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Doordarshan industrial training report


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doordarshan industrial report on television broadcast system

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Doordarshan industrial training report

  1. 1. SUMMER INDUSTRIAL TRAINING REPORT ON TELEVISION BROADCAST SYSTEM Submitted in partial fulfillment of the requirement for the Award of The Degree of Bachelor of Technology IN Electronics & Communication Engineering Submitted By: Name: SATYENDRA GUPTA Univ. Roll no: 1005631086 BBDNIIT,Lucknow (Affilated to Gautam Buddh Technical University) (2013-14)
  2. 2. 2 Acknowledgement “It is not possible to prepare a summer training report without the assistance & encouragement of other people. This one is certainly no exception.” On the very outset of this report, I would like to extend my sincere & heartfelt obligation towards all the personages who have helped me in this endeavor. Without their active guidance, help, cooperation & encouragement, I would not have made headway in the project. First and foremost, I would like to express my sincere gratitude to my project guide, Mr. R.Naithani I was privileged to experience a sustained enthusiastic and involved interest from his side. This fuelled my enthusiasm even further and encouraged me to boldly step into what was a totally dark and unexplored expanse before me. He always fuelled my thoughts to think broad and out of the box. Thanking You Satyendra gupta
  3. 3. 3 Table of contents Preface .......................................................................................................................... 4 Introduction of Doordarshan lucknow........................................................................... 5 Fundamentals of monochrome and Colour TV system ................................................... 6 Colour Composite Video Signal (CCVS) ......................................................................... 9 TV Camera.................................................................................................................... 13 TV Lighting.................................................................................................................... 18 Microphones.................................................................................................................. 24 Principles of video tape recording ................................................................................. 29 Vision mixing................................................................................................................. 39 3 –D Graphics ............................................................................................................... 42 Television Transmission................................................................................................ 44 TV Transmitter and Antenna System ............................................................................ 48 Outdoor Broadcasting van............................................................................................. 50 Earth Station ................................................................................................................. 51 Direct-to-Home Satellite Broadcasting (DTH)................................................................ 58 Conclusion .................................................................................................................... 61
  4. 4. 4 Preface Training is important phase of student life. During this period student gets both theoretical as well as practical knowledge of the subject. Training also impresses a student 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 division here-  1) Studio  2)Transmitter  3)Earth Station 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. Transmitter - Here the transmission of both audio and video has been made. The transmission section does the function of modulation of signal. Power amplification of the signal & mixing of audio and video signal is done here. 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.
  5. 5. 5 Introduction of Doordarshan lucknow Lucknow Doordarshan started functioning on 27th Nov. 1975 with an interim setup at 22, Ashok Marg, Lucknow. The colour transmission service of National Channel (only with Transmitter) started from 15-8-82. While the regular colour transmission service from studio was started in 1984 with ENG gadgets. During Reliance Cup, OB Van came to Kendra for outdoor telecast having 4 colour camera chain, recording equipments, portable microwave link. In March 1989 new studio complex started functioning. EFP Van came to DDK Lucknow in 1989 with compliment of 3 colour camera chain and recording setup for outdoor telecast. The entire recording of studio/van have been replaced to Beta format High Band edit VCR and still in use as the old recording are on H.B. UP Regional Service telecast with up linking facility from studio (DDK, Lucknow) started in January 1998 on INSAT-2B. This service was changed to INSAT-2D (T) ARAB SAT. on 14- 7-98. The news feeds are up-linked to Delhi occasionally from Lucknow Earth Station. Studio program is transmitted from 10 KW-TV transmitter installed at Hardoi Road through Studio Transmitter Microwave Link. Besides this, one 16 feet PDA is being installed at TV Transmitter site to receive the down link signal of Regional Service telecast from studio via ARAB SAT. on INSAT-2D (T). Site of 22 Ashok Marg, Lucknow is being utilized by Doordarshan Training Institute (for staff training) having one studio (12m x 6m) and colour camera chain. The DTI Lucknow was inaugurated in September 1995. In the beginning, only the development programmes were telecast but later on to enlighten the viewers as per their needs, expectations, many more informative, educative and entertaining programmes have been introduced from time to time. Lucknow Doordarshan produced some of the best programmes in the country as "BIBI NATIYON WALI", "NEEM KA PED" and "HATIM TAI" etc. To entertain cross-section of the society.
  6. 6. 6 Fundamentals of monochrome and Colour TV system 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 photosensitive surface of pick up device and a optical image is formed. The photoelectric properties of the pick up device convert the optical image to a 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 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 horizontal 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 scanned 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 heartz.
  7. 7. 7 Number of TV Lines per Frame – If the number of TV lines is high largerbandwidth of video and hence larger R.F. channel width is required. If we go for larger RF channel width the number of channels 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. 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) 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). Brightness - Brightness 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).
  8. 8. 8 Contrast - Contrast is the relative difference between black and white parts of the reproduced picture. In a TV set the contrast control adjusts the level of video signal fed to the picture tube. 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.
  9. 9. 9 Colour Composite Video Signal (CCVS)  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 then 16 picture per sec our eyes can not recognize the difference and we see the continuous motion. In Tv cameras image is converted in electrical signal using photo sensitive material. Whole image is divided into many micro particle known as Pixels. These pixels small enough so that our eyes cannot recognize pixel and we see continuous 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 practice this problem is solved by scanning method in which information is converted in one by one pixel line by line and frame by frame .
