Components of Tv System

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Analog (oranalogue) television is theanalog transmissionthat involves the broadcastingof

encoded analog audioand analog videosignal:[1] one in which the message conveyed by the

broadcast signal is a function of deliberate variations in the amplitude and/orfrequencyof the signal.

All broadcast television systems preceding digital transmissionofdigital television (DTV) were systems

utilizing analog signals. Analog television may bewireless or can require copperwire used by cable

converters.

Early Monochrome Analog receiver

Contents

[hide]

1 Development

1.1 Standards

1.2 Displaying an image

1.3 Other types of display screens

2 Receiving signals

2.1 Extracting the sound

2.2 Structure of a video signal

2.3 Monochrome video signal extraction

2.4 Color video signal extraction

3 Synchronization

3.1 Horizontal synchronization

3.2 Vertical synchronization

3.3 Horizontal hold and vertical hold
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4 Transition to digital broadcasts

5 Other technical information

5.1 Components of a television system

5.2 Sync Separator

5.3 Timebase circuits

5.4 CRT flyback power supply design and operation

principles

6 See also

7 External links

8 References

[edit]Development

Main article: History of Television

The earliest mechanical television systems used spinning disks with patterns of holes punched into the

disc to "scan" an image. A similar disk reconstructed the image at the receiver. Synchronization of the

receiver disc rotation was handled through sync pulses broadcast with the image information. However

these mechanical systems were slow, the images were dim and flickered severely, and the image

resolution very low. Camera systems used similar spinning discs and required intensely bright illumination

of the subject for the light detector to work.

Analog television did not really begin as an industry until the development of the cathode-ray tube (CRT),which uses a steered electron beam to "write" lines of electrons across a phosphorcoated surface. The

electron beam could be swept across the screen much faster than any mechanical disc system, allowing

for more closely spaced scan lines and much higher image resolution, while slow-fade phosphors

removed image flicker effects. Also far less maintenance was required of an all-electronic system

compared to a spinning disc system.

[edit]Standards

Further information: Broadcast television system

Broadcasters using analog television systems encode their signal usingNTSC, PALorSECAManalog

encoding[2] and then useRF modulationto modulate this signal onto a Very high frequency (VHF) orUltra

high frequency (UHF) carrier. Each frame of a television image is composed of lines drawn on the screen.The lines are of varying brightness; the whole set of lines is drawn quickly enough that the human eye

perceives it as one image. The next sequential frame is displayed, allowing the depiction of motion. The

analog television signal contains timing and synchronization information so that the receiver can

reconstruct a two-dimensional moving image from a one-dimensional time-varying signal.
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In many countries, over-the-airbroadcast television ofanalog audio and analog video signals is being

discontinued, to allow the re-use of the television broadcast radio spectrumfor other services such

as datacasting and subchannels.

The first commercial televisionsystems were black-and-white; The beginning ofcolor televisionwas in

the 1950s.[3]

A practical television system needs to take luminance,chrominance (in a color system), synchronization

(horizontal and vertical), and audiosignals, andbroadcastthem over a radio transmission. The

transmission system must include a means oftelevision channel selection.

Analog broadcast television systems come in a variety of frame rates and resolutions. Further differences

exist in the frequency and modulation of the audio carrier. The monochrome combinations still existing in

the 1950s are standardized by the International Telecommunication Union(ITU) as capital letters A

through N. When color television was introduced, the hue and saturation information was added to the

monochrome signals in a way that black & white televisions ignore. This way backwards compatibility was

achieved. That concept is true for all analog television standards.

However there are three standards for the way the additional color information can be encoded andtransmitted. The first was the American NTSC (National Television Systems Committee) color television

system. The European/Australian PAL (Phase Alternation Line rate) and the French-Former Soviet Union

SECAM (Squentiel Couleur Avec Mmoire) standard were developed later and attempt to cure certain

defects of the NTSC system. PAL's color encoding is similar to the NTSC systems. SECAM, though, uses

a different modulation approach than PAL or NTSC.

In principle all three color encoding systems can be combined with any scan line/frame rate combination.

Therefore, in order to describe a given signal completely, it's necessary to quote the color system and the

broadcast standard as capital letter. For example the United States uses NTSC-M, the UK uses PAL-I,

France uses SECAM-L, much of Western Europe and Australia uses PAL-B/G, most of Eastern Europe

uses PAL-D/K or SECAM-D/K and so on.

