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  1. 1. project report ONTHE TELEVISION SYSTEMStaff Training Institute (technical) Lucknow Ishank Ranjan 5th Sem B.Tech(EEE) H.C.S.T. Mathura
  2. 2. AcknowledgementThis report is an outcome of the contributions made by someof the peoples. Therefore it is my sole responsibility toacknowledge them. I am greatly thankful to the sincereefforts made by Mr. Ravindra Naithani without whom thisproject would be abstract. I also thank the staff of DDK, Lko(Doordarshan Kendra ,Lucknow) who took out there precioustime to tell me about the various equipments. My specialthanks is dedicated to Mr. K. S. Chauhan (AssistantEngineer, Doordarshan Kendre -Leh).I would also mention the outstanding support given by myparents who paved the way for me to overcome with thisproject report.ISHANK RANJANB.Tech (5th Sem)Electrical & Electronics EngineeringHindustan College Of Science And TechnologyMathura.
  3. 3. CertificateThis is to certify that ISHANK RANJAN, a student ofHindustan College Of Science And Technology in Electrical & Electronics Engineering branch hasundergone industrial training in Doordarshan Kendra Lucknowfrom 4th of July,2012 to 28th of July,2012. And this projectreport is based on it. Dated- (Signature) Mr. R. Naithani Training coordinator Doordarshan Kendra ,Lucknow
  4. 4. ContentsPART (1) Fundamentals Of Monochrome And Colour Tv System a) Picture Formation b) Number Of TV Lines Per Frame c) Resolution d) Brightness e) Contrast f) Colour Composite Video Signal (CCVS)PART (2) The Colour Television a) Introduction b) Additive Colour Mixing c) Colour Difference Signals d) Band Width Requirement e) Colour Carrier And Modulation Of R-Y And B-Y Signals f) Croma VectorPART (3) The PAL System a) Introduction b) Pal Encoder c) Pal DecoderPART (4) Audio Video Chain In a TV Statio a) Introduction b) Studio Center c) Action Area d) Production Control Area e) Central Apparatus Room(CAR) f) Sync Pulse-Generator(SPG) g) Camera Control Unit (CCU)PART (5) DTH Broadcasting a) Introduction b) Down-Link Chain c) Uplink Chain
  5. 5. Dedicated To My ParentsMrs. Ranjana Srivastava & Mr. R.C. Srivastava
  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 pickup 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 Hertz (Field rate is the same as power supply frequency). Page 1 of 36
  7. 7. • 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 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. A compromise between quality and conservation of r.f. spectrum led to the selection of 625 lines in CCIR system B. Odd number is preferred for ease of sync pulse generator (SPG) circuitary to enable interlace of fields.• Resolution The scanning spot (beam) scans from left to right. The beam starts at the left hand edge of the screen and goes to right hand edge in a slightly slanty way as the beam is progressively pulled down due to vertical deflection of beam (as top to bottom scanning is to take place simultaneously). When the beam reach the right hand edge of the screen the direction of beam is reversed and goes at a faster rate to the left hand edge (below the line scanned). Once again the beam direction is reversed and scanning of next line starts. This goes on till the beam completes scanning 312 and half lines reaching the bottom of the screen. At this moment the beam flies back to top and starts scanning starting from half line to complete the next 312 and half lines of the frame. To avoid distortions in the picture whenever the beam changes its direction, it is blanked out for a certain duration. The horizontal blanking period is 12 microseconds. Since each line takes 64 micro seconds the active period of line is 64 -12 = 52 micro seconds. Page 2 of 36
  8. 8. (Since 625 lines are scanned at the rate of 25 Hz i.e. 25 cycles persecond, the number of lines scanned in one second is 625 multiplied by25 which yields 15,625. So the horizontal frequency is 15,625 hertz andhence each line takes 64 micro seconds).Similarly there is vertical blanking period and 25 TV lines are blankedout during the period. So in one frame 50 TV lines are blanked out.Hence effective lines are 625 minus 50 i.e. 575.The vertical resolution depends on the number of scanning lines andthe resolution factor (also known as Kell factor). Assuming a reasonablevalue of Kell factor as 0.69. The vertical resolution is 575 multiplied by0.69 which gives nearly 400 lines.The capability of the system to resolve maximum number of pictureelements along scanning lines determines the horizontal resolution. Itmeans how many alternate black and white elements can be there in aline. Let us also take another factor. It is realistic to aim at equal verticaland horizontal resolution. We have seen earlier that the verticalresolution is limited by the number of active lines. We have alreadyseen that the number of active lines are 575. so for getting the sameresolution in both vertical and horizontal directions the number ofalternate black and white elements on a line can be 575 multiplied byKell factor and aspect ratio. Therefore, the number of alternate blackand white dots on line can be 575 x 0.69 x 4/3 which is equal to 528. • Grey ScaleIn black and white (monochrome) TV system all the colours appear asgray on a 10-step gray scale chart.TV white corresponds to a reflectance of 60% and TV black 3 % givingrise to a Contrast Ratio of 20:1 (Film can handle more than 30:1 andeye‟s capability is much more). Page 3 of 36