  10. 10. 10 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 figure. 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 frequency components. (In film the reproduction of frequencies is much higher than 5 MHz and hence clarity 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 minimum. In fact TV is a medium of close ups and mid close ups. 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 elements 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.
  11. 11. 11 RF Transmission of Vision and Sound Signals TV Transmission takes place in VHF Bands I and III and UHF Bands IV and V. Picture 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 the average power is lower resulting in energy saving. (Bright picture points correspond to a low carrier amplitude and sync pulse to maximum carrier amplitude). Interference such as car ignition interfering signals appear as black which is less objectionable. Picture information is in linear portion of modulation characteristic and hence does not suffer compression. Any compression that may take place is confined to sync pulse only.The design of AGC circuit for TV Receiver is simpler. AM produces double side bands. The information is the same in both side bands. It is enough to transmit single side band only. Carrier also need not be transmitted in full and a pilot carrier can help. 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. Sound Signal Transmission In CCIR system B sound carrier is 5.5 MHz above the vision carrier and is frequency 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 assume maximum audio signal is 15 KHz the band width is 130 KHz.According to Carson‟ s Rule the bandwidth is 2 x (Maximum frequency deviation + highest modulating frequency). However, calculated value(using Bessel‟ s function) of Bandwidth is 150
  12. 12. 12 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. The Colour Television It is possible to obtain any desired colour by mixing three primary colours i.e. Red, Blue a proportion. The retina of human eye consists of very large number of light- sensitive cells. These and cones. Rods are sensitive only to the intensity of the incident light and cones are responsible The small range of frequencies to which the human eye is responsive is known as visible spectrum is from 780 mm (Red) to 380 mm(Violet). 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.
  13. 13. 13 TV Camera 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 device. b)A transducer or pick up device: To convert optical image into a electrical signal. c)Electronics: To process output of a transducer to get a CCVS signal. TYPES OF PICK - UP DEVICES There are three types of pick up devices based on : a) Photo emissive material: These material emits electrons when the light falls on them. Amount of emitted electrons depends on the light . Monochrome 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. b) Photo conductive material: The conductivity of these material changes with amount of light falling on them. Such material with variable conductivity 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
  14. 14. 14 lead to the development of Plumb icon and Sat icon cameras. c) 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 . 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 (negative 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 Frame transfer (FT) Frame transfer was the first of the CCDs to be developed and it consists of two identical 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 electrical charge image is built up during one field period, and during field blanking this
  15. 15. 15 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 register where, during line –time, one line of pixel information is „clocked‟ through the register to produce the video signal. 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 highlight. This was caused by excessive highlights penetrating deeply into the semiconductor material, leaking directly into the vertical shift register. Later IT devices have improved the technology to make this a much less objectionable effect. Frame interline transfer (FIT) Frame interline transfer CCDs are a further development of the interline transfer device to overcome the problem of vertical smear. As its name suggests, it is a combination 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 microlens on each pixel to collect the
  16. 16. 16 light more efficiently (this gave a one stop increase in sensitivity over the HAD sensor);  The power HAD sensor with improved signal-to- noise ratio which has resulted in at least half an ƒ-stop gain in sensitivity; in some cases a full ƒ-stop of extra sensitivity has been realized. Optical block for Video Cameras
  17. 17. 17 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 channel. 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 inserts 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 adjustments in static mode and dynamic mode by readjusting the gain. After this correction the signal is passed through a variable gain amplifier which provides adjustment 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 aperture 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 electron 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 section these R, G, B signals are modulated with SC to get V and U signals. These signals are then mixed with luminance, sync, burst, & blanking etc. to provide colour composite video signal (CCVS Signal). Power supply board provides regulated voltages to various sections.
  18. 18. 18 TV Lighting 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. Light Source: Any light source has a Luminance intensity (I) which is measured in Candelas. One Candela is equivalent to an intensity released by standard one candle source of light. Luminance flux (F): It is a radiant energy weighted by the photonic curve and is measured in Lumens. One Lumen is the luminous flux emitted by a point source of 1 Candela. Illumination (E): It is a Luminous Flux incident onto a surface. It is measured 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. Luminance (L): It is a measure of the reflected light from a surface. Measured in Apostilbs. A surface which reflects a total flux of 1 lumen/m2 has a luminance of 1 Aposilbs . Elementary theory of light also says that: 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 concept 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 19300K b)Fluorescent Lamps range 3000-6500oK c)HMI lamp 5600+- 400oK
  19. 19. 19 (H=Hg, M=Medium arc, I=Metal Iodide} d) CSI (Compact Source Iodide) 4000+- 400oK e) CID (Compact Iodide Daylight) 5500+- 400o Colour TV Display,white 6500oK f) Monochrome TV 9300oK g)Blue sky 12000 – 18000oK h)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 determined. All the color temperature meter are based on this principle. 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 transmission. 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 reduce 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 filter :- 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.
