Training Report

On

Vocational trainingSubmitted in the partial fulfillment of the requirement for the award of degree of Bachelors of Technology

In

Electronics & Communication Engineering

Submitted by:

NAME: VIVEK KUMAR VICKY REG. NO: 10904953 NAME AND LOCATION OD THE COMPANYDOORDARSHAN KENDRA, PATNA

29-05-12 TO 09-07-12

Department of Electronics & Comm. Engg Lovely Professional University Phagwara–140 401, Punjab (India)

ACKNOWLEDGEMENT

I take immense pleasure in thanking All Doordarshan employees, our beloved Associates employee for having permitted me to carry out this project work.

I wish to express my deep sense of gratitude to my Internal Guide, Mr. Ushuf, Mr. N K Singh, Mr. Mahesh and all Staff of Doordarshan for their guidance and useful suggestions, which helped me in completing the project work, in time.

Words are inadequate in offering my thanks to the Project Trainees and Project Assistants, Doordarshan members for their encouragement and cooperation in carrying out the project work.

Finally, yet importantly, I would like to express my heartfelt thanks to my beloved parents for their blessings, my friends/classmates for their help and wishes for the successful completion of this project.

VIVEK KUMAR VICKY

10904953

TABLE OF CONTENTS

1. INTRODUCTION2. ORGANIZATION AND REQUIREMENT3. COLOUR COMPOSITE VIDEO SIGNAL.4. STUDIO:

3.1 TYPES OF STUDIO3.2 DIFFERENT AREA OF STUDIO3.3 TV LIGHTING3.4 CCD

5. TRANSMITTER 4.1 TYPES OF TRANSMITTER4.2 MODULATION4.3 AMPLIFICATION

6. EARTH STATION.7. SATELLITE COMMUNICATION.8. FUTURE SCOPE9.REFERENCE.

INTRODUCTION:

Doordarshan Kendra was stabilized in India on 15sept 1959. At that time only half an hour program were transmitted by the Doordarshan Kendra. The transmission was in black and white. The first colour transmission was transmitted by Doordarshan Kendra in 1982 at the time of Asian games.DD India has many parts in all over in India and Doordarshan Kendra Patna is also one of them. DD India is one of the largest television networks in the world. Doordarshan Kendra Patna has 5 high power terrestrial transmitters, 62 low power transmitter, 5 very low power transmitter and 3 production centers in Bihar. The first studio was inaugurated on 28 th may 2000 by the ARUN JATELY. At that time Doordarshan Kendra Patna was reaching to 85% of total population of Bihar without any cost but now with the introduction of DTH it is reaching to 100% of population of Bihar.Doordarshan Kendra Patna is established near Gandhi maiden, Patna.There are 4 main sections in DD Patna:

1. Engineering section.2. Program section.3. News section.4. Administrative section.

In technical section Doordarshan Kendra has 6 parts: 1. STUDIO

2. PRODUCTION CONTROL ROOM (PCR).3. VIDEO STORAGE AND TRANSMISSION ROOM (VTR).4. MAIN SWITCHING ROOM (MSR).5. DIGITAL EARTH LINK STATION.6. TRANSMITTER.

1. STUDIO:

There are 2 studios in DD Patna. One is named as MAIN STUDIO and other is CB STUDIO.MAIN STUDIO is used for the larger events like discussion of 4-5 people and recording of any show and CB STUDIO is used for the small events like news reading or interview of any single person. Camera, microphone and lights equipments are the basic requirements of the STUDIO.

2. PRODUCTION CONTROL ROOM (PCR):

PCR section is the part of the DD Patna, where the production activities take places like minor editing and management of feed during a live program. The production manager gives direction to the camera men and selects the angles sound parameters etc during the production stage in the production control room. In the PCR section we control studio lights and microphones and other

aspects. The PCR section has an audio mixer and a vision mixer. The phone in console and other systems are also kept in PCR section.

3. VIDEO STORAGE AND TRANSMISSION ROOM (VTR):

In the VTR section we store copies of all programs. All the programs shot in the camera are simultaneously recorded in the VTR and with the help of VTR, we can play back all the videos, when required. In the VTR, videos of pre-recorded events are queued up and are played back without a break. Videos of famous people and important events are stored in the central film pool.