  9. 9. In black and white TV the concept of gray scale is adopted forcostumes, scenery etc. If the foreground and back ground are identicalin gray scale, they may merge and the separation may not be noticedclearly on the screen. • BrightnessBrightness reveals the average illumination of the reproduced image onthe TV screen.Brightness control in a TV set adjusts the voltage between grid andcathode of the picture tube (Bias voltage). • ContrastContrast is the relative difference between black and white parts of thereproduced picture.In a TV set the contrast control adjusts the level of video signal fed tothe picture tube. • Colour Composite Video Signal (CCVS)Colour Composite Video Signal is formed with Video, sync and blankingsignals. The level is standardized to 1.0 V peak to peak (0.7 volts ofVideo and 0.3 volts of sync pulse). The Colour Composite Video Signal(CCVS) has been shown in figure. Page 4 of 36
  10. 10. It consists of:- i. Video signal along with synchronizing singal,composed of line and field synchronizing pulses to ensures the locking of scanning systems of a source and destination. ii. Blanking pulses to blank retrace period around the horizontal and vertical synchronizing periods.iii. Sub carrier and its modulated components to carry the colour information.iv. Burst gate signal (responsible for correct positioning of colour burst). Page 5 of 36
  11. 11. The Colour TelevisionIntroductionIt is possible to obtain any desired colour by mixing three primarycolours 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 aresensitive only to the intensity of the incident light and cones areresponsible for normal colour vision.The small range of frequencies to which the human eye is responsive isknown as visible spectrum. This visible spectrum is from 780 mm (Red)to 380 mm(Violet). Fig. Approximate relative sensitivity of the average human eye to different wave lengths Page 6 of 36
  12. 12. • Additive Colour MixingThe figure 10 shows the effect of projecting red, green, bluebeams of light so that they overlap on screen.Y= 0.3 Red + 0.59 Green + 0.11 Blue Fig. Additive Colour MixingIt is possible to obtain any desired colour by mixing three primarycolours i.e., red, blue and green in suitable proportion. Thus it is onlyrequired to convert optical information of these three colours toelectrical signals and transmit it on different carriers to be decoded bythe receiver. This can then be converted back to the optical image atthe picture tube. The phosphors for all the three colours i.e. R, G and Bare easily available to the manufacturers of the picture tube. So thepick up from the cameras and output for the picture tube shouldconsists of three signals i.e. R, G and B. It is only in between the camera Page 7 of 36
  13. 13. and the picture tube of the receiver we need a system to transmit thisinformation. Fig. Colour Tv SystemColour television has the constraint of compatibility and reversecompatibility with the monochrome television system which makes itslightly complicated. Compatibility means that when colour TV signal isradiated the monochrome TV sets should also display Black & Whitepictures. This is achieved by sending Y as monochrome informationalong with the chroma signal. Y is obtained by mixing R, G & B as perthe well-known equation:Y = 0.3 R + 0.59 G + 0.11 BReverse compatibility means that when Black & White TV signal isradiated the colour TV sets should display the Black & White pictures.In view of the above the colour TV system should have:a) Same line and field standards as that of existing monochrome.b) The same bandwidth as that of the existing monochrome system.c) The monochrome information in the Luminance signal along withcolour signal. Page 8 of 36