  20. 20. 20 Day Light: The sun does not changes its colour temperature during the day it is only its appearance 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 correction and light loss. NEUTRAL DENSITY FILTERS In addition to colour temperature correction sometimes it may be necessary to reduce the intensity of daylight at an interior location. Neutral density filters available to attenuate the light are of:0.3 Density which has a transmission of 50%= 6dB=1 f stop 0.6 Density which has a transmission of 25%= 9dB=2 f stop 0.9 Density which has a transmission of 13%= 12dB=3f stop COMBINATION OF CTC FILTERS AND NEUTRAL DENSITY FILTERS: Single filters exist which are a combination of full colour temperature orange and neutral density as follows:- Full Orange + 0.3 N.D. with a transmission of 50% Full Orange + 0.6 N.D. with transmission of 38% The HMI light source has a colour temperature of about 60000K and can be used with exterior daylight without the need for a colour temperature correction filter. 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
  21. 21. 21 side of the actor - Limbo Lighting, Only subject is visible, no back ground light - Sillhoutt lighting, No light on subject, BG is highly lit . 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 plon, a console should provide :- a) One man operation and a centralised 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 lighting consoles also provide file & memory to enable the console operator to store and recall the appropriate luminaries used for a particular lighting plot. These console also provide Mimic panels to show which channels are in use and which memories or files have been recalled. DIMMERS Three basic methods for dimming are- 1. Resistance This is the simplest and cheapest form of dimmer. It consists of a wire wound resistor with a wiper .It is used in series with the load. 2. Saturable Reactor (System SR) The basic principle of the saturable reactor is to connect an iron cored choke in series with the lamp. LIGHTING THE SET FOR DRAMA:--Openings such as windows within a set should be highlighted without overstating them. Where the walls having such feature should be lit to reveal these features but care must be taken to ensure that there is only one shadow. The top of the set should be darkened off by using the barndoors, this puts a "ceiling" on the set by giving the feeling of a roof. If more than the top of the set is darkened, that gives enclosed feeling. Indoor day time:
  22. 22. 22 1.If there is a choice in the direction of the 'sun'(Key) take the shortest route inside the set to a wall, and if possible throw the shadow of window bars onto a door - it usually is in shot. 2.A patch of light on the floor inside the set, backlight from outside using a soft source at steep elevation adds realism. 3.When a set does not have a window, a window pattern can be projected onto a wall to produce a suitable window effect. 4.Roof and Ceiling Pieces - if they make lighting impossible, check if they can be removed at the planning state. Light any ceiling pieces from outside, use a soft source at ground level. If the ceiling has plaster moulding or ornamentation, a hard source may be used. Indoor night time: - The outside of the window should be dark, except for a possible dim skyline if the room is well above adjacent streets, or lit by an outside practical lamp i.e. street lighting. - The wall with the window in it should be lit at night to be brighter than for the day condition. Subjectively the walls appear brighter at night than at daytime. . - Often a completely different 'feel' to the set can be obtained by reversing he direction of lighting in the set compared to that used for day. - General for night effects it is not a good plan to just simply dim the set lighting when changing from day to night. This is because the excessive change in colour temperature of the light source and the apparent increase in saturation of surfaces at low luminance. Outdoor daylight and Moonlight: The direction of the light is dictated by the position of the 'sun' or 'moon'. As a general 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 apparent 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. The exact lighting treatment will depend on the situation but as a general rule, moonlight effects are normally achieved by back lighting to give a more softer,
  23. 23. 23 romantic mood than would be achieved than a frontal key. 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 localised lighting than for daylight and light only the artists and odd parts of the set.
  24. 24. 24 Microphones Introduction Microphone plays a very important role in the art of sound broadcasting. It is a device which converts accoustical 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. 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 In such microphones only one side of the diaphragm is exposed to the sound wave. The output voltage is proportional to the sound pressure on the exposed face of the diaphragm with respect to the constant pressure on the other face. Moving coil, carbon, crystal and condenser microphones are mostly of this type. In their basic forms, the pressure operated microphones are omni-directional. Velocity or Pressure Gradiant Type In these microphones both sides of the diaphragm are exposed to the sound wave. Thus the output voltage is proportional to the instantaneous difference in pressure on the two sides of the diaphragm. Ribbon microphone belongs to this category and its polar diagram is figure of eight. Types of Microphones There are many types of microphones. But only the most common types used in
  25. 25. 25 broadcasting have been described here. Dynamic or Moving Coil Microphone This is common broadcast quality microphone which is rugged and can be carried to outside broadcast/recording etc. It consists of a strong permanent magnet whose pole extensions form a radial field within a round narrow gap. A moving coil is supported within this gap and a dome shaped diaphragm usually of aluminium foil is attached to the coil. The coil is connected to a microphone transformer whose secondary has sometimes tapings to select proper impedance for matching. With sound pressure changes, the diaphragm and coil move in the magnetic field, therefore, emf is induced in the speech coil, which is proportional to the incoming sound. The primary impedance of the matching transformer is generally high (5 to 6 times of the speech coil impedance so that low frequencies are not lost and rising impedance frequency characteristic is avoided as best as possible. The resonant frequency is generally damped with special arrangements of absorption in acoustic cavity, Bass/boost arrangements are provided by an equalising tube connecting the rear side of diaphragm i.e. inside of microphone with the atmosphere. The diameter and length of the tube is critically adjusted for achieving good frequency response. Ribbon/ Velocity Microphone Corrugated aluminium foil about 0.1 mm thick forms a ribbon which is suspended within two insulated supports. The ribbon is placed within the extended poles of a strong horse shoe magnet. The ribbon moves due to the difference in pressure (at right angles to its surface) i.e. from the front or rear of the mike. There exists the maximum pressure difference between the front and rear of ribbon because of maximum path difference. The sound does not develop any pressure gradient when it comes from the sides of the Dynamic Microphone (Moving Coil)
