50 Hz mains supply), the content is PAL speedup, while a technique known as "3:2 pulldown" is used for 30 frame/s formats (North America among other countries with 60 Hz mains supply) to match the film frame rate to the video frame rate without speeding up the play back.
(CRT), and so the physics of these devices necessarily controls the format of the video signal. The image on a CRT is painted by a moving beam of electrons which hits a phosphor
coating on the front of the tube. This electron beam is steered by a magnetic field generated by powerful electromagnet
s close to the source of the electron beam.
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.
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 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.
and closed captioning
:
, the maximum luminance value is represented by zero carrier power. All newer analog video systems use negative modulation with the exception of the French System L.
Impulsive noise, especially from older automotive ignition systems, caused white spots to appear on the screens of television receivers using positive modulation but they could use simple synchronization circuits. Impulsive noise in negative modulation systems appears as dark spots that are less visible, but picture synchronization was seriously degraded when using simple synchronization. The synchronization problem was overcome with the invention of phase-locked synchronization circuits. When these first appeared in Britain in the early 1950s one name used to describe them was "flywheel synchronisation".
Older televisions for positive modulation systems were sometimes equipped with a peak video signal inverter that would turn the white interference spots dark. This was usually user-adjustable with a control on the rear of the television labelled "White Spot Limiter" in Britain or "Antiparasite" in France. If adjusted incorrectly it would turn bright white picture content dark. Most of the positive modulation television systems ceased operation by the mid 1980s. The French System L continued on up to the transition to digital broadcasting. Positive modulation was one of several unique technical features that originally protected the French electronics and broadcasting industry from foreign competition and rendered French TV sets incapable of receiving broadcasts from neighboring countries.
Another advantage of negative modulation is that, since the synchronizing pulses represent maximum carrier power, it is relatively easy to arrange the receiver Automatic Gain Control
to only operate during sync pulses and thus get a constant amplitude video signal to drive the rest of the TV set. This was not possible for many years with positive modulation as the peak carrier power varied depending on picture content. Modern digital processing circuits have achieved a similar effect but using the front porch of the video signal.
which can be modulated onto a radio-frequency carrier and transmitted through an antenna. All analog television systems use vestigial sideband modulation, a form of amplitude modulation
in which one sideband is partially removed. This reduces the bandwidth of the transmitted signal, enabling narrower channels to be used.
is used for the standard monaural
audio; systems with positive video use AM sound and intercarrier receiver technology can not be incorporated. 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 into the FM audio carrier. All three systems are compatible with monaural FM audio, but only NICAM
may be used with the French AM audio systems.
than they do on the VHF bands. In a few countries, most notably the United Kingdom
, television broadcasting on VHF has been entirely shut down. Note that the British 405-line
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 (although was never officially broadcast with color encoding). 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 819 line system E was a post-war effort to advance France
's standing in television technology. Its 819-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 1984 in France and 1985 in Monaco. 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 many parts of the world, analog television broadcasting has been shut down completely, or restricted only to low-power relay transmitters; see Digital television transition
for a timeline of the analog shutdown.
in 1961, the International Telecommunications Union has defined an identification scheme for broadcast television systems. 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 analog television systems in the world (for example, PAL-B, NTSC-M, etc.).
The following table gives the principal characteristics of each system. Defunct TV systems are shown in grey text, previous ones never designated by ITU are not yet shown. Except for lines
and frame rate
s, other units are megahertz (MHz).
.
Therefore there has to be a straightforward mathematical relationship between the line and field frequencies, the latter being derived by dividing down from the former. Technology constraints of the 1930s meant that this division process could only be done using small integers, preferably no greater than 7, for good stability. The number of lines was odd because of 2:1 interlace. The 405 line system used a vertical frequency of 50 Hz
(Standard AC mains supply frequency in Britain) and a horizontal one of 10,125 Hz (50 × 405 ÷ 2)
Notes
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. Historically this required a frame store to hold those parts of the picture not actually being output (since the scanning of any point was not time coincident). In more recent times, conversion of standards is a relatively easy task for a computer.
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 conversion 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 every 5th line from every frame (when converting from 625 to 525) or duplicate every 4th line (when converting from 525 to 625), and then duplicate or drop some of those frames to make up the difference in frame rate. More complex systems include inter-field interpolation, adaptive interpolation, and phase correlation.
video codec
. They differ significantly in the details of how the transport stream is converted into a broadcast signal, in the video format prior to encoding (or alternatively, after decoding), and in the audio format. 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 Standards, 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. 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. While the ATSC standard also includes support for satellite and cable television systems, operators of those systems have chosen other technologies (principally DVB-S or proprietary systems for satellite and 256QAM replacing VSB for cable). Japan uses a third system, closely related to DVB-T, called ISDB-T, which is compatible with Brazil
's SBTVD
. The People's Republic of China
has developed a fourth system, named DMB-T/H
.
. This system was chosen specifically to provide for maximum spectral compatibility between existing analog TV and new digital stations in the United States' already-crowded television allocations system, although it is inferior to the other digital systems in dealing with multipath interference
; however, it is better at dealing with impulse noise
which is especially present on the VHF bands that other countries have discontinued from TV use, but are still used in the U.S. There is also no hierarchical modulation
. After demodulation and error-correction, the 8-VSB modulation supports a digital data stream of about 19.39 Mbit/s, enough for one high-definition video stream or several standard-definition services. See Digital subchannel#Technical considerations for more information.
On cable, ATSC usually uses 256QAM, although some use 16VSB
. Both of these double the throughput
to 38.78 Mbit/s within the same 6 MHz bandwidth. ATSC is also used over satellite. While these are logically called ATSC-C and ATSC-S, these terms were never officially defined. ATSC was never designed for mobile use, but the ATSC group is currently considering how this can be done through its ATSC-M/H
.
, Hong Kong
and Macau
. This is a fusion system, which is a compromise of different competing proposing standards from different Chinese Universities, which incorporates elements from DVB-T
, ADTB-T and TiMi 3.
, and has a choice of system variants which allow data rates from 4 MBit/s up to 24 MBit/s. 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.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
).
DVB-S is the original Digital Video Broadcasting forward error coding and modulation standard for satellite television
and dates from 1995. 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 TV in Canada
. The MPEG transport stream delivered by DVB-S is mandated as MPEG-2.
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
. This system transmits an MPEG-2
family digital audio/video stream, using a QAM modulation with channel coding
.
, or for the 1seg
(ISDB-H) service. Like the other DTV systems, the ISDB types differ mainly in the modulations used, due to the requirements of different frequency bands. 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 was developed in Japan with MPEG-2, and is now used in Brazil with MPEG-4. Unlike other digital broadcast systems, ISDB includes digital rights management
to restrict recording of programming.
