Misplaced Pages

#569430

62-563: The band is subdivided into seven channels for television broadcasting, each occupying 6 MHz. European Band III allocations vary from country to country, with channel widths of 7 or 8 MHz. The standard channel allocations for European countries that use System B with 7 MHz channel spacing are as follows: The Irish (8 MHz) system is shown below. Australia has allocated 8 channels in Band III for digital television, each with 7 MHz bandwidth. Russian analog television

124-404: 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

186-495: 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

248-433: 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

310-467: 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. In a purely analog system, field order is merely a matter of convention. For digitally recorded material it becomes necessary to rearrange

372-566: 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

434-510: 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. 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

496-478: 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

558-562: 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

620-464: 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

682-582: 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. The situation with worldwide digital television

SECTION 10

#1732790164570

744-503: 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

806-417: 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

868-511: Is encoded into a video signal using a subcarrier frequency. Depending on the video standard, the chrominance subcarrier may be either quadrature-amplitude-modulated ( NTSC and PAL ) or frequency-modulated ( SECAM ). In the PAL system, the color subcarrier is 4.43 MHz above the video carrier, while in the NTSC system it is 3.58 MHz above the video carrier. The NTSC and PAL standards are

930-477: 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

992-660: 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

1054-473: Is now used in Brazil with MPEG-4. Unlike other digital broadcast systems, ISDB includes digital rights management to restrict recording of programming. 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

1116-614: Is represented by the U-V color plane in PAL and SECAM video signals, and by the I-Q color plane in NTSC. Digital video and digital still photography systems sometimes use a luma/chroma decomposition for improved compression. For example, when an ordinary RGB digital image is compressed via the JPEG standard, the RGB color space is first converted (by a rotation matrix ) to a YCbCr color space, because

1178-498: 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

1240-580: Is transmitted using System D with 8 MHz channel bandwidth. The band came into use for radio broadcasting at the turn of the 21st century and is used for Digital Audio Broadcasting . It is subdivided into a number of frequency blocks: In the UK and part of Ireland, Band III was originally used for monochrome 405-line television ; however, this was discontinued by the mid-1980s. Other European countries (including Ireland) continued to use Band III for analogue 625-line colour television. Digital television in

1302-740: 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

SECTION 20

#1732790164570

1364-464: 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

1426-706: The Advanced Television Systems Committee and adopted as a standard in most of North America , and DVB-T , the D igital V ideo B roadcast – T errestrial 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

1488-789: The DVB-T standard can be used in conjunction with VHF Band III and is used as such in some places. The use of sub-band 2 and sub-band 3 band for Digital Audio Broadcasting is now being widely adopted. Sub-band 1 is used for MPT-1327 trunked PMR radio, remote wireless microphones and PMSE links. In North America, use of the band for television broadcasts is still widespread. Favorable propagation characteristics and reasonable power limits (up to 65  kW for full-power digital television , versus 20 kW or less on VHF Band I ) has meant that many US broadcasters elected to move their full-power ATSC stations from UHF frequencies to Band III VHF when all full-power NTSC analog television services in

1550-499: The International Telecommunication Union (ITU) in 1961, with each system designated by a letter ( A - N ) in combination with the color standard used ( NTSC , PAL or SECAM ) - for example PAL-B, NTSC-M, etc.). These analog systems for TV broadcasting dominated until the 2000s. With the introduction of digital terrestrial television (DTT), they were replaced by four main systems in use around

1612-454: The International Telecommunication Union designated standards for broadcast television systems ( ITU System Letter Designation ). Each standard is designated by a letter (A-M). On VHF bands I , II and III the 405 , 625 and 819-line systems could be used: On UHF bands Bands IV and V only 625-line systems were adopted, with the difference being transmission parameters like channel bandwidth. Following further conferences and