  14. 14. If we transmit R, G, B, the reverse compatibility cannot be achieved. Letus see how :If we transmit Y, R & B and derive G then :Since,Y = 0.3R + 0.59G + 0.11 BG = 1.7Y - 0.51 R - 0.19 BIn such a case what happens with a colour TV set when we transmitblack and white signal. R and B are zero, but G gun gets 1.7 Y. The netresult is black & white pictures on a colour TV screen appear as Greenpictures. So reverse compatibility is not achieved. • Colour Difference SignalsTo achieve reverse compatibility, when we transmit Y, R-Y and B-Yinstead of Y, R & B, we do not take G-Y as this will always be muchlower than R-Y and B-Y and hence will needs more amplification andwill cause more noise into the system. G-Y can be derived electronicallyin the TV receiver.In the previous paragraph we have seen G = 1.7 Y - 0.51 R - 0.19 BSo G-Y = -0.51 (R-Y) - 0.19 (B-Y)Thus, colour difference signals fulfill the compatibility and reversecompatibility. Because in this case the colour difference signals are zeroif the original signal is monochrome (i.e. R = B = G)So if we take R – YR - Y = R - (0.3 R + 0.59 R + 0.11 R) = 0Similarly , B-Y=0 Page 9 of 36
  15. 15. As such colour difference signals are zero for white or any shade of graywhereas, Y carries the entire Luminance information.It is to be noted while R, G, B signals always have positive value R-Y,B-Y and G-Y signals can either be positive or negative or even zero. • Band Width RequirementWe have already seen that compatibility calls for utilizing the samebandwidth as that of existing monochrome. In the system we arefollowing it is 5 Megahertz for Video. Restricting the bandwidth ofLuminance results in poor resolution. Then how to share the same 5megahertz bandwidth between Y and the colour difference signals R-Yand B-Y. A way is to be found to accommodate the colour differencesignal within the Luminance bandwidth WITHOUT CAUSING ANYSIGNIFICANT INTERFERENCE. Also Luminance signal is to betransmitted in the same way as that monochrome receiver can receiveit. Hence a method of inter leaving is to be adopted to suitcompatibility. • Colour Carrier And Modulation of R-Y And B-Y SignalsSpectral analysis of luminance Signal shows that various frequencycomponents occur at multiples of line (H frequency) due to the periodicscanning. The space between the two energy contents is utilized toaccommodate Chrominance signal within Luminance Signal.Assume an oscillator output is connected to the TV picture tube input.Severe patterns appear on the screen. When the Oscillator frequency isa multiple of TV line frequency (H frequency) the patterns becomestable. As the oscillator frequency rises through the Luminance bandthe pattern becomes finer eventually becoming a series of dots. If theoscillator frequency is an odd multiple of Line frequency then the dots Page 10 of 36
  16. 16. pattern of one field lies exactly between the dots produced two fieldslater. Persistence of vision will cause dot pattern to go to a minimum. minimuThis has led to the selection of a carrier frequency that gets modulatedby the colour difference signal which is close to the edge of bandwidthon the high frequency side.Fig. Energy Spectrum Of TV SignalAs we know the video spectrum is occupied only at multiples of Linefrequency and in their vicinity. The spectrum exhibits gaps in betweenthese frequency groups. So if the chrominance spectrum is placed inthese gaps the interference will be negligible. That means the subcarrier frequency should be an odd multiple of half-line frequency. lineFrom the above it is clear that sub carrier frequency should be near tothe upper edge of video bandwidth (i.e. as high as possible) and alsoshould be an odd multiple of half half-line frequency. Page 11 of 36
  17. 17. This sub-carrier gets modulated by colour difference signals R - Y andB - Y to produce Chrominance that gets interleaved with Luminancesignal. • Croma VectorLuckily the requirement of bandwidth of chrominance signal is less. Thisis because of the capacity of human eye. The capacity of human eye todistinguish between hues depends on the size of the objects, thelighting condition and the distance. In a very badly lit room you cannotdistinguish the colour of the objects if they are small in size and are at adistance. However, you can notice the objects by their Luminancevalue. It means they give rise to Luminance signal but not chrominancesignal.Even in good lighting condition we cannot notice hue till we go near theobjects. However their brightness value is first noticed as we go nearand when go still nearer we see colour. This only shows that thebandwidth requirement of chrominance signal is much. In the PALsystem the chrominance bandwidth is restricted to 1.3 MHz. The sub-carrier frequency is 4.43 MHz.Though carrier is single we need two carriers for R - Y and B - Y tomodulate independently. How do we get two carriers? In fact both areof the same frequency but are displaced in phase by 90 degrees. Hencewe speak of quadrature modulation of sub-carrier frequency by thecolour difference signals. The type of modulation used is AmplitudeModulation. One carrier is amplitude modulated with R - Y and theother with B - Y and in both cases the carrier is suppressed. The twomodulated signals at 90 degrees to each other produce the resultantchrominance signal which gets added to Luminance signal to formComposite colour Video Signal (CCVS). Page 12 of 36
