Broadcast television systems (or terrestrial television systems outside the US and Canada) are the encoding or formatting standards for the transmission and reception of terrestrial television signals. There were three main analog television systems in use around the world until the late 2010s: NTSC, PAL, and SECAM. Now in digital terrestrial television (DTT), there are four main systems in use around the world: ATSC, DVB, ISDB and DTMB.
All but one analog television system began as black-and-white systems. Each country, faced with local political, technical, and economic issues, adopted a color television system 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 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 systems: NTSC, PAL, or SECAM. For example, CCIR System M was often used in conjunction with NTSC to provide color analog television, and the two together were known as NTSC-M.
Ignoring color, all television systems work in essentially the same manner. The monochrome image seen by a camera (later, 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 necessity of limit became fixed. All 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 field are transmitted is one of the fundamental parameters of a video system. It is related to the utility frequency 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 scanning and must deinterlace an interlaced source. Use of inexpensive deinterlacing hardware is a typical difference between lower- vs. higher-priced flat panel displays (Plasma display, LCD, etc.).
All films and other filmed material shot at 24 frames per second must be transferred to video frame rates 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.
Analog television signal standards are designed to be displayed on a 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 electromagnets 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.
Broadcasters later developed mechanisms to transmit digital information on the phantom lines, used mostly for teletext and closed captioning:
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 ]
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.
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.
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 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.
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 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.
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 separate aural and visual antennas can be used. In all cases where negative video is used, 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 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.
For historical reasons, some countries use a different video system on UHF 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 in process of shutdown; see Digital television transition for a timeline of the analog shutdown.
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.
On an international conference in Stockholm in 1961, the International Telecommunication Union designated standards for broadcast television systems.Each standard is designated a letter (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 standard. Defunct TV systems are shown in grey text, previous ones never designated by ITU are not yet shown. Except for lines and frame rates, other units are megahertz (MHz).
|Standard||Introduced||Lines||Frame rate||Channel bandwidth||Video bandwidth (MHz)||Vision sound carrier separation (MHz)||Vestigial sideband (MHz)||Vision modulation||Sound modulation||Frequency of chrominance subcarrier (MHz)||Vision/sound power ratio||Usual color|
The situation with worldwide digital television is much simpler by comparison. Most digital television systems are based on the MPEG transport stream standard, and use the H.262/MPEG-2 Part 2 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 most of North America, 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.
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 modulation. 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 November 17, 2017, the FCC voted 3-2 in favor of authorizing voluntary deployments of ATSC 3.0, which was designed as the successor to the original ATSC "1.0", and issued a Report and Order to that effect. Full-power stations will be required to maintain a simulcast of their channels on an ATSC 1.0-compatible signal if they decide to deploy an ATSC 3.0 service.
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.
DTMB is the digital television broadcasting standard of the Mainland China, 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 DMB-T, ADTB-T and TiMi 3.
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 interference, and has a choice of system variants which allow data rates from 4 MBit/s up to 24 MBit/s. One US 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 US), but this request was denied. (However, one US 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 back to 1995. It is used via satellites serving every continent of the world, including 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 and Freesat in the British Isles, Sky Deutschland and HD+ in Germany and Austria, TNT SAT/FRANSAT and CanalSat in France, Dish Network in the US, and Bell Satellite 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.
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 band, 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.