However not all of these possible combinations actually exist. NTSC is currently onlyused with system M,

even though there were experiments with NTSC-A (405 line) and NTSC-I (625 line) in the UK. PAL is

used with a variety of 625-line standards (B,G,D,K,I,N) but also with the North American 525-line

standard, accordingly named PAL-M. Likewise, SECAM is used with a variety of 625-line standards.

For this reason many people refer to any 625/25 type signal as "PAL" and to any 525/30 signal as

"NTSC", even when referring to digital signals, for example, onDVD-Videowhich don't contain any

analog color encoding, thus no PAL or NTSC signals at all. Even though this usage is common, it is

misleading as that is not the original meaning of the terms PAL/SECAM/NTSC.

Although a number of different broadcast television systems were in use worldwide, the same principles

of operation apply.[4]

[edit]Displaying an image

Acathode-ray tube(CRT) television displays an image by scanning a beam ofelectronsacross the

screen in a pattern of horizontal lines known as araster. At the end of each line the beam returns to the

start of the next line; at the end of the last line it returns to the top of the screen. As it passes each point

the intensity of the beam is varied, varying the luminance of that point. A color television system is

identical except that an additional signal known aschrominance controls the color of the spot.
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Raster scanning is shown in a slightly simplified form below.

When analog television was developed, no affordable technology for storing any video signals existed;

the luminance signal has to be generated and transmitted at the same time at which it is displayed on the

CRT. It is therefore essential to keep the raster scanning in the camera (or other device for producing the

signal) in exactsynchronization with the scanning in the television.

The physics of the CRT require that a finite time interval is allowed for the spot to move back to the start

of the next line (horizontal retrace) or the start of the screen (vertical retrace). The timing of the luminancesignal must allow for this.

The human eye has a characteristic called Persistence of vision. Quickly displaying successive scan

images will allow the apparent illusionof smooth motion. Flickering of the image can be partially solved

using a long persistence phosphor coating on the CRT, so that successive images fade slowly. However,

slow phosphor has the negative side-effect of causing image smearing and blurring when there is a large

amount of rapid on-screen motion occurring.

The maximum frame rate depends on the bandwidth of the electronics and the transmission system, and

the number of horizontal scan lines in the image. A frame rate of 25 or 30 hertzis a satisfactory

compromise, while the process ofinterlacing two video fields of the picture perframeis used to build the

image. This process doubles the apparent number of video fields per second and further reduces flickerand other defects in transmission.
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Close up image of analog color screen

[edit]Other types of display screens

Plasma screens andLCDscreens have been used in analog television sets. These types of display

screens use lower voltages than older CRT displays. Many dual system television receivers, equipped to

receive both analog transmissionsanddigital transmissionshave analogtuner (television) receiving

capability and must use atelevision antenna.

[edit]Receiving signals

The television system for each country will specify a number oftelevision channels within

the UHForVHF frequency ranges. A channel actually consists of two signals: the picture information is

transmitted using amplitude modulation on one frequency, and the sound is transmitted withfrequency

modulation at a frequency at a fixed offset (typically 4.5 to 6 MHz) from the picture signal.

The channel frequencies chosen represent a compromise between allowing enoughbandwidth for video

(and hence satisfactory picture resolution), and allowing enough channels to be packed into the available

frequency band. In practice a technique called vestigial sidebandis used to reduce the channel spacing,

which would be at least twice the video bandwidth if pure AM was used.

Signal reception is invariably done via a superheterodyne receiver: the first stage is a tunerwhich selects

atelevision channel and frequency-shifts it to a fixedintermediate frequency(IF). The

signal amplifier(from the microvolt range to fractions of a volt) performs amplification to the IF stages.

[edit]Extracting the sound

At this point the IF signal consists of a video carrier wave at one frequency and the sound carrier at a

fixed offset. Ademodulatorrecovers the video signal and sound as an FM signal at the offset frequency(this is known as intercarrier sound).

The FM sound carrier is then demodulated, amplified, and used to drive a loudspeaker. Until the advent of

the NICAM and MTSsystems, TV sound transmissions were invariably monophonic.

[edit]Structure of a video signal

The video carrier is demodulated to give a composite videosignal; this contains luminance, chrominance

and synchronization signals;[5] this is identical to the video signal format used by analog video devices
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such as VCRsorCCTV cameras. Note that the RF signal modulation is inverted compared to the

conventional AM: the minimum video signal level corresponds to maximum carrier amplitude, and vice

versa. The carrier is never shut off altogether; this is to ensure that intercarrier sound demodulation can

still occur.

Each line of the displayed image is transmitted using a signal as shown above. The same basic format

(with minor differences mainly related to timing and the encoding of color) is used

forPAL,NTSCandSECAM television systems. A monochrome signal is identical to a color one, with the

exception that the elements shown in color in the diagram (the color burst, and the chrominance signal)

are not present.