Transmission technology standards
Defunct analog systems
Analog television systems
Analog television system audio
Digital television systems
History
Terrestrial television
Terrestrial television is a mode of television broadcasting which does not involve satellite transmission or cables — typically using radio waves through transmitting and receiving antennas or television antenna aerials...
signals. There are three main analog television
Analog television
Analog television is the analog transmission that involves the broadcasting of encoded analog audio and analog video signal: one in which the message conveyed by the broadcast signal is a function of deliberate variations in the amplitude and/or frequency of the signal...
systems in current use around the world: NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
, PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
, and SECAM
SECAM
SECAM, also written SÉCAM , is an analog color television system first used in France....
. These systems have several components, including a set of technical parameters for the broadcasting
Broadcasting
Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...
signal, a encoder
Encoder
An encoder is a device, circuit, transducer, software program, algorithm or person that converts information from one format or code to another, for the purposes of standardization, speed, secrecy, security, or saving space by shrinking size.-Media:...
system for encoding color, and possibly a system for encoding multichannel television sound
Multichannel television sound
Multichannel television sound, better known as MTS , is the method of encoding three additional channels of audio into an NTSC-format audio carrier.- History :...
(MTS).
In digital television
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
(DTV), all of these elements are combined in a single digital transmission system.
Analog television systems
All but one analog television system began as black-and-whiteBlack-and-white
Black-and-white, often abbreviated B/W or B&W, is a term referring to a number of monochrome forms in visual arts.Black-and-white as a description is also something of a misnomer, for in addition to black and white, most of these media included varying shades of gray...
systems. Each country, faced with local political, technical, and economic issues, adopted a color television
Color television
Color television is part of the history of television, the technology of television and practices associated with television's transmission of moving images in color video....
system which was grafted onto an existing monochrome
Monochrome
Monochrome describes paintings, drawings, design, or photographs in one color or shades of one color. A monochromatic object or image has colors in shades of limited colors or hues. Images using only shades of grey are called grayscale or black-and-white...
system, using gaps in the video spectrum (explained below) to allow color transmission information to fit in the existing channels allotted. The grafting of the color transmission standards onto existing monochrome systems permitted existing monochrome television receivers predating the change over to color television to continue to be operate as monochrome television. Because of this compatibility requirement, color standards added a second signal to the basic monochrome signal, which carries the color information. The color information is called chrominance
Chrominance
Chrominance is the signal used in video systems to convey the color information of the picture, separately from the accompanying luma signal . Chrominance is usually represented as two color-difference components: U = B' − Y' and V = R' − Y'...
or C for short, while the black and white information is called the luminance or Y for short. Monochrome television receivers only display the luminance, while color receivers process both signals. Though in theory any monochrome system could be adopted to a color system, 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 now use one of three color systems: NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
, PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
, or SECAM
SECAM
SECAM, also written SÉCAM , is an analog color television system first used in France....
.
Frames
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. 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 current analog television systems are interlaced; alternate rows of the frame are transmitted in sequence, followed by the remaining rows in their sequence. Each half of the frame is called a video field, and the rate at which fields are transmitted is one of the fundamental parameters of a video system. It is related to the utility frequencyUtility frequency
The utility frequency, line frequency or mains frequency is the frequency at which alternating current is transmitted from a power plant to the end-user. In most parts of the world this is 50 Hz, although in the Americas it is typically 60 Hz...
at which the electricity distribution
Electricity distribution
File:Electricity grid simple- North America.svg|thumb|380px|right|Simplified diagram of AC electricity distribution from generation stations to consumers...
system operates, to avoid flicker resulting from the beat
Beat (acoustics)
In acoustics, a beat is an interference between two sounds of slightly different frequencies, perceived as periodic variations in volume whose rate is the difference between the two frequencies....
between the television screen deflection system and nearby mains generated magnetic fields. All digital, or "fixed pixel", displays have progressive scan
Progressive scan
Progressive scanning is a way of displaying, storing, or transmitting moving images in which all the lines of each frame are drawn in sequence...
ning and must deinterlace an interlaced source. Use of inexpensive deinterlacing hardware is a typical difference between lower- vs. higher-priced flat panel display
Flat panel display
Flat panel displays encompass a growing number of electronic visual display technologies. They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes , and are usually less than thick...
s (Plasma display
Plasma display
A plasma display panel is a type of flat panel display common to large TV displays or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent...
, LCD, etc.).
All film
Film
A film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...
s and other filmed material shot at 24 frames per second must be transferred to video frame rate
Frame rate
Frame rate is the frequency at which an imaging device produces unique consecutive images called frames. The term applies equally well to computer graphics, video cameras, film cameras, and motion capture systems...
s using a telecine
Telecine
Telecine is transferring motion picture film into video and is performed in a color suite. The term is also used to refer to the equipment used in the post-production process....
in order to prevent severe motion jitter effects. Typically, for 25 frame/s formats (European among other countries with 50 Hz mains supply), the content is PAL speedup, while a technique known as "3:2 pulldown" is used for 30 frame/s formats (North America among other countries with 60 Hz mains supply) to match the film frame rate to the video frame rate without speeding up the play back.
Viewing technology
Analog television signal standards are designed to be displayed on a cathode ray tubeCathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
(CRT), and so the physics of these devices necessarily controls the format of the video signal. The image on a CRT is painted by a moving beam of electrons which hits a phosphor
Phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
coating on the front of the tube. This electron beam is steered by a magnetic field generated by powerful electromagnet
Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...
s close to the source of the electron beam.
In order to reorient this magnetic steering mechanism, a certain amount of time is required due to the inductance
Inductance
In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...
of the magnets; the greater the change, the greater the time it takes for the electron beam to settle in the new spot.
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
Vertical blanking interval
The vertical blanking interval , also known as the vertical interval or VBLANK, is the time difference between the last line of one frame or field of a raster display, and the beginning of the first line of the next frame. It is present in analog television, VGA, DVI and other signals. During the...
). 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
Frequency spectrum
The frequency spectrum of a time-domain signal is a representation of that signal in the frequency domain. The frequency spectrum can be generated via a Fourier transform of the signal, and the resulting values are usually presented as amplitude and phase, both plotted versus frequency.Any signal...
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.
Hidden signalling
Broadcasters later developed mechanisms to transmit digital information on the phantom lines, used mostly for teletextTeletext
Teletext is a television information retrieval service developed in the United Kingdom in the early 1970s. It offers a range of text-based information, typically including national, international and sporting news, weather and TV schedules...
and closed captioning
Closed captioning
Closed captioning is the process of displaying text on a television, video screen or other visual display to provide additional or interpretive information to individuals who wish to access it...