1674-487: The bandwidth of each to be determined separately. Typically, the chrominance bandwidth is reduced in analog composite video by reducing the bandwidth of a modulated color subcarrier, and in digital systems by chroma subsampling . The idea of transmitting a color television signal with distinct luma and chrominance components originated with Georges Valensi , who patented the idea in 1938. Valensi's patent application described: The use of two channels, one transmitting

1736-422: The color information of the picture (see YUV color model), separately from the accompanying luma signal (or Y' for short). Chrominance is usually represented as two color-difference components: U =  B′ − Y′ (blue − luma) and V =  R′ − Y′ (red − luma). Each of these different components may have scale factors and offsets applied to it, as specified by

1798-567: 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

1860-451: 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

1922-464: 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

Band III - Misplaced Pages Continue

1984-623: 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 ( MUSE ), with design efforts going back to 1979. The country began broadcasting wideband analog high-definition video signals in

2046-505: 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

2108-441: 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

2170-617: The UK), 441-line (used in Germany, France, Italy, US) or 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. On an international conference in Stockholm in 1961,

2232-488: The US shut down in 2009. Amateur (Ham) Radio has a small allocation of the band, known as the 1.25meter band, from 219 to 220MHz and 222.0 to 225.0MHz for communications. Broadcast television systems#ITU standards Broadcast television systems (or terrestrial television systems outside the US and Canada) are the encoding or formatting systems for the transmission and reception of terrestrial television signals. Analog television systems were standardized by

2294-617: 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

2356-539: 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,

2418-508: The applicable video standard. In composite video signals, the U and V signals modulate a color subcarrier signal, and the result is referred to as the chrominance signal; the phase and amplitude of this modulated chrominance signal correspond approximately to the hue and saturation of the color. In digital-video and still-image color spaces such as Y′CbCr , the luma and chrominance components are digital sample values. Separating RGB color signals into luma and chrominance allows

2480-446: 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

2542-436: The color burst signal were visible on a television screen, it would appear as a vertical strip of a very dark olive color. In NTSC and PAL , hue is represented by a phase shift of the chrominance signal relative to the color burst, while saturation is determined by the amplitude of the subcarrier. In SECAM (R′ − Y′) and (B′ − Y′) signals are transmitted alternately and phase does not matter. Chrominance

Band III - Misplaced Pages Continue

2604-422: 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 History Chrominance Chrominance ( chroma or C for short) is the signal used in video systems to convey

2666-412: 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

2728-434: 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

2790-424: 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

2852-466: The introduction of color television, by 1966 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. Except for lines and frame rates , other units are megahertz (MHz). For historical reasons, some countries use

2914-523: 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

2976-466: 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. Ignoring color, all television systems work in essentially the same manner. The monochrome image seen by

3038-477: The most commonly used, although there are other video standards that employ different subcarrier frequencies. For example, PAL-M (Brazil) uses a 3.58 MHz subcarrier, and SECAM uses two different frequencies, 4.250 MHz and 4.40625 MHz above the video carrier. The presence of chrominance in a video signal is indicated by a color burst signal transmitted on the back porch , just after horizontal synchronization and before each line of video starts. If

3100-400: 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

3162-416: 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

SECTION 50

#1732790164570

3224-576: The predominating color (signal T), and the other the mean brilliance (signal t) output from a single television transmitter to be received not only by color television receivers provided with the necessary more expensive equipment, but also by the ordinary type of television receiver which is more numerous and less expensive and which reproduces the pictures in black and white only. Previous schemes for color television systems, which were incompatible with existing monochrome receivers, transmitted RGB signals in various ways. In analog television , chrominance

3286-479: 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

3348-549: 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 ,

3410-425: 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

3472-568: 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. 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 (used in Germany, Italy, US), 405-line (used in

3534-403: 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

3596-415: The world: ATSC , DVB , ISDB and DTMB . 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

3658-412: 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

3720-541: 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

3782-458: 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 ) 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

SECTION 60

#1732790164570

3844-406: 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

#569430