Portion of a PAL videosignal. From left to right: end of a video scan line, front porch, horizontalsync pulse,back

porchwith color burst, and beginning of next line
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The front porch is a brief (about 1.5 microsecond) period inserted between the end of each transmitted

line of picture and the leading edge of the next line sync pulse. Its purpose was to allowvoltage levels to

stabilise in older televisions, preventing interference between picture lines. The front porch is the first

component of the horizontal blanking intervalwhich also contains the horizontalsync pulse and the back

porch.[6][7]

The back porch is the portion of each scan line between the end (rising edge) of the horizontalsync

pulse and the start of active video. It is used to restore the black level (300 mV.) reference in analog

video. In signal processing terms, it compensates for the fall timeand settling time following the sync

pulse.[6][7]

In color TV systems such as PAL and NTSC, this period also includes the colorburst signal. In

the SECAMsystem it contains the reference subcarrier for each consecutive color difference signal in

order to set the zero-color reference.

In some professional systems, particularlysatellite links between locations, the audio is embedded within

the back porch of the video signal, to save the cost of renting a second channel.

[edit]Monochrome video signal extractionThe luminance component of a composite video signal varies between 0 V and approximately 0.7 V

above the 'black' level. In the NTSC system, there is a blankingsignal level used during the front porch

and back porch, and a blacksignal level 75 mV above it; in PAL and SECAM these are identical.

In a monochrome receiver the luminance signal is amplified to drive the control gridin theelectron gunof

the CRT. This changes the intensity of the electron beam and therefore the brightness of the spot being

scanned. Brightness and contrast controls determine the DC shift and amplification, respectively.

[edit]Color video signal extraction

Color bar generator test signal

A color signal conveys picture information for each of the red, green, and blue components of an image

(see the article on Color space for more information). However, these are not simply transmitted as three

separate signals, because:

such a signal would not be compatible with monochrome receivers (an important consideration when

color broadcasting was first introduced)
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it would occupy three times the bandwidth of existing television, requiring a decrease in the number

of TV channels available

typical problems with signal transmission (such as differing received signal levels between different

colors) would produce unpleasant side effects.

Instead, the RGB signals are converted into YUV form, where the Y signal represents the overallbrightness, and can be transmitted as the luminance signal. This ensures a monochrome receiver will

display a correct picture. The U and V signals are the difference between the Y signal and the B and R

signals respectively. The U signal then represents how "blue" the color is, and the V signal how "red" it is.

The advantage of this scheme is that the U and V signals are zero when the picture has no color content.

Since the human eye is more sensitive to errors in luminance than in color, the U and V signals can be

transmitted in a relatively lossy (specifically: bandwidth-limited) way with acceptable results. The G signal

is not transmitted in the YUV system, but rather it is recovered electronically at the receiving end.

Color signals mixed with video signal

In the NTSC andPALcolor systems, U and V are transmitted by adding a color subcarrierto the

composite video signal, and using quadrature amplitude modulation on it. For NTSC, the subcarrier is

usually at about 3.58 MHz, but for the PAL system it is at about 4.43 MHz. These frequencies are withinthe luminance signal band, but their exact frequencies were chosen such that they are midway between

two harmonics of the horizontal line repetition rate, thus ensuring that the majority of the power of the

luminance signal does not overlap with the power of the chrominance signal.

In the British PAL (D) system, the actual chrominance center frequency is 4.43361875 MHz, a direct

multiple of the scan rate frequency. This frequency was chosen to minimize the chrominance beat

interference pattern that would be visible in areas of high color saturation in the transmitted picture.

The two signals (U and V) modulate both theamplitude and phaseof the color carrier, so to demodulate

them it is necessary to have a reference signal against which to compare it. For this reason, a short burst

of reference signal known as the color burstis transmitted during the back porch (re-trace period) of each

scan line. A reference oscillator in the receiver locks onto this signal (seephase-locked loop) to achieve aphase reference, and uses its amplitude to set an AGC system to achieve an amplitude reference.

