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CHAPTER 1INTRODUCTION

Training is important phase of student life. During this period student gets both theo-retical as well as practical knowledge of the subject. Training also impresses a stu-dent overall approaches to life and impress his personality and confidence.Our training was in Doordarshan Kendra Lucknow. This report contains a detailed study of Doordarshan Kendra Lucknow.

There are 3 divisions here:-

1) Studio2) Transmitter3) Earth Station

1.1) STUDIO -

Doordarshan is a leading broadcasting service provider in india. DD Lucknow is full-flathead broadcast set up. Many serials &program are being made here like "BIBI NATIYON WALI", "NEEM KA PED" and "HATIM TAI" etc. recorded in studio.

1.2) TRANSMITTER -

Here the transmission of both audio and video has been made. The transmission sec-tion does the function of modulation of signal. Power amplification of the signal & mixing of audio and video signal is done here.

1.3) EARTH STATION -

The main function of earth station is to make contact with satellite or communicate with it. The signals from other transmitter are down linked here.Also the signals here are uplinked to send it to larger distance.

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CHAPTER 2 FUNDAMENTALS OF

MONOCHROME & COLOUR TV SYSTEM

Fig 2.1) TV Transmission Model

2.1) PICTURE FORMATION

A picture can be considered to contain a number of small elementary areas of light or shade which are called PICTURE ELEMENTS. The elements thus contain the visual image of the scene. In the case of a TV camera the scene is focused on the photosensi-tive surface of pick up device and a optical image is formed. The photoelectric prop-erties of the pick up device convert the optical image to a electric charge image de-pending 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 charge image and

produces optical image. The electron beam scans the image line by line and field by field to provide signal variations in a successive order. The scanning is both in hori-zontal and vertical direction simultaneously. The horizontal scanning frequency is 15,625 Hertz. The vertical scanning frequency is 50 Hz. The frame is divided in two fields. Odd lines are scjanned first and then the even lines. The odd and even lines are interlaced. Since the frame is divided into 2 fields the flicker reduces. The field rate is 50 Hertz. The frame rate is 25 Hert.

2.2) NUMBER 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 chan-nels in the R.F. spectrum will be reduced. However, with more no. of TV lines on the screen the clarity of the picture i.e. resolution improves. With lesser number of TV lines per frame the clarity (quality) is poor.

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2.3) RESOLUTION-The capability of the system to resolve maximum number of picture elements along scanning lines determines the horizontal resolution. It means how many alternate black and white elements can be there in a line. The vertical resolution depends on the number of scanning lines and the resolution factor (also known as Kell factor)

2.4) GREY SCALE- In black and white (monochrome) TV system all the colours appear as gray on a 10-step gray scale chart. TV white corresponds to a reflectance of 60% and TV black 3 % giving rise to a Contrast Ratio of 20:1 (Film can handle more than 30:1 and eye‟s capability is much more).

2.5) BRIGHTNESSBrightness reveals the average illumination of the reproduced image on the TV screen. Brightness control in a TV set adjusts the voltage between grid and cathode of the picture tube (Bias voltage).

2.6) CONTRAST-Contrast is the relative difference between black and white parts of the reproduced pic-ture. In a TV set the contrast control adjusts the level of video signal fed to the picture tube.

2.7) VIEWING DISTANCE- Optimum viewing distance from TV set is about 4 to 8 times the height of the TV screen. While viewing TV screen one has to ensure that no direct light falls on the TV screen.

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CHAPTER 3 COLOUR COMPOSITE VIDEO SIGNAL (CCVS)

3.1) WHAT IS VIDEO SIGNAL?

Video is nothing but a sequence of picture .The image we see is maintained in our eye for a 1/16 sec so if we see image at the rate more than 16 picture per sec our eyes cannot recognize the difference and we see the continuous motion.In TV cameras image is converted in electrical signal using photo sensitive ma-terial. Whole image is divided into many micro particles known as Pixels.These pixels small enough so that our eyes cannot recognize pixel and we see continu-ous image ,thus at any instant there are almost an infinite no. of pixel that needs to be converted in electrical signal simultaneously for transmitting picture details. However this is not practicable because it is no feasible to provide a separate path for each pixel in practicethis problem is solved by scanning method in which information is converted in one by one pixel line by line and frame by frame .Colour Composite Video Signal is formed with Video, sync and blanking signals. The level is standardized to 1.0 V peak to peak (0.7 volts of Video and 0.3 volts of sync pulse). The Colour Composite Video Signal (CCVS) has been shown in fig-ure.

Fig 3.1 Colour Composite video signal

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3.2) FREQUENCY CONTENT OF TV SIGNAL

The TV signals have varying frequency content. The lowest frequency is zero. (when we are transmitting a white window in the entire active period of 52 micro seconds the frequency is Zero). In CCIR system B the highest frequency that can be transmitted is 5 MHz even though the TV signal can contain much higher fre-quency components.

(In film the reproduction of frequencies is much higher than 5 MHz and hence clar-ity is superior to TV system.) long shots carry higher frequency components than mid close ups and close ups. Hence in TV productions long shots are kept to a mini-mum. In fact TV is a medium of close ups and mid close ups.