  26. 26. 26 microphones because there is no path difference. It reaches the front and rear of ribbon at the same time, hence no movement of ribbon. Thus, this microphone is bi-directional and follows figure of eight directivity pattern with no pick up from sides. Such a microphone has a clarity filter. This is a series resonant circuit at low frequencies across the primary of microphone transformer. When switched to the “Talk” or “Voice” position, the response is modified cutting down low frequencies by about 8 dB at 50 Hz. This filter should therefore not be in circuit during music performances. All the other types of microphones are pressure operated whereas ribbon mike operates on pressure gradient which results in the change in velocity of the ribbon. Thus it is also called the „Velocity‟ microphone. This microphone is very good for balancing of programmes. In case of Orchestra, instruments with strong output are positioned towards the dead side and week voices or instruments are arranged on the front and rear of the mike. The distance and location with respect to microphone are considered against loudness of voice or musical instrument during balancing. Ribbon Microphone Output Magnets Corrugated ribbon Transformer N S
  27. 27. 27 Electrostatic or Condenser Microphone This consists of a thick metallic plate insulated from the body of the microphone and connected to polarising voltage through a resistance. Another thin foil is fitted close to the above plate forming a condenser. The sound pressure variations on the foil, change the capacitance due to increase and decrease of distance between foil and the plate. With fixed DC voltages across the two, the quantity of charge changes due to the variation of capacity. The changes in electrical charge form the sound signals and are picked up through a coupling capacitor. This microphone delivers – 80 dBv with a very good frequency response. The output impedance of this microphone is high. The popular method of providing d.c. voltage to the condenser is known as “Phantom Powering‟ . Variable directivity capacitor microphones are becoming popular these days. Fig. 3 Condenser Microphone Output Phantom power Head Amplifier Output Transformer Very high resistance Insulator Phantom power DC blocking capacitor Earthed back-plate Diaphragm.
  28. 28. 28 Electret ‘Microphone’ It is a modified form of condenser microphone in which the polarising voltage is avoided. In fact a plastic polymer containing metallic dust keeps the metal particles permanently charged within the plastic insulation and such a polymer within the diaphragm foil or fixed plate delivers the electrical signal on the principle of the condenser mike. The hissing noise gets avoided since there is no external polarising resistor as a load. The microphone has high impedance and is generally having FET pre-amplifier. The microphone costs very little but developes excellent quality designs in many forms.
  29. 29. 29 Principles of video tape recording Introduction Video tape recorder is a most complex piece of studio equipment with analog and digital processing servo system, microprocessors, memories, logic circuits and mechanical 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 being made to improve its performance so as to reproduce cameras faithfully by improving S/N ratio and resolution. Designer for video tape recorders had to consider the following differences in the video and audio signals: 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
  30. 30. 30 the material used for video heads as the heads are not required to retain information. WRITING SPEED AND FREQUENCY RESPONSE Recording Process With reference to figure 1(d) when a tape is passed over the magnetic flux bubble, the electric signal in the coil will cause the electric lines of force from the head gap to pass through the magnetic material of the tape producing small magnets depending upon the strength of the current. Polarity of the magnetic field which causes these bar magnets depends on the change of current. Decreasing current will cause NS magnet and vice versa. Power of these magnets is as per BH curve. Thus the magnetic flux strengthens the unarranged magnetic particles as per the signal and they stay in that condition after the tape has already passed the magnetic head (fig. 2). Length of the magnet thus formed is directly proportional to writing speed of the head v, and inversely proportional to the frequency of the signal to be recorded, i.e. Recorded wavelength for one cycle of signal = speed x time Or Wave length of the magnetic signal tape = v / f the problem to be solved in the development of VTRs was how to provide higher speed to record very high frequencies. The other limitation of recording medium is the range, during when the extracted signal is more than noise. This range is only 10 octaves. Thus the system can no longer be used for recording/reproduction after this dynamic range of 60 db, because of 6 dB/octave playback response characteristics. Beyond this range the low frequencies becomes inaudible and the higher frequencies become distorted. Recording process
  31. 31. 31 During the initial stages it was tried to record video signal with stationary video heads and longitudinal tracks using tape speed of the order of 9 m/s which was very difficult to control besides very high tape consumption i.e, miles of tape for 3 to 4 minutes of recording and this was coupled with breaking of video signal frequencies into 10 parts recorded by 10 different video heads and then switched during playback to retrieve the signal. The quality of the reproduced signal was also compromised up to the resolution of 1.7 MHz or so. Around 1956 the „AMPEX‟ company of USA then came out with Quadruplex machines having two revolutionary ideas which laid the foundation of present day VTRs/VCRs. These ideas were: 1. Rotating Video Heads and 2. Frequency Modulation before recording Increase in writing speed by rotating head When a video head mounted on a rotating head wheel writes on a tape moving across it, will lay a track of length which will depend not only on the speed of the tape but also on the rotating speed of the head. Single head with diameter d number of rotation per sec as r and full omega wrap or two heads in ½ omega wrap i.e. little over 180 degree, which most of the present day VCR are using, will have a writing speed of dr minus or plus the linear tape speed (which is negligible as compared to the rotating speed). This avoids the requirements of miles of tape for few minutes of recording in a stationary head type of recorders tried earlier. Monitoring During Recording Most of the video tape recorders provide Electronics to Electronics monitoring (EE Mode) at the time of recording. The video signal is monitored after routing it through all the signal system electronics of the recorders excluding the video heads and preamplifiers etc. Some of the recorders also provide simultaneous playback for the off tape monitoring by using additional heads during recording called confidence heads. Thus the VTRs could achieve wider frequency range with: a)Faster writing speed b) Smaller gap, and c) Octave band compression with frequency modulation.