  18. 18. Fig. Generation Of Croma VectorThe R-Y and B - Y chrominance signals may be recovered at thetelevision receiver by suitable synchronous demodulation. But sub sub-carrier is to be generated by a local oscillator. This generated subsub-carrier in the receiver must have same frequency as that of transmittedsub-carrier and also the same phase. This is achieved by transmitting 10 carriercycles of sub-carrier frequency on the back porch of H synchronizing carrierpulse. This 10 cycles sub-carrier signal is known as BURST or colour sub carrierBURST. One line display is shown below:- Page 13 of 36
  19. 19. The PAL System (Phase Alteration By Line)You may note that in view of the phase alternation line by line, a givenhue will be represented on a vector diagram at two alternatingpositions symmetrically displaced above and below B-Y axis in alternate BYlines. You might have noticed two colour vectors for each colours on avector scope display because of this reason. Fig. Colour bar Display On VectroscopeIn the case of PALs Receiver the ability of eyes to combine the hues onthe adjacent lines is utilised. However the resultant picture is less essatisfactory for phase errors exceeding 15 degrees. Fig. PAL-D Receiver Page 14 of 36
  20. 20. • PAL EncoderThe design of PAL Encoder may vary from manufacturer tomanufacturer. In some of the PAL encoder instead of reversing thephase of V component on every alternating line, it has been foundmuch easier to change the phase of carrier modulating the R-Ycomponent by 180 degree every alternate line. This switching iscontrolled by the H/2 oscillator i.e., by a 7.80 kHz PAL Indent pulse.(H/2 because of alternate line phase reversal). In order to facilitate TVreceiver to decode which line has +V component and which line has -Vcomponent we send additional information by modifying the burst.Burst preceding a line carry this information. This is achieved bychanging its phase. It is 135 and 225 degrees for +V & -V respectively. Itis also known as swinging burst.The block diagram of PAL encoder explains a system having thefollowing steps:- 1) Add R G B to generate Y, R-Y & B-Y 2) Modulate R-Y by SC at 90o for line n and 270 o for line n+1. Switching of SC phase is controlled by 7.80 kHz, switching pulse. 3) Modulate B-Y by SC at 0o phase. 4) To generate SC with V switching information i.e. either at 135/225o (burst) each alternate line. (Swinging burst) 5) Generation of pulse called PAL-indent signal of 7.80 kHz. 6) Generating of burst gate or K pulse to define the parking space for burst at the back porch. 7) Adding of 2, 3, 4, Y and sync to generate CCVS i.e., colour composite Video signal as Encoder output. Page 15 of 36
  21. 21. Also the burst preceding the line indicates whether the V componentis +ve or -ve, and it contains equal component of U and V. ve, Fig. Block Diagram Of PAL Encoder Fig. PAL Encoder Angle System Page 16 of 36
  22. 22. • PAL DecoderPAL decoder is a reverse of encoding process. The objectives ofrecovering R G & B from the received signal is achieved in the followingsteps: 1) Y & S is recovered by decoding video & using LPF and Sync separator circuit of receiver. 2) Chroma is separated by using BPF (center at 4.43 MHz) 3) Chrome is keyed or gated to get back the burst i.e. SC by using K - Pulse. 4) L.O. 4.43 MHz is phase locked with the recovered burst to make it of same phase as that of the transmitted one. 5) 4.43 MHz SC is processed further to get the same pulse at 90 degree phase as well. 6) Modulated chroma is demodulated by these two SC at 0 & 90 degree. This will retrieve U & V components. 7) Phase of the V component is restored back to normal by using the concerned information from the transmitted burst. 8) U & V are demodulated back to R-Y & B-Y. 9) Y, R-Y & B-Y are mixed to retrieve R G B which will control the three grids of picture tube. Page 17 of 36
  23. 23. Fig. Block Diagram Of PAL Decoder Page 18 of 36
  24. 24. AUDIO VIDEO CHAIN IN A TV STATION • Introduction:Studio centers of Doordarshan kendras are required to generateprogrammes. The delivery of these programes to the viewers is eitherdone by satellite or terrestrial mode. As a satellite channel theprograms have larger reach across the entire country. Sate Satellite channelsare radiated from the respected Earth StationIn a terrestrial Mode, the programes are having a limited range in a city.These programes are radiated by TV transmitter as an RF signal andreceived by TV receiver by using TV antenna. antenna Page 19 of 36
