A TRAINING REPORT ON

INDUSTRIAL TRAINING AT DDK , IMPHAL

Submitted by

VISHWANATH RAJKUMAR

(T.E.E&C)

In partial fulfillment of the award of

Bachelor of Electronics and Communication Engineering

North Maharashtra University, Jalgaon

Department of Electronics and Communication Engineering

SHRI SANT GADGE BABACOLLEGE OF ENGINEERING &TECHNOLOGY,

BHUSAWAL(2010-2011)

CERTIFICATE

This is to certify that the report entitled Industrial Training

at

DDK, IMPHAL

submitted by

VISHWANATH RAJKUMAR

As a part of Term work prescribed by North Maharashtra University, Jalgaon,

as record of his own carried out by his session of third year Electronics & Communication

Engineering 2010-2011

Prof. G. A. Kulkarni Dr. R. P. Singh

Head of the Department Principal

E&C Engineering S.S.G.B.C.O.E.T. Bhusawal

ACKNOWLEDGEMENT

Words often fail to express one’s feeling towards others, still I express my sincere

gratitude to Shri. N. Nandakumar Singh, Station Engineer DOORDARSHAN KENDRA,

IMPHAL for his valuable guidance, who help me a lot in understanding the various process

and concepts involved, without which it would have been difficult for me to complete my

training. It was really a great experience working in the DDK, IMPHAL and learning from

such experienced engineers with hands on experience on the subject.

I would also like to give my heartiest thanks to our Prof.G.A. Kulkarni,

HOD Electronics & Communication Engg. Department for giving his precious time,

incessant encouragement and guidance to make this training a success.

Vishwanath Rajkumar

(T.E E&C)

INDEX

1. INTRODUCTION TO TELEVISION

2. HISTORY OF TELEVISION

3. ABOUT DOORDARSHAN

4. PICTURE TRANSMISSION

5. TELEVISION TRANSMITTER

6. TELEVISION RECEIVER

7. STANDARD TELEVISION SYSTEM

8. APPLICATION OF TELEVISION

9. TELEVISION VIA SATTELITE

10. ADVANTAGES AND DISADVANTAGES OF TELEVISION

11. CONCLUSION

ABSTRACT

The aim of a television system is to extend the sense of sight beyond its natural limits

and to transmit sound associated with the scene. The picture signal is generated by a TV

camera and sound signal by a microphone. In the 625 lines CCIR monochrome and PAL-B

colour TV systems adopted by India, the picture signal is amplitude modulated and sound

signal is frequency modulated before transmission. The two carrier frequencies are suitably

spaced and their modulation products radiated through a common antenna. As in radio

communication, each television station is allotted different carrier frequencies to

enable selection of desired station at the receiving end. Doordarshan is the public television

broadcaster of India and a division of ParsarBharti a public service broadcaster nominated

by the Government of India.It is one of the largest broadcasting organizations in the world in

terms of the infrastructure of studios and transmitters.

1. INTRODUCTION TO TELEVISION

The aim of a television system is to extend the sense of sight beyond its natural limits

and to transmit sound associated with the scene. The picture signal is generated by a TV

camera by a TV camera and sound signal by a microphone. In the 625 lines CCIR

monochrome and PAL-B colour TV systems adopted by India, the picture signal is amplitude

modulated and sound signal frequency modulated before transmission. The two carrier

frequencies are suitably spaced and their modulation products radiated through a common

antenna. As in radio communication, each television station is allotted different carrier

frequencies toenable selection of desired station at the receiving end. The TV receiver has

tuned circuits in its input section called ‘tuner’. It selects desired channel signal out of the

many picked up by the antenna. The selected RF band is converted to a common fixed IF

band for convenience of providing large amplification to it. The amplified IF signals are

detected to obtain video (picture) and audio (sound) signals. The video signal after large

amplification drives the picture tube to reconstruct the televised picture on the receiver

screen. Similarly, the audio signal is amplified and fed to the loudspeaker to produce sound

output associated with the scene

2. HISTORY OF TELEVISION

In its early stages of development , television employed a combination of

optical, mechanical and electronic technologies to capture , transmit and display a visual

image. By the late 1920s, however, those employing only optical and electronic technologies

were being explored. All modern television systems rely on the latter, although the

knowledge gained from the work on mechanical-dependent systems was crucial in the

development of fully electronic television The first time images were transmitted electrically

were via early mechanical fax machines, including the pan telegraph, developed in the late

1800s. The concept of electrically-powered transmission of television images in motion was

first sketched in 1878 as the telephonoscope, shortly after the invention of the telephone. At

the time, it was imagined by early science fiction authors, that someday that light could be

transmitted over wires, as sounds were.

The idea of using scanning to transmit images was put to actual practical use in 1881

in the pan telegraph, through the use of a pendulum-based scanning mechanism. From this

period forward, scanning in one form or another has been used in nearly every image

transmission technology to date, including television. This is the concept of "rasterization",

the process of converting a visual image into a stream of electrical pulses.

In 1884 Paul Gottlieb Nipkow, a 20-year old university student in Germany, patented

the first electromechanical television system which employed a scanning disk, a spinning

disk with a series of holes spiraling toward the center, for rasterization. The holes were

spaced at equal angular intervals such that in a single rotation the disk would allow light to

pass through each hole and onto a light-sensitive selenium sensor which produced the

electrical pulses. As an image was focused on the rotating disk, each hole captured a

horizontal "slice" of the whole image.

Nipkow's design would not be practical until advances in amplifier tube technology

became available. The device was only useful for transmitting still "halftone" images —

represented by equally spaced dots of varying size — over telegraph or telephone lines. Later

designs would use a rotating mirror-drum scanner to capture the image and a cathode ray

tube (CRT) as a display device, but moving images were still not possible, due to the poor

sensitivity of the selenium sensors. In 1907 Russian scientist Boris Rosing became the first

inventor to use a CRT in the receiver of an experimental television system. He used mirror-

drum scanning to transmit simple geometric shapes to the CRT.