  32. 32. 32 Also achieving accurate speed for motors with servo system reduces the timing errors. Play back process During play back when the recorded tape is passed over the head gap at the same speed at which it was recorded, flux lines emerging from the tape on crossing the head gap induce voltage in the coil proportional to the rate of change of flux, i.e. d /dt and this in turn depends on the frequency of the recorded signal. Doubling of frequency causes voltage to increase by 6 dB. This accounts for the well known 6 dB/octave playback characteristics of the recording medium. This holds good only up to a certain limit thereafter at very high frequencies, lot of losses take place during playback and recording process causing noise to be more than the signal itself. It may be noted that when the gap becomes equal to the wavelength of the recorded signal, two adjoining bar magnets may produce opposite current during playback and the output becomes zero. Similar thing happens when the gap equals 2, 3 …n. times the wavelength. First extinction frequency occurs when gap becomes equal to wavelength. For getting maximum output, head gap has to be one half of wavelength. Frequency at which zero output occurs is called extinction frequency (Fig. 3). Thus the maximum usable frequency becomes half of the extinction frequency. These parameters are related by: So in order to record the higher frequencies we must increase the writing speed for a minimum value of wave length recorded on tape i.e. tape. This minimum value of tape is again restricted by the minimum practically possible head gap. Now the ratio of video and audio frequencies is approximately 300, so we must increase the writing speed or reduce the gap by the same factor of 300 to get the desired results. Perhaps a speed of 60 mph will be required to cope with the higher video frequencies.
  33. 33. 33 Playback Process VIDEO TAPE FORMATS- INTRODUCTION Format of Video tape recorder defines the arrangement of magnetic information on the tape. It specifies: 1.The width of tape, 2.Number of tracks for Video, Audio, Control, time code and cue, 3.Width of tracks, 4.Their electrical characteristics and orientation. All machines conforming to one format have similar parameters to enable compatibility or interchange i.e. the tape recorded on one machine is faithfully reproduced on the other. There are a number of formats in Video tape recording and the number further gets multiplied due to different TV. Standards prevailing in various countries e.g. PAL, SECAM, NTSC and PAL-M. CLASSIFICATION OF FORMAT: A) Analog Formats: VTRs using composite Video for professional Broadcast use were , Quadruplex 2” , 1" format and C ( All reel/Spool Type) which were then replaced by U- matic cassette recorders followed by best quality analog format with separate luminance & chrominance recording called component Analog formats. These were Betacam SP from SONY & M-II from Panasonic.
  34. 34. 34 a) Quadruplex Format (Segmented) b) Type B Format (Segmented helical) c) Type C Format (field per scan helical) B) DIGITAL FORMATS: Modern television post production demands multi-layer special effects with several manipulations having first generation quality. This requires multi-generation playback & a transparent recordings from Video cassette players./recorders. which can be met only by the digital formats without loss in picture quality. Digital Composite/Component Formats- D1,D2,D3,D4,D5 Digital Betacam: It is based on CCIR 601, and allows 16:9 upgrades. To reduce data rate it uses Bit Rate reduction (BRR).Bit rate reduction is in the ratio of 2:1. This has been made possible because of the conversion of data from time domain to frequency domain and removing the redundancy from the digital video data. Equivalent system without BRR would have required more tape speed, extra thin tape, and extra narrow tracks and would have also needed double the number of heads on drum or double the drum speed. It is compatible with Betacam SP and is having 4 PCM Digital Audio Track. Scanner for this machine is larger then that of Betacam SP but the helix is such that when rotated at frame rate ,track angle of analog Betacam is traced .This gives a time compressed replay is which is then expanded in TBC. For digital Betacam, to handle large data the scanner speed is increased to 3 times. One field is recorded in one and half revolution in 6 tracks of 26 Micrometers each. BETACAM VIDEO CASSETTE RECORDERS- INTRODUCTION: Betacam series of VCRs are based on analog component system. These VCRs had become popular because of their low initial and running costs in comparison to B and C Format machines. The quality of reproduction of Betacam SP was near to these analog formats. Betacam format was introduced in 1982 followed by Betacam SP in 1987. Popular Betacam SP VCRs which are being replaced with digital VCRs in doordarshan
  35. 35. 35 are:- BVW 75P - SP Recorder cum player, with DT head (Slow motion heads for dynamic tracking) & PVW 2800P PRO SERIES besides camcorder and portable version of this format. Head drum: Head drum for BVW 75P carries as many as 10 video heads, two heads for Luminance Ya, Yb, two heads for chrominance Ca, Cb, two heads for Dynamic tracking Luminance DTYa, DTYb, two heads for Dynamic tracking chrominance DT Ca, DT Cb, and finally two heads for Eraser REa & REb (Rotary erase). In some of the models where slow motion is not available DT heads and associated electronics is not required. This makes those models cheaper to BVW 75P. VIDEO SYSTEM Video system is based on component analog system. Composite video is decoded into its component, Luminance Y and colours as R-Y & B-Y. You may note that these colour signal are base band signal and have nothing to do with 4.43MHz subcarrier frequency. Y is recorded directly after FM on one of the video tracks by Ya & Yb head. Chrominance signals are first compressed as CTDM signal (Compressed time division multiplexing) and then frequency modulated. This FM chroma is then mixed with AFM audio channel 3 & 4 before it is recorded along with chrominance information.