  25. 25. • STUDIO CENTERA Studio center of Doordarshan has the following objectives: 1) To originate programmes from studios either for live telecast or for recording on a video tape. 2) To knit various other sources of programs available at the production desk i.e., camera output from studios, feed from other kendras, outdoor, playback from prerecorded tape, film based programs slides, video graphics and characters generator etc. This knitting or live editing includes generation of special effects and desired transitions between various sources. 3) Processing/distribution of different sources to various destinations in technical areas. 4) Routing of mixed programme for recording/transmission via master switching room and Micro Wave to the transmitter or any other desired destinations.Activities in a television studio can be divided into three major areassuch as : 1) Action area, 2) Production control room, and 3) Central apparatus room, Action areaThis place requires large space and ceiling as compared to any othertechnical area. Action in this area includes staging, lighting,performance by artists, and arrangement to pick up picture and sound. Page 20 of 36
  26. 26. Hardware required for these activities in a studio (typical size 20 x20x8.5 cubic meters) are: i. Very efficient air conditioning because of lot of heat dissipation by studio light and presence of large number of persons including invited audience performing artists and operational crew. ii. Uniform and even flooring for smooth operation of camera dollies and boom microphone etc. iii. Acoustic treatment keeping in mind that a television studio is a multipurpose studio with lot of moving person and equipment during a production. iv. Supporting facilities like properties, wardrobe, and makeup etc. v. Effective communication facilities for the floor crew with the production control area. vi. Studio cameras (three to four) with one of the cameras fitted with teleprompter system and pressure dolly.vii. Luminaires and suspension system having grids or battens (hand/motorised operation).viii. Pick up wall sockets for audio operations. ix. Tie lines box for video and audio lines from control room. x. Cyclorama and curtain tracks for blue and black curtain for chroma keying and limbo lighting respectively. xi. Audio and video monitoring facilities.xii. Studio warning light and safety devices like fire alarm system and firefighting equipment etc.xiii. Digital clock display. Page 21 of 36
  27. 27. Fig. Use of synchronizing signals to generate Colour Composite Video Signal (CCVS) Production control areaActivities in this area are:- i. Direction to the production crew by the producer of the programme. ii. Timing a production/telecast. iii. Editing of different sources available at the production desk. iv. Monitoring of output/off air signal. Hardware provided in this area include: 1. Monitoring facilities for all the input and output sources(audio/video). 2. Remote control for video mixer, telecine and library store and special effect (ADO) etc. 3. Communication facilities with technical areas and studio floor. Page 22 of 36
  28. 28. Vision mixing and switchingUnlike films, television media allows switching between differentsources simultaneously at the video switcher in Production controlroom operated by the Vision Mixer on the direction of the programproducer. The producer directs the cameramen for proper shots onvarious cameras through intercom and the vision mixer (also called VMengineer) switches shots from the selected camera/cameras with splitsecond accuracy, in close cooperation with the producer. The shots canbe switched from one video source to another video source,superimposed, cross faded, faded in or faded out electronically withactual switching being done during the vertical intervals between thepicture frames. Electronics special effects are also used now days as atransition between the two sources.For most of the Video Switcher Mixing between the sources is possibleonly if the sources are having timing accuracy between 50 ns to 200 nsand Burst phase for SC with an accuracy of 1.5 to 5 deg.Though the video switching is done by the VM at the remote panel, theelectronics is located in CAR. The vision mixer is typically a 10 x 6 or 20 x10 cross bar switcher selecting anyone of the 10 or 20 input sources to6 or 10 different output lines. The input sources include: Camera 1,camera 2, camera 3, VTR1, VTR2, Telecine 1, Telecine 2, Test signal etc.Some of the sources that have their sync coincident with the stationsync are called synchronous, while others having their ownindependent sync are called non-synchronous. Page 23 of 36