Scottish inventor John Logie Baird demonstrated the transmission of moving

silhouette images in London in 1925, and of moving, monochromatic images in 1926. Baird's

scanning disk produced an image of 30 lines resolution, just enough to discern a human face,

from a double spiral of lenses. Remarkably, in 1927 Baird also invented the world's first

video recording system, "Phonovision" — by modulating the output signal of his TV camera

down to the audio range he was able to capture the signal on a 10-inch wax audio disc using

conventional audio recording technology. A handful of Baird's 'Phonovision' recordings

survive and these were finally decoded and rendered into viewable images in the 1990s using

modern digital signal-processing technology.

In 1926, Hungarian engineer Kálmán Tihanyi designed a television system utilizing

fully electronic scanning and display elements, and employing the principle of "charge

storage" within the scanning (or "camera") tube. By 1927, Russian inventor Léon Theremin

developed a mirror drum-based television system which used interlacing to achieve an image

resolution of 100 lines.

Also in 1927, Herbert E. Ives of Bell Labs transmitted moving images from a 50-

aperture disk producing 16 frames per minute over a cable from Washington, DC to New

York City, and via radio from Whippany, New Jersey. Ives used viewing screens as large as

24 by 30 inches (60 by 75 centimeters). In 1927, Philo Farnsworth made the world's first

working television system with electronic scanning of both the pickup and display devices,

which he first demonstrated to the press on 1 September 1928.

2.1 HISTORY OF TELEVISION IN INDIA

Television in India has been in existence for nigh on four decades. For the first 17

years, it spread haltingly and transmission was mainly in black & white. The thinkers and

policy makers of the country, which had just been liberated from centuries of colonial rule,

frowned upon television, looking on at it as a luxury Indians could do without. In 1955 a

Cabinet decision was taken disallowing any foreign investments in print media which has

since been followed religiously for nearly 45 years. Sales of TV sets, as reflected by licenses

issued to buyers were just 676,615 until 1977. Television has come to the forefront only in

the past 21 years and more so in the past 13. There were initially two ignition points: the first

in the eighties when colour TV was introduced by state-owned broadcaster Doordarshan

(DD) timed with the 1982 Asian Games which India hosted. It then proceeded to install

transmitters nationwide rapidly for terrestrial broadcasting. In this period no private

enterprise was allowed to set up TV stations or to transmit TV signals. The second spark

came in the early nineties with the broadcast of satellite TV by foreign programmers like

CNN followed by Star TV and a little later by domestic channels such as Zee TV and Sun

TV into Indian homes. Prior to this, Indian viewers had to make do with DD's chosen fare

which was dull, non-commercial in nature, directed towards only education and socio-

economic development. Entertainment programmes were few and far between. And when the

solitary few soaps like Hum Log (1984), and mythological dramas: Ramayana (1987-88) and

Mahabharata (1988-89) were televised, millions of viewers stayed glued to their sets. When,

urban Indians learnt that it was possible to watch the Gulf War on television, they rushed out

and bought dishes for their homes. Others turned entrepreneurs and started offering the signal

to their neighbours by flinging cable over treetops and verandahs. From the large metros

satellite TV delivered via cable moved into smaller towns, spurring the purchase of TV sets

and even the up gradation from black & white to colour TVs.

DD responded to this satellite TV invasion by launching an entertainment and

commercially driven channel and introduced entertainment programming on its terrestrial

network. This again fuelled the purchase of sets in the hinterlands where cable TV was not

available. The initial success of the channels had a snowball effect: more foreign

programmers and Indian entrepreneurs flagged off their own versions. From two channels

prior to 1991, Indian viewers were exposed to more than 50 channels by 1996. Software

producers emerged to cater to the programming boom almost overnight. Some talent came

from the film industry, some from advertising and some from journalism.

More and more people set up networks until there was a time in 1995-96 when an

estimated 60,000 cable operators existed in the country. Some of them had subscriber bases

as low as 50 to as high as in the thousands. Most of the networks could relay just 6 to 14

channels as higher channel relaying capacity required heavy investments, which cable

operators were loathes making. American and European cable networks evinced interest, as

well as large Indian business groups, who set up sophisticated head ends capable of

delivering more than 30 channels. These multi-system operators (MSOs) started buying up

local networks or franchising cable TV feeds to the smaller operators for a fee. This

phenomenon led to resistance from smaller cable operators who joined forces and started

functioning as MSOs. The net outcome was that the number of cable operators in the country

has fallen to 30,000. The rash of players who rushed to set up satellite channels discovered

that advertising revenue was not large enough to support them. This led to a shakeout. At

least half a dozen either folded up or aborted the high-flying plans they had drawn up, and

started operating in a restricted manner. Some of them converted their channels into basic

subscription services charging cable operators a carriage fee.

Foreign cable TV MSOs discovered that the cable TV market was too disorganized

for them to operate in and at least three of them decided to postpone their plans and got out

of the market. The government started taxing cable operators in a bid to generate revenue.

The rates varied in the 26 states that go to form India and ranged from 35 per cent upwards.

The authorities moved in to regulate the business and a Cable TV Act was passed in 1995.

The apex court in the country, the Supreme Court, passed a judgment that the air waves are

not the property of the Indian government and any Indian citizen wanting to use them should

be allowed to do so. The government reacted by making efforts to get some regulation in

place by setting up committees to suggest what the broadcasting law of India should be, as

the sector was still being governed by laws which were passed in 19th century India.

A broadcasting bill was drawn up in 1997 and introduced in parliament. But it was

not passed into an Act. State-owned telecaster Doordarshan and radio caster All India Radio

were brought under a holding company called the Prasar Bharti under an act that had been

gathering dust for seven years, the Prasar Bharti Act, 1990. The Act served to give autonomy

to the broadcasters as their management was left to a supervisory board consisting of retired

professionals and bureaucrats.

The first practical use of television was in Germany. Regular television broadcasts

began in Germany in 1929 and in 1936 the Olympic Games in Berlin were broadcast to

television stations in Berlin and Leipzig where the public could view the games live.

