SUMMER TRAINING REPORT ON DOORDARSHAN KENDRA SILCHER

INSTITUTE OF SCIENCE & TECHNOLOGY, KLAWAD (2013-14)

CHAPTER-1

INTRODUCTION TO DOORDARSHAN

1.1 INTRODUCTION

TYPE Broadcast television network.

COUNTRY : India.

AVAILABILITY : National.

OWNER : Prasar Bharati.

LAUNCH DATE : 1959.

PAST NAME All India Radio.

WEBSITE http://www.ddindia.gov.in

Doordarshan is a public broadcast terrestrial television channel run by PrasarBharati ,a board

nominated by the Government of india.it is one of the largest broadcasting organization in this

world in terms of the infrastructure of studios and transmitters recently it has also started terrestrial

transmitters.

Beginning

Doordarshan had a modest beginning with the experimental telecast stating in Delhi in September

1959 with a small transmitter and a make shift studio. The regular daily transmission started in

1965 as a part of all India radio. The television service was extended to Mumbai(then Bombay)

and Amritsar in 1972 till 1975 seven India 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 NewDelhi. Finally Doordarshan as a national Broadcaster came in to existence.

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Doordarshan Silchar has uplinking frequency 6.0565GHZ and downlinking frequency

3.8315GHZ.The location of INSAT-4B is 93.5° east.

1.2 SATELLITE UPLINKING AND DOWNLINKING FREQUENCIES

TABLE-1.1

BANDS DOWNLOAD FREQ(GHz) UPLINK FREQ (GHz)

S 2.555 to 2.635 5.855 to 5.935

C(Lower) 3.4 to 3.7 5.725 to 5.925

C(Upper) 4.5 to 4.8 6.425 to 7.075

KU 10.7 to 13.25 12.75 to 14.25

KA 18.3 to 22.20 27.0 to 31.00

1.3 TERRESTRIAL TELEVISION

BAND-(I) (40 to 68MHZ)

TABLE-1.2

CHANNEL RANGE VISION FREQ. AURAL FREQ.

1 ` 41.25 46.75

2 47-54 48.25 53.75

3 54-61 55.25 60.75

4 61-68 62.25 67.75

BAND-(II) 88MHZ to 108MH (FOR FM)

108MHZ to 174MHZ (Other Telecommunication)

BAND-(III) T.V TRANSMITTION.(174MHZ to 230MHZ)

TABLE-1.4

CHANNEL RANGE VISION FREQ. AURAL FREQ.

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5 174-181 175.25 179.75

6 181-188 182.25 187.75

7 188-195 189.25 194.75

8 195-202 196.25 201.75

9 202-209 203.25 208.75

10 209-216 210.25 215.75

11 216-223 217.25 222.75

12 223-230 224.25 229.75

BAND- (IV) (470MHZ to582MHZ) CHANNEL (21-27)

BAND- (V) (582MHZ to 790MHZ) CHANNEL (28-60) FOR U.H.F

BAND-(VI) (11.7GHZ to 12.5GHZ) FOR KU BAND

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CHAPTER-2

FUNDAMENTAL OF MONOCROME AND COLOR TV SYSTEM

2.1 PICTURE FORMATION

A picture can be considered to a number of small elementary areas of light or shade which are

called PICTURRE ELEMENTS. The thus contain the visual image of scene.

In the case of TV camera the scene is focused on the photosensitive surface of pick up device and

a optical image is formed. The photoelectric properties of pick up device convert the optical image

to electric charge image depending on the light and shade of the scene(picture elements).Now it is

necessary to pick up this information and transmit it. For this purpose scanning is employed.

Electron beam scans the image line by line and field to provide signal variation s in a successive

order.

The scanning is both in horizontal and vertical direction simultaneously.

The horizontal scanning frequency is 15,625 Hertz.

The vertical scanning frequency is 50 Hz.

The frame is divided into two fields. Odd lines are scanned first and then the even lines. The odd

and even lined are interlaced. Since the frame is divided into 2 fields the flicker reduces The field

rate is 50 Hertz. The frame rate is 25 Hertz (Field rate is the same as power supply frequency).

2.1.1NUMBER OF TV LINES PER FRAME

If the number of TV lines is high larger bandwidth of video and hence larger R.F. channel width is

required. If we go for larger RF channel width the number of channel in the R.F. spectrum will be

reduce. However with more number of TV lines on the screen the clarity of the picture i.e.

resolution of improves. With lesser number of TV lines per frame the clarity(quality) is poor.