The U and V signals are then demodulated by band-pass filtering to retrieve the color subcarrier, mixing it

with the in-phase and quadraturesignals from the reference oscillator, and low-pass filtering the results.
http://en.wikipedia.org/wiki/YUVhttp://en.wikipedia.org/wiki/Lossy_compressionhttp://en.wikipedia.org/wiki/NTSChttp://en.wikipedia.org/wiki/PALhttp://en.wikipedia.org/wiki/PALhttp://en.wikipedia.org/wiki/PALhttp://en.wikipedia.org/wiki/Quadrature_amplitude_modulationhttp://en.wikipedia.org/wiki/United_Kingdomhttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Phase_(waves)http://en.wikipedia.org/wiki/Phase_(waves)http://en.wikipedia.org/wiki/Phase-locked_loophttp://en.wikipedia.org/wiki/Phase-locked_loophttp://en.wikipedia.org/wiki/Automatic_gain_controlhttp://en.wikipedia.org/wiki/Quadrature_phasehttp://en.wikipedia.org/wiki/File:Waveform_monitor.jpghttp://en.wikipedia.org/wiki/File:Waveform_monitor.jpghttp://en.wikipedia.org/wiki/YUVhttp://en.wikipedia.org/wiki/Lossy_compressionhttp://en.wikipedia.org/wiki/NTSChttp://en.wikipedia.org/wiki/PALhttp://en.wikipedia.org/wiki/Quadrature_amplitude_modulationhttp://en.wikipedia.org/wiki/United_Kingdomhttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Phase_(waves)http://en.wikipedia.org/wiki/Phase-locked_loophttp://en.wikipedia.org/wiki/Automatic_gain_controlhttp://en.wikipedia.org/wiki/Quadrature_phase


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Test card showing "Hanover Bars" (color banding phase effect) in Pal S (simple) signal mode of transmission.

NTSC uses this process unmodified. Unfortunately, this often results in poor color reproduction due to

phase errors in the received signal. The PAL D (delay) system corrects this by reversing the phase of the

signal on each successive line, and the averaging the results over pairs of lines. This process is achieved

by the use of a 1H (where H = horizontal scan frequency) duration delay line. (A typical circuit used withthis device converts the low frequency color signal to ultrasonic sound and back again). Phase shift errors

between successive lines are therefore cancelled out and the wanted signal amplitude is increased when

the two in-phase (coincident) signals are re-combined.

In the SECAMtelevision system, U and V are transmitted on alternate lines, using simplefrequency

modulation of two different color subcarriers.

In analog color CRT displays, the brightness control signal (luminance) is fed to the cathodeconnections

of the electron guns, and the color difference signals (chrominance signals) are fed to the control grids

connections. This simple matrix mixing technique was replaced in latersolid state designs of signal

processing.

[edit]Synchronization

Synchronizing pulses added to the video signal at the end of every scan lineand video frame ensure that

the sweep oscillators in the receiver remain locked in step with the transmitted signal, so that the image

can be reconstructed on the receiver screen.[6][7][8]

A sync separatorcircuit detects the sync voltage levels and sorts the pulses into horizontal and vertical

sync. (see section below - Other technical information, for extra detail.)

[edit]Horizontal synchronization

The horizontal synchronization pulse (horizontal syncHSYNC), separates the scan lines. The horizontal

sync signal is a single short pulse which indicates the start of every line. The rest of the scan line follows,with the signal ranging from 0.3 V (black) to 1 V (white), until the next horizontal orvertical

synchronization pulse.

The format of the horizontal sync pulse varies. In the 525-lineNTSC system it is a 4.85 s-long pulse at

0V. In the 625-line PAL system the pulse is 4.7 s synchronization pulse at 0 V. This is lower than the

amplitude of any video signal (blacker than black) so it can be detected by the level-sensitive "sync

stripper" circuit of the receiver.
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[edit]Vertical synchronization

Vertical synchronization (Also vertical syncorV-SYNC) separates the video fields. In PAL and NTSC, the

vertical sync pulse occurs within the vertical blanking interval. The vertical sync pulses are made by

prolonging the length of HSYNC pulses through almost the entire length of the scan line.

The vertical syncsignal is a series of much longer pulses, indicating the start of a new field. The syncpulses occupy the whole of line interval of a number of lines at the beginning and end of a scan; no

picture information is transmitted during vertical retrace. The pulse sequence is designed to allow

horizontal sync to continue during vertical retrace; it also indicates whether each field represents even or

odd lines in interlaced systems (depending on whether it begins at the start of a horizontal line, or mid-

way through).

The format of such a signal in 525-line NTSC is:

pre-equalizing pulses (6 to start scanning odd lines, 5 to start scanning even lines)

long-sync pulses (5 pulses)

post-equalizing pulses (5 to start scanning odd lines, 4 to start scanning even lines)

Each pre- or post- equalizing pulse consists in half a scan lineof black signal: 2 s at 0 V, followed by

30 s at 0.3 V.

