Editing Broadcast television systems (section)

== Analog television systems ==
[[File:Analog-TV-Systems.jpg|thumb|500px|Analog television system by nation]]
{{Analog television encoding systems by nation}}

Every analog television system bar one began as a [[black-and-white]] system. Each country, faced with local political, technical, and economic issues, adopted a [[color television]] standard which was grafted onto an existing [[monochrome]] system such as [[CCIR System M]], 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 changeover to color television to continue to be operated 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]] with the symbol C, while the black and white information is called the [[Luma (video)|luminance]] with the symbol Y. 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 used one of three color standards: NTSC, PAL, or SECAM. For example, CCIR System M was often used in conjunction with NTSC standard, to provide color analog television and the two together were known as NTSC-M.

=== Pre–World War II systems ===
{{Main|Television systems before 1940}}

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, and usually mentioned by their line number: [[375-line television system|375-line]] (used in Germany, Italy, US), [[405-line television system|405-line]] (used in the UK), [[441-line television system|441-line]] (used in Germany, France, Italy, US) or [[567-line television system|567-line]] (used in the Netherlands). These systems were mostly experimental and national, with no defined international standards, and didn't resume broadcasting after the war. An exception was the UK 405-line system, that resumed broadcasts and was the first to be standardized by ITU as [[System A]], remaining in operation until 1985.

=== ITU standards ===
On an international conference in [[Stockholm]] in 1961, the [[International Telecommunication Union]] designated standards for broadcast television systems ('''ITU System Letter Designation''').<ref name="auto1"/> Each standard is designated by a letter (A-M).

On [[Very high frequency|VHF]] [[Band I|bands I]], [[Band II|II]] and [[Band III|III]] the [[405-line television system|405]], [[625 lines|625]] and [[819 line|819-line]] systems could be used:
* [[CCIR System A|A]] – 405-line system, 5&nbsp;MHz video bandwidth
* [[CCIR System B|B]] – 625-line system, 7&nbsp;MHz video bandwidth
* [[CCIR System C|C]] – Belgian 625-line system, 7&nbsp;MHz video bandwidth
* [[CCIR System D|D]] – [[International Radio and Television Organisation|I.B.T.O.]] 625-line system, 8&nbsp;MHz video bandwidth
* [[CCIR System E|E]] – French 819-line system, 14&nbsp;MHz video bandwidth
* [[CCIR System F|F]] – Belgian 819-line system, 7&nbsp;MHz video bandwidth

On [[Ultra high frequency|UHF]] bands [[Band IV|Bands IV]] and [[Band V|V]] only 625-line systems were adopted, with the difference being transmission parameters like channel bandwidth.
* [[CCIR System G|G]] – 625-line system, 5&nbsp;MHz video bandwidth
* [[CCIR System H|H]] – 625-line system, 5&nbsp;MHz video bandwidth
* [[CCIR System I|I]] – 625-line system, 5.5&nbsp;MHz video bandwidth
* [[CCIR System K|K]] – 625-line system, 6&nbsp;MHz video bandwidth
* [[CCIR System L|L]] – 625-line system, 6&nbsp;MHz video bandwidth

Following further conferences and the introduction of color television, by 1966<ref name="auto2">{{Cite web |title=C.C.I.R - Documents of the Xlth Plenary Assembly Oslo, 1966 |url=https://search.itu.int/history/HistoryDigitalCollectionDocLibrary/4.277.43.en.1006.pdf}}</ref> each standard was designated by a letter (A-M) in combination with a color standard (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 standard.<ref name="auto2"/> Except for [[display resolution|lines]] and [[frame rate]]s, other units are [[Hertz|megahertz]] (MHz).
* ''Also see:'' [[television channel frequencies]]