  29. 29. The vision mixer provides for the following operational facilities forediting of TV programs:- a. Take: Selection of any input source or Cut: switching clearly from one source to another. b. DISSOLVE: Fading out of one source of video and fading in another source of video. c. SUPERPOSITION OF TWO SOURCES: Keyed caption when selected inlay is superimposed on the background picture. d. SPECIAL EFFECTS: A choice of a number of wipe patterns for split screen or wipe effects. The selected output can be monitored in the corresponding pre-view monitor. All the picture sources are available on the monitors. The preview monitors can be used for previewing the telecine, VTR; test signals etc. with any desired special effect, prior to its actual switching.The switcher also provides cue facilities to switch camera tally lights asan indication to the cameraman whether his camera is on output of theswitcher. Character Generator(CG)Character Generator provides titles and credit captions duringproduction in Roman script. It provides high resolution characters,different colours for colorizing characters, background, edges etc. Atpresent bilingual and trilingual C.G are also being used by Doordarshan.Character Generator is a microcomputer with Texts along instructionswhen typed in at the keyboard is stored on a floppy or a Hard disk.Many pages of scripts can be stored on the disk and recalled when Page 24 of 36
  30. 30. needed, by typing the addresses for the stored pages, to appear as oneof the video sources. Central Apparatus Room(CAR)This is the nerve center for a television station. Activities in this areainclude:1) Distribution of stabilised power supply to different technical areas with protection devices.2) Sync pulse generation and distribution.3) Distribution of sources to various destinations4) Video processing and routing.5) Electronics for camera chain, video switchers, special effect generator, and test signal and pattern generator.6) Monitoring facilities7) Patch panel for video and audio lines8) Electronics for micro wave links Sync Pulse-Generator(SPG)It is essential that all the video sources as input to the switcher are insynchronism i.e., start and end of each line or all the frames of videosources is concurrent. This requirement is ensured by the sync pulsegenerator (SPG). SPG consists of highly stable crystal oscillator. Variouspulses of standard width and frequency are derived from this crystalelectronically which form clock for the generation of video signal. Thesepulses are fed to all the video generating equipment to achieve thisobjective of synchronism. Because of its importance, SPG is normallyduplicated for change over in case of failure.It provides the following outputs: Page 25 of 36
  31. 31. • Line drive • Field drive • Mixed blanking • Mixed sync • colour subcarrier • A burst insertion pulse • PAL phase Indent pulses Fig. Typical Studio Timing Arrangement Camera Control Unit (CCU)The television cameras which include camera head with its opticalfocusing lens, pan and tilt head, video signal pre-amplifier view finder pre amplifierand other associated electronic circuitry are mounted on camerastrolleys and operate inside the studios. The output of cameras is pre- preamplified in the head and then connected to the camera control unit(CCU) through long triax cable. All the camera control voltages are fedfrom the CCU to the camera head over the Triax cable. The view view-findersignal is also sent over the camera cable to the camera head view- view Page 26 of 36
  32. 32. finder for helping the cameraman in proper focusing, adjusting andcomposing the shots.The video signal so obtained is amplified, H.F. corrected, equalized forcable delays, D.C. clamped, horizontal, and vertical blanking pulses areadded to it. The peak white level is also clipped to avoid overloading ofthe following stages and avoiding over modulation in the transmitter.The composite sync signals are then added and these video signals arefed to a distribution amplifier, which normally gives multiple outputsfor monitoring etc. • Light ControlThe scene to be televised must be well illuminated to produce a clearand noise free picture. The lighting should also give the depth, thecorrect contrast and artistic display of various shades without multipleshadows.The lighting arrangements in a TV studio have to be very elaborate. Alarge number of lights are used to meet the needs of „key‟, „fill‟, and„back‟ lights etc. Lights are classified as spot and soft lights. These aresuspended from motorized hoists and telescopes. The up and downmovement is remotely controlled. The switching on and off the lights atthe required time and their dimming is controlled from the light controlpanel inside a lighting control room using SCR dimmer controls. Theseremotely control various lights are inside the studios.Modern TV studios have a computer-controlled lighting system. Theintensities of various lights can be adjusted independently andmemorised for reproduction. The status indication of lights regardingtheir location and intensity is available on a monitor/MIMIC display. Page 27 of 36