|Frame rate||Data rate||Hierarchical Mod.||Ch. B/W (MHz)||Video B/W||Audio offset||Video Coding||Audio Coding||Interactive TV||Digital subchannels||Single-Frequency Network||Predecessor format(s)||Mobile?|
|ATSC 1.0||8VSB, A-VSB and E-VSB in the works||1080||up to 60p||19.39 Mbit/s||No||6||4.25?|
digital carrier at 1.31 MHz
|?||H.262|| Dolby Digital, AC3,|
MPEG-1 Layer II
| DSM-CC MHEG-5,|
|Yes||Partial||NTSC||Not yet, ATSC-M/H in the works|
|ATSC 3.0|| COFDM |
|2160p/4K||up to 120p||57 Mbit/s||Yes||6||4.5||?||H.265/Scalable HEVC||Dolby AC-4, MPEG-H||Yes||Yes||Yes||NTSC, ATSC 1.0||Yes|
|DVB-T|| COFDM |
|1080||up to 50p||Up to 31.668 Mbit/s||Yes||5, 6, 7, or 8||?||?||H.262, H.264|| MPEG-1 Layer II,|
| DSM-CC MHEG-5,|
|Yes||Yes||PAL, SECAM||Yes (DVB-H)|
|DVB-T2|| COFDM |
(QPSK, 16QAM, 64QAM, 256QAM)
|1080||up to 50p||Up to 50.34 Mbit/s||Yes||1.7, 5, 6, 7, 8, or 10||?||?||H.264, H.262|| MPEG-1 Layer II,|
| DSM-CC MHEG-5,|
|DTMB||TDS-OFDM||1080||up to 50p||?||?||6, 7, or 8||?||?||MPEG-2, H.264/MPEG-4 AVC, AVS||MPEG-1 Audio Layer II, AC3, DRA||Yes||?||Yes||PAL||Yes|
|ISDB-T|| 16/64QAM-OFDM |
|1080?||up to 60p||23 Mbit/s||Yes||6 (5.572 + 428 kHz guard band)||?||?|| H.262/|
| ISDB-Tb |
|BST-OFDM||1080||?||?||Yes||6||?||?||H.264||HE-AAC||Yes, Ginga||Yes||Yes||PAL-M, PAL-N, PAL-Nc, NTSC||Yes, 1seg|
|MediaFLO||OFDM (QPSK/16QAM)||?||?||?||?||5.55||?||?||?||?||Yes||?||?||NTSC (Channel 55)||Yes|
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 number.
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)
engineers during the mid-late 1940s, introduced to Western Europe by German engineers.)
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 59.94 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.
Transmission technology standards
Defunct analog systems
Analog television systems
Analog television system audio
Digital television systems
Analog television is the original television technology that uses analog signals to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by amplitude, phase and frequency of an analog signal.
The abbreviation NTSC can refer to the National Television System Committee, which developed the analog television color system that was introduced in North America in 1954 and stayed in use until digital conversion. NTSC is also an abbreviation for the National Television Standards Committee, a subset of the National Television System Committee that was responsible for producing the detailed technical specifications for the transmission standard. It is one of three major analog color television standards, the others being PAL and SECAM.
Phase Alternating Line (PAL) is a colour encoding system for analogue television used in broadcast television systems in most countries broadcasting at 625-line / 50 field per second (576i). It was one of three major analogue colour television standards, the others being NTSC and SECAM.
Standard-definition television is a television system which uses a resolution that is not considered to be either high or enhanced definition. SDTV and high-definition television (HDTV) are the two categories of display formats for digital television (DTV) transmissions. "Standard" refers to the fact that it was the prevailing specification for broadcast television in the mid- to late-20th century.
SECAM, also written SÉCAM, is an analog color television system first used in France. It was one of three major color television standards, the others being PAL and NTSC.
Terrestrial television is a type of television broadcasting in which the television signal is transmitted by radio waves from the terrestrial (Earth-based) transmitter of a television station to a TV receiver having an antenna. The term terrestrial is more common in Europe and Latin America, while in Canada and the United States it is called broadcast or over-the-air television (OTA). The term "terrestrial" is used to distinguish this type from the newer technologies of satellite television, in which the television signal is transmitted to the receiver from an overhead satellite; cable television, in which the signal is carried to the receiver through a cable; and Internet Protocol television, in which the signal is received over an Internet stream or on a network utilizing the Internet Protocol. Terrestrial television stations broadcast on television channels with frequencies between about 52 and 600 MHz in the VHF and UHF bands. Since radio waves in these bands travel by line of sight, reception is generally limited by the visual horizon to distances of 64–97 kilometres (40–60 mi), although under better conditions and with tropospheric ducting, signals can sometimes be received hundreds of kilometers distant.
Advanced Television Systems Committee (ATSC) standards are an American set of standards for digital television transmission over terrestrial, cable and satellite networks. It is largely a replacement for the analog NTSC standard and, like that standard, is used mostly in the United States, Mexico, Canada, and South Korea. Several former NTSC users, in particular Japan, have not used ATSC during their digital television transition, because they adopted their own system called ISDB.