{| class="wikitable sortable" | border="1"
|+ '''World analog television systems'''<ref name="auto2"/>
|- style="background:rgb (170, 160, 150);"
! <small>Usual [[Color television|color standard]]</small>
! <small>System</small>
! <small>Introduced</small>
! [[Scan line|<small>Lines</small>]]
! <small>[[Frame rate]] (fps)</small>
! <small>[[Broadcasting|Channel]] bandwidth</small> <small>(MHz)</small>
! <small>[[VF bandwidth|Video bandwidth]] (MHz)</small>
! <small>Vision/sound carrier separation (MHz)</small>
! <small>[[Single-sideband modulation|Vestigial sideband]] (MHz)</small>
! <small>[[Modulation|Vision modulation]] (+, -)</small>
! <small>[[Modulation|Sound modulation]] (AM, FM)</small>
! <small>[[Chrominance]] [[subcarrier]] frequency (MHz)</small>
! <small>Vision/sound power ratio</small>
! <small>Assumed display device [[Gamma correction|gamma]]<ref>{{cite web |title=C.C.I.R. Report 624-4 Characteristics of television systems, 1990 |url=https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.624-4-1990-PDF-E.pdf}}</ref><ref name="auto2" /></small>
|- style="text-align:center;"
|
| [[CCIR System A|A]]
| 1936
| 405
| 25
| 5
| 3
| −3.5
| 0.75
| +
| AM
| none
| 4:1
| 2.5 - 2.0
|- style="text-align:center;"
| [[PAL]]/[[SECAM]]
| [[CCIR System B|B]]
| 1950
| 625
| 25
| 7
| 5
| +5.5
| 0.75
| -
| FM
| 4.43
|
| 2.8
|- style="text-align:center;"
|
| [[CCIR System C|C]]
| 1953
| 625
| 25
| 7
| 5
| +5.5
| 0.75
| +
| AM
| none
|
| 2.0
|- style="text-align:center;"
| SECAM/PAL
| [[CCIR System D|D]]
| 1948
| 625
| 25
| 8
| 6
| +6.5
| 0.75
| -
| FM
| 4.43
|
| 2.8
|- style="text-align:center;"
|
| [[CCIR System E|E]]
| 1949
| 819
| 25
| 14
| 10
| ±11.15
| 2.00
| +
| AM
| none
|
| 1.7
|- style="text-align:center;"
|
| [[CCIR System F|F]]
| 1953
| 819
| 25
| 7
| 5
| +5.5
| 0.75
| +
| AM
| none
|
| 2.0
|- style="text-align:center;"
| PAL/SECAM
| [[CCIR System G|G]]
| 1961
| 625
| 25
| 8
| 5
| +5.5
| 0.75
| -
| FM
| 4.43
| 5:1
| 2.8
|- style="text-align:center;"
| PAL
| [[CCIR System H|H]]
| 1961
| 625
| 25
| 8
| 5
| +5.5
| 1.25
| -
| FM
| 4.43
| 5:1
| 2.8
|- style="text-align:center;"
| PAL
| [[CCIR System I|I]]
| 1962
| 625
| 25
| 8
| 5.5
| +5.9996
| 1.25
| -
| FM
| 4.43
| 5:1
| 2.8
|- style="text-align:center;"
| [[NTSC]]
| [[NTSC-J|J]]
| 1953
| 525
| 30
| 6
| 4.2
| +4.5
| 0.75
| -
| FM
| 3.58
|
| 2.2
|- style="text-align:center;"
| SECAM/PAL
| [[CCIR System K|K]]
| 1961
| 625
| 25
| 8
| 6
| +6.5
| 0.75
| -
| FM
| 4.43
| 5:1
| 2.8
|- style="text-align:center;"
| SECAM
| [[CCIR System K1|K1]]
| 1964
| 625
| 25
| 8
| 6
| +6.5
| 1.25
| -
| FM
| 4.43
|
| 2.8
|- style="text-align:center;"
| SECAM
| [[CCIR System L|L]]
| 1961
| 625
| 25
| 8
| 6
| -6.5
| 1.25
| +
| AM
| 4.43
| 8:1
| 2.8
|- style="text-align:center;"
| NTSC/PAL
| [[CCIR System M|M]]
| 1941
| 525
| 30
| 6
| 4.2
| +4.5
| 0.75
| -
| FM
| 3.58/3.56
|
| 2.2
|- style="text-align:center;"
| PAL
| [[CCIR System N|N]]
| 1951
| 625
| 25
| 6
| 4.2
| +4.5
| 0.75
| -
| FM
| 3.58
|
| 2.8
|}