Each long sync pulse consists in an equalizing pulse with timings inverted: 30 s at 0 V, followed by 2 s

at 0.3 V.

In video production and computer graphics, changes to the image are often kept in step with the vertical

synchronization pulse to avoid visible discontinuity of the image. Since the frame bufferof a computer

graphics display imitates the dynamics of a cathode-ray display, if it is updated with a new image while

the image is being transmitted to the display, the display shows a mishmash of both frames, producing

apage tearing artifact partway down the image.

Vertical synchronization eliminates this by timing frame buffer fills to coincide with the vertical blanking

interval, thus ensuring that only whole frames are seen on-screen. Software such asvideo

games and computer aided design(CAD) packages often allow vertical synchronization as an option,

because it delays the image update until the vertical blanking interval. This produces a small penalty in

latency, because the program has to wait until the video controller has finished transmitting the image to

the display before continuing. Triple buffering reduces this latency significantly.

Two timing intervals are defined - the front porch between the end of displayed video and the start of the

sync pulse, and the back porch after the sync pulse and before displayed video. These and the sync

pulse itself are called the horizontal blanking(orretrace) intervaland represent the time that the electron

beam in the CRT is returning to the start of the next display line.

[edit]Horizontal hold and vertical hold

The lack of precision timing components available in early television receivers meant that the timebase

circuits occasionally needed manual adjustment. The adjustment took the form ofhorizontal

holdand vertical holdcontrols, usually on the rear of the television set. Loss of horizontal synchronization

usually resulted in an unwatchable picture; loss of vertical synchronization would produce an image rolling

up or down the screen.
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[edit]Transition to digital broadcasts

Main article: Digital television transition

Main article: Digital television

As of late 2009, ten countries had completed the process of turning off analog terrestrial broadcasting.Many other countries had plans to do so or were in the process of a staged conversion. The first country

to make a wholesale switch to digital over-the-air (terrestrial television) broadcasting was Luxembourgin

2006, followed later in 2006 bythe Netherlands; in 2007 byFinland,Andorra,Sweden,Norway,

andSwitzerland; in 2008 by Belgium (Flanders)and Germany; in 2009 by the United States (high power

stationsthe important ones), southernCanada, the Isle of Man,Norway, and Denmark. In 2010, Belgium

(Wallonia),Spain, Wales, Latvia,Estonia, the Channel Islands, andSlovenia; in

2011 Israel,Austria,Monaco,Scotland,Cyprus,Japan (excluding Miyagi, Iwate,

andFukushimaPrefectures), Malta and Francecompleted the transition.

In the United States, high-power over-the-air broadcasts are solely in the ATSC digital format since June

12, 2009, the date that theFederal Communications Commission(FCC) set for the end of all high-power

analog TV transmissions. As a result, almost two million households could no longer watch TV because

they were not prepared for the transition. The switchover was originally scheduled for February 17, 2009,

until the U.S. Congress passed the DTV Delay Act.[9] By special dispensation, some analog TV signals

ceased on the original date.[10]While the majority of the viewers of over-the-air broadcast television in the

U.S. watch full-power stations (which number about 1800), there are three other categories of TV stations

in the U.S.: low-power broadcasting stations, Class A stations, andTV translator stations. There is

presently no deadline for these stations, about 7100 in number, to convert to digital broadcasting.

It is necessary to be cognizant of the fact that in broadcasting, whatever happens in the United States

also happens simultaneously in southern Canada and in northern Mexico because those areas are

covered by TV stations in the U.S. Furthermore, the major cities of southern Canada made their

transitions to digital TV broadcasts simultaneously with theU.S.: Toronto,Montreal,Vancouver,Ottawa,Winnipeg, Sault Ste. Marie,Quebec

City,Charlottetown, Halifax, and so forth.

In Japan, the switch to digital occurred on the 24th of July, 2011 (with the exception of Fukushima, Iwate,

and Miyagi prefectures, where conversion was delayed one year due to complications from the 2011

Thoku earthquake and tsunami). In Canada, it is scheduled to happen August 31, 2011. China is

scheduled to switch in 2015. In the United Kingdom, the digital switchover has different times for each

part of the country. However, the entire U.K. should be on digital TV by 2012.