  36. 36. 36 TAPE TRANSPORT FOR PVW SERIES OF BETACAM DIGITAL VIDEO CASSETTE RECORDER PROFESSIONAL(DVCPRO)- INTRODUCTION With the advent of digital signals, breakthrough came in the field of recording 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 companies 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).
  37. 37. 37 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. What is DV? DV is a consumer video recording format, developed by a consortium of 10 companies 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 intra frame DCT compression using 4:1:1 chroma subsampling for NTSC (or 4:2:0 for PAL). This makes it straightforward to transfer the video onto computer for editing due to its intra frame compression technique. DV tapes come in two formats: MiniDV size (66mm x 48mm x 12.2mm) and DV, the standard full size (125mm x 78mm x 14.6mm). They record digital compressed video by a DCT method at 25 Megabit per second. In terms of video quality, it is a step up from consumer analog formats, such as 8mm, VHS-C and Hi-8. What is DVCPRO? DVCPRO is a professional variant of the DV, developed by Panasonic. In DVCPRO, the baseband video signal is converted to 4:1:1 sampled data sequence from the originally sampled 4:2:2 signal by the method of subsampling and the resulted data are converted into blocks which are shuffled before passing through compression circuitry and again reshuffled back to their original position after compression. It is to mention here that still pictures containing little or no movement are compressed using intra frame compression whereas the pictures with large amounts of movements are coded and compressed in intra field form. Error correction code is added to the compressed and reshuffled data sequence by using Reed Solomon product code before it is sent to recording modulation method. The modulated data sequence generated by 24-25 coding method using scrambled NRZI is recorded onto the tape via video head. Within the DV(Digital Video) format, audio can be recorded in either 2 channel (1 left and 1 right) or 4 channel mode (2 stereo pairs). In the DVCPRO format the audio is 2 channel record mode only, though provision is made to replay 4 channel type DV tapes. It is to mention here that audio data is recorded un-compressed.
  38. 38. 38 Recording process for audio signal
  39. 39. 39 Vision mixing Introduction Vision mixing is a process of creating composite pictures from various sources. Vision mixing involves basically three types of switching or transitions between various sources. These are mixing, wiping and keying. These transitions can also be accompanied by special effects in some of the vision mixers. Mixing- Two 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. Wipe- In 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. Key- In 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.
  40. 40. 40 NON LINEAR EDITING & 3-D GRAPHICS- INTRODUCTION Fundamentally editing is a process where one places Audio video clips in an appropriate sequence and mainly used in video post production. Linear editing is tape based and is sequential in nature. It has various problems like long hours spent on rewinding of tapes in search of material, potential risk of damage to original footage, difficult to insert a new shot in an edit, difficult to experiment with variations, quality loss is more, limited composting effects and color correction capability. Non-linear editing (NLE) is a video editing in digital format with standard computer based technology. NLE can also be extended to film editing. Computer technology is harnessed in Random access, computational and manipulation capability, multiple copies, multiple versions intelligent search, sophisticated project and media management tools, standard interfaces and powerful display. ADVANTAGES OF NLE NLE has various advantages over tape based (linear) editing. Flexibility in all editing functions. Easy to do changes, undo, copy, duplicate and multiple version Easy operation for cut, dissolve, wipes and other transition effects. Multi-layering of video is easy. Powerful integration of video and graphics, tools for filtering, color correction, key framing and special 2D/3D effects. Equally powerful audio effects and mixing. Possible to trim ; compress or expand the length of the clip. Intelligent and powerful 3D video effect can be created and customized. Efficient and intelligent storage . Standard NLE System
  41. 41. 41 BREAKOUT BOX- Various video sources like VTR, CD player, camera and other playback/recording devices are connected to NLE machine through breakout box. The NLE machine takes input from various video sources for editing and gives output for monitoring and recording through break out box. INPUTS- Video Inputs There are three analog inputs (1) Component Video (2) S-Video (3) Composite video. Audio Inputs To capture synchronized audio with your video, you must connect audio out from the VTR or other play back device to the audio inputs. You can also connect audio only devices for sound track production etc. the dps reality board (NLE hardware) has three analog audio options ; balanced, unbalanced and Aux. Time Code Time code is simply a series of labels attached to a recording at timed intervals, generally fractions of sounds. Each label contains a time of recording. Time code is used for editing; in order to be able to return repeatedly to a selected time, and for synchronization among audio and video recorders and players. The two versions of time code that are available with dps. OUTPUTS- Video Output Component (CAV) Video has three connectors, labeled Y, B-Y, R-Y. A cable connects each of these three outputs to your video monitor or VTR. Audio Output Choose what type of video to output based on whether your VTR and other video and audio equipment can receive balance or unbalance audio. Audio out is connected to speakers for playback or to a VTR or other audio recording device during recording.