3.3) DC COMPONENT OF VIDEO SIGNAL AND DC RESTORATION

A TV signal is a continuously varying amplitude signal as the picture elements give rise to varying level which depends on how much of incident light the picture ele-ments can reflect and transmit the light signal to the TV camera. Hence the video signal has an average value i.e. a DC component corresponding to the average brightness of the scene to scene.

Fig 3.2 Seperation of H & v Sync Pulses from CVS

3.4) RF TRANSMISSION OF VISION AND SOUND SIGNALS

TV Transmission takes place in VHF Bands I and III and UHF Bands IV and V. Pic-ture is amplitude modulated and sound is frequency modulated on different carriers separated by 5.5 MHz.Also for video amplitude modulation negative modulation is employed because of the following main advantages.Pictures contain more information towards white than black and hence average power is lowerResulting in energy saving. (Bright picture points correspond to a low carrier amplitude and sync pulse to maxi-mum carrier amplitude).Interference such as car ignition interfering signals appear as black which is less objec-tionable.AM produces double side bands. The information is the same in both side bands. It is enough to transmit single side band only. Carrie r also need not be transmitted in full and a pilot carrier can help.

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However, suppressing the carrier and one complete side band and transmitting a pilot carrier leads to costly TV sets. A compromise to save RF channel capacity is to resort to vestigial side band system in which one side band in full, carrier and a part of other side band are transmitted

3.5) SOUND SIGNAL TRANSMISSION

In CCIR system B sound carrier is 5.5 MHz above the vision carrier and is fre-quency modulated. The maximum frequency deviation is 50 KHz. Also the ratio of vision and sound carriers is 10:1 (20:1 is also employed in some countries) If we as-sume maximum audio signal is 15 KHz the band width is 130 KHz. According to Car-son‟s Rule the bandwidth is 2 x (Maximum frequency deviation + highest modulating frequency). However, calculated value(using Bessel‟s function) of Bandwidth is 150 KHz i.e. 75 KHz on either side of sound carrier. In CCIR system picture IF is 38.9 MHz and sound. IF is 33.4 MHz. At the receiver end it is necessary to ensure that signal frequencies in the region of the vestigial side band do not appear with double amplitude after detection. For this purpose the IF curve..employs NYQUIIST slope.

Fig 3.3 Receiver Pass Band Characterstics

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3.6) THE COLOUR TELEVISION

It is possible to obtain any desired colour by mixing three primary colours i.e. Red, Blue and green in a suitable proportion. The retina of human eye consists of very large number of light- sensitive cells. These are of two types, rods and cones. Rods are sensitive only to the intensity of the incident light and cones are responsible for normal colour vision. The small range of frequencies to which the human eye is re-sponsive is known as visible spectrum. This visible spectrum is from 780 mm (Red) to 380 mm(Violet).

3.7) ADDITIVE COLOUR MIXING

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

on screen. Y= 0.3 Red + 0.59 Green + 0.11 Blue

Fig. 3.4 Additive Colour Mixing

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CHAPTER 4

TV CAMERA

Fig 4.1 Camera

4.1) INTRODUCTION:A TV Camera consists of three sections.a) A Camera lens & Optics: To form optical image on the face plate of a pick up de-viceb) A transducer or pick up device: To convert optical image into a electrical signalc) Electronics: To process output of a transducer to get a CCVS signal

4.2) TYPES OF PICK - UP DEVICESThere are three types of pick up devices based on :

4.2.1) PHOTO EMISSIVE MATERIAL: These material emits electrons when the light falls on them. Amount of emitted electrons depends on the light . Mono-chrome cameras used in Doordarshan were based on this material. These cameras were called Image Orticon Cameras. These cameras were bulky and needed lot of light. These are no longer in use at present.

4.2.2) PHOTO CONDUCTIVE MATERIAL: The conductivity of these material changes with amount of light falling on them. Such material with variable conductiv-ity is made part of a electrical circuit. Voltage developed across this material is thus recovered as electrical signal. Earlier cameras based on this principle were Videocon Cameras. Such cameras were often used in the monochrome televise chain . These cameras had serious Lag & other problems relating to dark currents. Improvement in these cameras lead to the development of Plumb icon and Sat icon cameras.

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4.2.3) CHARGE COUPLED DEVICES: These are semiconductor devices which convert light into a charge image which is then collected at a high speed to form a signal.Most of the TV Studios are now using CCD cameras instead of Tube cameras. Tube cameras have become obsolete & are not in use .

4.3) CAMERA SENSORS – CCD BASICS

The CCD is a solid-state device using special integrated circuitry technology, hence it is often referred to as a chip camera. The complete CCD sensor or chip has at least 450 000 picture elements or pixels, each pixel being basically an isolated (insulated) photodiode. The action of the light on each pixel is to cause electrons to be released which are held by

the action of a positive voltage. The Charge held under electrode can be moved to electrode by changing the potential on the second electrodes. The electrons (neg-ative charges) follow the most positive attraction. A repeat of this process would move the charges to next electrode, hence charge-coupled device. A system of transfer clock pulses is used to move the charges in CCDs to achieve scanning.