A committee headed by a senior Congress (I) politician Sharad Pawar and consisting

of other politicians and industrialist was set up to review the contents of the Broadcasting

Bill. It held discussions with industry, politicians, and consumers and a report was even

drawn up. But the United Front government fell and since then the report and the Bill have

been consigned to the dustbin. ISkyB, the Murdoch DTH venture, has since been wallowing

in quicksand and in recent times has even shed a lot of employees.

3. ABOUT DOORDARSHAN

It is the public television broadcaster of India and a division of ParsarBharti a public

service broadcaster nominated by the Government of India. It is one of the largest

broadcasting organizations in the world in terms of the infrastructure of studios and

transmitter.

3.1 Beginning

Doordarshan had a modest beginning with the experimental telecast starting in Delhi

on 15 September 1959 with a small transmitter and a makeshift studio. The regular daily

transmission started in 1965 as a part of All India Radio. The television service was

extendedto Bombay and Amritsar in 1972. Till 1975, seven Indian cities had television

service and Doordarshan remained the only television channel in India. Television services

were separated from radio in 1976. Each office of All India Radio and Doordarshan were

placed under the management of two separate Director Generals in New Delhi. Finally

Doordarshan as a National Broadcaster came into existence.

3.2 Nation Wide Telecast

National telecasts were introduced in 1982. In the same year, colour TV was

introduced in the Indian market with the live telecast of the Independence Day speech by

then Prime minister Indira Gandhion 15 August 1982, followed by the 1982 Asian Games

being held in Delhi. Now more than 90 percent of the Indian population can receive

Doordarshan (DD National) programmes through a network of nearly 1400 terrestrial

transmitters and about 46 Doordarshan studios produce TV programs today.

3.3 International Broadcasting

DD-India is being broadcasted internationally through Satellite. It is available in 146

countries worldwide, however the information on picking up this channel in other countries

is not easily available. In the UK, DD-India was available through the Eurobird Satellite on

the Sky system on Channel 833 (the logo is shown as Rayat TV). The timing and

programming of DD-India international is different from that of India. Transmissions for Sky

Digital U.K. stopped in June 2008 and DirecTV U.S stopped in July 2008.

3.4 Commercial Viability

Once private television channels were allowed in the 1991, Doordarshan has seen a

steep decline in viewership in homes with Cable and Satellite Television which in 2002 was

just at 2.38% for DD National. While it earns significant advertising revenue due to the

compulsory feed given to it by the highest bidder to national events including cricket

tournaments, there has been a proposal to give it funds by imposing a license fee to own a

television in India like the BBC. However this is unlikely to be imposed keeping in view the

financial constraints of the average Indian viewer.

3.5 Channels

Presently, Doordarshan operates 19 channels – two All India channels-DD National

and DD News, 11 Regional languages Satellite Channels (RLSC), four State Networks (SN),

an International channel, a Sports Channel and two channels (DD-RS & DD-LS) for live

broadcast of parliamentary proceedings.(DD-1), Regional programmes and Local

Programmes are carried on time-sharing basis. DD-News channel, launched on 3

November 2003, which replaced the DD-Metro Entertainment channel, provides 24-Hour

news service.

The Regional Languages Satellite channels have two components – The Regional

service for the particular state relayed by all terrestrial transmitters in the state and additional

programmes in the Regional Language in prime time and non-prime time available only

through cable operators. DD-Sports Channel is exclusively devoted to the broadcasting of

sporting events of national and international importance. This is the only Sports Channels

which telecasts rural sports like Kho-Kho, Kabbadi etc. something which private

broadcasters will not attempt to telecast as it will not attract any revenues.

3.6 Active Doordarshan

It is an interactive service of Tata Sky to show 4 TV channels of Doordarshan which

are not available on Tata Sky as normal channels. Active Doordarshan channels are

Rajyasabha TV, Gyan Darshan, DD Urdu and DD Bharti.

3.7 Regional Language Satellite Service  

All DoordarshanKendras generate programmes in their respective regional

languages.  The Regional Language Satellite Services and Regional State Networks

broadcast wide spectrum of programmes covering developmental news, serials,

documentaries, news and current affairs programmes to communicate with the people in their

own language.   Programmes in regional languages are available in the respective states,

terrestrially during the regional window of DD National and round the clock on the Regional

Language Satellite Channels across the country.

 3.7.1 DD North East

 DD North East Channel is a composite satellite television service for the North

Eastern states broadcasting programmes in Assamese, English and other languages and

dialects of the North East. The programme mix includes entertainment serials, informative

programmes, social programmes, news and current affairs, art and culture.  The programmes

are produced at Doordarshan studios in Guwahati, Agartala, Kohima, Imphal, Silchar,

Dibrugarh, Tura, Aizawl, Itanagar and Shillong.

3.7.2 DD Oriya

DD Oriya is a leading round the clock satellite channel broadcasting in Oriya

language. Launched in 1994 DD Oriya broadcasts serials, cultural programmes, infotainment

programmes, news and current affairs etc.  Most of its programmes are produced at

DoordarshanKendras of Bhubaneshwar, Sambalpur and Bhawanipatna.

 3.7.3 DD Podhigai

DD Podhigai is the Tamil language channel launched in 1993.  Tamil films shown on

DD Podhigai attract a large number of viewers within as well as outside Tamil Nadu. 

Serials, films, infotainment programmes, news and current affairs are the prominent

programme genres.  DD – Podhigai is the only regional language satellite channel, that has

eight hours of terrestrial transmission.  In the terrestrial mode, from 3 p.m. to 11 p.m., DD

Podhigai reaches 94% population of Tamil Nadu.  The channel originates its programmes in

Chennai.

3.7.4 DD Punjabi

  DD Punjabi Channel was launched in 1998 which became a 24 hour service within

two years. The cultural programmes broadcast on DD Punjabi are watched with interest

across the state and by lakhs of Punjabi viewers residing in different parts of India.   In its

terrestrial mode DD Punjabi has near 100 per cent reach in the State of Punjab.  Doordarshan

Kendra, Jalandhar is the hub of DD Punjabi productions.