The capability of the system to resolve maximum no. Of picture elements along scanning linens

determines the horizontal resolution. It means how many alternate black and white

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elements can be there in a line. Let us also takeanotherfactor. It is realistic to aim at equal

vertical black and white dots on line can be 575x0.69x4/3 which is equal to 528.

It means there are 528 divided by 2 cyclic changes i.e. 264 cycles. There 264 cycle are there

during 52 micro seconds. Here the highest frequency is 5MHz

fhighest =264x10⁶/52= 5MHz

Therefore the horizontal resolution of the system is MHz A similar calculation for 525 linens

system limits the highest a frequency to 4 MHz and hence the horizontal resolutions of same

value.

In view of the above the horizontal bandwidth of signal in 625 lines system is 5 MHz.

2.2 THE PALCOLOR TELEVISION SYSTEM

2.2.1 THE COLOR TELEVISION

It is possible to obtain any desired color by mixing three primary color i.e. Red, Blue and green in

a suitable proportion.

figure 10 shows the effect of projecting red , green , blue beans of light so that they The overlap

on screen.

Y = 0.3 Red + 0.59 Green+ 0.11Blue

Fig.2.1 Additive colour mixing

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2.3 THE COLOUR TELEVISION

It is possible to obtain any desirecolour by mixing three primary colours i.e., red, blue , and green

in suitable proportion . Thus it only required to convert optical information of these of these three

colour to electrical signals and transmit it on different carriers to bbe deco\deed by the receiver .

This can then converted back to the optical image at the picture tube. The phosphors for all the

three colour i.e. R, G and B are easily available to the manufactures of the picture tube should

consists of three signals i.e. R , G and B. It is between the camera and picture tube of the receiver

we a system to transmit this information.

Fig. 2.2 Colour TV system.

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Colourtelevision has the constraint of compatibility and reverse compatibility with the

monochrome television system which make it slightly complicated. Compatibility means that

when colour TV signal is radiated the monochrome TV sets should also display Black and White

pictures . This is achieved by sending Y is monochrome information among with the croma

signal . Y is obtained by mixing Black and White as per the known equation.

If wetransmit R,G, B, the reserved comp ability cannot be achieved. Let us how :

If transmit Y , R & B and derive G then :

Since Y = 0.3R + 0.59G + 0.11B

G = 1.7Y - 0.51R - 0.19B

In such a case what happen with a color TV set when we transmit black and signal. R and B are

zero , but G gun sets 1.7 Y. The net result is black and white picture on a colour TV screen

appear as Green pictures. So reverse comp ability is not achieved .

2.4 COLOR DIFFERENCE SIGNAL

To achieve reverse capability when we transmit Y ,R –Y and B-Y instead of Y,R ,B . We take G

Y as this will always be much lower than R-Y and hence will need more amplification and will

cause more noise into the system. G-Y can be derived electronically in TV receiver .

In the previous paragraph we have seen.

Direction to the production crew by the producer of the programs.

Timing a production telecast.

Editing of different sources available at the production desk

Minting of output of signal .

Hardware provided in this area included:-

Monitoring facility for all the input or output sources ( audio –video)

Remote cannot for video mixer , telecine and library store and especial effect (ADO) etc.

Communication facility with technical and studio floor.

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2.5 VISION MIXING

Unlike films , television media allow switching between different source simultanouslyt at the

video switcher in production control room operator by the vision Mixer on the various cameras

through inters com and the vision mixer (also called VM engineer switcher shots form they

selected camas/cameras with split second accuracy in close corporation , superimposed , cross

faded , in or fadeout electronically either actual being done during the vertical intervals between

the picture the frames. Electronics effects are used now days as a transition between in the two

sources.

Figure 2.3 Diagram of vision mixer.

2.6 VISION MIXER (OR VIDEO SWITCHER)

Though the video switching is done by the VM at remote panel , the electronic is located in the

CAR . The vision mixer is typically a 10 x 6 or 20 x 10 cross bar switcher selecting anyone of the

10n or 20 input sources to 6 or 10 different output lines . The input sources include : Camera 1,

Camera 2, Camera 3, VTR1 , VTGR2 , Telecine 1 , Telecine 2 , T EST Signal etc. The vision

mixer provides for the following operational facilities for editing of TV programs :-

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Thus , colour difference signals fulfill the compatibility and reverse capability . Because in this

case the colour difference signals are zero if the original signal is monochrome (i.e. . R = B = G)

So if we take R –Y =R – (0.3R + 0.59R + 0.11R) = 0

Similarly B –Y = 0

As such colour difference signals are zero for white or any shade of gray where ,Y carries the

entire Luminance information.