:
- PAL-PlusPALplusPALplus is an extension of the PAL analogue broadcasting system for transmitting 16:9 programs without sacrificing vertical resolution. It followed experiences with the HD-MAC and D2-MAC, standards that were incompatible with existing receivers but featured a 16:9 aspect ratio...
uses a hidden signallingWidescreen signalingIn television technology, widescreen signaling is a digital stream embedded in the TV signal describing qualities of the broadcast, in particular the intended aspect ratio of the image...
scheme to indicate if it exists, and if so what operational mode it is in. - NTSCNTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
has been modified by the Advanced Television Standards CommitteeATSCATSC standards are a set of standards developed by the Advanced Television Systems Committee for digital television transmission over terrestrial, cable, and satellite networks....
to support an anti-ghosting signalGhost-canceling referenceGhost-canceling reference, or GCR, is a special sub-signal on a television channel that receivers can use to attenuate the ghosting effect of a television signal split into multiple paths between transmitter and receiver....
that is inserted on a non-visible scan line. - TeletextTeletextTeletext is a television information retrieval service developed in the United Kingdom in the early 1970s. It offers a range of text-based information, typically including national, international and sporting news, weather and TV schedules...
uses hidden signalling to transmit information pages. - NTSCNTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
Closed CaptioningClosed captioningClosed captioning is the process of displaying text on a television, video screen or other visual display to provide additional or interpretive information to individuals who wish to access it...
signalling uses signalling that is nearly identical to teletextTeletextTeletext is a television information retrieval service developed in the United Kingdom in the early 1970s. It offers a range of text-based information, typically including national, international and sporting news, weather and TV schedules...
signalling. - WidescreenWidescreenWidescreen images are a variety of aspect ratios used in film, television and computer screens. In film, a widescreen film is any film image with a width-to-height aspect ratio greater than the standard 1.37:1 Academy aspect ratio provided by 35mm film....
All 625 line systems incorporate pulses on line 23 that flag to the display that a 16:9 widescreen image is being broadcast, though this option is not currently used on analog transmissions.
Overscan
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.Interlacing
In a purely analog system, field order is merely a matter of convention. For digitally recorded material it becomes necessary to rearrange the field order when conversion takes place from one standard to another.Image polarity
Another parameter of analog television systems, minor by comparison, is the choice of whether vision modulation is positive or negative. Some of the earliest electronic television systems such as the British 405-line (system A) used positive modulation. It was also used in the two Belgian systems (system C, 625 lines, and System F, 819 lines) and the two French systems (system E, 819 lines, and system L, 625 lines). In positive modulation systems, the maximum luminance value is represented by the maximum carrier power; in negative modulationModulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
, the maximum luminance value is represented by zero carrier power. All newer analog video systems use negative modulation with the exception of the French System L.
Impulsive noise, especially from older automotive ignition systems, caused white spots to appear on the screens of television receivers using positive modulation but they could use simple synchronization circuits. Impulsive noise in negative modulation systems appears as dark spots that are less visible, but picture synchronization was seriously degraded when using simple synchronization. The synchronization problem was overcome with the invention of phase-locked synchronization circuits. When these first appeared in Britain in the early 1950s one name used to describe them was "flywheel synchronisation".
Older televisions for positive modulation systems were sometimes equipped with a peak video signal inverter that would turn the white interference spots dark. This was usually user-adjustable with a control on the rear of the television labelled "White Spot Limiter" in Britain or "Antiparasite" in France. If adjusted incorrectly it would turn bright white picture content dark. Most of the positive modulation television systems ceased operation by the mid 1980s. The French System L continued on up to the transition to digital broadcasting. Positive modulation was one of several unique technical features that originally protected the French electronics and broadcasting industry from foreign competition and rendered French TV sets incapable of receiving broadcasts from neighboring countries.
Another advantage of negative modulation is that, since the synchronizing pulses represent maximum carrier power, it is relatively easy to arrange the receiver Automatic Gain Control
Automatic gain control
Automatic gain control is an adaptive system found in many electronic devices. The average output signal level is fed back to adjust the gain to an appropriate level for a range of input signal levels...
to only operate during sync pulses and thus get a constant amplitude video signal to drive the rest of the TV set. This was not possible for many years with positive modulation as the peak carrier power varied depending on picture content. Modern digital processing circuits have achieved a similar effect but using the front porch of the video signal.
Modulation
Given all of these parameters, the result is a mostly-continuous analog signalAnalog signal
An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
which can be modulated onto a radio-frequency carrier and transmitted through an antenna. All analog television systems use vestigial sideband modulation, a form of amplitude modulation
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
in which one sideband is partially removed. This reduces the bandwidth of the transmitted signal, enabling narrower channels to be used.
Audio
In analog television, the analog audio 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 all cases where negative video is used, FMFrequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
is used for the standard monaural
Monaural
Monaural or monophonic sound reproduction is single-channel. Typically there is only one microphone, one loudspeaker, or channels are fed from a common signal path...
audio; systems with positive video use AM sound and intercarrier receiver technology can not be incorporated. 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
NICAM
Near Instantaneous Companded Audio Multiplex is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks...
, which uses a digital audio encoding; double-FM (known under a variety of names, notably Zweikanalton
Zweikanalton
Zweikanalton is a television sound transmission system used in Germany, Austria, Switzerland, and other countries that use or used PAL-B or PAL-G...
, 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
Multichannel television sound
Multichannel television sound, better known as MTS , is the method of encoding three additional channels of audio into an NTSC-format audio carrier.- History :...
), which multiplexes additional audio channels into the FM audio carrier. All three systems are compatible with monaural FM audio, but only NICAM
NICAM
Near Instantaneous Companded Audio Multiplex is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks...
may be used with the French AM audio systems.
Evolution
For historical reasons, some countries use a different video system on UHFUltra high frequency
Ultra-High Frequency designates the ITU Radio frequency range of electromagnetic waves between 300 MHz and 3 GHz , also known as the decimetre band or decimetre wave as the wavelengths range from one to ten decimetres...
than they do on the VHF bands. In a few countries, most notably the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, television broadcasting on VHF has been entirely shut down. Note that the British 405-line
405-line
The 405-line monochrome analogue television broadcasting system was the first fully electronic television system to be used in regular broadcasting....
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 (although was never officially broadcast with color encoding). 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 819 line system E was a post-war effort to advance France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
's standing in television technology. Its 819-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 1984 in France and 1985 in Monaco. 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 many parts of the world, analog television broadcasting has been shut down completely, or restricted only to low-power relay transmitters; see Digital television transition
Digital television transition
The digital television transition is the process in which analog television broadcasting is converted to and replaced by digital television. This primarily involves both TV stations and over-the-air viewers; however it also involves content providers like TV networks, and cable television...
for a timeline of the analog shutdown.
Pre–World War II systems
A number of experimental and broadcast pre WW2 systems were tested. The first ones were mechanically based and of very low resolution, sometimes with no sound. Later TV systems were electronic.- The UK 405 line system was the first to have an allocated ITU System Letter Designation.