4. MAIN SWITCHING ROOM (MSR):

In MSR section DD Patna stores all the circuitry of the DDK like camera base units, vision mixer base units and audio processor base units are kept in MSR. In MSR, we monitor and control of all activities. It is the MSR which decides what is to go in air. Some other functions are also take places in MSR like logo addition etc.

5. DIGITAL EARTH LINK STATION:

Earth station is the next and very important part of the DD Patna which has an uplink chain, simulcast transmitters, audio processors video processors, up converters, modulators etc. It is fully digital.

6. TRANSMITTER:

Transmitter is a part of DOORDARSHAN from which we transmit the our signal. Today DOORDARSHAN has almost 1429 transmitters in all over India.Transmitter has three types:

A. VERY LOW POWER TRANSMITTER (VLPT).B. LOW POWER TRANSMITTER (LPT).C. HIGH POWER TRANSMITTER (HPT).

All these transmitters is used to transmit single at different places where it is required.

TYPES OF COMMUNICATION:

1. ANALOG COMMUNICATION.2. DIGITAL COMMUNICATION.

DD Kendra uses both types of communication for transmission of the signal. Delhi, Mumbai, Chennai, Kolkata uses digital communication but rest of the DD Kendra are still using the analog

communication. But now in upcoming day all the DD Kendra will use digital communication. Because digital communication has many advantage over analog communication like we can increase number of channels in same bandwidth, better quality etc.

STANDARD OF TELEVISION SYSTEM:

Mostly there are 3 types of television standard whose whole world are using for television broadcasting.

1. NTSC.2. SECAM.3. PAL.

Mainly America uses NTSC television standard. It required 60 Hz and 525 lines.Mainly France uses SECAM television standard. it required 800 lines.But in India uses PAL (phase alternating line) television standard because it requires 50 Hz and 625 lines for the broadcasting. Our all the equipments are working on this frequency. We inherit this television standard from Germany because all the machines are bought from Germany. PAL was developed by Walter Bruch at Telefunken in Germany in 1963, with first broadcasts beginning in United Kingdom and West Germany in 1967.The frequency of chrominance subcarrier is 4.43MHz. In a PAL system the phase of color information on the video signal reverses each line. The phase reversal of color information corrects the phase error of each signal. The cancellation of phase error also degrades the vertical frame color resolution but it is a very small value and thus neglected.The 4.43 MHz frequency of the color carrier is a result of 283.75 color clock cycles per lines plus a 25 Hz offset to avoid interferences.

Now, vertical line frequency =50 Hz

number of lines at the rate of 25 Hz = 625 linesHorizontal line frequency = 625 x 25=15625 Hz

Line duration of PAL signal = 1

15625=64 µs

We have total 625 total lines in which we have The line which consist no information lines = 50The line which consist video information Lines = 625-50= 575

COLOUR COMPOSITE VIDEO SIGNAL:

Colour composite video signal is formed with Video, sync and blanking signals. The level is standardized to peak to peak 1 volt in which 0.7 volts is used for the video and 0.3 volts is used for sync pulse . The colour composite video signals (CCVS) are shown in the fig:

It consists of front portch, back portch, pedestal level, colour burst and sync pulses. The TV signals have different types of frequency. It has total time period of 64us. In which it has active period of 52us and the rest of 12us is known as vertical blanking period.

PICTURE FORMATION:

A picture is formed by picture elements which consist of light or shades. In this case TV camera

the scene is focused on the photoelectric surface of pick up device and a optical image is formed. The pick up device convert the optical image to the electrical charge image due to photoelectric property. Now it is necessary to pick up this information and transmit it. For this purpose scanning is employed. Electric beam scans the charge image. The electrical beam scans the image line by line and field by field to provide signal variation in a successive order.A frame is firstly divided into two fields. Odd field and Even field. Odd field are scanned first and then it scans even field.We have 625 lines for one frame.We have field rate of 50Hz. But it is divided into 2 parts so the frame rate is 25Hz.The horizontal lines scan at the rate of 25 Hz.So the horizontal frequency is = 25*625=15625 Hz.And the vertical frequency is = 50Hz.