  33. 33. During reproduction of a particular sequence, the information from thememory operates the respective light dimmers. Hand held controlboxes are also available for controlling light intensities inside thestudios which communicate via a control panel. Most of the operationalcontrols of the computerised light control system can also beperformed manually with the back –up matrix and fader controls. • Sound mixing and controlAs a rule, in television, sound accompanies the picture. Severalmicrophones are generally required for production of complextelevision programs besides other audio sources also called marredsound from telecine, VTR, and audio tape/disc replays. All these audiosources are connected to the sound control console.The sounds from different sources are controlled and mixed inaccordance with the requirement of the program. Split second accuracyis required for providing the correct audio source in synchronisationwith the picture thus requiring lot of skill from the engineer. Even thelevel of sound sometimes is varied in accordance with the shotcomposition called prospective. • Audio facilitiesAn audio mixing console, with a number of inputs, say about 32 inputsis provided in major studio. This includes special facilities such asequalisation, PFL, phase reversal, echo send/receive and digitalreverberation units at some places Meltron console tape recorders andEMI 938 disc reproducers are provided for playing back/creating audioeffects as independent sources (Unmarried) to the switcher. Page 28 of 36
  34. 34. • Video Tape recordersVTR room is provided at each studio center. It houses a few Broadcaststandard Videocassette recorders (VCRs). In these recorders, sound andvideo signals are recorded simultaneously on the same tape. • Post Production SuitesModern videotape editing has revolutionised the production oftelevision programs over the years. The latest trend all over the world isto have more of fully equipped post production suites than number ofstudios. Most of the present day shootings are done on locations usingsingle camera. The actual production is done in these suites. The job forpost-production suites is:- 1. To knit program available on various sources. 2. While doing editing with multiple sources, it should be possible to have any kind of transition. 3. Adding/Mixing sound tracks. 4. Voice over facilities. 5. Creating special effects.The concept of live editing on vision mixer is being replaced by “to do itat leisure” in post production suites.A well equipped post production suite will have four NLE & 3-D graphicsmachines and Betacam SP or DVC Pro Recorders. Page 29 of 36
  35. 35. Coverage of Outside eventsOutside broadcasts(or OBs) provide an important part of the televisionprograms. Major events like sports, important functions andperformances are covered with an O.B. van which contains all theessential production facilities. • Video ChainThe block diagram on facing page connects all these sections and it canbe observed that the CAR is the nodal area. Now let us follow a CAM-Isignal. CAM-I first goes to a Camera electronics in CAR via a multi-corecable, the signal is then matched/adjusted for quality in CCU and thenlike any other sources it goes to video switcher via PP (Patch Panel) andrespective VDAs(Video Distribution Amplifiers) and optional Humcompensator/Cable equalizers.Output from the switcher goes to stabilizing amplifier via PP and VDAs.Output from the stab. Is further distributed to various destinations. Itmay be noted that the use of VDAs helps to monitor the video signal atdifferent locations and the use of PP is very helpful for emergencyarrangements during breakdowns and trouble shooting. A separatemonitoring bus is provided in CCU, LCU and END CONTROL with sourcesas shown.END CONTROL also has a remote for the adjustment of levels etc. in theSTAB AMP unit. Route for the other sources is similar to this and can beunderstood from the block schematic. Page 30 of 36
  36. 36. DTH Broadcasting (Direct To Home)• IntroductionThere was always a persistent quest to increase the coverage area ofbroadcasting. Before the advent of the satellite broadcasting, theterrestrial broadcasting, which is basically localized, was mainlyproviding audio and video services. The terrestrial broadcasting has amajor disadvantage of being localized and requires a large number oftransmitters to cover a big country like India. It is a gigantic task andexpensive affair to run and maintain the large number oftransmitters. Satellite broadcasting, came into existence in midsixties, was thought to provide the one-third global coverage simplyby up-link and down-link set-ups. In the beginning of the satellitebroadcasting, up-linking stations (or Earth Stations) and satellitereceiving centers could had only been afforded by the Governmentsorganizations. The main physical constraint was the enormous size ofthe transmitting and receiving parabolic dish antennas (PDA).In the late eighties the satellite broadcasting technology hadundergone a fair improvements resulting in the birth of cable TV.Cable TV operators set up their cable networks to provide theservices to individual homes in local areas. It rapidly grew in anunregulated manner and posed a threat to terrestrial broadcasting.People are now mainly depending on cable TV operators. Since cableTV services are unregulated and unreliable in countries like Indianow, the satellite broadcasting technology has ripened to a level Page 31 of 36