ITU identification scheme
On an international conference in StockholmStockholm
Stockholm is the capital and the largest city of Sweden and constitutes the most populated urban area in Scandinavia. Stockholm is the most populous city in Sweden, with a population of 851,155 in the municipality , 1.37 million in the urban area , and around 2.1 million in the metropolitan area...
in 1961, the International Telecommunications Union has defined an identification scheme for broadcast television systems. 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 analog television systems in the world (for example, PAL-B, NTSC-M, etc.).
The following table gives the principal characteristics of each system. Defunct TV systems are shown in grey text, previous ones never designated by ITU are not yet shown. Except for lines
Display resolution
The display resolution of a digital television or display device is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resolution is controlled by all different factors in cathode ray tube , flat panel or projection...
and frame rate
Frame rate
Frame rate is the frequency at which an imaging device produces unique consecutive images called frames. The term applies equally well to computer graphics, video cameras, film cameras, and motion capture systems...
s, other units are megahertz (MHz).
- Also see: television channel frequenciesTelevision channel frequenciesThe 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. The frequencies shown are for the video and audio carriers. The channel itself occupies several megahertz of bandwidth....
| System | Introduced | Lines | Frame rate | Channel bandwidth | Video bandwidth | Audio offset | Vestigial sideband | Video mod. | Sound mod. | Usual color |
|---|---|---|---|---|---|---|---|---|---|---|
| A | 1936 | 405 | 25 | 5 | 3 | −3.5 | 0.75 | pos. | AM | none |
| B | 1950 | 625 | 25 | 7 | 5 | +5.5 | 0.75 | neg. | FM | PAL/SECAM |
| C | 1953 | 625 | 25 | 7 | 5 | +5.5 | 0.75 | pos. | AM | none |
| D | 1948 | 625 | 25 | 8 | 6 | +6.5 | 0.75 | neg. | FM | SECAM/PAL |
| E | 1949 | 819 | 25 | 14 | 10 | ±11.15 | 2.00 | pos. | AM | none |
| F | 819 | 25 | 7 | 5 | +5.5 | 0.75 | pos. | AM | none | |
| G | 625 | 25 | 7 | 5 | +5.5 | 0.75 | neg. | FM | PAL/SECAM | |
| H | 625 | 25 | 8 | 5 | +5.5 | 1.25 | neg. | FM | PAL | |
| I | 1962 | 625 | 25 | 8 | 5.5 | +5.9996 | 1.25 | neg. | FM | PAL |
| J | 1953 | 525 | 30 | 6 | 4.2 | +4.5 | 0.75 | neg. | FM | NTSC |
| K | 625 | 25 | 8 | 6 | +6.5 | 0.75 | neg. | FM | SECAM/PAL | |
| K' | 625 | 25 | 8 | 6 | +6.5 | 1.25 | neg. | FM | SECAM | |
| L | 625 | 25 | 8 | 6 | -6.5 | 1.25 | pos. | AM | SECAM | |
| M | 1941 | 525 | 30 | 6 | 4.2 | +4.5 | 0.75 | neg. | FM | NTSC/PAL** |
| N | 1951 | 625 | 25 | 6 | 4.2 | +4.5 | 0.75 | neg. | FM | PAL |
Line count
As interlaced systems require accurate positioning of scanning lines, it is important to make sure that the horizontal and vertical timebase are in a precise ratio. This is accomplished by passing the one through a series of electronic divider circuits to produce the other. Each division is by a prime numberPrime number
A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. A natural number greater than 1 that is not a prime number is called a composite number. For example 5 is prime, as only 1 and 5 divide it, whereas 6 is composite, since it has the divisors 2...
.
Therefore there has to be a straightforward mathematical relationship between the line and field frequencies, the latter being derived by dividing down from the former. Technology constraints of the 1930s meant that this division process could only be done using small integers, preferably no greater than 7, for good stability. The number of lines was odd because of 2:1 interlace. The 405 line system used a vertical frequency of 50 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
(Standard AC mains supply frequency in Britain) and a horizontal one of 10,125 Hz (50 × 405 ÷ 2)
- 2 × 3 × 3 × 5 gives 90-lines (non interlaced)
- 2 × 2 × 2 × 2 × 2 × 3 gives 96-lines (non interlaced)
- 2 × 2 × 3 × 3 × 5 gives 180 lines180 lines180 lines is an early electronic television system. It was used in Germany after on March 22, 1935, using telecine transmission of film, intermediate film system, or cameras using the Nipkow disk...
(non interlaced) (used in Germany in mid-1930s before switch to 441-line system) - 2 × 2 × 2 × 2 × 3 × 5 gives 240-lines (used for the experimental BairdJohn Logie BairdJohn Logie Baird FRSE was a Scottish engineer and inventor of the world's first practical, publicly demonstrated television system, and also the world's first fully electronic colour television tube...
transmissions in Britain [See Note 1]) - 3 × 3 × 3 × 3 × 3 gives 243-lines
- 7 × 7 × 7 gives 343-lines (early North American system also used in Poland and in Soviet Union before WW2)
- 3 × 5 × 5 × 5 gives 375-lines
- 3 × 3 × 3 × 3 × 5 gives 405 lines (used in Britain, Ireland and Hong Kong before 1985)
- 2 × 2 × 2 × 5 × 11 gives 440-lines (non interlaced)
- 3 × 3 × 7 × 7 gives 441 lines441 lines441 lines, or 383i if named using modern standard, is an early electronic television system. It was used with 50 interlaced frames per second in France and Germany, where it was an improvement over the previous 180 lines system...
(used by RCARCARCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
in North America before the 525-lines NTSCNTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
standard was adopted and widely used before WW2 in Continental Europe with different frame rates) - 2 × 3 × 3 × 5 × 5 gives 450-lines (non interlaced)
- 5 × 7 × 13 gives 455-lines (used in France before WW2)
- 3 × 5 × 5 × 7 gives 525-lines System MSystem MSystem M, sometimes called 525 line, is the analog broadcast television system used in the United States since July 1, 1941, and also in most of the Americas and Caribbean, South Korea, and Taiwan. In addition, Japan uses System J, which is nearly identical to System M. The systems were given...
(a compromise between the RCA and Philco systems. Still used today in most of the Americas and parts of Asia) - 3 × 3 × 3 × 3 × 7 produces 567 line television567 Line televisionAn experimental broadcast, and a proposal by Philips of Holland, was a 567 line televisionsystem for Europe, running at 50 fields per second.Most of the technology was to be borrowed from NTSC, the difference from NTSC being the...
(used for a while after WW2 in the Netherlands) - 5 × 11 × 11 gives 605-lines (proposed by PhilcoPhilcoPhilco, the Philadelphia Storage Battery Company , was a pioneer in early battery, radio, and television production as well as former employer of Philo Farnsworth, inventor of cathode ray tube television...
in North America before the 525 standard was adopted) - 5 × 5 × 5 × 5 gives 625 (576i576i576i is a standard-definition video mode used in PAL and SECAM countries. In digital applications it is usually referred to as "576i", in analogue contexts it is often quoted as "625 lines"...