Brazil switched to digital TV on December 2, 2007, in its major cities, and now it is estimated that it will

take about seven years for complete conversion over all of Brazilbut understand that large parts of

Brazil are unpopulated by people who have electricity and TV. Australia will turn off analog TV in steps,

TV network by network, between 2010 and 2013, region by region.[11]

In Malaysia, the Malaysian Communications & Multimedia Commission (MCMC) advertised for tender

bids to be submitted in the third quarter of 2009 for the 470 through 742 MHz UHF allocation, to enable

Malaysia's broadcast system to move into DTV. The new broadcast bandallocation would result in

Malaysia's having to build an infrastructure for all broadcasters, using a single digital terrestrial

transmission/TV broadcast (DTTB) channel.
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wiki/Waleshttp://en.wikipedia.org/wiki/Latviahttp://en.wikipedia.org/wiki/Estoniahttp://en.wikipedia.org/wiki/Channel_Islandshttp://en.wikipedia.org/wiki/Sloveniahttp://en.wikipedia.org/wiki/Israelhttp://en.wikipedia.org/wiki/Austriahttp://en.wikipedia.org/wiki/Monacohttp://en.wikipedia.org/wiki/Scotlandhttp://en.wikipedia.org/wiki/Cyprushttp://en.wikipedia.org/wiki/Japanhttp://en.wikipedia.org/wiki/Miyagi_Prefecturehttp://en.wikipedia.org/wiki/Iwate_Prefecturehttp://en.wikipedia.org/wiki/Fukushima_Prefecturehttp://en.wikipedia.org/wiki/Maltahttp://en.wikipedia.org/wiki/Francehttp://en.wikipedia.org/wiki/ATSChttp://en.wikipedia.org/wiki/Federal_Communications_Commissionhttp://en.wikipedia.org/wiki/U.S._Congresshttp://en.wikipedia.org/wiki/DTV_Delay_Acthttp://en.wikipedia.org/wiki/Low-power_broadcastinghttp://en.wikipedia.org/wiki/Class_A_television_servicehttp://en.wikipedia.org/wiki/Broadcast_relay_stationhttp://en.wikipedia.org/wiki/Torontohttp://en.wikipedia.org/wiki/Montrealhttp://en.wikipedia.org/wiki/Vancouverhttp://en.wikipedia.org/wiki/Ottawahttp://en.wikipedia.org/wiki/Winnipeghttp://en.wikipedia.org/wiki/Sault_Ste._Marie,_Ontariohttp://en.wikipedia.org/wiki/Quebec_Cityhttp://en.wikipedia.org/wiki/Quebec_Cityhttp://en.wikipedia.org/wiki/Charlottetownhttp://en.wikipedia.org/wiki/Halifax_County,_Nova_Scotiahttp://en.wikipedia.org/wiki/2011_T%C5%8Dhoku_earthquake_and_tsunamihttp://en.wikipedia.org/wiki/2011_T%C5%8Dhoku_earthquake_and_tsunamihttp://en.wikipedia.org/wiki/Brazilhttp://en.wikipedia.org/wiki/UHFhttp://en.wikipedia.org/wiki/Broadcast_bandhttp://en.wikipedia.org/wiki/Infrastructurehttp://en.wikipedia.org/w/index.php?title=Digital_terrestrial_transmission&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Digital_terrestrial_transmission&action=edit&redlink=1


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People also need to understand that large portions of Malaysia are covered by TV broadcasts

from Singapore,Thailand,Brunei, and/orIndonesia (from Borneo).

Users may then encode and transmit theirtelevision programson this channels` digital data stream. The

winner was to be announced at the end of 2009 or early 2010. A condition of the award is that digital

transmission must start as soon as possible, and analog switch-off was proposed for 2015. The scheme

may not go ahead as the Government successor, Najib Tun Razak deferred the transition indefinitely in

favor of his own 1Malaysia concept, which means that analog television will continue for longer than

originally planned.[citation needed]

[edit]Other technical information

Further information: Broadcast engineering

Further information: Electronic engineering

[edit]Components of a television system

A typical analogtelevision receiveris based around the block diagram shown below:

[edit]Sync Separator
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Portion of a PAL videosignal. From left to right: end of a video line, front porch, horizontal sync pulse,back porchwithcolor

burst, and beginning of next line

Beginning of the frame, showing several scan lines; the terminal part of the vertical sync pulse is at the left