There are three types of CCD device:FRAME TRANSFER (FT).

INTERLINE TRANSFER (IT).

FRAME INTERLINE TRANSFER (FIT).Size of the chip used for broadcast cameras varies from ½ inch to 2/3inch.

4.4) FRAME TRANSFER (FT)

Frame transfer was the first of the CCDs to be developed and it consists of two iden-tical areas, an imaging area and a storage area. The imaging area is the image plane for the focused optical image, the storage area is masked from any light. The elec-trical charge image is built up during one field period, and during field blanking this charge is moved rapidly into the storage area. A mechanical shutter is used during field blanking to avoid contamination of the electrical charges during their transfer to the storage area. The storage area is „emptied‟ line by line into a read- out regis-ter where, during line –time, one line of pixel information is „clocked‟ through the register to produce the video signal.

4.5) INTERLINE TRANSFER (IT)Interline transfer CCDs were developed to avoid the need for a mechanical shutter The storage cell is placed adjacent to the pick-up pixel; during field blanking the charge generated by the pixel is shifted sideways into the storage cell. The read-out process is similar to the frame transfer device, with the storage elements being „clocked‟ through the vertical shift register at field rate into the horizontal shift register, then the charges read out at line rate. Earlier forms of IT devices suffered from severe vertical smear, which produced a vertical line running through a high-light. This was caused by excessive highlights penetrating deeply into the semicon-

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ductor material, leaking directly into the vertical shift register. Later IT devices have improved the technology to make this a much less objectionable effect.

4.6) FRAME INTERLINE TRANSFER (FIT)Frame interline transfer CCDs are a further development of the interline transfer de-vice to overcome the problem of vertical smear. As its name suggests, it is a combi-nation of both types. The FIT sensor has a short-term storage element adjacent to each pixel (as IT) and a duplicated storage area (as FT). During field blanking the charges are moved from the pixels into the adjacent short-term storage element and then moved at 60 times field frequency into the storage area. This rapid moving of the charge away from the vulnerable imaging area overcomes the vertical smear problem.Development in CCD technology has seen the introduction of:

The hole accumulated Diode (HAD) sensor which enabled up to 750 pixels/line, with increased sensitivity and a reduction in vertical smear;

The hyper HAD sensor, which included a micro lens on each pixel to collect the light more efficiently (this gave a one stop increase in sensitiv-ity over the HAD sensor);

The power HAD sensor with improved signal-to- noise ratio which has re-sulted in at least half an ƒ-stop gain in sensitivity; in some cases a full ƒ-stop of extra sensitivity has been realized.

Fig 4.2) Optical block for Video Camera

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4.7) CCD CAMERAS (CHARGE COUPLED DEVICES)-

A typical three tube camera chain is described in the block diagram. The built in sync pulse generator provides all the pulses required for the encoder and colour bar generator of the camera. The signal system is described below:

The signal system in most of the cameras consists of processing of the signal from red, blue and green CCD respectively. The processing of red and blue channel is exactly similar. Green channel which also called a reference channel has slightly different electronic concerning aperture correction. So if we understand a particular channel, the other channels can be followed easily. So let us trace a particular chan-nel. The signal picked up from the respective CCD is amplified in a stage called pre-pre amplifier. It is then passed to a pre amplifier board with a provision to in-serts external test signal. Most of the cameras also provide gain setting of 6 dB, 9dB and 18dB at the pre amplifier. Shading compensator provides H and V shading ad-justments in static mode and dynamic mode by readjusting the gain. After this cor-rection the signal is passed through a variable gain amplifier which provides adjust-ment for auto white balance, black balance and aperture correction.

Gama correction amplifier provides suitable gain to maintain a gamma of 0.45 for each channel. Further signal processing includes mixing of blanking level, black clip, white clip and adjustment for flare correction. The same processing take place for blue and red channels. Green channel as an additional electronic which provides aper-ture correction to red and blue channels. Aperture correction provide corrections to improve the resolution or high frequency lost because of the finite size of the elec-tron beam . Green channel has fixed gain amplifier instead of variable gain amplifier in the red and blue channels.

All the three signals namely R, G and B are then fed to the encoder section of the camera via a colour bar/camera switch. This switch can select R, G and B from the camera or from the R, G, B Signal from colour bar generator. In the encoder sec-tion these R, G, B signals are modulated with SC to get V and U signals. These sig-nals are then mixed with luminance, sync, burst, & blanking etc. to provide colour composite video signal (CCVS Signal). Power supply board provides regulated volt-ages to various sections.

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CHAPTER 5 TV LIGHTING

5.1) GENERAL PRINCIPLES:Lighting for television is very exciting and needs creative talent. There is always a tremendous scope for doing experiments to achieve the required effect. Light is a kind of electromagnetic radiation with a visible spectrum from red to violet i.e., wave length from 700 nm to 380 nm respectively. However to effectively use the hardware and software connected with lighting it is important to know more about this energy

5.1.1) Light Source: Any light source has a Lumnance intensity (I) which is measured in Candelas. One Candela is equivalent to an intensity released by stan-dard one candle source of light.