==== Notes by system ====
; [[CCIR System A|A]]: Early [[United Kingdom]] and [[Ireland]] VHF system (B&W only). First electronic TV system, introduced in 1936. Vestigial sideband filtering introduced in 1949. Discontinued on 23 November 1982 in Ireland and on 2 January 1985 in the UK.<ref>{{cite web |date=2012-02-12 |title=The UK 405-Line Television Network |url=http://www.pembers.freeserve.co.uk/405-Lines/index.html |access-date=2021-12-31 |website= |archive-url=https://web.archive.org/web/20120212100552/http://www.pembers.freeserve.co.uk/405-Lines/index.html |archive-date=12 February 2012 |url-status=dead}}</ref><ref name="auto">{{cite web |date=2012-03-06 |title=World Analogue Television Standards and Waveforms |url=http://www.pembers.freeserve.co.uk/World-TV-Standards/Transmission-Systems.html |access-date=2021-12-31 |website= |archive-url=https://web.archive.org/web/20120306185600/http://www.pembers.freeserve.co.uk/World-TV-Standards/Transmission-Systems.html |archive-date=6 March 2012 |url-status=dead}}</ref>
; [[CCIR System B|B]]: VHF-only in most Western European countries (combined with system G and H on UHF); VHF and UHF in [[Australia]]. Originally known as the Gerber standard.<ref>{{cite web |title=625-Line Television Broadcast Standards - UK Vintage Radio Repair and Restoration Discussion Forum |url=https://www.vintage-radio.net/forum/showthread.php?t=36027 |access-date=2021-12-31 |website=www.vintage-radio.net}}</ref>
; [[CCIR System C|C]]: Early VHF system; used only in [[Belgium]], [[Italy]], the [[Netherlands]] and [[Luxembourg]], as a compromise between Systems B and L. Discontinued in 1977.<ref name="auto"/>
; [[CCIR System D|D]]: The first 625-line system. Used on VHF only in most countries (combined with system K on UHF); VHF and UHF in [[China]].
; [[CCIR System E|E]]: Early [[France|French]] VHF system (B&W only); very good (near [[High-definition television|HDTV]]) picture quality but uneconomical use of bandwidth. Sound carrier separation +11.15&nbsp;MHz on odd numbered channels, -11.15&nbsp;MHz on even numbered channels. Discontinued in 1984 (France) and 1985 (Monaco).<ref>{{cite web |date=2012-08-30 |title=World Analogue Television Standards and Waveforms |url=http://www.pembers.freeserve.co.uk/World-TV-Standards/Transmission-Systems.html |access-date=2021-12-31 |website= |archive-url=https://web.archive.org/web/20120830232230/http://www.pembers.freeserve.co.uk/World-TV-Standards/Transmission-Systems.html |archive-date=30 August 2012 |url-status=dead}}</ref>
; [[CCIR System F|F]]: Early VHF system used only in Belgium and Luxembourg; allowed French 819-line [[Television show|television programming]] to be broadcast on the 7&nbsp;MHz VHF channels used in those countries, at a substantial cost in horizontal resolution. Discontinued in 1968 (Belgium) and 1971 (Luxembourg).<ref name="auto"/>
; [[CCIR System G|G]]: UHF only; used in countries with [[CCIR System B|System B]] on VHF, except Australia.
; [[CCIR System H|H]]: UHF only; used only in Belgium, Luxembourg and Netherlands. Similar to System G with a 1.25&nbsp;MHz vestigal sideband.
; [[CCIR System I|I]]: Used in the [[United Kingdom|UK]], [[Ireland]], [[Southern Africa]], [[Macau]], [[Hong Kong]] and [[Falkland Islands]].
; [[NTSC-J|J]]: Used in [[Japan]] (see system M below). Identical to system M except that a different black level of 0 [[IRE (unit)|IRE]] is used instead of 7.5 IRE. Although the ITU specified a frame rate of 30 fields, 29.97 was adopted with the introduction of NTSC color to minimize visual artifacts. Discontinued in 2012, when Japan transitioned to [[Digital television transition|digital]].
; [[CCIR System K|K]]: UHF only; used in countries with system D on VHF, except China, and identical to it in most respects.
; [[CCIR System K1|K1]]: Used only in [[Overseas France|French overseas departments and territories]].
; [[CCIR System L|L]]: Used only in [[France]]. On VHF Band 1 only, the audio is at −6.5&nbsp;MHz. Discontinued in 2011, when France transitioned to [[Digital television transition|digital]]. It was the last system to use positive video modulation and AM sound.
; [[CCIR System M|M]]: Used in most of the [[Americas]] and [[Caribbean]] (except [[Argentina]], [[Paraguay]], [[Uruguay]] and [[French Guiana]]), [[Myanmar]], [[South Korea]], [[Republic of China|Taiwan]], [[Philippines]] (all NTSC-M), [[Brazil]] ([[PAL-M]]), [[Vietnam]], [[Cambodia]] and [[Laos]] (SECAM-M). Although the ITU specified a frame rate of 30 fields, 29.97 was adopted with the introduction of NTSC color to minimize visual artifacts.
; [[CCIR System N|N]]: Adopted by [[Argentina]], [[Paraguay]] and [[Uruguay]] (all [[PAL#PAL-N|PAL-N]] since 1980).