Number of TV lines per frame:

Bandwidth of video is directly proportional to the RF channel width. If the number of the TV lines has larger bandwidth of video then it requires larger RF channel width. But if we use larger RF channel width then number of channel will decrease. But with more TV lines on the screen the clarity of picture (resolution) increases and if there is lesser TV lines then picture quality decrease. As we know that we have 625 lines for scanning a frame of a picture but there is no information in all the signals. In these line 50 lines has no information. So the line which have video information is: 675 - 50 = 575 lines.And the resolution factor is 0.69.So the video information after introducing resolution factor will be limited to: 575*0.69=~ 400 lines.As we know that the Aspect ratio of our television is 4/3.If we multiplied the Aspect ratio with 400 lines then the lines will be: 400*4/3=~528 lines.But we divided it into two fields so number of lines in one field 528/2 = 264 lines.And we calculated that the time period of active video signal is 52us. So the bandwidth of active video is 264/52*10^-6 = 5MHz.

THE COLOUR SYSTEM:

We have three primary colour:1. Red.

2. Blue.3. Green.

With the help of these three colour we can form any colour in a suitable proportion. So, we have to transmit these colours to one place to another place then we have to convert these colour to the electrical signals and transmit it on different carriers but at the receiver end we have to convert these electrical signal to the pictures. We can do that with the help of the picture tube.The phosphors for all the three colours i.e. R, B, G are easily available to the manufactures of the picture tube. So, there is only three signals R,B,G is between the camera and the picture tube of the receiver.

Colour television has the constraint of compatibility and reverse compatibility with the monochrome television system. The meaning of the compatibility is when colour TV signal is radiated the monochrome TV sets should display Black and White pictures. This features can be achieved by sending Y(luminance) as monochrome information along with the chrome signal. We can get Y(luminance) by mixing these three primary colour: Y = 0.3R + 0.59G + 0.11BBut there is a problem of reverse compatibility means when Black and White TV signal is radiated the colour tv sets should display the black and white pictures.If we transmit Y, R , B and derive G thenSince Y=0.3R+0.59G +0.11B G= 1.7Y-0.52R-0.19BSo, in such a case what happened with a colour TV set when we transmit black and white signal. R and B are zero , but G gets 1.7Y. the net result is pictures on a colour TV screen appear as Green pictures.

COLOUR DIFFERENCE SIGNALS:

If we want to achieve the reverse compatibility then we transmit Y,R-Y and B-Y in place of Y, R and B. we do not transmit G-Y because its value is very less as compared to rest of them and if we send it then it will create noise in the signal so we didn’t send this and we can generate it at the receiver end. We can monitor these colours on VECTROSCOPE. If 100% of R then R=1, G=0, B=0.Weighting factor of R-Y=0.877Weighting factor of B-Y=0.493And when calculate it then we can see the perfect picture of any colour on the VECTROSCOPE.

STUDIO:

A Studio is a place in which we make programs either for live telecast or for the recording for the video tape. We mix many other things before the broadcast like output of the camera, feed from the other DD Kendra, video graphics characters generators, playback from pre recorded tape and other program slides. In DD Kendra we also use live editing that includes formation of special effects. We send our signal to the different areas before uplink to the satellite like PCR, CCU, MSR, VTR and then via earth station to the transmitter.

DD Kendra, Patna has two studios:1. MAIN STUDIO.2. CB STUDIO(continuity booth studio)

1. MAIN STUDIO:

MAIN Studio is also known as Studio-A. Features of the MAIN Studio of DD Kendra, Patna:

It has a dimension of 400 sq m. It has 3 cameras for recording the action that is happening in the ACTION area. Every camera is connected with the microphone to record the audio. It is uses for the larger events like discussion of 4-5 people, recording of any musical

program, recording of any celebrity where studio audience is present etc. Different kinds of lights are used there for the action area like key light, fill light, back

light, background light. The MAIN Studio is connected via Production control room where production

Manager controls all the actions that is happening in the action area.

2. CB STUDIO (CONTINUITY BOOTH):

CB Studio is another studio of the DD Kendra, Patna. It is also known as Studio-B.Features of the CB Studio of DD Kendra, Patna:

It has a dimension of 50 sq m. It has 2 cameras of THOMSON for recording purpose. Every camera is connected with microphone. It is used for news telecast or interview of any single person. In this studio, Teleprompter is used for reading the news. It has two techniques.

In first technique, there is a monitor in front of the news reader and the news display on the monitor. In the second technique the news reader uses a mouse to

scroll the news and then the news reader reads the news.

There are different areas in studio:1. Action area:

It has the largest space then any area in the technical area. This area consist of camera, microphone, staging, lighting and performance by artist

FEATURES OF THE ACTION AREA:

The floor of this area is very smooth so that there should be no sound of camera dollies.