5.1.2) Luminance flux (F): It is a radiant energy weighted by the pho-tonic curve & is measured in Lumens. One Lumen is the luminous flux emitted by a point source of 1 Candela.

5.1.3) Illumination (E): It is a Luminous Flux incident onto a surface. It is mea-sured in LUMENS/m2, which is also called as LUX. A point source of 1 candela at a uniform distance of 1 meter from a surface of 1 square meter gives illumination of 1 LUX.

5.1.4) Luminance (L): It is a measure of the reflected light from a surface mea-sured in Apostilbs. A surface which reflects a total flux of 1 lumen/m2 has a lumi-nance of 1 Apostilbs.

5.2) COLOUR TEMPERATURE:One may wonder, how the light is associated with colour . Consider a black body being heated; you may observe the change in colour radiated by this body as the temperature is increased. The colour radiated by this body changes from reddish to blue and then to white as the temperature is further increased. This is how the con-cept of relating colour with temperature became popular. Colour temperature is measured in degree Kelvin i.e., 0C +273) . The table below gives idea about the kind of radiation from different kinds of lamps in terms of colour temperature.

a) Standard candle 19300Kb) Fluorescent Lamps range 3000-6500oKc) HMI lamp 5600+- 400oK (H=Hg, M=Medium arc, I=Metal Iodide}d) CSI (Compact Source Iodide) 4000+- 400oK

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e) CID (Compact Iodide Daylight) 5500+- 400oColour TV Display, white 6500oKf) Monochrome TV 9300oKg) Blue sky 12000 – 18000oKh) Tungsten Halogen 3200oK

i) Average summer sunlight (10am –3pm) 5500oK

It can be noted that as the temperature is increased, the following things happen:1) Increase in maximum energy released

2) Shift in peak radiation to shorter wavelengths (Blue)

3) Colour of radiation is a function of temperature Hence by measuring the energy content of the source over narrow bands at the red and blue ends of the spectrum , the approximate colour temperature can be de-termyined. All the color temperature meter are based on this principle.

5.3) COLOUR FILTERS AND THEIR USE:Colour filters are used to modify the colour temperature of lights and to match colour temperature for cameras while shooting with different colour temperature. These filters change the colour temperature at the cost of reduction in light transmis-sion. Colour temperature filters are also introduced in the optical path of cameras to facilitate camera electronics to do the white balance without loading the amplifier chain. Cameras electronics is generally optimized for a colour temperature of 3200K, hence it uses reddish filter while shooting at higher colour temperatures.Generally it is normal to correct daylight to produce tungsten quality light, because it is usually easier to do and saves lot of power, otherwise blue filters are going to re-duce lot of light thus requiring the use of higher wattage lamps.. However, when the amount of tungsten to be corrected is small it may be more practical to convert it to daylight, but with a considerably reduced light output form the luminaries. There are two basic types of filters : i) One which is orange in colour and converts Daylight to Tungsten Light.ii) One which is blue in colour and converts Tungsten to Daylight.

5.3.1) DAY LIGHT:The sun does not changes its colour temperature during the day it is only its appear-ance from a fixed point on earth. It is because the sunlight gets scattered because of the medium , shorter wavelengths like blue gets more effected. Certain situations like, sunrise and sunset causes the light to be more yellow than midday, because the light has to travel the long distance so a careful note should be made of the Transmission factor of each of the filters. Often a compromise has to be reached in terms of cor-rection and light loss.

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5.4) DIFFERENT LIGHTING TECHNIQUES:

-Eye light, Low intensity light on camera itself to get extra sparkle to an actor's eye

-Rim light, to highlight actor's outline, it is an extra back on entire body at camera level

-Kickkar light, Extra light on shadow side of the face at an angle behind and to the side of the actor.-Limbo Lighting, Only subject is visible, no back ground light-Sillhoutt lighting, No light on subject, BG is highly lit

5.5) LIGHTING CONSOLE

In a television production, each scene will require its own lighting plan to give the desired effect. In order to assist in setting up a particular lighting plan, a console should provide :

a) One man operation and a centralized control desk with ability to switch any circuit.b) Facilities to obtain good balance with flexibility to have dimming on any circuit.c) With all controls for power at low voltage and current.Modern light-ing consoles also provide file & memory to enable the console operator to store and recall the appropriate luminaries used for a particular light-ing plot. These console also provide Mimic panels to show which channels are in use and which memories or files have been recalled.

5.6) DIMMERSThree basic methods for dimming are :-

5.6.1) ResistanceThis is the simplest and cheapest form of dimmer. It consists of a wire wound re-sistor with a wiper .It is used in series with the load.5.6.2) Saturable Reactor (System SR)The basic principle of the saturable reactor is to connect an iron cored choke in series with the lamp.