It is to be noted while R , G , B signals always have positive value R N-Y and B-Y chrominance

signals synchronous demodulation. But sub carrier is to generated by a local oscillator . This

generated sub- carrier in the receiver and also the same phase . This is achieved by porch of H

synchronizing pulse. This 10 cycle’s sub- carrier signal is known as BURST or color BURST.

Figure. 2.4 One line display of TV signal.

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2.7 PAL ENCODER

Figure . 2.5 Block diagram of PAL Encoder.

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CHAPTER-3

VIDEO CHAIN IN A TYPICAL DOORDARSHAN STUDIO

3.1STUDIO CENTRE

A Studio Centre of Doordashan has the following objectives :-

To originate program from studio for live telecast or for recording originated video tape.

To knit various coerces of program available at the production camera output videos , feed

from others films , videos and characters of especial studios.

Procession transitions alert series of various destination of channel.

Routing of switching room and micro watching transmitter or any other desired

destination.

3.1.1ACTIVITIES IN A TELEVISION STUDIO CAN BE DIVIDED INTO THREE

MAJOR AREA SUCH AS

Action area

Production Control room , and

Central apparatus room.

This palace required large space and ceiling as compared to any other technical area. Action in

thus area included staging , lighting , performance by artiest , and arrangement to pick up picture

and sound. Hardware required for these activities in a studio ( typical size 20 x 20 x8.5 cubic

meters.) are :-

Very efficient air controlling because a lot of heat dissipation by studio light and presence of large

number of persons invited audience performing artists and operational crew.

Uniform and even flooring for smooth operation of camera dollies and boom microphones

etc.

1. ACTION AREA -

Acoustic treatment keeping in mind that a television studio is a multi-purpose studio with 11


a lot of moving persons and equipment during a production.

Supporting facilities like properties wardrobes and makeup etc.

Effective communication facilities for the crew with the production control area.

Studio camera (three to four ) one of the camera fitted with the telecast system and

pressure dolly.

Luminary and suspension

Pick up wall sockets for audio operations.

Tie lines box for video and audio lines from control of room.

Cyclorama and curtain tracks for blue and black curtain for chroma keying and

limboillghtine respectively.

Audio and video monitoring facilities

Studio warning light and safety devices like fire alarm system and

firefightingequipment’s etc.

Digital clock display.

Operational requirement from the technical crew may vary from programme. These requirements

for lighting , audio pick up and special effects etc. depends upon he programme requirement such

as establishing a period , time, formal or informal or informal situation.

2. PRODUCTION CONTROL AREA –

Activities in this area are

Take : Selection of any input source

Or

Cut : Switching clearly from one source to another.

Dissolve: Fading out of one source of video and fading in another source of video.

Superposition of Two sources Keyed caption when selected inlays superimposed on the

background picture.

Special Effects A Choice of a number of a number of wipe patterns for slip screen on wipe

effects.

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The selected output can be moment in the crooning preview monitors. The picture element are

available on the monitors, VT test signals etc with any desire special effect, prior to its switching.

The switcher also provides cue facilities to switch camera tally light as an indication to the

cameraman whether his camera is on output of the switcher.

Present day PCR’s have :-

24 input video special effects switchers

(CD 680 or CD 682-SP)

Character generators

Telecom/ DLS remote controls

Adequate monitoring equipment.

3.1.2CHARACTER GENERATOR (CG)

Character Generator provides titles and credit captions during production in Roman script. It

provides high resolution characters, different color for colorizing characters, background , edge

etc. At present bilingual band triangular C.G are also being used by Doordarshan.

Character Generators is a microcomputer with Text along instructions when typed in at the

keyboard is stored on a floppy or hard disk. Many page of scripts can be stored on hard disk and

recalled when needed by typing the address for the stored page , to appear as one of the video

sources.

3.1.3 SYNC PULSE GENERATOR (SPG)

It is essential that all video sources as input to the switcher are in synchs are stars all the frames of

video sources is conductor. It consist of highly stable camera from this crystal oscillation vacuum

pulse of stand width and frequency are derived from the crystal electronically which from clock

for generation of video signal. These pulses this objective of synchronism. Because of its

importance, SPG is normally duplicate for change over cases of failure.

It provide the following output:

1) Line drive.

2) Field drive.

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3) Mixed blanking.

4) Mixed sync.

5) Colour sub –carrier.

6) A burst insertion pulse.