)-lines (developed independently by German http://www.bvws.org.uk/405alive/faq/405_hist.html http://www.vintage-radio.net/forum/showthread.php?t=36027 and Soviet engineers during the mid-late 1940s. Still used today in most parts of the world) - 2 × 3 × 5 × 5 × 5 gives 750-lines at 50 frames (used for 720p/50720p720p is the shorthand name for 1280x720, a category of High-definition television video modes having a resolution of 1080 or 720p and a progressive scan...
[See Note 2]) - 2 × 2 × 2 × 2 × 3 × 3 × 5 gives 750-lines at 60 frames (used for 720p/60 [See Note 2])
- 3 × 3 × 7 × 13 gives 819-lines (737i) (used in France in the 1950s)
- 3 × 7 × 7 × 7 gives 1029-lines (proposed but never adopted around 1948 in France)
- 3 × 3 × 5 × 5 x 5 gives 1125-lines at 25 frames (used for 1080i25 but not 1080p25 [See Note 2])
- 3 × 3 × 5 × 5 x 5 gives 1125-lines at 30 frames (used for 1080i30 but not 1080p30 [See Note 2])
Notes
- The division of the 240-line system is academic as the scan ratio was determined entirely by the construction of the mechanical scanning system used with the cameras used with this transmission system.
- The division ratio though relevant to RT] based systems is largely academic today because modern LCD and plasma displayPlasma displayA plasma display panel is a type of flat panel display common to large TV displays or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent...
s are not constrained to having the scanning in precise ratios. The 1080p high definition system requires 1126-lines in a CRT display.
Converting from one TV system to another
Converting between different numbers of lines and different frequencies of fields/frames in video pictures is not an easy task.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. Historically this required a frame store to hold those parts of the picture not actually being output (since the scanning of any point was not time coincident). In more recent times, conversion of standards is a relatively easy task for a computer.
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 conversion 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 every 5th line from every frame (when converting from 625 to 525) or duplicate every 4th line (when converting from 525 to 625), and then duplicate or drop some of those frames to make up the difference in frame rate. More complex systems include inter-field interpolation, adaptive interpolation, and phase correlation.
Digital television systems
The situation with worldwide digital television is much simpler by comparison. Most current digital television systems are based on the MPEG transport stream standard, and use the H.262/MPEG-2 Part 2H.262/MPEG-2 Part 2
H.262 or MPEG-2 Part 2 is a digital video compression and encoding standard developed and maintained jointly by ITU-T Video Coding Experts Group and ISO/IEC Moving Picture Experts Group . It is the second part of the ISO/IEC MPEG-2 standard...
video codec
Codec
A codec is a device or computer program capable of encoding or decoding a digital data stream or signal. The word codec is a portmanteau of "compressor-decompressor" or, more commonly, "coder-decoder"...
. They differ significantly in the details of how the transport stream is converted into a broadcast signal, in the video format prior to encoding (or alternatively, after decoding), and in the audio format. 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 Standards, developed by the Advanced Television Systems Committee
Advanced Television Systems Committee
The Advanced Television Systems Committee is the group, established in 1982, that developed the eponymous ATSC Standards for digital television in the United States, also adopted by Canada, Mexico, South Korea, and recently Honduras and is being considered by other countries.-See also:*ATSC...
and adopted as a standard in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, and DVB-T
DVB-T
DVB-T is an abbreviation for Digital Video Broadcasting — Terrestrial; it is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in the UK in 1998...
, the Digital Video Broadcast – Terrestrial system used in most of the rest of the world. DVB-T
DVB-T
DVB-T is an abbreviation for Digital Video Broadcasting — Terrestrial; it is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in the UK in 1998...
was designed for format compatibility with existing direct broadcast satellite
Direct broadcast satellite
Direct broadcast satellite is a term used to refer to satellite television broadcasts intended for home reception.A designation broader than DBS would be direct-to-home signals, or DTH. This has initially distinguished the transmissions directly intended for home viewers from cable television...
services in Europe (which use the DVB-S
DVB-S
DVB-S is an abbreviation for Digital Video Broadcasting — Satellite; it is the original Digital Video Broadcasting forward error coding and demodulation standard for satellite television and dates from 1994, in its first release, while development lasted from 1993 to 1997...
standard, and also sees some use in direct-to-home satellite dish providers in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
), and there is also a DVB-C
DVB-C
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...
version for cable 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 or proprietary systems for satellite and 256QAM replacing VSB for cable). Japan uses a third system, closely related to DVB-T, called ISDB-T, which is compatible with Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
's SBTVD
SBTVD
ISDB-T International or SBTVD, short for Sistema Brasileiro de Televisão Digital is a technical standard for digital television broadcast used in Brazil, Peru, Argentina, Chile, Venezuela, Ecuador, Costa Rica, Paraguay, Philippines, Bolivia, Nicaragua and Uruguay, based on the Japanese ISDB-T...
. The People's Republic of China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
has developed a fourth system, named DMB-T/H
DMB-T/H
DTMB is the TV standard for mobile and fixed terminals used in the People's Republic of China, Hong Kong and Macau. Although at first this standard was called DMB-T/H , the official name is DTMB.DTT broadcasting systems...
.
ATSC
The terrestrial ATSC system (unofficially ATSC-T) uses a proprietary Zenith-developed modulation called 8-VSB; as the name implies, it is a vestigial sideband technique. Essentially, analog VSB is to regular amplitude modulation as 8VSB is to eight-way quadrature amplitude modulationQuadrature amplitude modulation
Quadrature amplitude modulation is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing the amplitudes of two carrier waves, using the amplitude-shift keying digital modulation scheme or amplitude modulation analog...
. This system was chosen specifically to provide for maximum spectral compatibility between existing analog TV and new digital stations in the United States' already-crowded television allocations system, although it is inferior to the other digital systems in dealing with multipath interference
Multipath interference
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, the two components of the wave interfere...
; however, it is better at dealing with impulse noise
Electromagnetic interference
Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
which is especially present on the VHF bands that other countries have discontinued from TV use, but are still used in the U.S. There is also no hierarchical modulation
Hierarchical modulation
Hierarchical modulation, also called layered modulation, is one of the signal processing techniques for multiplexing and modulating multiple data streams into one single symbol stream, where base-layer symbols and enhancement-layer symbols are synchronously overplayed before...
. After demodulation and error-correction, the 8-VSB modulation supports a digital data stream of about 19.39 Mbit/s, enough for one high-definition video stream or several standard-definition services. See Digital subchannel#Technical considerations for more information.
On cable, ATSC usually uses 256QAM, although some use 16VSB
16VSB
16VSB is an abbreviation for 16-level vestigial sideband modulation, capable of transmitting four bits at a time.-How it works:Other slower but more rugged forms of VSB include 2VSB, 4VSB, and 8VSB...