3.7.5 DD Sahyadri

DD Sahyadri is the Marathi language channel, launched in 1994.  Supported by

Doordarshan studios in Mumbai, Pune and Nagpur, DD Sahyadri is a household name in

Maharashtra, largely because of its programmes with high production values. Despite stiff

competition from private satellite channels, DD Sahyadri holds its own with acclaimed

serials, informative programmes, public debates and film based programmes.

3.7.6 DD Saptagiri

DD Saptagiri is the Telugu language satellite channel supported by Doordarshan

studios in Hyderabad and Vijaywada.  Launched in 1993 DD Saptagiri has entertainment

serials, infotainment programmes, news & current affairs, social programmes and film

programmes as its major content. In terrestrial mode, DD Saptagiri is available to 90% of the

population of Andhra Pradesh. 

3.7.7 DD Bangla

DD Bangla is the Bengali language satellite channel supported by Doordarshan

studios in Kolkata, Shantiniketan and Jalpaiguri.  Launched in 2001 DD Bangla has

entertainment serials, infotainment programmes, news & current affairs, social programmes

and film programmes as its major content. In terrestrial mode, DD Bangla is available to 97.1

% of the population of West Bengal.

 

3.7.8 DD Gujarati

DD Gujarati is the Gujarati language satellite channel supported by Doordarshan

studios in Ahmedabad and Rajkot.  Launched in 1992 DD Gujarati has entertainment serials,

infotainment programmes, news & current affairs, social programmes and film programmes

as its major content. In terrestrial mode, DD Gujarati is available to 84.8% of the population

of Gujarat. 

 3.7.9 DD Chandana

DD Chandana is the Kannada language satellite channel supported by Doordarshan

studios in Bangalore and Gulbarga.  Launched in 1994 DD Chandana has entertainment

serials, infotainment programmes, news & current affairs, social programmes and film

programmes as its major content. In terrestrial mode, DD Chandana is available to 81.7% of

the population of Karnataka. 

  3.7.10 DD Kashir

DD Kashir is the Kashmiri language satellite channel supported by Doordarshan

studios in Srinagar, Jammu and Leh.  Launched in 2003 DD Kashir has entertainment serials,

infotainment programmes, news & current affairs, socialprogrammes and film programmes

as its major content. In terrestrial mode, DD Kashiris available to 96 % of the population

of the valley 

 

3.7.11. DD Malayalam

 DD Malayalam is the Malayalam language satellite channel supported by

Doordarshan studios in Thiruvanthapuram and Thrissur.  Launched in 1994 DD Malayalam

has entertainment serials, infotainment programmes, news & current affairs, social

programmes and film programmes as its major content. In terrestrial mode, DD Malayalam is

available to 99.2 % of the population of Kerala. 

 Satellite Transponder D/L

FreqD/L Pol

FEC

Sym. Rate

B/W

DD-NE INSAT-4B C-04 3840.5 H ¾ 6.25 9.0DD-Bangla INSAT-3A C-01 3731.5 V ¾ 6.25 9.0DD-Oriya INSAT-3A C-02 3771.5 V ¾ 6.25 9.0DD-Sapthagiri INSAT-3A C-03 3820.5 V ¾ 6.25 9.0DD-Podhigai INSAT-3A C-03 3831.0 V ¾ 8.60 12DD-Malyalam INSAT-3A C-03 3811.5 V ¾ 6.25 9.0DD-Chandana INSAT-3A C-01 3758.5 V ¾ 6.25 9.0DD-Sahayadri INSAT-3A C-02 3791.0 V ¾ 8.60 12DD-Girnar INSAT-3A C-01 3749.5 V ¾ 6.25 9.0DD-Panjabi INSAT-3A C-01 3740.5 V ¾ 6.25 9.0DD-Kashir INSAT-3A C-02 3780.5 V ¾ 6.25 9.0

4. PICTURE TRANSMISSION

The picture information is optical in character and may be thought of as an

assemblage of a largenumber of tiny areas representing picture details. These elementary

areas into which picture details may be broken up are known as ‘picture elements’ or

‘pixels’, which when viewed together represent visual information of the scene. Thus, at any

instant there are almost an infinite number of pieces of information that need to be picked up

simultaneously for transmitting picture details. However, simultaneous pick-up is not

practicable because it is not feasible to provide a separate signal path(channel) for the signal

obtained from each picture element. In practice, this problem is solved by a method known as

‘scanning’ where conversion of optical information to electrical form is carried out element

by element, one at a time and in a sequential manner to cover the entire picture. Besides,

scanning is done at a very fast rate and repeated a large number of times per second to create

an illusion(impression at the eye) of simultaneous reception from all the elements, though

using only one Signal path.

4.1 Black And White Pictures

In a monochrome (black and white) picture, each element is either bright, some shade

of grey ordark. A TV camera, the heart of which is a camera tube, is used to convert this

optical information into corresponding electrical signal, the amplitude of which varies in

accordance with variations of brightness. Fig. 1.1 shows very elementary details of one type

of camera tube (vidicon) and associated components to illustrate the principle. An optical

image of the scene to be transmitted is focused by a lens assembly on the rectangular glass

face-plate of the camera tube. The inner side of the glass face-plate has a transparent

conductive coating on which is laid a very thin layer of photoconductive material. The

photolayer has very high resistance when no light falls on it, but decreases depending on the

intensity of light falling on it. Thus depending on light intensity variations in the focused

optical image, the conductivity of each element of photolayer changes accordingly. An

electron beam is used to pick-up picture information now available on the target plate in

terms of varying resistance at each point.

FIG1.1: Simplified Version of A Cross Sectional View Of A Vidicon Camera Tube And

Associated Component

The beam is formed by an electron gun in the TV camera tube. On its way to the

inner side of glass face-plate, it is deflected by a pair of deflecting coils mounted on the glass

envelope and kept mutually perpendicular to each other to achieve scanning of the entire

target area. Scanning is done in the same way as one reads a written page to cover all the

words in one line and all the lines on the page see (Fig. 1.2). To achieve this, the deflecting

coils are fed separately from two sweep oscillators which continuously generate suitable

waveform voltages, each operating at a different desired frequency.Magnetic deflection

caused by the current in one coil gives horizontal motion to the beam from left to right at

uniform rate and then brings it quickly to the left side to commence trace of the next line.