3.2 PAL PHASE INDENT PULSES

3.2.1 CAMERA CONTROL UNIT (CCU)

The television cameras which include camera head with its optical focusing lens , pan and tilt

head , video signal pre –amplifier view finder and other associated electronic circuitry are mounted

on cameras trolley and operate inside the studios. The output of camera is pre –amplifier in the

head and then connected to the camera control unit (CCU) through long multi – core cable (35 to

40 cores) , or triad cable.

All the camera control voltages are fed from the CCU to the camera head over the multi-core

camera cable . The view –finder signal is also sent over the camera cable to thecamera head

view- finder for helping the camera in proper focusing, adjusting composing the shots.

The video signal obtain is amplifier the corrected, equalized for cable decays , D C clamped

horizontal and vertical blanking pulses added to it the peak white levee is also clipped a video

overloading on the following stage and avoiding over modulation in the transistor. The composite

sync signals are then added and these video signal are fed to a distribution amplifier , which

normally give multiple outputs for monitoring etc.

Figure . 3.1 Diagram of CCU.

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3.2.2 LIGHT CONTROL

The scene to be telecasted most be well laminated to produce a clear and noise free picture. The

lighting should give the depth , the correct contrast and artistic display various shade without

multi shadows .

The lighting arrangement I a TV studio have to be very elaborated. A large number of lights to

used meet the needs of ‘key’, ‘fill’,and ‘back’ light etc. Lights are classified as spot and soft lights.

These are suspended from motorized hoists and telescopes. The up and down movement is

remotely controlled . The switching on and off lights at the required time and diming is

controlled from the light controlled panel in siding a lighting control room using SCR dimmer

controls . Type remotely control various lights are inside the studios.

3.2.3 SOUND MIXING

As a rule in Television, sound accompanies the picture. Several microphones are generally

required for production of complex television program beside the other audio sources inthe

synchronization with the level of sound sometimes is varied in accidence with the shot

composition called “Prospective ".

3.2.4 AUDIO FACILITIES

An audio mixing console with a number say about 32 inputs is provided in major studio. This

include specter facilities such as equalization PFL , phased reverberation chosen / receive and

digital reverberation units at some places tape recorders and FM 98 disrupt[roved playing back/

creating audio effects important sources (married) to the switcher.

3.2.5 VIDEO TAPE RECORDER

VTR room is provided at studio center. It houses is few broadcast standard videocassettes (VCRs).

In these recorders , sound and video signals are recorded simultaneously on the same tape.

Most of the TV center have professional quality B-Format BCN-51 inch VTRs. For broadcast

quality play back it is required with correction electronics i.e. a processer which comprise

velocity error compensation, drop- out compensation and time based correction. It also comprise

a digital variable motion unit enabling still reproduction, slow motion and visible search operation.

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New centers are being supplied with Sony U-mastic high band VCRs along with ½” Beta cam SP

VCTs , DVC pro

Fig. 3.2 Diagram ofVideo tape recorder.

3.2.6 POST PRODUCTION SUITES

Modern videotape editing has revolutionized the production of television programs over years. The

latest tend all over the world is to have more of fully equipped post production suites than

number of studios. Most of present day shooting are done on location using single camera. The

actual production is done in tease suites. The job for post-production suitsis: -

To knit program available on various sources..

While doing editing with multiple sources it should be possible to have any kind of

transition .

Adding / Mixing sound tracks.

Voice over facilities.

Creating spectra effects.

The concept of live editing of sound mixer is replaced by “to do it at post production suites’.

Well-equipped post production suites with have : -

Five VTRs/VCRs may be different format remotely controlled by the editor.

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Visi0n mixing with especial effect and wipes of with control from remote editor panel .

Apex Digital Optics (ADO) for especial effects.

Audio mixer with remote control from the editor remote panel.

Multi – track audio recorder with time code facilities and remote operation.

Character generator for titles.

Adequate monitoring facilities.

Supported by “offline editing system” to save time in post-production

suite.

One man operation.

3.2.7 COVERAGE OF OUTSIDE EVENTS

Outside broadcaster (OBs) provide an important part of the television programs. Major events like

Spots , important functions , and performance are covered with an O.B van which contain all the

essential facilities.

3.3 VIDEO CHAIN

The block diagram of facing page contain all these section and it can be observed that the CAR

is the nodal data. Now let us follow the CAM – signal. CAM –I first goes to a camera electronics

in CAR via a multi core cable, the signal is then matched / adjusted for quality in CCU and then

like any sources it goes to video switcher via PP (Patch Panel) and respective VDAs ( Video

Distribution Amplifiers) and optional Hum compensator / Cable equalizers.