  42. 42. 42 3 –D Graphics THE FIVE MODULES OF SOFTIMAGE Softimage 3 D Extreme has given different modules that correspond to different phases of the workflow process you use to create animation. Each of the modules replaces some of the menu cells on the left and right menu columns, while leaving other menu cells that are applicable in all modules. The modules are listed along the top right corner of the screen: Model, Motion, Actor, Matter, and Tools. You can enter these modules either by clicking the text labels in the top right corner, or by pressing the supra keys that represent them: F1 for Model, F2 for Motion, F3 for Actor, F4 for Matter, and F5 for Tools. MODEL You start your workflow in the Model module, where you construct all your scene elements. Model‟ s tools enable you to create objects from primitive shapes, draw curves, and develop surfaces from those curves. MOTION You then move to animate some parts of your scene, using the animation tools found in the Motion module. The Motion module allows you to set animation keyframes for objects, assign objects to paths, and to see and edit the resulting animation on screen. After you have refined your animation using the F Curve tools, you move to the next module, Actor. ACTOR The Actor module contains the special Softimage tools for setting up virtual actors, assigning inverse kinematic skeletons, assigning skin, adjusting skeletons deformations, and weighting the skin to the IK skeletons. Actor also contains the controls for physical- based animation – Dynamics, Collisions, and Qstretch – which is an automatic squash- and-stretch features. MATTER When your modeling, animation, and acting are complete, you move to the fourth module: Matter. In the Matter module, you assign color and material values to the
  43. 43. 43 objects in your scene, determining how they will look in the final render. At any time in the first four modules, you can create lights and adjust their effect on the scene. The Matter module is also where you perform the last step in the workflow process, rendering. TOOLS Tools contains a variety of utility programs for viewing, editing and exporting your work. You may view individual images, sequences of images, and line tests. You may bring in images created in other programmes as image maps or import objects created in other programs as geometry. You can composite sequences of images together, reduce colours in sequences of images for reduced colour games systems, and move your finished work to video disk recorders and film recorders. The four view windows
  44. 44. 44 Television Transmission 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 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 spectrum, reduction in transmission BW was considered necessary. The transmission BW could be reduced to around 5.75 MHz 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. Design All the TV transmitters have the same basic design. They consist of an exciter followed by power amplifiers which boost the exciter power to the required level. Exciter The 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 subsequent transmitter stages, an acceptable signal is available. Since the number and type of amplifier stages, may differ according to the required output power, the characteristics of the pre-correction circuits can be varied over a wide range.
  45. 45. 45 Block Diagram of TV Exciter (Mark-II) 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 errors 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 amplification requires fewer amplifier stages. IF Modulation It has following advantages  Ease of correcting distortions  Ease in Vestigial side band shaping  IF modulation is available easily and economically 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 15000 CX) are used in vision transmitter chain. Aural transmitter chain is fully solid state in Mark III transmitter.
  46. 46. 46 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. BEL 10 kW TV TRANSMITTER (MARK-II) Block Diagram of BEL 10kW TV Transmitter (Mark-II) TRANSMITTER CONTROL SYSTEM The transmitter control unit performs the task of transmitter interlocking and control. Also it supports operation from control console. The XTR control unit (TCU) has two independent system viz. 1.Main control system. (MCS) 2.Back-up Control System (BCS) Functions performed by MCS (Main Control System)- - XTR control - Interlocking - RF monitoring - Supporting operation from control console
  47. 47. 47 - Three second logic for protection against sudden fluctuation. - Thermal protection for 1 kW and 10 kW 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 inputs 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 information, is used by both the MCS and BCS (Back up Control Unit). Main Control System (MCS) The MCS consists of the following : 1.Mother Board with the following PCBs. CPU BIT I/O Interlock Interface Board (IIB). Analog I/O Board (AIO) Control Interface Board (CIB) Analog Receiver Board (An Rx) Rectifier and Regulator Board (RRB mcs) : 2.Key Board 3.LED Bar Display Board 4. Relay Board 5.LCD Display Unit 6.Transformers T1 and T2. 7.+ 5V/3A. Power Supply Unit.
  48. 48. 48 TV Transmitter and Antenna System Antenna System is that part of the Broadcasting Network which accepts RF Energy from transmitter and launches electromagnetic waves in space. The polarization of the radiation as adopted by Doordarshan is linear horizontal. The system is installed on a supporting tower and consists of antenna panels, power dividers, baluns, branch feeder cable, junction boxes and main feeder cables. Dipole antenna elements, in one or the other form are common at VHF frequencies where as slot antennae are mostly used at UHF frequencies. Omni directional radiation pattern is obtained by arranging the dipoles in the form of turnstile and exciting the same in quadrature phase. Desired gain is obtained 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 vertical plane is minimized. The installed
  49. 49. 49 antenna system should fulfil the following requirements : a)It should have required gain and provide desired field strength at the point of reception. b)It should have desired horizontal radiation pattern and directivity for serving the planned area of interest. The radiation pattern should be omni directional if the location of the transmitting station is at the center of the service area and directional one, if the location is otherwise. c)It should offer proper impedance to 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 RF impedance at VHF/UHF is 50 ohms.