The other coil is used to deflect the beam from top to bottom at a uniform rate and for its

quick retrace back to the top of the plate to start this process over again.

.

Fig 1.2: Path of Scanning Beam In Covering Picture Area

Two simultaneous motions are thus given to the beam, one from left to right across

the target plate and the other from top to bottom thereby covering entire area on which

electrical image of the picture is available. As the beam moves from element to element, it

encounters a different resistance across the target-plate, depending on the resistance of

photoconductive coating. The result is a flow of current which varies in magnitude as the

elements are scanned. This current passes through a load resistance RL, connected to the

conductive coating on one side and to a dc supply source on the other. Depending on the

magnitude of current, a varying voltage appears across resistance RL and this corresponds to

optical information of the picture.

Fig1.3: Simplified Block Diagram of AColour Camera

If the scanning beam moves at such a rate that any portion of the scene content does

not havetime to change perceptibly in the time required for one complete scan of the image,

the resultant electrical signal contains true information existing in the picture during the time

of scan. The desired information is now in the form of a signal varying with time and

scanning may thus be identified as a particular process which permits conversion of

information existing in space and time co-ordinates into time variations only. The electrical

information thus obtained from the TV camera tube is generally referred to as video signal

(video is Latin for ‘see’).

4.2 Colour Pictures

It is possible to create any colour including white by additive mixing of red, green

and bluecolour lights in suitable proportions. For example, yellow can be obtained by mixing

red and green colour lights in intensity ratio of 30 : 59. Similarly, light reflected from any

colour picture element can be synthesised (broken up) into red, green and blue colour light

constituents. This forms the basis of colour television where Red (R), Green (G) and Blue

(B) colours are called primary colours and those formed by mixing any two of the three

primaries as complementary colours. A colour camera, the elements of which are shown in

Fig. 1.3, is used to develop signal voltages proportional to the intensity of each primary

colour light.It contains three camera tubes (vidicons) where each pick-up tube receives light

of only oneprimary colour. Light from the scene falls on the focus lens and through that on

special mirrors.Colour filters that receive reflected light via relay lenses split it into R, G and

B colour lights.

Thus, each vidicon receives a single colour light and develops a voltage proportional

to the intensity of one of the primary colours. If any primary colour is not present in any part

of the picture, the corresponding vidicon does not develop any output when that picture area

is scanned. The electron beams of all the three camera tubes are kept in step (synchronism)

by deflecting them horizontally and vertically from common driving sources. Any colour

light has a certain intensity of brightness. Therefore, light reflected from any colour element

of a picture also carries information about its brightness called luminance. A signal

voltage(Y) proportional to luminance at various parts of the picture is obtained by adding

definite proportions of VR, VG and VB (30:59:11). This then is the same as would be

developed by a monochrome (black and white) camera when made to scan the same colour

scene. This i.e., the luminance (Y) signal is also transmitted alongwithcolour information

and used at picture tube in the receiver for reconstructing the colour picture with brightness

levels as in the televised picture.

5. TELEVISION TRANSMITTER

An oversimplified block diagram of a monochrome TV transmitter is shown in Fig.

1.4. The luminance signal from the camera is amplified and synchronizing pulses added

before feeding it to the modulating amplifier. Synchronizing pulses are transmitted to keep

the camera and picture tube beams in step.The allotted picture carrier frequency is generated

by a crystal controlled oscillator. The continuous wave (CW) sine wave output is given large

amplification before feeding to the power amplifier where its amplitude is made to vary

(AM) in accordance with the modulating signal received from the modulating amplifier. The

modulated output is combined (see Fig. 1.4) with the frequency modulated (FM) sound

signal in the combining network and then fed to the transmitting antenna for radiation.

Fig1.4: Elementary Block Diagram of A Monochrome Television Transmitter

5.1 COLOUR TRANSMISSION:

A colour TV transmitter is essentially the same as the monochrome transmitter except

for the additional need that colour (chroma) information is also to be transmitted. Any colour

system is made compatible with the corresponding monochrome system. Compatibility

means that the colour TV signal must produce a normal black and white picture on a

monochrome receiver and a colour receiver must be able to produce a normal black and

white picture from a monochrome TV signal. For this, the luminance (brightness) signal is

transmitted in a colour system in the same way as in the monochrome system and with the

same bandwidth. However, to ensure compatibility, the colour camera outputs are modified

to obtain (B-Y) and (R-Y) signals. These are modulated on the colour sub-carrier, the value

of which is so chosen that on combining with the luminance signal, the sidebands of the two

do not interfere with each other i.e., the luminance and colour signals are correctly

interleaved. A colour sync signal called ‘colour burst’ is also transmitted for correct

reproduction of colours.

5.2 SOUND TRANSMISSION

There is no difference in sound transmission between monochrome and colour TV

systems. Themicrophone converts the sound associated with the picture being televised into

proportionate electrical signal, which is normally a voltage. This electrical output, regardless

of the complexity of its waveform, is a single valued function of time and so needs a single

channel for its transmission. The audio signal from the microphone after amplification is

frequency modulated, employing the assigned carrier frequency. In FM, the amplitude of

carrier signal is held constant, whereas its frequency is varied in accordance with amplitude

variations of the modulating signal. As shown in Fig. 1.4, output of the sound FM transmitter

is finally combined with the AM picture transmitter output, through a combining network,

and fed to a common antenna for radiation of energy in the form of electromagnetic waves.

6. TELEVISION RECEIVER

A simplified block diagram of a black and white TV receiver is shown in Fig. 1.5.