5.7) OUTDOOR DAYLIGHT AND MOONLIGHT:

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The direction of the light is dictated by the position of the 'sun' or 'moon'. As a gen-eral principle one should remember that sunlight (hard source) is accompanied by the reflected "skylight" (soft source) whereas moonlight is a single hard source. One of the biggest problems when lighting exteriors is the maintenance of “single shadow" philosophy - double shadows on a long shot will quickly destroy the appar-ent realism created in the set. Very large area filler light is ideal for exterior daylight scenes.This can be achieved by using a suspended white screen 12' x 8' where the filler would be positioned then lighting it with hard light.In colour, to obtain a night effect, blue cinemoid is used over the luminaries. This gives a stylized effect. An alternative is to use much more localized lighting than for daylight and light only the artists and odd parts of the set.

CHAPTER 6

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MICROPHONES

Fig 6.1 Microphone

6.1) INTRODUCTIONMicrophone plays a very important role in the art of sound broadcasting. It is a de-vice which converts acoustical energy into electrical energy. In the professional broadcasting field microphones have primarily to be capable of giving the highest fidality of reproduction over audio bandwidth. 6.2) MICROPHONE CLASSIFICATION

Depending on the relationship between the output voltage from a microphone and the sound pressure on it, the microphones can be divided into two basic groups.

Pressure Operated Type. Velocity or Pressure Gradiant Type

6.3) TYPES OF MICROPHONESThere are many types of microphones. But only the most common types used in broadcasting have been described here:.6.3.1) Dynamic Or Moving Coil Microphone6.3.2) Ribbon/ Velocity Microphone6.3.3) Electrostatic or Condenser Microphone6.3.4) Electret ‘Microphone

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CHAPTER 7 RECORDING

7.1) INTRODUCTION

Video tape recorder is a most complex piece of studio equipment with analog and digital processing servo system, microprocessors, memories, logic circuits and me-chanical devices etc. Also these recorders have been the main limitation so for as the quality output from studio is concerned. Right from fifties, continuous efforts are be-ing made to improve its performance so as to reproduce cameras faithfully by improv-ing S/N ratio and resolution. Designer for video tape recorders had to consider the fol-lowing differences in the video and audio signals:

principles of video tape

Fig 7.1 Magnetic Principle

7.2) MAGNETIC PRINCIPLE

Magnetic Field Intensity H=NI / L Magnetic flux density B = H Magnetic Flux Ø= BA( is of the order of 100 to few 10,000 for ferromagnetic materials)Property of the ferromagnetic materials to retain magnetism even after the current or the H is removed is called retentivity and is used for recording electrical signals in magnetic form on magnetic tapes. This relationship can also be represented by a curve called BH curve. Magnetic tapes are made of ferromagnetic materials with broader BH curve than the material used for video heads as the heads are not re-quired to retain information.

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CHAPTER 8 DIGITAL VIDEO CASSETTE RECORDING

PROFESSIONAL(DVCPRO)

8.1) INTRODUCTION

With the advent of digital signals, breakthrough came in the field of record-ing from analog recording to digital recording around the year 1990. In the series of development of digital tape recording systems, it is felt to have a system which should be handy for the purpose of field recording along with capability of long duration recording. A recording format is developed by a consortium of ten compa-nies as a consumer digital video recording format called “DV”. DV (also called ”mini DV” in its smallest tape form) is known as DVC (Digital Video cassette).DVCAM is a professional variant of the DV, developed by Sony and DVCPRO on the other hand is a professional variant of the DV, developed by Panasonic. These two formats differ from the DV format in terms of track width, tape speed and tape type. Before the digitized video signal hits the tape, it is the same in all three formats.

8.2) WHAT IS DV?

DV is a consumer video recording format, developed by a consortium of 10 compa-nies and later on by 60 companies including Sony, Panasonic, JVC, Phillips etc., was launched in 1996. in this format, video is encoded into tape in digital format with in-tra frame DCT compression using 4:1:1 chroma subsampling for NTSC (or 4:2:0 for PAL).

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CHAPTER 9VISION MIXING

9.1) INTRODUCTION

Vision mixing is a process of creating composite pictures from various sources. Vision mixing involves basically three types of switching or transitions between var-ious sources. These are mixing, wiping and keying. These transitions can also be ac-companied by special effects in some of the vision mixers.

9.2) MIXINGTwo input sources are mixed in proportion in a summing amplifier as decided by the position of control fader. Two extreme position of the fader gives either of the sources at the output. Middle of the fader gives mixed output of the two sources; control to the summing amplifier is derived from the fader.

9.3) WIPEIn this case the control for the two input sources is generated by the wipe pattern generator (WPG), which can either be saw tooth or parabola at H, V or both H & V rate. Unlike in MIX, during WIPE, one source is present in one side of the wipe and the second source on other side of the wipe. A very simple to very complex wipe patterns can be generated from the WPG.

9.4) KEYIn the Key position between two sources i.e. foreground (FG) and background (BG) the control derived from one of the source itself (overlay), or by the third source (external key). This keying signal can be generated either by the luminance, Hue or chrominance of the source input. The keyed portion can be filled with the same or with matte or external source. Matte means internally generated BG with choice of colors from the vision mixer itself.