=== Evolution ===
For historical reasons, some countries use a different video system on [[Ultra high frequency|UHF]] than they do on the [[Very high frequency|VHF]] bands. In a few countries, most notably the [[United Kingdom]], television broadcasting on VHF has been entirely shut down. The British [[405-line television system|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 standards, 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 system, 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 standard in the early stages, but later the decision was made to adopt color in 625-lines L system only. Thus, France adopted system L both on UHF and VHF networks and abandoned system E.

Japan had the earliest working HDTV system ([[Multiple sub-Nyquist sampling encoding|MUSE]]), with design efforts going back to 1979. The country began broadcasting wideband analog [[high-definition video]] signals in the late 1980s using an interlaced resolution of 1,125 lines, supported by the [[Sony HDVS]] line of equipment.

In many parts of the world, analog television broadcasting has been shut down completely, or in process of shutdown; see [[Digital television transition]] for a timeline of the analog shutdown.

=== Technical aspects ===

==== Frames ====
{{Main|Film frame}}

Ignoring color, all television systems work in essentially the same manner. The monochrome image seen by a camera (later, the [[Luma (video)|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 (signal processing)|bandwidth]] of the television signal, which puts an ultimate limit on the horizontal resolution possible. When color was introduced, this limit necessarily became fixed. All analog television systems are ''[[Interlaced video|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 ''[[Field (video)|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 frequency]] at which the [[Electric power distribution|electricity distribution]] system operates, to avoid flicker resulting from the [[Beat (acoustics)|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 [[Deinterlacing|deinterlace]] an interlaced source. Use of inexpensive deinterlacing hardware is a typical difference between lower- vs. higher-priced [[Flat-panel display|flat panel displays]] ([[Plasma display]], [[Liquid-crystal display|LCD]], etc.).

All [[film]]s and other filmed material shot at 24&nbsp;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&nbsp;frame/s formats (European among other countries with 50&nbsp;Hz mains supply), the content is [[576i#PAL speed-up|PAL speedup]], while a technique known as "[[Three-two pull down|3:2 pulldown]]" is used for 30&nbsp;frame/s formats (North America among other countries with 60&nbsp;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 tube|cathode ray tube]] (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 [[Spectral density|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.

==== Hidden signaling ====
Broadcasters later developed mechanisms to transmit digital information on the phantom lines, used mostly for [[teletext]] and [[closed captioning]]:

* [[PALplus]] uses a [[Widescreen signaling|hidden signaling]] scheme to indicate if it exists, and if so what operational mode it is in.
* [[NTSC]] was modified by the [[ATSC standards|Advanced Television Systems Committee]] to support an [[ghost-canceling reference|anti-ghosting signal]] that is inserted on a non-visible scan line.
* [[Teletext]] uses hidden signaling to transmit information pages.
* [[NTSC]] [[Closed captioning|Closed Captioning]] signaling uses signaling that is nearly identical to [[teletext]] signaling.
* [[Widescreen signaling]] enables a flag to indicate that a 16:9 widescreen image is being broadcast, and allows the TV set to switch to the appropriate display mode.

==== Overscan ====
{{Main|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.{{Vague|date=September 2017}}

==== Interlacing ====
{{Main|Interlaced video}}

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 signal 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, as in the earlier [[white facsimile transmission]] standard, the maximum luminance value is represented by the maximum carrier power; in negative [[modulation]], 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.

Impulse 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. Impulse 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 loop|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 labeled "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.

==== Modulation ====
Given all of these parameters, the result is a mostly-continuous [[analog signal]] which can be modulated onto a radio-frequency carrier and transmitted through an antenna. All analog television systems use [[Single-sideband modulation#Vestigial sideband (VSB)|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.

==== Audio ====
In analog television, the [[Analog recording|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 separate aural and visual antennas can be used. In all cases where negative video is used, [[frequency modulation|FM]] is used for the standard [[monaural]] audio; systems with positive video use AM sound and intercarrier receiver technology cannot 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 [[Multichannel Television Sound|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.