. Both of these double the throughput
Throughput
In communication networks, such as Ethernet or packet radio, throughput or network throughput is the average rate of successful message delivery over a communication channel. This data may be delivered over a physical or logical link, or pass through a certain network node...
to 38.78 Mbit/s within the same 6 MHz bandwidth. ATSC is also used over satellite. While these are logically called ATSC-C and ATSC-S, these terms were never officially defined. ATSC was never designed for mobile use, but the ATSC group is currently considering how this can be done through its ATSC-M/H
ATSC-M/H
ATSC-M/H is a standard in the USA for mobile digital TV, that allows TV broadcasts to be received by mobile devices.....
.
DMB-T/H
DMB-T/H is the digital television broadcasting standard of the People's Republic of ChinaPeople's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
, Hong Kong
Hong Kong
Hong Kong is one of two Special Administrative Regions of the People's Republic of China , the other being Macau. A city-state situated on China's south coast and enclosed by the Pearl River Delta and South China Sea, it is renowned for its expansive skyline and deep natural harbour...
and Macau
Macau
Macau , also spelled Macao , is, along with Hong Kong, one of the two special administrative regions of the People's Republic of China...
. This is a fusion system, which is a compromise of different competing proposing standards from different Chinese Universities, which incorporates elements from DVB-T
DVB-T
DVB-T is an abbreviation for Digital Video Broadcasting — Terrestrial; it is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in the UK in 1998...
, ADTB-T and TiMi 3.
DVB
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. This system was designed to provide superior immunity from multipath interferenceMultipath interference
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, the two components of the wave interfere...
, and has a choice of system variants which allow data rates from 4 MBit/s up to 24 MBit/s. One U.S. broadcaster, Sinclair Broadcasting, petitioned the Federal Communications Commission
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
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.S.), but this request was denied. (However, one U.S. digital station, WNYE-DT in New York
New York City
New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...
, was temporarily converted to COFDM modulation on an emergency basis for datacasting
Datacasting
Datacasting is the broadcasting of data over a wide area via radio waves. It most often refers to supplemental information sent by television stations along with digital television, but may also be applied to digital signals on analog TV or radio...
information to emergency services personnel in lower Manhattan
Manhattan
Manhattan is the oldest and the most densely populated of the five boroughs of New York City. Located primarily on the island of Manhattan at the mouth of the Hudson River, the boundaries of the borough are identical to those of New York County, an original county of the state of New York...
in the aftermath of the September 11 terrorist attacks
September 11, 2001 attacks
The September 11 attacks The September 11 attacks The September 11 attacks (also referred to as September 11, September 11th or 9/119/11 is pronounced "nine eleven". The slash is not part of the pronunciation...
).
DVB-S is the original Digital Video Broadcasting forward error coding and modulation standard for satellite television
Satellite television
Satellite television is television programming delivered by the means of communications satellite and received by an outdoor antenna, usually a parabolic mirror generally referred to as a satellite dish, and as far as household usage is concerned, a satellite receiver either in the form of an...
and dates from 1995. It is used via satellites serving every continent of the world, this is even true in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. DVB-S is used in both MCPC and SCPC modes for broadcast network
Broadcast network
A broadcast network is an organization, such as a corporation or other voluntary association, that provides live television or recorded content, such as movies, newscasts, sports, Public affairs programming, and other television programs for broadcast over a group of radio stations or television...
feeds, as well as for direct broadcast satellite
Direct broadcast satellite
Direct broadcast satellite is a term used to refer to satellite television broadcasts intended for home reception.A designation broader than DBS would be direct-to-home signals, or DTH. This has initially distinguished the transmissions directly intended for home viewers from cable television...
services like Sky Digital (UK & Ireland)
Sky Digital (UK & Ireland)
Sky is the brand name for British Sky Broadcasting's digital satellite television and radio service, transmitted from SES Astra satellites located at 28.2° east and Eutelsat's Eurobird 1 satellite at 28.5°E. The service was originally launched as Sky Digital, distinguishing it from the original...
via Astra
SES Astra
Astra is the name for the geostationary communication satellites, both individually and as a group, which are owned and operated by SES S.A., a global satellite operator based in Betzdorf, in eastern Luxembourg. The name is sometimes also used to describe the channels broadcasting from these...
in Europe, Dish Network
Dish Network
Dish Network Corporation is the second largest pay TV provider in the United States, providing direct broadcast satellite service—including satellite television, audio programming, and interactive television services—to 14.337 million commercial and residential customers in the United States. Dish...
in the U.S., and Bell TV in Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. The MPEG transport stream delivered by DVB-S is mandated as MPEG-2.
DVB-C stands for Digital Video Broadcasting - Cable and it is the DVB European consortium standard for the broadcast transmission of digital television
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
over cable
Coaxial cable
Coaxial cable, or coax, has an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis...
. This system transmits an MPEG-2
MPEG-2
MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission...
family digital audio/video stream, using a QAM modulation with channel coding
Channel code
In digital communications, a channel code is a broadly used term mostly referring to the forward error correction code and bit interleaving in communication and storage where the communication media or storage media is viewed as a channel...
.
ISDB
ISDB is very similar to DVB, however it is broken into 13 subchannels. Twelve are used for TV, while the last serves either as a guard bandGuard band
-Radio and electronic signalling:In radio, a guard band is an unused part of the radio spectrum between radio bands, for the purpose of preventing interference....
, or for the 1seg
1seg
is a mobile terrestrial digital audio/video and data broadcasting service in Japan, Argentina, Brazil, Chile and Peru. Service began experimentally during 2005 and commercially on April 1, 2006. In Brazil, the broadcast started in late 2007 in just a few cities, with a slight difference from...
(ISDB-H) service. Like the other DTV systems, the ISDB types differ mainly in the modulations used, due to the requirements of different frequency bands. 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 was developed in Japan with MPEG-2, and is now used in Brazil with MPEG-4. Unlike other digital broadcast systems, ISDB includes digital rights management
Digital rights management
Digital rights management is a class of access control technologies that are used by hardware manufacturers, publishers, copyright holders and individuals with the intent to limit the use of digital content and devices after sale. DRM is any technology that inhibits uses of digital content that...
to restrict recording of programming.