The receivingantenna intercepts radiated RF signals and the tuner selects desired channel’s

frequency band andconverts it to the common IF band of frequencies. The receiver employs

two or three stages ofintermediate frequency (IF) amplifiers. The output from the last IF

stage is demodulated to recover the video signal. This signal that carries picture information

is amplified and coupled to the picture tube which converts the electrical signal back into

picture elements of the same degree of black and white. The picture tube shown in Fig. 1.6 is

very similar to the cathode-ray tube used in an oscilloscope. The glass envelope contains an

electron-gun structure that produces a beam of electrons aimed at the fluorescent screen.

When the electron beam strikes the screen, light is emitted. The beam is deflected by a pair

of deflecting coils mounted on the neck of picture tube in the same way as the beam of

camera tube scans the target plate. The amplitudes of currents in the horizontal and vertical

deflecting coils are so adjusted that the entire screen, called raster, gets illuminated because

of the fast rate of scanning.

Fig 1.5: Simplified Block Diagram of A Black And White TV Receiver

The video signal is fed to the grid or cathode of picture tube. When the varying signal

voltage makes the control grid less negative, the beam current is increased, making the spot

of light on the screen brighter. More negative grid voltage reduces brightness. If the grid

voltage is negative enough to cut-off the electron beam current at the picture tube, there will

be no light. This state corresponds to black. Thus the video signal illuminates the fluorescent

screen from white to black through various shades of grey depending on its amplitude at any

instant. This corresponds to brightness changes encountered by the electron beam of the

camera tube while scanning picture details element by element. The rate at which the spot of

light moves is so fast that the eye is unable to follow it and so a complete picture is seen

because of storage capability of the human eye.

.

Fig 1.6: Elements of A Picture Tube

6.1 SOUND RECEPTION

The path of sound signal is common with the picture signal from antenna to video

detector section of the receiver. Here the two signals are separated and fed to their respective

channels. The frequency modulated audio signal is demodulated after at least one stage of

amplification. The audio output from the FM detector is given due amplification before

feeding it to the loudspeaker.

6.2 COLOUR RECEIVER

A colour receiver is similar to the black and white receiver as shown in Fig. 1.7. The

main difference between the two is the need of a colour or chroma subsystem. It accepts only

the colour signal and processes it to recover (B-Y) and (R-Y) signals. These are combined

with the Y signal to obtain VR, VG and VB signals as developed by the camera at the

transmitting end. VG becomes available as it is contained in the Y signal. The three colour

signals are fed after sufficient amplification to the colour picture tube to produce a colour

picture on its screen.

Fig 1.7 : Simplified Block Diagram Of A Colour Receiver

As shown in Fig. 1.7, the colour picture tube has three guns corresponding to the

three pick-up tubes in the colour camera. The screen of this tube has red, green and blue

phosphors arranged in alternate stripes. Each gun produces an electron beam to illuminate

corresponding colour phosphor separately on the fluorescent screen. The eye then integrates

the red, green and blue colourinformations and their luminance to perceive actual colour and

brightness of the picture being televised. The sound signal is decoded in the same way as in a

monochrome receiver

6.3 SYNCHRONIZATION

It is essential that the same co-ordinates be scanned at any instant both at the camera

tube target plate and at the raster of picture tube, otherwise, the picture details would split

and get distorted. To ensure perfect synchronization between the scene being televised and

the picture produced on the raster, synchronizing pulses are transmitted during the retrace,

i.e., fly-back intervals of horizontal and vertical motions of the camera scanning beam. Thus,

in addition to carrying picture details, the radiated signal at the transmitter also contains

synchronizing pulses. These pulses which are distinct for horizontal and vertical motion

control, are processed at the receiver and fed to the picture tube sweep circuitry thus ensuring

that the receiver picture tube beam is in step with the transmitter camera tube beam. As stated

earlier, in a colour TV system additional sync pulses called colour burst are transmitted along

with horizontal sync pulses. These are separated at the input of chroma section and used to

synchronize the colour demodulator carrier generator. This ensures correct reproduction of

colours in the otherwise black and white picture.

6.4 RECEIVER CONTROL

Most black and white receivers have on their front panel (i) channel selector, (ii) fine

tuning,(iii) brightness, (iv) contrast, (v) horizontal hold and (vi) volume controls besides an

ON-OFF switch. Some receivers also provide a tone control. The channel selector switch is

used for selecting the desired channel. The fine tuning control is provided for obtaining best

picture details in the selected channel. The hold control is used to get a steady picture in case

it rolls up or down. The brightness control varies beam intensity of the picture tube and is set

for optimum average brightness of the picture. The contrast control is actually gain control of

the video amplifier. This can be varied to obtain desired contrast between white and black

contents of the reproduced picture. The volume and tone controls form part of the audio

amplifier in sound section, and are used for setting volume and tonal quality of the sound

output from the loudspeaker. In colour receivers there is an additional control called ‘colour’

or ‘saturation’ control. It is used to vary intensity or amount of colours in the reproduced

picture. In modern colour receivers that employ integrated circuits in most sections of the

receiver, the hold control is not necessary and hence usually not provided.

7. STANDARD TELEVISION SYSTEMS

Some of the standard television systems used around the world are:

7.1 NTSC SYSTEM

NSTC, named for the National Television System Committee, is the analog television

system used in most of North America, South America, Japan, South Korea, Taiwan, Burma,

and some Pacific island nations and territories (see map). NTSC is also the name of the U.S.

standardization body that developed the broadcast standard. The first NTSC standard was

developed in 1941 and had no provision for color TV.

NTSC color encoding is used with the system M television signal, which consists of

29.97 interlaced frames of video per second, or the nearly identical system J in Japan. Each

frame consists of a total of 525 scanlines, of which 486 make up the visible raster. The

remainder (the vertical blanking interval) are used for synchronization and vertical retrace.