It requires very efficient air conditioning because of light and presence of the artist.

Acoustic technique is used in this area because there are many people are present there are lot of equipments are working there at that time

Silent communication is used between floor crew members and the production control room.

Cyclorama and curtain tracks for the blue and black curtain for chroma keying and limbo lighting respectively.

There is digital clock display.

2. CAMERA CONTROL UNIT (CCU):

It is a part of studio. The output of the camera is pre amplified in camera head and then feed into the camera control unit through triax cable. All the camera control voltages are fed from the CCU unit to the camera head through Triax cable. The viewfinder signal is also sent to the camera head so that cameraman so that he or she can easily adjust, focus and compose the videos.

3. Production control room:

This room consists of these activities: With the help of this room production manager gives the direction to the

production crew. Editing of different source available at the production desk. From this room Production manager operates the camera and manage that which

camera is going to telecast. Production manager monitors the output/off air signal from this room.

It also consists of vision mixer and audio mixer. It consists of a character generator (CG), which creates majority of names and

digital on screen graphics that are inserted into the program lower third portion of the television screen. There are also a software named MOV-CG is used for this purpose.

4. Vision mixer:

Vision mixer is also known as the video switcher. The vision mixer is typically 10*6 or 20*10 cross bar switcher selecting anyone of the 10 or 20 input to 6 or 10 different output lines. The input may be different cameras, VTR1, VTR2 etc. The features of vision mixer:a. Take: we can take any input.b. Cut: we can switch from one source to another.c. Dissolve: we can mix different-different audio and video together.d. Special effects: we can add special effects in the pictures.

5. Character generator:

It provides the title, characters, different colours for colorizing characters, background, edges etc. Character generator is a microcomputer with text along instruction when typed in at the keyboard is stored on a floppy or a hard disk. Many scripts can store on floppy and recalled when needed by the address of the stored pages.

6. Master switching room (MSR):

The MSR is the most important area of the broadcasting chain of a broadcasting station. With the help of this room we switch the activities from camera to camera and other part of studio. This room also controls the television programs that are going to telecast and the television commercials, switch local or national network feed, record satellite feeds and monitor the transmission of signals to other parts of studio.If we have to telecast any television program live then the signal goes from PCR to MSR and then out to the transmitter. After that transmitter these signal to the satellite.The MSR at DDK Patna has an installation of 16x16 router to cater its switching needs. It also has VDA (Video Distribution Amplifier).

TV LIGHTING:

There are mainly three types of lighting:1. Key light.2. Fill light.

3. Back light.

Key light: This is main and primary light source of illumination. It constructs the shape and size of the any object by shadows. It is treated like a sun in the sky and it should cast a shadow.

Fill light:

It is used to control the contrast of the key light by filling in shadows. It can also provide catch light in the eyes.

Back light:

It is used to separate the object from the background. If we do not use this light then it will appears that the object is attached with the background.In the three point lighting the ratio of 3/2/1 (back/key/fill) for mono and 3/2/2 for the colour provides good portrait lighting.

CCD (charge coupled device):

We use camera for shooting a picture. It happens through lens and the picture form with the help of the three primary colours. But we have to transmit these pictures. So, we have to convert into the electrical signals. This work could be done with the help of CCD (charge coupled device).It is a semiconductor device just like MOSFET. It consists of photodiodes.

TRANSMITTER:

Transmitter is used to transmit the signal from one place to another place. There are mainly three types of transmitter that are used to transmit the signals:

1. Very low power transmitter.2. Low power transmitter.3. High power transmitter.

1. Very low power transmitter:

It has a capacity of 10w to 50w. This type of transmitter is used in that place where very small populations are living.

2. Low power transmitter :

It has a capacity of 100w to 500w. This types of transmitter is used for small population.

3. High power transmitter:

It has a capacity of 1Kw to 30Kw. It is used for the large population. In Patna there are 2 transmitter of 10Kw. At the border areas we uses high power transmitter so that the people of border country can see our television programs. Wide band antenna is used for transmission. Air cooling facilities is available in DD Patna. It has 2 audio and 10 video amplifiers. AOL (aviation obstruction light)There are many companies which manufacture transmitter: BEL, NEC, HARRIS, THOMCAST, GCEL etc.