Comparison of digital terrestrial television systems
| System | Digital Modulation | Lines | Frame rate | Data rate | Hierarchical Mod. Hierarchical modulation Hierarchical modulation, also called layered modulation, is one of the signal processing techniques for multiplexing and modulating multiple data streams into one single symbol stream, where base-layer symbols and enhancement-layer symbols are synchronously overplayed before... |
Ch. Television channel A television channel is a physical or virtual channel over which a television station or television network is distributed. For example, in North America, "channel 2" refers to the broadcast or cable band of 54 to 60 MHz, with carrier frequencies of 55.25 MHz for NTSC analog video and... B/W (MHz) |
Video B/W | Audio offset | VSB | Video Codec | Sound Codec | Interactive TV Interactive television Interactive television describes a number of techniques that allow viewers to interact with television content as they view it.- Definitions :... |
Digital subchannel Digital subchannel In broadcasting, digital subchannels are a means to transmit more than one independent program at the same time from the same digital radio or digital television station on the same radio frequency channel. This is done by using data compression techniques to reduce the size of each individual... s |
Single-Frequency Network | Predecessor format(s) | Mobile? |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ATSC ATSC ATSC standards are a set of standards developed by the Advanced Television Systems Committee for digital television transmission over terrestrial, cable, and satellite networks.... |
8VSB 8VSB 8VSB is the modulation method used for broadcast in the ATSC digital television standard. ATSC and 8VSB modulation is used primarily in North America; in contrast, the DVB-T standard uses COFDM.... , A-VSB A-VSB A-VSB or Advanced VSB is a modification of the 8VSB modulation system used for transmission of digital television using the ATSC system. One of the constraints of conventional ATSC transmission is that reliable reception is difficult or impossible when the receiver is moving at speeds associated... and E-VSB E-VSB E-VSB or Enhanced VSB is an optional enhancement to the original ATSC Standards that use the 8VSB modulation system used for transmission of digital television. It is intended for improving reception where signals are weaker, including fringe reception areas, and on portable devices such as... in the works |
1080 | up to 60p | 19.39 MB/s | No | 6 | 4.25? digital carrier at 1.31 |
? | 8VSB 8VSB 8VSB is the modulation method used for broadcast in the ATSC digital television standard. ATSC and 8VSB modulation is used primarily in North America; in contrast, the DVB-T standard uses COFDM.... |
MPEG-2 MPEG-2 MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission... |
Dolby Digital Dolby Digital Dolby Digital is the name for audio compression technologies developed by Dolby Laboratories. It was originally called Dolby Stereo Digital until 1994. Except for Dolby TrueHD, the audio compression is lossy. The first use of Dolby Digital was to provide digital sound in cinemas from 35mm film prints... AC3 |
No, EPG Electronic program guide Electronic program guides and interactive program guides provide users of television, radio, and other media applications with continuously updated menus displaying broadcast programming or scheduling information for current and upcoming programming... is available |
Yes | Partial Distributed transmission system In North American digital terrestrial television broadcasting, a distributed transmission system is a form of single-frequency network in which a single broadcast signal is fed via microwave, landline, or communications satellite to multiple synchronised terrestrial radio transmitter sites... |
NTSC NTSC NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as... |
Not yet, ATSC-M/H ATSC-M/H ATSC-M/H is a standard in the USA for mobile digital TV, that allows TV broadcasts to be received by mobile devices..... in the works |
| DVB-T DVB-T DVB-T is an abbreviation for Digital Video Broadcasting — Terrestrial; it is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in the UK in 1998... |
COFDM (QPSK/16/64QAM) |
1080 | up to 50p | Up to 31.668 MB/s | Yes | 5, 6, 7, or 8 | ? | ? | ? | MPEG-2 MPEG-2 MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission... , H.264/MPEG-4 AVC H.264/MPEG-4 AVC H.264/MPEG-4 Part 10 or AVC is a standard for video compression, and is currently one of the most commonly used formats for the recording, compression, and distribution of high definition video... |
? | Yes? | Yes? Télévision Numérique Terrestre TNT is the national digital terrestrial service for France. It formally arrived on 31 March 2005 after a short testing period. Like Freeview in the United Kingdom it will support many new channels as well as the current terrestrial television stations... |
Yes | PAL PAL PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system... , SECAM SECAM SECAM, also written SÉCAM , is an analog color television system first used in France.... |
Yes (DVB-H DVB-H DVB-H is one of three prevalent mobile TV formats. It is a technical specification for bringing broadcast services to mobile handsets. DVB-H was formally adopted as ETSI standard EN 302 304 in November 2004. The DVB-H specification can be downloaded from the official DVB-H website... ) |
| DMB-T/H DMB-T/H DTMB is the TV standard for mobile and fixed terminals used in the People's Republic of China, Hong Kong and Macau. Although at first this standard was called DMB-T/H , the official name is DTMB.DTT broadcasting systems... |
TDS-OFDM | ? | ? | ? | ? | ? | ? | ? | ? | ? | ? | ? | ? | Yes | PAL PAL PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system... |
Yes |
| ISDB-T | 16/64QAM-OFDM (QPSK-OFDM/ DQPSK-OFDM) |
1080? | up to 60p | 19.39 MB/s | Yes | 6 (5.572 + 428 kHz guard band) | ? | ? | ? | MPEG-2 MPEG-2 MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission... / H.264/MPEG-4 AVC H.264/MPEG-4 AVC H.264/MPEG-4 Part 10 or AVC is a standard for video compression, and is currently one of the most commonly used formats for the recording, compression, and distribution of high definition video... (1seg 1seg is a mobile terrestrial digital audio/video and data broadcasting service in Japan, Argentina, Brazil, Chile and Peru. Service began experimentally during 2005 and commercially on April 1, 2006. In Brazil, the broadcast started in late 2007 in just a few cities, with a slight difference from... ) |
AAC Advanced Audio Coding Advanced Audio Coding is a standardized, lossy compression and encoding scheme for digital audio. Designed to be the successor of the MP3 format, AAC generally achieves better sound quality than MP3 at similar bit rates.... |
No | Yes | Yes | NTSC NTSC NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as... |
Yes, ISDB-Tmm/1seg 1seg is a mobile terrestrial digital audio/video and data broadcasting service in Japan, Argentina, Brazil, Chile and Peru. Service began experimentally during 2005 and commercially on April 1, 2006. In Brazil, the broadcast started in late 2007 in just a few cities, with a slight difference from... |
| MediaFLO MediaFLO MediaFLO is a technology developed by Qualcomm for transmitting audio, video and data to portable devices such as mobile phones and personal televisions, used for mobile television... |
OFDM (QPSK/16QAM) | ? | ? | ? | ? | 5.55 | ? | ? | ? | ? | ? | Yes | ? | ? | NTSC NTSC NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as... (Ch. 55 Channel 55 Channel 55 refers to several television stations. This frequency is also in use by MediaFLO, a US system developed by Qualcomm to send video and media to mobile devices:... ) |
Yes |
| SBTVD SBTVD ISDB-T International or SBTVD, short for Sistema Brasileiro de Televisão Digital is a technical standard for digital television broadcast used in Brazil, Peru, Argentina, Chile, Venezuela, Ecuador, Costa Rica, Paraguay, Philippines, Bolivia, Nicaragua and Uruguay, based on the Japanese ISDB-T... |
BST-OFDM | 1080? | ? | ? | Yes | 6 | ? | ? | ? | H.264/MPEG-4 AVC H.264/MPEG-4 AVC H.264/MPEG-4 Part 10 or AVC is a standard for video compression, and is currently one of the most commonly used formats for the recording, compression, and distribution of high definition video... |
HE-AAC HE-AAC High-Efficiency Advanced Audio Coding is a lossy data compression scheme for digital audio defined as a MPEG-4 Audio profile in ISO/IEC 14496-3. It is an extension of Low Complexity AAC optimized for low-bitrate applications such as streaming audio... |
No | Yes | Yes | PAL-M | Yes, 1seg 1seg is a mobile terrestrial digital audio/video and data broadcasting service in Japan, Argentina, Brazil, Chile and Peru. Service began experimentally during 2005 and commercially on April 1, 2006. In Brazil, the broadcast started in late 2007 in just a few cities, with a slight difference from... |
| T-DMB | OFDM-DQPSK | ? | ? | ? | ? | ? | ? | ? | ? | MPEG-2 MPEG-2 MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission... / H.264/MPEG-4 AVC H.264/MPEG-4 AVC H.264/MPEG-4 Part 10 or AVC is a standard for video compression, and is currently one of the most commonly used formats for the recording, compression, and distribution of high definition video... |
HE-AAC HE-AAC High-Efficiency Advanced Audio Coding is a lossy data compression scheme for digital audio defined as a MPEG-4 Audio profile in ISO/IEC 14496-3. It is an extension of Low Complexity AAC optimized for low-bitrate applications such as streaming audio... |
? | ? | ? | NTSC NTSC NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as... |
Yes |
See also
- Characteristics of television systems. International Telecommunication UnionInternational Telecommunication UnionThe International Telecommunication Union is the specialized agency of the United Nations which is responsible for information and communication technologies...