Output from the switcher goes to stabilizing amplifier via PP and VDAs , output from the

distributed to various destination.

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Fig. 3.3 Block diagram of video chain.

3.4TV LIGHTING

Lighting for television is very exciting and needs creative talent. There is always tremendous scope

for doing experiments to achieve the required effect. Light a kind of electromagnetic radiation

with a visible spectrum from red to violet i.e wave length fro 700 nm to 380 nm respectively.

However to effectively use the hardware and software connected with lighting. It is important to

know more about the energy.

LIGHT SOURCE

Any light source has luminance energy which measured in Candelas. Candela is equivalent an

intensity created by standard one candid source of light.

BASIC THREE POINT LIGHTING

Key light - This is the principal light source of illumination it give shape and modeling by

casting shadows. It is tartest like sum of the sky and it should cast only is a one showdown .

Normally it the hand spectrum.

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Fill Light - Controls the lighting contrast by filling in shadows. It can also provide catch

light in the eyes. Normally it soft source.

Back Light - Separated the body from the background , roundness to the subject and

reveals texture. Normally it is hard source.

BACKGROUND LIGHT-Separate the person from the background , reveals background interest

and shade . Normally it is a hard source . In three point lighting the radio of 3/2/1 (Back/Key/Fill)

for mono and 3/2/2 for coluor provide good portrait lighting.

3.5 TV CAMERA

INTRODUCTION

A TV CAMERA CONSISTS OF THREE SECTION

a) A Camera lens and optics : To from optical image on the face plate of a pick up device

b) A transducer or pick up device : To convert optical image into an electrical signal.

c) Electronic : To process output of a transducer to get a CCCVS signal.

3.5.1CCD CAMERA

INTRODUCTION

Any camera will need a device to optical an electrical signal. Let us consider a picture or better

resolution small picture element . For more snappish or better resolution , we have to increase

these element. The picture arrange now be focused on to signature of so many CCD elements.

Each CCD element will now convert the light information to on it to charge signal. All need now

to have an arrangement ton collect this and convert to it voltage the basic principle on which CCD

camera are based.

3.5.2LATEST CCD CAMERA

CCD were launched in 1983 from broadcast with pixel count from a more 2,50,000 which

increased to 20,00,000 in 1994 for HHDTV application . Noise and aliasing has been reduced to

negligible level . CCD camera now offer fully modulated video output as light level as 6.0

lumens. Atypical specification for a studio now available in something like 2/3 inch , Fit lens on

chop CCD with 6,00,000 pixel 850 Linea H resolution , Sensitivity F-8(2000 Lux) etc.

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Fig. 3.4 CCD Camera.

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Fig.3.5 Block diagram of Typical Camera.

Fig.3.6 Block diagram of Optical part of 3CCD.

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Fig. 3.7 Block diagram of electronics part of 3CCD.

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CHAPTER-4

HIGH POWER TV TRANSMITTER

4.1DESIGN OF TRANSMITTER

All the TV transmitters have the same basicdesign. The of an exciter followed by power

amplifiers which boost the exciter power to the required level. In BEL mark transmitted three

valve stage 450 CX , BEL 4500 CX are seen vision transmitter chain and two BEL transmitter

50 aural transmitter chain in BEL make the transmitters only the wave stage ( BEL 4500 and

BEL - CX) and vision transmitter chain . Aural transmitter chain is fully solid stage in mark all

transmitter. But now a days use VHF TV Transmitter (NEC JAPAN).

4.1.1PCN-1610SSPH/1VHF TV TRANSMITTER

It is a digital transmitter.

Its power rating is 10KW.

The main parts of the transmitter are :

(1) Exciter

(2) Amplifier.

Fig. 4.1 Block diagram of PCN-1610SSPH/1 VHF TV Transmitter.

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4.2 EXCITER

In exciter there are to separate inputs for video & audio signal.

The video signal is first applied to A/D - D/A.

Then the video signal is modulated with frequency 38.9MHZ in if Modulator(AM).

The output of IF modulator is then given to a mixer where it is mixed With a low

frequency of 249.15MHZ generated by a synthesizer.

The o/p of mixer (V) is amplitude modulated wave with frequency 210.25MHZ.

The o/p of mixer (A) frequency modulated wave with frequency 215.75MHZ.

Frequency of video signal 5 MHZ and that of the audio signal it is about 15 KHZ.