There are mainly three steps in any transmitter:

1. Modulation.2. Amplification.3. Antenna.

1. Modulation:

Modulation is a process in which we superimposed a modulating signal (which has lower frequency) on carrier single (which has higher frequency) so that the modulating signal can travel for a longer distance.The modulation is required for the transmission of the modulating signal because the energy of modulating is very low and it can travel for a longer distance. So if want to send a modulating signal for longer distance that we have to modulate the modulating signal over a carrier signal.The modulation depth should be 87.5% maintain. The reason behind it is that:1. To avoid the picture distortion at receiver side.2. To avoid undesired sound buzz in the TV receiver.

For transmission we firstly modulate our signal in IF modulation. The advantage of IF modulation is:

1. Easily available and economical.2. Ease of VSB shaping.3. Ease of correction distortion.

Types of IF modulation:1. Positive modulation.

2. Negative modulation.

We use negative IF modulation for our signal because it help us to save our signal to lost.Negative modulation the amplitude of the signal is in middle and sync pulse is at the top. So if there is any distortion in the signal then that will be in the sync pulse which we can generate at any time. So due to this modulation we can save our single more efficiently. EXICTER determines the quality of a transmitter. It consists of DP/DG corrector, video input processor, IF carrier generator, up converter, aural modulator and video and audio mixer, band pass filter, delay equalizer, receiver pre-corrector, low pass filter.

VISION AND SOUND SIGNAL AMPLIFICATION:

In low power transmitter sound and vision are modulated separately but amplified jointly. In high power transmitter vision and sound carriers can be generated, modulated and amplified, separately and then combined in the diplexer. Because of the errors caused by the TV diplexer, we need delay equalization. But in second case we need filter for suppressing.

EARTH STATION:

DOORDARSHAN Kendra Patna uses earth station for uplink and downlink of the programs like news, interviews, local activities etc.We use earth station as an uplink center from which the signals are given to Satellite for distribution in an area covered by the Satellite. We uplinked the signal from the earth station and received by many down link centers in TV broad casting. It is a very important part of satellite communication system for broadcasting of signals.

We use mainly three types of mode to distribute the signal from the earth station to the receiver:1. CABLE DISTRIBUTION.2. SATELLITE DISTRIBUTION.3. TERRESTRIAL DISTRIBUTION.In these three distribution private sectors can use only two types of distribution i.e. cable and satellite. Terrestrial distribution can be used only government. Private sectors have no authority to use this distribution. These whole three modes of communication are controlled by ITU (International Telecommunication union).This international telecommunication union is divided into three parts:

1. ITU (1).2. ITU (2).3. ITU (3).

ITU (1) is established at 35 degree east to 56 degree west. It covers the area of Europe, Africa and Middle East part of the globe.ITU (2) is established at 57 degree east and 156 degree west. It covers the whole America.And the rest part is ITU (3) and this part covers rest of the world like Asia, south pacificEtc.

SATELLITE COMMUNICATION:

Satellite communication is a mode of communication in which signal transferring between the sender and receiver is done with the help of satellite. In this process, the signal which is basically a beam of modulated microwaves is sent towards the satellite. Then the satellite amplifies the signal and sent it back to the receiver’s antenna present on the earth’s surface. So, all the signal transferring is happening in space.In recently time we use satellite communication more than other because it has many advantages:

1. Due to this we get wideband bandwidths for the distribution.2. It is cheaper than other mode of distribution.3. It is ideal for the broadcasting applications4. A single satellite can give coverage to 30% of the surface area of the earth.5. This is only the solution for the growing requirement of the communication.6. It can be rapidly deployed.7. It can be used for two way communication or broadcast purpose with the covered area.

We can use satellite communication in these areas:1. In the field of communication.2. In the field of weather forecasting.3. In the field of military application.4. In the field of remote sensing

5. In the field of navigation.

GROUND SEGMENT:

The ground segment's job is in two part. In the case of an uplink, or transmitting station, terrestrial data in the form of baseband signals, is passed through a baseband processor, an up converter, a high powered amplifier, and through a parabolic dish antenna up to an orbiting satellite. In the case of a downlink, or receiving station, works in the reverse fashion as the uplink, ultimately converting signals received through the parabolic antenna to base band signal.