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CHAPTER 10TELEVISION TRANSMISSION

10.1) VESTIGIAL SIDE BAND TRANSMISSION-

If normal amplitude modulation technique is used for picture transmission, the mini-mum transmission channel bandwidth should be around 11 MHz taking into account the space for sound carrier and a small guard band of around 0.25 MHz Using such large transmission BW will limit the number of channels in the spectrum allotted for TV transmission. To accommodate large number of channels in the allotted spec-trum, reduction in transmission BW was considered necessary. The transmission BW could be reduced to around 5.75MHz by using single side band (SSB) AM technique, because in principle one side band of the double side band (DSB) AM could be suppressed, since the two side bands have the same signal content.

Fig 10.1

10.2) DESIGNAll the TV transmitters have the same basic design. They consist of an exciter fol-lowed by power amplifiers which boost the exciter power to the required level. 10.3) EXCITERThe exciter stage determines the quality of a transmitter. It contains pre-corrector units both at base band as well as at IF stage, so that after passing through all sub-sequent transmitter stages, an acceptable signal is available. Since the number and type of amplifier stages, may differ according to the required output power, the char-acteristics of the pre-correction circuits can be varied over a wide range.

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Fig 10.2) Block Diagram Of Tv Exciter (Mark-11)

10.4) VISION AND SOUND SIGNAL AMPLIFICATION

In HPTs the vision and sound carriers can be generated, modulated and amplified separately and then combined in the diplexer at the transmitter output.In LPTs, on the other hand, sound and vision are modulated separately but amplified jointly. This is common vision and aural amplification.A special group delay equalization circuit is needed in the first case because of er-rors caused by TV diplexer. In the second case the intermodulation products are more prominent and special filters for suppressing them is required.As it is difficult to meet the intermodulation requirements particularly at higher power ratings, separate amplification is used in HPTs though combined amplifi-cation requires fewer amplifier stages.

10.5) IF MODULATION

It has following advantages Ease of correcting distortions Ease in Vestigial side band shaping IF modulation is available easily and economically

10.6) POWER AMPLIFIER STAGES

In BEL mark I & II transmitters three valve stages (BEL 450 CX, BEL 4500 CX and BEL 15000 CX) are used in vision transmitter chain and two valves (BEL 450 CX and BEL 4500 CX) in aural transmitter chain. In BEL mark III transmitter only two valve stages (BEL 4500 CX and BEL 15000CX) are used in vision transmitter chain. Aural transmitter chain is fully solid state in Mark III transmitter.

10.7) CONSTANT IMPEDANCE NOTCH DIPLEXER (CIND)Vision and Aural transmitters outputs are combined in CIN diplexer. Combined power is fed to main feeder lines through a T-transformer.

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10.8) TRANSMITTER CONTROL SYSTEMThe transmitter control unit performs the task of transmitter interlocking and con-trol. Also it supports operation from control console. The XTR control unit (TCU) has two independent systemviz.

1. Main control system. (MCS)2. Back-up Control

Functions performed by MCS (Main Control System)- XTR control -Interlocking.- RF monitoring- Supporting operation from control console- Three second logic for protection against sudden fluctuation.- Thermal protection for 1 kW and 10 k vision PAs- Thermal protection for 130 Watt vision PA and Aural XTRa- Mimic diagram

Functions performed by BCS (Backup control system)- Transmitting control- Interlocking.

The block diagram of the TCU (Transmitter control unit) indicates the connectivity of TCU with control console and the control elements of the transmitter. Commands are in-puts through the key board. The control elements are controlled in accordance with the programme fused in the EPROMS.

Only while operating from the MCS (Main Control System), the interaction with TCU is supported through a LCD display unit. The LED bar display board showing the status in-formation, is used by both the MCS and BCS (Back up Control Unit).

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CHAPTER 11OUTDOOR BROADCASTING VAN

OB van is used for live broadcasting like any match or any event. It consist all the equipment’s that is present in the studio for telecasting. It also referring as mini stu-dio. It has mainly 3 parts:

1) Power supply unit 2) Production control unit 3) Audio console and VTR

Fig 11.1) Inner View Of OB Van

Fig 11.2) Inner Structure of OB van

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CHAPTER 12EARTH STATION

12.1) SATELLITE COMMUNICATIONSatellite Communication is the outcome of the desire of man to achieve the concept of global village. Penetration of frequencies beyond 30 Mega Hertz through iono-sphere force people to think that if an object (Reflector) could be placed in the space above ionosphere then it could be possible to use complete spectrum for communica-tion purpose.

Intelsat-I (nick named as Early Bird) was launched on 2 April 1965. This was parked in geosynchronous orbit in Atlantic ocean and provided telecommunication or televi-sion service between USA and Europe. It had capacity for 240 one way telephone channels or one television channel. Subsequently Intelsat-II generation satellites were launched and parked in Atlantic ocean and Pacific Ocean. During Intelsat III genera-tion, not only Atlantic and Pacific ocean got satellites but also Indian Ocean got satellite for the first time. Now Arthur C.Clarke‟s vision of providing global com-munication using three Satellites with about 120 degrees apart became a reality. So far Intelsat has launched 7 generations of geosynchronous satellites in all the three re-gions namely Atlantic Ocean, Pacific Ocean and Indian Ocean.For national as well as neighbouring countries coverage, some of the following satellites are used: ANIK : Canadian satellite system INSAT : Indian Satellites