The audio signal is modulated in IF modulator with carrier frequency33.4 MHZ.

FM is done with audio signal, where as AM is done with video signal.

Fig. 4.2 Diagram of Exciter.

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4.3 AMPLIFIRE

The o/p of video & audio mixer are only of power approx. Equal to 15 dB

The modulated video (AM-VSB) signal amplified up to 10 KW by video amplifier.

The modulated audio (FM) signal is amplified up to 1 KW by audio Amplifier.

The video amplifier consist of 10 power amplifier of 1 KW each.

The audio amplifier consist of 2 power amplifier of 1 KW each.

The amplified video & audio waves are then given to a DIPLEXER ,it accept the

modulated and amplified video and audio signal and mix them to generate a signal with a

frequency width of 7 MHZ in IF region.

The signal at the o/p of the diplexer is carried through coaxial pipe to the antenna which

transmits the information in the form of electromagnetic wave of a fixed frequency range in

to the space (air).

The reception of the information is done by Receiver tuned to the above Frequency range.

Here the wave is demodulated and information is recovered as it was prior to modulation.

The reception unit may be a home TV set .

The PCN-1610SSPH/1 VHF TV Transmitter is used for terrestrial Transmission.it is used

for transmission of DD1 on channel 10 at DDK Silchar.

A 1 KW transmitter is also used at DDK Silchar for the transmission of DD News on

channel 12 at DDK Silchar.

Each channel has a fixed operating frequency range.

The channel width is 7 MHZ.

Frequency of channel 10 is 210.25 MHZ for video & 215.75 MHZ for audio

There is difference of frequency 5.5MHZ between audio & video signal in Each channel.

The frequency of channel 12 is 224.25MHZ for video and 229.75 MHZ For audio.

4.4 SOLID STAGE POWER AMPLIFIERS

Has got two identical section . Each capable of delivering 10.

Get x28 V power supply through relay in 80 W AMP.

Sample of output is available at front panel for RF monitoring.

Provides A DC output corresponding to sync peak output for vision monitoring unit.

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Thermostat on heat sink connected in series with thermostat or 80 W AMP and provide

thermal protection.( operating temp. 70 c).

4.5 TRANSMITTER SECTION

Its section is situated at KANKARBAGH. It main work function is to provided TV signal

transmitted to a range of 7KM.DDK, Silchar transmitter is 150m.for transmitting the signal, first

of all receive, the signal of satellite. This transmitted signal is catched by TV receiver and to see

the programe.

Fig.4.4 Block diagram Transmitter.

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4.6 TRANSMITTER CONTROL SYSTEM

The transmitter control unit performs the task of transmitter interlocking andcontrol. Also it

support operation from control console. The XTR control unit (TCU) has two depended system

viz.

1. Main Control System (MCS)

2. Back –up Control System

4.6.1 SYSTEM DESCRIPTION OF EXITER

VIDEO CHAIN-The signal is fed to a video processor. In VHF transmitter , equalizer

andreceiver pre –corrected , pre0 rerecorded video processor.

LOW PASS FILTER-Filter has limit in combine video signal to 5 MHz

RECEIVER PRE – CORRECTOR

Pre- distorts the signal providing partial compensation o GD which occurs in domestic receivers.

Both the delay equalizer and receiver pre-recorded are combined in delay equalizer module in

mark III vision.

4.6.2 VIDEO PROCESSOR

The block diagram of video processor is given below.

Functions

Amplification of video signal

Clamping at back porch of video signal.

Clamping give contrast peak power. Zero volt reference line is steady irrespective of video signal

pattern when clamping takes place otherwise the base line starts an excursion about the zero

reference depending on the video signal.

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Fig.4.5 Block diagram of Video Processor.

4.6.3 VISION MODULATOR

The block diagram of vision modulator is given below.

Functions

Amplification of vision IF at 38.9 MHz

Liner amplitude modulation of vision IF by video from the video processor in a balanced

modulator.

IF MODULATOR

IF is amplified to provide sufficient level to the modulator. It operate as an amplitude limiter for

maintaining constant output.

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MODULATOR

A balanced modulator using two IS- 1993 diodes used in the modulator.

BAND PASS AMPLIFIER

Modulated Signal is amplified to 10 mW in double tuned amplifier which provides a flat response

within 0.5 dB in 7 MHZ

Fig. 4.6 Block diagram of Vision Modulator.

4.7 VSBF AND MIXER

The block diagram of vision and Mixer is given below and it consists following stages.