  37. 37. where an individual can think of having direct access to the satelliteservices, giving the opportunity to viewers to get rid of cable TV.Direct-to-Home satellite broadcasting (DTH) or Direct SatelliteBroadcasting (DBS) is the distribution of television signals from highpowered geo-stationary satellites to a small dish antenna andsatellite receivers in homes across the country. The cost of DTHreceiving equipments is now gradually declining and can be affordedby common man. Since DTH services are fully digital, it can offervalue added services, video-on-demand, Internet, e-mail and lotmore in addition to entertainment. DTH reception requires a smalldish antenna (Dia 60 cm), easily be mounted on the roof top, feedalong with Low Noise Block Converter (LNBC), Set-up Box (IntegratedReceiver Decoder, IRD) with CAS (Conditional Access System). Abouquet of 40 to 50 video programs can simultaneously be receivedin DTH mode.• UPLINK CHAINDTH broadcasting is basically satellite broadcasting in Ku-Band(14/12 GHz). The main advantage of Ku-Band satellite broadcasting isthat it requires physically manageable smaller size of dish antennacompared to that of C-Band satellite broadcasting. C-Bandbroadcasting 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). Theshortfall of this 6 dB is compensated using Forward Error Correction(FEC), which can offer 8 to 9 dB coding gain in the digitalbroadcasting. Requirement of transmitter power (about 25 to 50Watts) is less than that of analog C-band broadcasting. The majordrawback of Ku-Band transmission is that the RF signals typically Page 32 of 36
  38. 38. suffer 8 to 9dB rain attenuation under heavy rainfall while rainattenuation is very low at C-Band. Fading due to rain can hamper theconnectivity of satellite and therefore rain margin has to be kept forreliable connectivity. Rain margin is provided by operatingtransmitter at higher powers and by using larger size of the dishantenna (7.2m PDA).Figure shows schematic of uplink chain proposed to broadcastbouquet of 30 video programs in Doordarshan, Prasar Bharati,India. 30 video programs may either be down-linked from satellitesor taken from other sources like video tape recorders, video camerasetc. in digital format. These sources are fed to Router whose outputsare divided in three groups A, B and C. Each group contains 10 videosources multiplexed in a Multiplexer. These three multiplexedstreams are digitally (QPSK modulation) modulated individually at 70MHz Intermediate Frequency (IF). Each group is further doubly up-converted, first conversion at L-Band(950-1450 MHz) and secondconversion at Ku-Band (12-14 GHz). Groups A, B and C are up-converted to Ku-Band frequencies, (=13778 MHz), (=13891 MHz) and(=13973 MHz), respectively and are individually amplified throughKlystron High Power Amplifiers (KHPA). The three RF signals arecombined in RF combiner and then finally fed to 6.2m dish antennafor up-linking. Page 33 of 36
  39. 39. Fig. DTH Uplinking Setup• DOWN-LINK CHAIN LINKDown-Link or receiving chain of DTH signal is depicted in Fig.2. There Linkare 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 orhouse. RF waves (12.534GHz, 12.647GHz, 12.729 GHz) from satelliteare picked up by a feed converting it into electrical signal. The Page 34 of 36
  40. 40. electrical signal is amplified and further down converted to L-Band L(950-1450) signal. Feed and LNBC are now combined in single unit 1450)called LNBF. The L- -Band signal goes to indoor unit, consisting a set oor set-top box and television through coaxial cable. The set-top box or setIntegrated Receiver Decoder (IRD) down converts the L L-Band first IFsignal to 70 MHz second IF signal, perform digital demodulation, de- demultiplexing, decoding and finally gives audio/video output to TV for finallyviewing. Fig. Receiving Chain of DTH signal Page 35 of 36
  41. 41. ConclusionNow I have studied a lot about the television. One must have neverthought 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. Hereman and electronics work as if they are a family. So many processand lots of hard work, sincerity is required to just have a show or saya movie on air i.e. to be broadcasted. So many people are involved init. I really enjoyed of being part of it. The saying is really true that…“Tell me ,I may forgetTeach me, I may rememberBut involve me, and I have learn it” Page 36 of 36