, ITU-R Recommendation BT.470-2.
Transmission technology standards
- Amateur televisionAmateur televisionAmateur television is the transmission of Broadcast quality video and audio over the wide range of frequencies of allocated for Radio amateur use. ATV is used for non-commercial experimentation, pleasure and public service events...
- Broadcast safe
- Channel (broadcasting)Channel (broadcasting)In broadcasting, a channel is a range of frequencies assigned by a government for the operation of a particular radio station, television station or television channel. In common usage, the term also may be used to refer to the station operating on a particular frequency.-See also:*Broadcast...
- Display resolutionDisplay resolutionThe display resolution of a digital television or display device is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resolution is controlled by all different factors in cathode ray tube , flat panel or projection...
- Lists of television channels for lists by country and language.
- North American cable television frequenciesNorth American cable television frequenciesIn North American cable TV networks, the radio frequencies used to carry signals to the customer are allocated to standardarized channel numbers listed in the CEA standard 542. Cable channel frequencies are generally different from off-air broadcast frequencies...
- Television channel frequenciesTelevision channel frequenciesThe 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. The frequencies shown are for the video and audio carriers. The channel itself occupies several megahertz of bandwidth....
Defunct analog systems
- 405 lines
- 819 lines
- MUSEMultiple sub-nyquist sampling Encoding systemMUSE , was a dot-interlaced digital video compression system that used analog modulation for transmission to deliver 1125-line high definition video signals to the home. Japan had the earliest working HDTV system, which was named Hi-Vision with design efforts going back to 1979...
an analog high-definition television system.
Analog television systems
- Intercarrier methodIntercarrier methodThe intercarrier method is a system in television that reduces the cost of transmitters and receiver sets by processing audio and video signals together and minimizing the number of separate stages for audio and video signals....
- NTSCNTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
(525/60) - PALPALPAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
(color encoding usually used with 625/50 systems) - PAL-M (television)PAL-M (television)PAL-M is the TV system used in Brazil since February 19, 1972. At that time, Brazil was the first South American country to broadcast in colour. Colour TV broadcast began on September 1972 when the TV networks Globo, Tupi and Bandeirantes TV transmitted the Caxias do Sul Grape Festival. Transition...
- PALplusPALplusPALplus is an extension of the PAL analogue broadcasting system for transmitting 16:9 programs without sacrificing vertical resolution. It followed experiences with the HD-MAC and D2-MAC, standards that were incompatible with existing receivers but featured a 16:9 aspect ratio...
- SECAMSECAMSECAM, also written SÉCAM , is an analog color television system first used in France....
- TransposerTransposerIn broadcasting, a transposer is a device in the service area of a transmitter which rebroadcasts signals to the receivers which can’t properly receive the signals of the transmitter because of a physical obstruction . A transposer receives the signals of the transmitter and rebroadcasts the...
s - TV transmitters
Analog television system audio
- BTSC
- NICAMNICAMNear Instantaneous Companded Audio Multiplex is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks...
(digital, analog pre-emphasis curve) - Zweiton
- The defunct MUSE system had a very unusual digital audio subsystem completely unrelated to NICAMNICAMNear Instantaneous Companded Audio Multiplex is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks...
.
Digital television systems
- ATSC Standards replace NTSCNTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
- ATSC tunerATSC tunerAn ATSC tuner, often called an ATSC receiver or HDTV tuner is a type of television tuner that allows reception of digital television television channels transmitted by television stations in North America, parts of Central America and South Korea that use ATSC standards...
- ATSC tuner
- DVB-TDVB-TDVB-T is an abbreviation for Digital Video Broadcasting — Terrestrial; it is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in the UK in 1998...
replaces PALPALPAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
, PALplusPALplusPALplus is an extension of the PAL analogue broadcasting system for transmitting 16:9 programs without sacrificing vertical resolution. It followed experiences with the HD-MAC and D2-MAC, standards that were incompatible with existing receivers but featured a 16:9 aspect ratio...
and SECAMSECAMSECAM, also written SÉCAM , is an analog color television system first used in France.... - HDTV systems all use MPEG transmission technology
- ISDBISDBIntegrated Services Digital Broadcasting is a Japanese standard for digital television and digital radio used by the country's radio and television stations. ISDB replaced the previously used MUSE "Hi-vision" analogue HDTV system...
replaces NTSCNTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
and the Analog high-definition television system 1125-line MUSE system
History
- History of televisionHistory of televisionThe history of television records the work of numerous engineers and inventors in several countries over many decades. The fundamental principles of television were initially explored using electromechanical methods to scan, transmit and reproduce an image...
- Oldest television stationOldest television stationThis is a list of prewar television stations of the 1920s and 1930s that were among the first in the world. Most of these experimental stations were located in Europe , Canada and the United States...
- Television systems before 1940Television systems before 1940A number of experimental and broadcast pre World War II television systems were tested. The first ones were mechanical based and of very low resolution, sometimes with no sound...
External links
- FARWAY IRFC, TV and Radio Transmission , Radio Data System Encoders , Broadcasting Technologies
- World Analog Television Standards and Waveforms by Alan Pemberton
- Analog TV Broadcast Systems by Paul Schlyter
- European Television Stations in 1932 a scan from a 1932 French magazine