VSB filter

ALC amplifier

Mixer

Helical Filter

Mixer Amplifier

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Fig. 4.7 Block diagram of VSBF Mixer.

4.7.1 VSB FILTER

Surface ACOUSTIIC wave (SAW) provide a very steep side band response with high attenuation

outside designated channel. It has a liner phase characteristic with a low amplitude and group

delay ripple.

4.7.2 LOCAL OSCILLATOR

The block of Local Oscillator is given in fig .8 .It supplies three equal outputs of +8 dBm at a

frequency of fv + fvif. This unit has 3 sub units.

(1) Fc/4 Oscillator - Generates frequency which is ¼ of desired channel frequency. Fine

freq. control is done by VC1.

(2) LO Mixer/Power divider - Here the above fc/4 frequency is multiplied by four to

obtain channel frequency of fc and them mixer with fvif . Power divided is also

incorporated to provide three isolated outputs equal level.

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Fig. 4.8 Block diagram of Local Oscillator

4.8 AUDIO CHAIN

4.8.1 AURAL MODULATOR

The aura l modulator unit consists of audio amplifier , VCR , Mixer and APC.

The block diagram of Aural of modulator is given below.

Fig. 4.9 Block diagram of Aural Modulator.

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4.9 AUDIO AMPLIFIER

A balanced audio signal at + dB from studio is converted to unbalance signal by audio

transformer T4. The output of this is taken through potentiometer to the input of Hybrid Audio

Amp BMC 1003. A 50 micro second pre-emphasis is also provided.

VCO

This is vector tuned oscillator, its frequency can be varied by coil L4. Transistor TR-17 from

the oscillator. VCO output level is 0 dB

4.10 EDITING

After recording a raw material using video tape recorders(VTR) different types of correction is

done using edit suit like as cutting unwanted video & audio, making suitable timing for Broad

casting, program name , actor name, director name etc. and also edit new audio & different types

of video pattern, new images , new pictures.

There are unit time for any program, therefore we need editing thus we can see continuous picture

in our television.

There are two types of editing

1. LINEAR EDITING

2. NON LINEAR EDITING

1. LINEAR EDITING

It is simple type of editing. In this type we can use only one or two Players & recorders .Different

video clips that we want to add or join with main program are played into cassettes players, and

graphics that we want to add is selected to record on the tape. On recorder the starting time and

ending time is selected in between which, mixing is done .Linear editing have disadvantage like it

takes more time. We can only add clip of length that we have space on tape, means to add long

clip, we can’t move video on tape, so overlapping occurs at that time. We can’t place more images

& pictures. Using linear editing we can interchange audio & video only.

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Other problems with linear tape based editing are:

Editing in sequence-first shot first.

Long hours spent on rewinding of tapes, Search of material.

Potential risk of damage to original footage.

Difficult to insert a new shot in edit.

2. NON LINEAR EDITING

NLE is video editing in digital format with standard computer based technology

Computer technology is harnessed in random access, computation and manipulation

capability ,multiple copies ,Intelligent search, sophisticates projects and media management

tools, standard interfaces, and powerful display

Flexibility in editing functions

Easy to do changes, undo, copy, duplicate and multiple version

Easy operation for cut, dissolve, wipes and other transition effects

Multilayer of video becomes easy

Powerful integration of video and graphics. Tools for filtering, color correction, key

framing &special 2D/3D effects.

Equally powerful audio effects and mixing.

Possible to trim, compress or expand the length of the clip

Support for multi format. Multi resolution clips

Intelligent and powerful 3D video effect can be created and customized.

Efficient and intelligent storage

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Nonlinear editing is done on time line using PC based software. The figure shows the

window of NLE software.

Fig.4.10 NLE Software

Video editing is done using multilayer technique and audio mixing is also possible on tome line

using multilayer. Photo shows the time line of video gallery, preview window and tool bar

Different clips of source programs are created and placed in gallery. Items from the gallery can be

used using simple drag & drop technique.

There are so many in built mixing styles, transition, effects, wrappings effects stored in the

software that we can apply over time line

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4.11 TRANSMITTER ANTENNA SYSTEM

TV Antenna system is that part of the Broadcast the Network which accept RF energy from

transmitter and launches electromagnetic wave in space . The polarization of the radiation as

adopted by Doordashan is linear horizontal. The system is installed on a supporting tower and

consists of antenna panels, power dividers, blunts branch feeder cable lunation boxes and main

feeder cables. Dipole antenna elements in one of the other form are common at VHF frequencies

whereas slat antennae are mostly used at UHF frequency directional radiation pattern is obtain by

arranging the dipoles in the form of turnstile and exciting the same in quadrature phase . Desired

gain is obtain by stacking the dipoles in vertical plane . As a result of stacking most of the RF

energy is directed in the horizontal plane. Radiation in the vertical plane is minimized. The

installed antenna system should fulfill the following requirements :

It should have required gain and provide desired field strength at the point of reception.