AUSSAT : Australian Satellites BRAZILSAT : Brazilian Satellites FRENCH TELECOM : French Satellites ITALSAT : Italian SatellitesCHINASAT : Chinese SatellitesSTATSIONAR, GORIZONT, Russian Satellites

12.2) ARCHITECTURE OF A SATELLITE COMMUNICATION SYSTEM

12.2.1) THE SPACE SEGMENTThe space segment contains the Satellite and all terrestrial facilities for the control and monitoring of the Satellite. This includes the tracking, telemetry and com-mand stations (TT&C) together with the Satellite control centre where all the opera-tions associated with station-keeping and checking the vital functions of the satellite are performed. In our case it is Master Control Facility (MCF) at Hassan.The radio waves transmitted by the earth stations are received by the satellite ; this is called the uplink. The satellite in turn transmits to the receiving earth stations ; this is the down link. The quality of a radio link is specified by its carrier-to-noise ratio. The important factor is the quality of the total link, from station to station, and this is determined by the quality of the up link and that of the down link. The quality of

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the total link determines the quality of the signals delivered to the end user in ac-cordance with the type of modulation and coding used.

Fig 12.1 Satellite Communication System

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12.2.2) THE GROUND SEGMENTThe ground segment consists of all the earth stations ; these are most often connected to the end- user‟s equipment by a terrestrial network or, in the case of small stations (Very Small Aperture Terminal, VSAT), directly connected to the end-user‟s equipment. Stations are distinguished by their size which varies according to the vol-ume of traffic to be carried on the space link and the type of traffic (telephone, televi-sion or data). The largest are equipped with antenna of 30 m diameter (Standard A of the INTELSAT network). The smallest have 0.6 m antenna (direct televi-sion receiving stations). Fixed, transportable and mobile stations can also be dis-tinguished. Some stations are both transmitters and receivers.

12.3) TYPES OF ORBIT The orbit is the trajectory followed by the satellite in equilibrium between two op-posing forces.These are the force of attraction, due to the earth‟s gravitation, directed towards the centre of the earth and the centrifugal force associated with the curvature of the satellite‟s trajectory. The trajectory is within a plane and shaped as an ellipse with a maximum extension at the apogee and a minimum at the perigee. The satellite moves more slowly in its trajectory as the distance from the earth increases .

12.4) MOST FAVOURABLE ORBITSElliptical orbits inclined at an angle of 64o with respect to the equatorial plane. This orbit enables the satellite to cover regions of high latitude for a large fraction of the or-bital period as it passes to the apogee. This type of orbit has been adopted by the USSR for the satellites of the MOLNYA system with a period of 12 hours. Please note that the satellite remains above the regions located under the apogee for a period of the order of 8 hours. Continuous coverage can be ensured with three phased satellites on different orbits.

12.5) CIRCULAR INCLINED ORBITS :The altitude of the satellite is constant and equal to several hundreds of kilometers. The period is of the order of one and a half hours. With near 90% inclination this type of orbit guarantees that the satellite will pass over every region of the earth. Several systems with world wide coverage using constellations of satellite carries in low alti-tude circular orbits are for e.g. IRIDIUM, GLOBAL STAR, ODYSSEY, ARIES, LEOSAT, STARNET, etc.

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12.6) CIRCULAR ORBITSwith zero inclination (Equatorial orbits). The most popular is the geo stationary satel-lite orbits ; the satellite orbits around the earth at an altitude of 35786 km, and in the same direction as the earth. The period is equal to that of the rotation of the earth and in the same direction. The satellite thus appears as a point fixed in the sky and en-sures continuous operation as a radio relay in real time for the area of visibility of the satellite (43% of the earth‟s surface).

12.7) FACTORS DECIDING THE SELECTION OF ORBITThe choice of orbit depends on the nature of the mission, the acceptable interfer-ence and the performance of the launchers :The extent and latitude of the area to be covered the elevation angle of earth stations. Transmission duration and delay. Interference the performance of launchers.

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CHAPTER 13 TVRO SYSTEM

Presently Doordarshan is up linking its national, metro and regional services to IN-SAT-2A (74oC) and INSAT-2B (93.5oE) and INSAT 2E (83o C). Down link fre-quency bands being used are C-Band (3.7-4.2 GHz) and Ex-C Band (4.5-4.8 GHz)

Fig 13.1) Satellite Earth Station Uplink / Downlink Chain

13.1) TRANSMISSION OF BASE BAND TO SATELLITEThe base band signal consists of video (5 MHz), two audio subcarriers (5.5 MHz & 5.75 MHz) and energy dispersal signal (25 Hz). After modulation (70 MHz) and up conversion (6 GHz) the carrier is amplified and uplinked through Solid Parabolic Dish Antenna (PDA). Down link signal can be received through same PDA using Trans-Receive Filter (TRF) and Low Noise Amplifier (LNA). After down conver-sion to 70 MHz, it is demodulated to get audio and video.