SPACE SEGMENT:

The space segment is divided into three separate units, namely the fuel system, the satellite and telemetry controls, and the transponder. The transponder includes the receiving antenna to pick-up signals from the ground station, a broad band receiver, an input multiplexer, and a frequency converter which is used to reroute the received signals through a high powered amplifier for downlink. The primary role of a satellite is to reflect electronic signals. In the case of a telecom satellite, the primary task is to receive signals from a ground station and send them down to another ground station located a considerable distance away from the first. This relay action can be two-way, as in the case of a long distance phone call. Another use of the satellite is when, as is the case with television broadcasts, the ground station's uplink is then down linked over a wide region, so that it may be received by many different customers possessing compatible equipment.

The range of the RF frequency band on which satellite communication work:1. C-BAND.2. KU BAND.3. Ka BAND.

1. C-Band Uplink Frequency 5.85 to 6.425 GHz

Downlink Frequency 3.4 to 4.2 GHz

2. Ku Band Uplink Frequency 13.75 to 14.5 GHzDownlink Frequency 10.7 to 11.2 GHz

11.2 to 12.2 GHz 12.25 to 12.75 GHz

Some time ago this communication is working is C band so we need a dish antenna of 7m diameter but now we are working in KU band so that we can receive our single with the help of small dish antenna. That’s why the invention of the DTH became possible.

PAREMETER OF THE SATELLITE OF DD,PATNA:1. Satellite 3A , 93.5 degree East2. Transponder C-01.3. Multiple Channels per Carrier (MCPC).4. Uplink Freq. 5965.5 MHz ,Pol. H5. Down link freq. 3740.5 MHz, Pol. V6. Symbol Rate 6.25 Mbps

UPLINK DOWNLINK

Direct-to-Home Satellite Broadcasting (DTH)

There was always a persistent quest to increase the coverage area of broadcasting. Before the advent of the satellite broadcasting, the terrestrial broadcasting, which is basically localized, was mainly providing audio and video services. The terrestrial broadcasting has a major disadvantage of being localized and requires a large number of transmitters to cover a big country like India. It is a gigantic task and expensive affair to run and maintain the large number of transmitters. Satellite broadcasting, came into existence in mid sixties, was thought to provide the one-third global coverage simply by up-link and down-link set-ups. In the beginning of the satellite broadcasting, up-linking stations (or Earth Stations) and satellite receiving centers could had only been afforded by the Governments organizations. The main physical constraint was the enormous size of the transmitting and receiving parabolic dish antennas (PDA). In the late eighties the satellite broadcasting technology had undergone a fair improvements resulting in the birth of cable TV. Cable TV operators set up their cable networks to provide the services to individual homes in local areas. It rapidly grew in an unregulated manner and posed a threat to terrestrial broadcasting. People are now mainly depending on cable TV operators. Since cable TV services are unregulated and unreliable in countries like India now, the satellite broadcasting technology has ripened to a level where an individual can think of having direct access to the satellite services, giving the opportunity to viewers to get rid of cable TV. Direct-to-Home satellite broadcasting (DTH) or Direct Satellite Broadcasting (DBS) is the distribution of television signals from high powered geo-stationary satellites to a small dish antenna and satellite receivers in homes across the country. The cost of DTH receiving equipments is now gradually declining and can be afforded by common man. Since DTH services are fully digital, it can offer value added services, video-on-demand, Internet, e-mail and lot more in addition to entertainment. DTH reception requires a small dish antenna (Dia 60 cm), easily be mounted on the roof top, feed along with Low Noise Block Converter (LNBC), Set-up Box (Integrated Receiver Decoder, IRD) with CAS (Conditional Access System). A bouquet of 40 to 50 video programs can simultaneously be received in DTH mode.

UPLINK CHAIN

DTH broadcasting is basically satellite broadcasting in Ku-Band (14/12 GHz). The main advantage of Ku-Band satellite broadcasting is that it requires physically manageable smaller size of dish antenna compared to that of C-Band satellite broadcasting. C-Band broadcasting requires about 3.6 m dia PDA (41dB gain at 4 GHz) while Ku-Band requires 0.6 m dia PDA

(35dB gain at 12 GHz). The shortfall of this 6 dB is compensated using Forward Error Correction (FEC), which can offer 8 to 9 dB coding gain in the digital broadcasting. Requirement of transmitter power (about 25 to 50 Watts) is less than that of analog C-band broadcasting. The major drawback of Ku-Band transmission is that the RF signals typically suffer 8 to 9dB rain attenuation under heavy rainfall while rain attenuation is very low at C-Band. Fading due to rain can hamper the connectivity of satellite and therefore rain margin has to be kept for reliable connectivity. Rain margin is provided by operating transmitter at higher powers and by using larger size of the dish antenna (7.2m PDA).