A tuner is a subsystem that receives radio frequency (RF) transmissions and converts the selected carrier frequency and its associated bandwidth into a fixed frequency that is suitable for further processing, usually because a lower frequency is used on the output. Broadcast FM/AM transmissions usually feed this intermediate frequency (IF) directly into a demodulator that converts the radio signal into audio-frequency signals that can be fed into an amplifier to drive a loudspeaker.
The following tables show the frequencies assigned to broadcast television channels in various regions of the world, along with the ITU letter designator for the system used. The frequencies shown are for the analogue video and audio carriers. The channel itself occupies several megahertz of bandwidth. For example, North American channel 1 occupies the spectrum from 44 to 50 MHz. See Broadcast television systems for a table of signal characteristics, including bandwidth, by ITU letter designator.
576i is a standard-definition video mode originally used for terrestrial television in most countries of the world where the utility frequency for electric power distribution is 50 Hz. Because of its close association with the colour encoding system, it is often referred to as simply PAL, PAL/SECAM or SECAM when compared to its 60 Hz NTSC-colour-encoded counterpart, 480i. In digital applications it is usually referred to as "576i"; in analogue contexts it is often called "625 lines", and the aspect ratio is usually 4:3 in analogue transmission and 16:9 in digital transmission.
The 405-line monochrome analogue television broadcasting system was the first fully electronic television system to be used in regular broadcasting.
Analog high-definition television has referred to a variety of analog video broadcast television systems with various display resolutions throughout history.
MUSE was an analog high-definition television system, using dot-interlacing and digital video compression to deliver 1125-line (1920x1035) high definition video signals to the home. Japan had the earliest working HDTV system, MUSE, which was named Hi-Vision with design efforts going back to 1979. The country began broadcasting wideband analog HDTV signals in 1989 using 1035 active lines interlaced in the standard 2:1 ratio (1035i) with 1125 lines total. By the time of its commercial launch in 1991, digital HDTV was already under development in the United States. Hi-Vision continued broadcasting in analog until 2007.
PAL-M is the analog TV system used in Brazil since February 19, 1972, considered with NTSC. At that time, Brazil was the first South American country to broadcast in color. Color TV broadcast began on February 19, 1972, when the TV networks Globo and Bandeirantes transmitted the Caxias do Sul Grape Festival. Transition from black and white to colour was not complete until 1978. Two years later, in 1980, colour broadcast nationwide in Brazil was commonplace.
Band I is a range of radio frequencies within the very high frequency (VHF) part of the electromagnetic spectrum. The first time there was defined "for simplicity" in Annex 1 of "Final acts of the European Broadcasting Conference in the VHF and UHF bands - Stockholm, 1961". Band I ranges from 47 to 68 MHz for the European Broadcasting Area, and from 54 to 88 MHz for the Americas and it is primarily used for television broadcasting in compliance with ITU Radio Regulations. With the transition to digital TV, most Band I transmitters in Europe, Africa, Asia and Australia have already been switched off.
Television standards conversion is the process of changing a television transmission or recording from one television system to another. The most common is from NTSC to PAL or the other way around. This is done so television programs in one nation may be viewed in a nation with a different standard. The video is fed through a video standards converter, which makes a copy in a different video system.
High-definition television (HD) describes a television system providing an image resolution of substantially higher resolution than the previous generation of technologies. The term has been used since 1936, but in modern times refers to the generation following standard-definition television (SDTV), often abbreviated to HDTV or HD-TV. It is the current de facto standard video format used in most broadcasts: terrestrial broadcast television, cable television, satellite television and Blu-ray Discs.
CCIR System B was the 625-line analog broadcast television system which at its peak was the system used in most countries. It is being replaced across Western Europe, part of Asia and Africa by digital broadcasting.
Multi-standard television sets were made for use in the television industry, so that one TV set or monitor could show video content from other television systems. Multistandard is only used with analogue television. In digital television, there are different standards, like DVB, ISDB, and ATSC. However digital multistandard tv set are not existing. Multistandard devices in digital TV may be PC extension card.
CCIR System I is an analog broadcast television system. It was first used in the Republic of Ireland starting in 1962 as the 625-line broadcasting standard to be used on VHF Band I and Band III, sharing Band III with 405-line System A signals radiated in the north and east of the country. The UK started its own 625-line television service in 1964 also using System I, but on UHF only – the UK has never used VHF for 625-line television except for some cable relay distribution systems.