13.2) SATELLITE TRANSPONDERAs shown in fig, the uplinked signal (6 GHz) at satellite is received, amplified and down converted to 4 GHz band and sent back through filter and power amplifier (TWT). The local oscillator frequency of down converter is 2225 MHz for C band and Ex-C band transponders.

13.3) RECEIVING SATELLITE SIGNAL

For receiving a satellite signal we need following equipment :

1. Satellite receiving antenna (PDA).2. Feed with low noise block converter (LNBC).3. Indoor unit consisting of satellite system unit and a Synthesised satellite receiver

13.4) AZIMUTH AND ELEVATION

For receiving a satisfactory signal from the satellite the dish antenna should be pointed towards the satellite accurately. For that we need to know the azimuth and

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elevation of a particular satellite from our place. The azimuth and elevation are an-gles which specify the direction of a satellite from a point on the earth's surface. In layman terms the azimuth is the east west movement and the elevation can be de-fined as the north south movement of the dish.

Both the azimuth and elevation of a dish can be affected by three factors for geo-sta-tionary satellites.They are1. The longitude of the satellite.2. The latitude of the place.3. The longitude of the place.

Calculation of Azimuth

13.5) INDOOR UNITS

The indoor unit contains two units. They are :1. System unit2. Satellite Receiver Unit

13.6) SYSTEM UNITThe system unit contains a passive power divider and power supply for the LNBC. The power divider divides the IF into two equal parts to be applied to the two re-ceivers. The power supply is fed through same cable to the LNBC. Satellite Receiver Unit The satellite receiver contains the down converter, video/audio demodulators and processing circuits. Finally we get two video/audio outputs. A synthesized re-ceiver accepts signal in the range of 900 to 1700 MHz. The block diagram of a typi-cal EC receiver is shown in figure 9. The IF is applied to a four-stage low noise ampli-fier for amplification. The overall gain of the amplifier is around 22 dB. This signal is then applied to FET mixer where a LO frequency of 1500 to 2300 MHz is mixed so that an IF of 600 MHz is produced. The local oscillator consists of two similar VCOs (voltage controlled oscillator) one operating in the range of 1500 - 1749 MHz and the other in the range of 1750 to 2300 MHz. They are controlled by a synthesizer IC. A sample of the LO frequency is taken and phase compared with a stable refer-ence crystal frequency of 4 MHz and error if any, is then applied to the VCO for fre-quency correction through a low pass filter. Thus the VCO works in a phase locked loop mode.

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CHAPTER 14DIRECT-TO-HOME SATELLITE BROADCASTING (DTH)

14.1) INTRODUCTIONThere was always a persistent quest to increase the coverage area of broadcast-ing. Before the advent of the satellite broadcasting, the terrestrial broadcasting, which is basically localized, was mainly providing audio and video services. The ter-restrial 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 ex-pensive affair to run and maintain the large number of transmitters. Satellite broadcast-ing, 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 an-tennas (PDA). In the late eighties the satellite broadcasting technology had under-gone 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 broadcast-ing. People are now mainly depending on cable TV operators. Since cable TV ser-vices are unregulated and unreliable in countries like India now, the satellite broad-casting 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 Broadcast-ing (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 equipment’s is now gradually declining and can be af-forded 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 entertain-ment. DTH reception requires a small dish antenna (Dia60 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 bou-quet of 40 to 50 video programs can simultaneously be received in DTH mode.

14.2) UPLINK CHAINDTH broadcasting is basically satellite broadcasting in Ku-Band (14/12 GHz). The main advantage of Ku-Band satellite broadcasting is that it requires physically man-ageable smaller size of dish antenna compared to that of C-Band satellite broadcast-ing. 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 50Watts) 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 oper-

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ating transmitter at higher powers and by using larger size of the dish antenna (7.2m PDA).

Fig 14.1 DTH to UPLINK Setup

Fig.1 shows schematic of uplink chain proposed to broadcast bouquet of 30 video pro-grams in Doordarshan, Prasar Bharati, India. 30 video programs may either be down-linked from satellites or taken from other sources like video tape recorders, video cameras etc. in digital format. These sources are fed to Router whose outputs are divided in three groups A, B and C. Each group contains 10 video sources multi-plexed in a Multiplexer.These three multiplexed streams are digitally (QPSK modu-lation) modulated individually at 70 MHz Intermediate Frequency (IF). Each group is further doubly up-converted, first conversion at L-Band (950-1450 MHz) and second conversion at Ku-Band (12-14 GHz)

14.3) DOWN-LINK CHAINDown-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 sig-nal. 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 digi-tal demodulation, de-multiplexing, decoding and finally gives audio/video output to TV for viewing.

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Conclusion

Doordarshan is the oldest and the biggest Broadcasting media in India.

In my training session I learned a lot. Not only in technical field but also in social

field too. I got a great experience of working in a Public Sector Company.

I learned about the recent trends in Broadcasting Media and also the market strategies

to maximize the profit using limited resources.

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References

1) http://www.ddlucknow.com2) http://www.ddinews.gov.in/Opportunities/3) www.ddindia.gov.in/4) www.slideshare.com/vivekgupta.ec5 ) http://www.slideshare.net/TechnoVivek/doordarshan-summer-training-at-

lucknowppt