DOWN-LINK CHAIN

Down-Link or receiving chain of DTH signal is depicted in Fig.2. There are mainly three sizes of receiving antenna, 0.6m, 0.9m, and 1.2m. Any of the sizes can easily be mounted on rooftop of a building or house. RF waves (12.534GHz, 12.647GHz, 12.729 GHz) from satellite are picked up by a feed converting it into electrical signal. The electrical signal is amplified and further down converted to L-Band (950-1450) signal. Feed and LNBC are now combined in single unit called LNBF. The L-Band signal goes to indoor unit, consisting a set-top box and television through coaxial cable. The set-top box or Integrated Receiver Decoder (IRD) down converts the L-Band first IF signal to 70 MHz second IF signal, perform digital demodulation, de-multiplexing, decoding and finally gives audio/video output to TV for viewing. IF signal (950-1450MHz).

DISH TRACKING: If we want to locate any place of the earth then we need some coordinates. So, for the reference we have north and south poles. Hence some imaginary lines were drawn, called longitudes and latitudes. With the help of these lines we can get the coordinates of any place with reasonable accuracy.

LATITUDES:

For a start a line was drawn equidistant to both north and south poles and this was called equator. Parallel lines were drawn depicting the angular distance north or south of equator. All latitudes are circles with different diameters the equator being the largest. As they are parallel to each other they are also called parallels. The equator as the reference and both north and south poles cover an angle of 90 degrees maximum.

LONGITUDE:

The longitude is another reference point that we need to locate a dish. The reference point i.e. 0 degree longitude is supposed to pass through the observatory at Greenwich, ENGLAND. The meridians or longitudes east of Greenwich are called east meridians and those lying in the west are called west meridians. The maximum is 180 degrees on both sides.

Azimuth and Elevation:

For deciding the longitude and latitude of a satellite and the place where we have to fix the dish antenna we need two angles known as AZIMUTH AND ELEVATION. So that we can get a satisfactory signal from the satellite the dish antenna should be pointed towards the satellite accurately. The azimuth and elevation are angles which specify the direction of a satellite from a point on the earth's surface.

Azimuth angle:

Azimuth refers to the rotation of the whole antenna around a vertical axis. It is the side to side angle. We can swing the whole dish all the way around in a 360 deg circle. By definition North is 0 deg, East is 90 deg, South is 180 deg and west is 270 deg. North can also be called 360 deg. Note that you find a satellite by pre-setting the elevation accurately and then swinging the whole antenna boldly in azimuth till the signal locks up - so an approximate azimuth angle is normally sufficient. The dish pointing calculator gives the required azimuth angle both relative to true north and relative to magnetic compass north.

Calculation of Azimuth:

• Where, D = lr - ls in degrees.• f = latitude of the given site in degrees. • lr = longitude of the given site in degrees. • ls = longitude of the satellite.

azimuth = 180o ± tan−1 ( tan D )(sin φ )

Elevation angle:

Elevation refers to the angle between the dish pointing direction, directly towards the satellite, and the local horizontal plane. It is the up-down angle.

When your dish is pointed low down near the horizon the elevation angle is only a few degrees. At low elevation angles, below 5 deg at C band and 10 deg at Ku band, the path through the atmosphere is longer and the signals are degraded by rain attenuation and rain thermal noise.

Calculation of elevation angle:

Where,r = Radius of the earth (6367 kms) R = Radius of Synchronous orbit (42,165 kms).f = Latitude of the earth stationD = difference in longitude of the earth station and the satellite. (lr - ls)

Elevation = tan−1 [ Cos D . Cos φ −rR

√1−(Cos D . Cos φ )2 ]

FUTURE SCOPE:

As we know that Doordarshan is the oldest Kendra in all India. But still there are some DD Kendra are using analog communication. But in upcoming days every DD Kendra will use digital communication after that the transmission of the signal will be more clear and effective.

REFERENCE:

http://www.thefreedictionary.com/transmitterhttp://en.wikipedia.org/wiki/Transmitterhttp://en.wikipedia.org/wiki/Earth_stationhttp://en.wikipedia.org/wiki/Television_studio