This blanking interval was originally designed to simply blank the receiver's CRT to allow

for the simple analog circuits and slow vertical retrace of early TV receivers. However, some

of these lines now can contain other data such as closed captioning and vertical interval time

code (VITC). In the complete raster (ignoring half-lines), the even-numbered or 'lower"

scanlines (Every other line that would be even if counted in the video signal, eg. {2, 4, 6,

524}) Are drawn in the first field, and the odd-numbered or "upper" (Every other line that

would be odd if counted in the video signal, eg. {1, 3, 5, 525}) Are drawn in the second field,

to yield a flicker-free image at the field refresh frequency of approximately 59.94 Hertz

(actually 60 Hz/1.001). For comparison, 576i systems such as PAL-B/G and SECAM uses

625 lines (576 visible), and so have a higher vertical resolution, but a lower temporal

resolution of 25 frames or 50 fields per second.

The NTSC field refresh frequency in the black-and-white system originally exactly

matched the nominal 60 Hz frequency of alternating current power used in the United States.

Matching the field refresh rate to the power source avoided inter modulation (also called

beating), which produces rolling bars on the screen. When color was later added to the

system, the refresh frequency was shifted slightly downward to 59.94 Hz to eliminate

stationary dot patterns in the difference frequency between the sound and color carriers, as

explained below in ”Colour encoding”. Synchronization of the refresh rate to the power

incidentally helped kinescope cameras record early live television broadcasts, as it was very

simple to synchronize a film camera to capture one frame of video on each film frame by

using the alternating current frequency to set the speed of the synchronous AC motor-drive

camera. By the time the frame rate changed to 29.97 Hz for color, it was nearly as easy to

trigger the camera shutter from the video signal itself. The figure of 525 lines was chosen as

a consequence of the limitations of the vacuum-tube-based technologies of the day. In early

TV systems, a master voltage-controlled oscillator was run at twice the horizontal line

frequency, and this frequency was divided down by the number of lines used (in this case

525) to give the field frequency (60 Hz in this case). This frequency was then compared with

the 60 Hz power-line frequency and any discrepancy corrected by adjusting the frequency of

the master oscillator. For interlaced scanning, an odd number of lines per frame was required

in order to make the vertical retrace distance identical for the odd and even fields; an extra

odd line means that the same distance is covered in retracing from the final odd line to the

first even line as from the final even line to the first odd line, so simplifying the retrace

circuitry. The closest practical sequence to 500 was 3 × 5 × 5 × 7 = 525. Similarly, 625-line

PAL-B/G and SECAM uses 5 × 5 × 5 × 5. The British 405-line system used 3 × 3 × 3 × 3 ×

5, the French 819-line system used 3 × 3 × 7 × 13.

7.2 PAL AND SECAM TELEVISION SYSTEM

PAL, short for phase alternate line, is an analogue television encoding system used in

broadcast television systems in large parts of the world. In the 1950s, when the Western

European countries were planning to establish colour television, they were faced with the

problem that the NTSC standard demonstrated several weaknesses, including colour tone

shifting under poor transmission conditions, earning it a comically maligned backronym

"Never Twice the Same Color". For these reasons the development of the SECAM and PAL

standards began. The goal was to provide a colour TV standard for the European

picturefrequency of 50 fields per second (50 hertz), and finding a way to eliminate the

problems with NTSC.

PAL was developed by Walter Bruch at Telefunken in Germany. The format was first

unveiled in 1963, with the first broadcasts beginning in the United Kingdom in 1964 and

Germany in 1967, though the one BBC channel initially using the broadcast standard only

began to broadcast in colour from 1967.

Telefunken was later bought by the French electronics manufacturer Thomson. Henri

de France developed SECAM, historically the first European colour television standard.

Thomson also co-owns the RCA brand for consumer electronics products, which created the

NTSC colour TV standard before Thomson became involved.

The term PAL is often used informally to refer to a 625-line/50 Hz (576i), television

system, and to differentiate from a 525-line/60 Hz (480i) NTSC system. Accordingly, DVDs

are labelled as either PAL or NTSC (referring informally to the line count and frame rate)

even though technically the discs do not have either PAL or NTSC composite colour. The

line count and frame rate are defined as EIA 525/60 or CCIR 625/50. PAL and NTSC are

only the method of the colour transmission used. The basics of PAL and the NTSC system

are very similar; a quadrature amplitude modulatedsubcarrier carrying the chrominance

information is added to the luminance video signal to form a composite video baseband

signal. The frequency of this subcarrier is 4.43361875 MHz for PAL, compared to

3.579545 MHz for NTSC. The SECAM system, on the other hand, uses a frequency

modulation scheme on its two line alternate colour subcarriers 4.25000 and 4.40625 MHz.

The name "Phase Alternating Line" describes the way that the phase of part of the

colour information on the video signal is reversed with each line, which automatically

corrects phase errors in the transmission of the signal by cancelling them out, at the expense

of vertical frame colour resolution. Lines where the colour phase is reversed compared to

NTSC are often called PAL or phase-alternation lines, which justifies one of the expansions

of the acronym, while the other lines are called NTSC lines. Early PAL receivers relied on

the imperfections of the human eye to do that cancelling; however this resulted in a comb

like effect known as Hanover bars on larger phase errors. Thus, most receivers now use a

chrominance delay line, which stores the received colour information on each line of display;

an average of the colour information from the previous line and the current line is then used

to drive the picture tube. The effect is that phase errors result in saturation changes, which are

less objectionable than the equivalent hue changes of NTSC. A minor drawback is that the

vertical colour resolution is poorer than the NTSC system's, but since the human eye also has

a colour resolution that is much lower than its brightness resolution, this effect is not visible.

In any case, NTSC, PAL and SECAM all have chrominance bandwidth (horizontal colour

detail) reduced greatly compared to the luminance signalThe 4.43361875 MHz frequency of

the colour carrier is a result of 283.75 colour clock cycles per line plus a 25 Hz offset to

avoid interferences. Since the line frequency is 15625 Hz, the colour carrier frequency

calculates as follows: 4.43361875 MHz = 283.75 * 15625 Hz + 25 Hz.

The original colourcarrier is required by the colour decoder to recreate the colour

difference signals. Since the carrier is not transmitted with the video information it has to be

generated locally in the receiver. In order that the phase of this locally generated signal can

match the transmitted information, a 10 cycle burst of coloursubcarrier is added to the video

signal shortly after the line sync pulse but before the picture information (the back porch).