  50. 50. 50 Outdoor Broadcasting van O B Van (Outdoor Broadcasting van )- OB van is used for live broadcasting like any match or any event. It consist all the equipments that is present in the studio for telecasting. It also referring as mini studio . It has mainly 3 parts : 1)Power supply unit 2)Production control unit 3)Audio console and VTR Inner View of OB van
  51. 51. 51 Earth Station SATELLITE COMMUNICATION Satellite Communication is the outcome of the desire of man to achieve the concept of global village. Penetration of frequencies beyond 30 Mega Hertz through ionosphere 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 communication 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 television 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 generation, 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 communication 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 regions 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 I NSAT : Indian Satellites AUSSAT : Australian Satellites BRAZILSAT : Brazilian Satellites FRENCH TELECOM : French Satellites ITALSAT : Italian Satellites CHINASAT : Chinese Satellites STATSIONAR, GORIZONT, Russian Satellites Architecture of a Satellite Communication System The Space Segment The space segment contains the Satellite and all terrestrial facilities for the control and monitoring of the Satellite. This includes the tracking, telemetry and command stations
  52. 52. 52 (TT&C) together with the Satellite control centre where all the operations 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 up link. 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 the total link determines the quality of the signals delivered to the end user in accordance with the type of modulation and coding used. The Ground Segment The 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 volume of traffic to be carried on the space link and the type of traffic (telephone, television 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 television receiving stations). Fixed, transportable and mobile stations can also be distinguished. Some stations are both transmitters and receivers.
  53. 53. 53 Space Geometry Types of Orbit The orbit is the trajectory followed by the satellite in equilibrium between two opposing 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 . Most favourable Orbits- Elliptical 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 orbital 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. 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 altitude circular orbits are for e.g. IRIDIUM, GLOBAL STAR, ODYSSEY, ARIES, LEOSAT, STARNET, etc. Circular orbits with zero inclination (Equatorial orbits). The most popular is the geo stationary satellite 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 ensures continuous operation as a radio relay in real time for the area of visibility of the satellite (43% of the earth‟ s surface).
  54. 54. 54 Factors deciding the selection of Orbit The choice of orbit depends on the nature of the mission, the acceptable interference 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 TVRO System Presently Doordarshan is up linking its national, metro and regional services to INSAT-2A (74oC) and INSAT-2B (93.5oE) and INSAT 2E (83o C). Down link frequency bands being used are C-Band (3.7-4.2 GHz) and Ex-C Band (4.5-4.8 GHz). Satellite Earth Station Uplink / Downlink Chain Transmission of base band to Satellite The 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 upconversion (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 conversion to 70 MHz, it is demodulated to get audio and video.
  55. 55. 55 Satellite Transponder As 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. Block diagram of Satellite Transponder 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. Parallels of Latitudes Latitude as angular distance
  56. 56. 56 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 elevation of a particular satellite from our place. The azimuth and elevation are angles 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 defined as the north south movement of the dish. Both the azimuth and elevation of a dish can be affected by three factors for geo-stationary satellites. They are 1. The longitude of the satellite. 2. The latitude of the place. 3. The longitude of the place. Calculation of Angle of Elevation Where r = Radius of the earth (6367 kms) R = Radius of Synchronous orbit (42,165 kms). = Latitude of the earth station D = difference in longitude of the earth station and the satellite. ( r - s) 2 1 Cos Calculation of Azimuth Indoor Units The indoor unit contains two units. They are : 1. System unit 2. Satellite Receiver Unit
  57. 57. 57 System unit The 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 receivers. 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 synthesised receiver accepts signal in the range of 900 to 1700 MHz. The block diagram of a typical EC receiver is shown in figure 9. The IF is applied to a four-stage low noise amplifier 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 synthesiser IC. A sample of the LO frequency is taken and phase compared with a stable reference crystal frequency of 4 MHz and error if any, is then applied to the VCO for frequency correction through a low pass filter. Thus the VCO works in a phase locked loop mode.
  58. 58. 58 Direct-to-Home Satellite Broadcasting (DTH) INTRODUCTION 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.
  59. 59. 59 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). Fig.1 shows schematic of uplink chain proposed to broadcast bouquet of 30 video programs 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 multiplexed in a Multiplexer. These three multiplexed streams are digitally (QPSK modulation) 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).
  60. 60. 60 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.
  61. 61. 61 Conclusion Now I have studied a lot about the television broadcast system. One must have never thought that so many things are required for watching a television. The camera, the studio, the transmitter, the PDA, the setup box (installed in houses) everything is connected to each other. Here man and electronics work as if they are a family. So many process and lots of hard work, sincerity is required to just have a show or say a movie on air i.e. to be broadcasted. So many people are involved in it. I really enjoyed of being part of it. The saying is really true that… “Tell me, I may forget Teach me, I may remember But involve me, and I have learnt it”
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