PAL videosignal frames. Left to right: frame with scan lines (overlapping together, horizontal sync pulses show as the

doubled straight horizontal lines), vertical blanking interval with vertical sync (shows as brightness increase of the bottom

part of the signal in almost the leftmost part of the vertical blanking interval), entire frame, another VBI with VSYNC,

beginning of third frame
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Image synchronization is achieved by transmitting negative-going pulses; in a composite video signal of 1

volt amplitude, these are approximately 0.3 V below the"black level". Thehorizontal syncsignal is a single

short pulse which indicates the start of every line. Two timing intervals are defined - the front

porch between the end of displayed video and the start of the sync pulse, and the back porch after the

sync pulse and before displayed video. These and the sync pulse itself are called the horizontal

blanking(orretrace) intervaland represent the time that the electron beam in the CRT is returning to thestart of the next display line. The vertical syncsignal is a series of much longer pulses, indicating the start

of a new field. The sync pulses occupy the whole of line interval of a number of lines at the beginning and

end of a scan; no picture information is transmitted during vertical retrace. The pulse sequence is

designed to allow horizontal sync to continue during vertical retrace; it also indicates whether each field

represents even or odd lines in interlaced systems (depending on whether it begins at the start of a

horizontal line, or mid-way through). In the TV receiver, async separatorcircuit detects the sync voltage

levels and sorts the pulses into horizontal and vertical sync. Loss of horizontal synchronization usually

resulted in an unwatchable picture; loss of vertical synchronization would produce an image rolling up or

down the screen.

[edit]Timebase circuits

Further information: Oscilloscope

In an analog receiver with a CRT display sync pulses are fed to horizontal and verticaltimebase amplifier

circuits. These generate modified sawtooth andparabolacurrent waveforms to scan the electron beam in

alinearway. The waveform shapes are necessary to make up for the distance variations from the

electron beam source and the screen surface. Each beam direction switching circuit is reset by the

appropriate sync timing pulse. These waveforms are fed to the horizontal and vertical scan coils wrapped

around the CRT tube. These coils produce amagnetic fieldproportional to the changing current, and this

deflects the electron beam across the screen. In the 1950s, television receiver timebase supply was

derived directly from the mains supply. A simple circuit consisted of a series voltage

dropperresistance and arectifiervalve (tube) orsemiconductordiode. This avoided the cost of a large

high voltage mains supply (50 or 60 Hz) transformer. This type of circuit was used forthermionic

valve(tube) technology. It was inefficient and produced a lot of heat which led to premature failures in the

circuitry. In the 1960s,semiconductortechnology was introdued into timebase circuits. During the late

1960s in the U.K., synchronous, (with the scan line rate), power generation was introduced intosolid

state receiver designs.[12] These had very complex circuits in which faults were difficult to trace, but had

very efficient use of power. In the early 1970s AC mains (50 Hz), and line timebase

(15,625 Hz), thyristorbased switching circuits were introduced. In the U.K. use of the simple (50 Hz)

types of power circuits were discontinued. The reason for design changes arose from the electricity

supply contamination problems arising from EMI,[13] and supply loading issues due to energy being taken

from only the positive half cycle of the mains supply waveform.[14]

[edit]CRT flyback power supply design and operation principles

Further information: Extra high tension

See also:Power supply

Most of the receiver's circuitry (at least intransistor- orIC-based designs) operates from a comparatively

low-voltageDC power supply. However, the anode connection for acathode-ray tuberequires a very high