This colour burst is not actually in phase with the original colour subcarrier but leads it by

45 degrees on the odd lines and lags it by 45 degrees on the even lines. This 'swinging burst'

(as it is known) enables the colour decoder circuitry to distinguish the phase of the R-Y

vector inch reverses every line.

7.3 PAL vs. NTSC

NTSC receivers have a tint control to perform colour correction manually. If this is

not adjusted correctly, the colours may be faulty. The PAL standard automatically removes

hue errors by utilizing phase alternation of the colour signal (see technical details), so a tint

control is unnecessary. Chrominance phase errors in the PAL system are cancelled out using

a 1H delay line resulting in lower saturation, which is much less noticeable to the eye than

NTSC hue errors.

However, the alternation of colour information — Hanover bars— can lead to picture

grain on pictures with extreme phase errors even in PAL systems, if decoder circuits are

misaligned or use the simplified decoders of early designs (typically to overcome royalty

restrictions). In most cases such extreme phase shifts do not occur. This effect will usually be

observed when the transmission path is poor, typically in built up areas or where the terrain is

unfavourable. The effect is more noticeable on UHF than VHF signals as VHF signals tend

to be more robust.

In the early 1970s some Japanese set manufacturers developed decoding systems to

avoid paying royalties to Telefunken. The Telefunken licence covered any decoding method

that relied on the alternating subcarrier phase to reduce phase errors. This included very basic

PAL decoders that relied on the human eye to average out the odd/even line phase errors.

One solution was to use a 1H delay line to allow decoding of only the odd or even lines. For

example the chrominance on odd lines would be switched directly through to the decoder and

also be stored in the delay line. Then on even lines the stored odd line would be decoded

again. This method effectively converted PAL to NTSC. Such systems suffered hue errors

and other problems inherent in NTSC and required the addition of a manual hue control.

PAL and NTSC have slightly divergent colour spaces, but the colour decoder

differences here are ignored.PAL supports SMPTE 498.3 while NTSC is compliant with

EBU Recommendation 14.The issue of frame rates and colour subcarriers is ignored in this

technical explanation. These technical details play no direct role (except as subsystems and

physical parameters) to the decoding of the signal

.

7.4 PAL vs. SECAM

SECAM is an earlier attempt at compatible colour television which also tries to

resolve the NTSC hue problem. It does so by applying a different method to colour

transmission, namely alternate transmission of the U and V vectors and frequency

modulation, while PAL attempts to improve on the NTSC method. SECAM transmissions

are more robust over longer distances than NTSC or PAL. However, owing to their FM

nature, the colour signal remains present, although at reduced amplitude, even in

monochrome portions of the image, thus being subject to stronger cross colour. Like PAL, a

SECAM receiver needs a delay line

8. APPLICATION OF TELEVISION

Television by its use in broadcasting has opened broad new avenues in the field of

entertainment and dissemination of information. The not so well known applications are in

the field of science, industry and education, where the television camera has contributed

immeasureably to man’s knowledge of his environment and himself. The television camera is

probably best described as an extension of the human eye because of its ability to relay

information instanstaneously. Its capability to view events occurring in extremely hazardous

locations has led to its use in atomic radiation, underwater environment and outer space.

Some of the application are as follows:

1. TELEVISION BROADCASTING

2. CABLE TELEVISION

3. CLOSED CIRCUIT TELEVISION

4. THEATRE TELEVISION

5. PICTURE PHONE AND FACSIMILE

6. VIDEO TAPE RECORDING

9. TELEVISION VIA SATELLITE

There are a number of ‘INTELSAT’ satellites over the Atlantic, Pacific, and Indian

Oceans operating as relay stations to some 40 ground stations around the world. The

international system of satellite communication caters to the continental 625/50 and the

American 525/60 systems. Frequency modulation is used for both ‘up channel’ and ‘down

channel’ transmission.FM though it needs a larger bandwidth offers good immunity from the

interference and requires less power in the satellite transmitter.

9.1 Frequency Allocation

The frequency bands recommended for satellite broadcasting are 620 to 790 MHz, 2.5

to 2.69GHz and 11.7 to 12.2 GHz on a shared bias with other fixed and mobile services. The

satellite antenna size and the RF power naturally depend upon the frequency of operation.

Space erectable antennas are used for the 620-790 MHz band, with the size limited to about

15 meters, while the rigid antennas are used both for 2.5 and 20 GHz bands the size being

limited to about 3 meters.For the ground terminal, the maximum diameter of the antenna is

restricted by the allowable beamwidth and frequency. The cost and complexity of the

receiver increases with the increase in frequency.

10. ADVANTAGES AND DISADVANTAGES OF

TELEVISION

10.1 Advantages of Television:

There are several advantages of television like we all know that we can have a clear

idea that what is happening in the world, we can have live information about the several

events like sports and any other good or bad events happening on the globe. One can have a

weather forecast and accordingly plan several things before time. It is also a good source of

entertainment which is very cheap and within the access of every one. Television has shrunk

the distance of the world you can watch what is happening several thousand miles away from

you. So in totality it is information from all over the world, and it is fun and enjoyment with

convenience.

10.2 Disadvantages of Television:

However along with some positive sides it has its disadvantages as well like watching

too much of television also affects your eye and nerves. Television creates such a spell on

children and in some cases it also effects the elders that they actually lose their own opinion

they feel whatever is being shown on television is correct and should be practised as such. In

such situation it is the responsibility of the broad caster to show what is safe to be shown on

the television. But still several irresponsible television channels show content which is not be

shown for every one like contents of violence.

11. CONCLUSION

The aim of a television system is to extend the sense of sight beyond its natural limits

and to transmit sound associated with the scene. As in radio communication, each television

station is allotted different carrier frequencies toenable selection of desired station at the

receiving end. Television by its use in broadcasting has opened broad new avenues in the

field ofentertainment and dissemination of information. There are several advantages of

television.However along with some positive sides it has its disadvantages as well.