It should have desired horizontal radiation pattern and direction for saving the planned

area of interest. The radiation pattern should be one direction if the location of the

transmitting station is at the service area direction one , if the location is otherwise.

It should offer proper impendence top the main feeder cable and thereby to the transmitter

so that optimum RF energy is transferred into space . Impedance mismatch results into

reflection of power and formation of standing waves. The standard RRF impedance at

VHF/UHF is 50 ohms.

Radiation Pattern and Gain

The horizontal and vertical radiation pattern are in the figures .The total gain depend upon

the type of the antenna panel and no. of stacks as in table -1.

Fig. 4.11 Doordarshan Logo

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4.12 DIGITAL SIDE BAND TRANSMISSION

Another feature of present day TV transmitter is vestigial side band transmission . If normal

amplitude modulation technique is used for picture transmission , the minimum transmission

channel bandwidth should be around 11 MHz taking into account the space for sound carrier

and a small guard band around of 0.25 MHz . Using such large transmission BW will limit the no.

of channels in the spectrum allotted for TV transmission . To accommodate large number of

channel in the allotted spectrum , reduction in transmission BW was considered necessary . The

BW could be reduced to around 5.75 MHz by using single side band ( SSB) AM in technique

because in principle one side of the double side band (DBB) AM could be suppressed, since the

two side band have the same signal content .

It was not considered feasible to suppress one complete side band in the case of TV signals

most of the energy obtained in lower frequency and these frequency unless obtained important

information of the picture. If these frequencies are removed ,it causes objectionable phase

distortional these frequencies which will affect picture quality .Thus as a compromise only part of

lower side band is suppress while taking full advantage of the fact that ;

Visual disturbance due to phase energy and unacceptable where large picture are

concerned ( i.e., at LF ) but

Phase errors becomes for see on small details ( i.e. in HF region) in thee picture . Thus

low modulating frequencies must minimize phase distortion where as high frequencies

are tolerant of phase distortions as they are very difficult to see.

The radiated signal thus contains full upper side band together with carrier and vestige

(remaining part) of the partially suppressed LSB . The lower side band contains frequencies up to

0.75 MHz with a supper of 0.5 MHz so that the final cut off 1.25 MHz

Standards The characteristics of the TV signal is sections 1 and 2 refer to CCCIR B/W standard.

Various other standards are given in table 1.

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(SPECIFFICATION OF DOORDARSHAN)

TABLE-4.12

Frequency Range Vision /sound carrier spacing channel width

Vision sound carrier spacing 5.5 MHz

Channel width 7MHz (B) in VHF OR 8MHz (G) in UHF

Sound Modulation FM

FM deviation (maximum) ± 50 kHz

4.13 EARTH STATION

Earth station is the unit from where program signal is sent to the geo stationary satellite (Uplink)

Program signal transmitted by the satellite is received at the earth station (downlink).

For a given channel an earth station is provided a fixed uplink frequency, and a different but fixed

downlink frequency.

An earth station is comprises of following :

Digital Transmitter.

Parabolic Antenna.

Power supply unit.

The following figure depicts the basic block diagram of digital earth station.

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Fig.4.13 block diagram of Earth Station DDK Silchar

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Fig.4.14 Block diagram of Earth Station DDK Silchar

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4.14ANTENNA ARRAYS

Waves undergo a phenomenon called interference.

Not noticeable for different signals. But for same signals (with perhaps different relative phase,

amplitude)patterns can be formed.

Used in many fields.

Radio, cell tower(dipole antennas). Helical antennas. High gain too: phased arrays.

Expensive, thermal management issues.

Satellites: many beams from one aperture. Terminals: Rapid beam steering.

Fig. 4.14 Diagram of Parabolic Dish Antenna

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REFERENCES

http://www.doordarshan.com

http://www.googleimage.com

Text material from DDK Silchar

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http://www.googleimage.com/

http://www.doordarshan.com/

SUMMER TRAINING REPORT ON DOORDARSHAN KENDRA SILCHER

Education

Transcript of SUMMER TRAINING REPORT ON DOORDARSHAN KENDRA SILCHER