voltage (typically 10-30 kV) for correct operation.
http://en.wikipedia.org/wiki/Black_levelhttp://en.wikipedia.org/wiki/Black_levelhttp://en.wikipedia.org/wiki/Black_levelhttp://en.wikipedia.org/w/index.php?title=Analog_television&action=edit&section=18http://en.wikipedia.org/wiki/Oscilloscopehttp://en.wikipedia.org/wiki/Cathode_ray_tubehttp://en.wikipedia.org/wiki/Sawtooth_wavehttp://en.wikipedia.org/wiki/Parabolahttp://en.wikipedia.org/wiki/Parabolahttp://en.wikipedia.org/wiki/Parabolahttp://en.wikipedia.org/wiki/Linearhttp://en.wikipedia.org/wiki/Linearhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Series_and_parallel_circuitshttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Rectifierhttp://en.wikipedia.org/wiki/Rectifierhttp://en.wikipedia.org/wiki/Rectifierhttp://en.wikipedia.org/wiki/Valvehttp://en.wikipedia.org/wiki/Tubehttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Diodehttp://en.wikipedia.org/wiki/Diodehttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Thermionic_valvehttp://en.wikipedia.org/wiki/Thermionic_valvehttp://en.wikipedia.org/wiki/Thermionic_valvehttp://en.wikipedia.org/wiki/Thermionic_valvehttp://en.wikipedia.org/wiki/Tubehttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/U.K.http://en.wikipedia.org/wiki/Synchronoushttp://en.wikipedia.org/wiki/Solid_state_(electronics)http://en.wikipedia.org/wiki/Solid_state_(electronics)http://en.wikipedia.org/wiki/Solid_state_(electronics)http://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Thyristorhttp://en.wikipedia.org/wiki/EMIhttp://en.wikipedia.org/wiki/EMIhttp://en.wikipedia.org/w/index.php?title=Analog_television&action=edit&section=19http://en.wikipedia.org/wiki/Extra_high_tensionhttp://en.wikipedia.org/wiki/Power_supplyhttp://en.wikipedia.org/wiki/Power_supplyhttp://en.wikipedia.org/wiki/Transistorhttp://en.wikipedia.org/wiki/Transistorhttp://en.wikipedia.org/wiki/Integrated_circuithttp://en.wikipedia.org/wiki/Integrated_circuithttp://en.wikipedia.org/wiki/Direct-currenthttp://en.wikipedia.org/wiki/Direct-currenthttp://en.wikipedia.org/wiki/Anodehttp://en.wikipedia.org/wiki/Cathode-ray_tubehttp://en.wikipedia.org/wiki/Cathode-ray_tubehttp://en.wikipedia.org/wiki/Cathode-ray_tubehttp://en.wikipedia.org/wiki/Black_levelhttp://en.wikipedia.org/w/index.php?title=Analog_television&action=edit&section=18http://en.wikipedia.org/wiki/Oscilloscopehttp://en.wikipedia.org/wiki/Cathode_ray_tubehttp://en.wikipedia.org/wiki/Sawtooth_wavehttp://en.wikipedia.org/wiki/Parabolahttp://en.wikipedia.org/wiki/Linearhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Series_and_parallel_circuitshttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Rectifierhttp://en.wikipedia.org/wiki/Valvehttp://en.wikipedia.org/wiki/Tubehttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Diodehttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Thermionic_valvehttp://en.wikipedia.org/wiki/Thermionic_valvehttp://en.wikipedia.org/wiki/Tubehttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/U.K.http://en.wikipedia.org/wiki/Synchronoushttp://en.wikipedia.org/wiki/Solid_state_(electronics)http://en.wikipedia.org/wiki/Solid_state_(electronics)http://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Thyristorhttp://en.wikipedia.org/wiki/EMIhttp://en.wikipedia.org/w/index.php?title=Analog_television&action=edit&section=19http://en.wikipedia.org/wiki/Extra_high_tensionhttp://en.wikipedia.org/wiki/Power_supplyhttp://en.wikipedia.org/wiki/Transistorhttp://en.wikipedia.org/wiki/Integrated_circuithttp://en.wikipedia.org/wiki/Direct-currenthttp://en.wikipedia.org/wiki/Anodehttp://en.wikipedia.org/wiki/Cathode-ray_tube


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This voltage is not directly produced by the main power supply circuitry; instead the receiver makes use of

the circuitry used for horizontal scanning.Direct current(DC), is switched though the line output

transformer, and alternating current ([AC]) is induced into the scan coils. At the end of each horizontal

scan line the magnetic field which has built up in both transformer and scan coils by the current, is a

source of latent electromagnetic energy. This stored collapsing magnetic field energy can be captured.

The reverse flow, short duration, (about 10% of the line scan time) current from both the line outputtransformer and the horizontal scan coil is discharged again into the primary windingof the flyback

transformerby the use of a rectifier which blocks this negative reverse emf. A small value capacitoris

connected across the scan switching device. This tunes the circuitinductances to resonate at a much

higherfrequency. This slows down (lengthens) the flyback time from the extremely rapid decay rate that

would result if they were electrically isolated during this short period. One of the secondary windings on

the flyback transformer then feeds this brief high voltage pulse to a Cockcroftdesignvoltage multiplier.

This produces the required EHTsupply. A flyback converteris a power supply circuit operating on similar

principles.

Typical modern design incorporates the flyback transformer and rectifier circuitry into a single unit with a

captive output lead, (known as a diode split line output transformer),

[15]

so that all high-voltage parts areenclosed. Earlier designs used a separate line output transformer and a well insulated high voltage

multiplier unit. The high frequency (15 kHz or so) of the horizontal scanning allows reasonably small

components to be used.

[edit]See also

Television portal

Amateur television

Analog transmission

Broadcast television system

Color burst

Digital television

Narrow-bandwidth television

Overscan

Slow-scan television

Television

Terrestrial television

TV transmitter

Vertical blanking interval
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Field (video)

Video frame
http://en.wikipedia.org/wiki/Field_(video)http://en.wikipedia.org/wiki/Video_framehttp://en.wikipedia.org/wiki/Field_(video)http://en.wikipedia.org/wiki/Video_frame

Documents

Components of Tv System