report doordarshan

7/30/2019 Report doordarshan

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Doordarshan Lucknow

Summer Training ReportYear 2012

Under the guidance of: Submitted by:Sushant Shankar

Mr.R.Naithani B.Tech.4

th

Year(ECE)


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Declaration

I hereby declare that work entitled summer training report, submitted towards

completion of summer training after 3rd year of B.Tech(ECE) at Institute of

Engineering and Technology, Dr. Ram Manohar Lohiya Avadh University

Faizabad, comprises of my original work pursued under the guidance of

Mr. R.Naithani.

The results embodied in this report have not been submitted to any other

Institute or University for any award.

Sushant Shankar

B.Tech. 4th year

Branch-E.C.E.


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Contents

1) Preface 1

2) Introduction of Doordarshan Lucknow 2

3)Fundamentals of monochromes and Colour TV System 3

4)Colour Composite Video Signal (CCVS) 5

5)TV camera 6

6) TV Lightning 11

7) Microphone 15

8) Vision Mixing 27

9) Television Transmission 33

10) TV Transmitter Antenna System 35

11) OB van 37

12) Earth station 38

13) DTH (Direct-To-Home) 43


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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 Bhopal. This report contains a

detailed study of Doordarshan Kendra Bhopal.

There are 3 division here :-

1) Studio 2)Transmitter

3)Earth Station

1) Studio -

Doordarshan is a leading broadcasting service provider in india. DD

Bhopal is full-flathead broadcast set up

2) 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.

3) Earth Station -

The main function of earth station is to make contact with satellite or

communicate with it. The signals from other transmitter are down linked here.

Also the signals here are uplinked to send it to larger distance.


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Introduction of Doordarshan Bhopal.

The studio of Doordarshan Kendra Bhopal was commissioned on 20th October 1992. It started as a

Regional Kendra and has ever since played a major role as a Public Service Broadcaster for viewers of

the state. It has enormously enriched the ethos of this land while projecting and promoting the culturalheritage of the State. With the passage of time, programme activities of the Kendra have witnessed

manifold changes through which basic objectives of Doordarshan viz. INFORMATION, EDUCATION,

AND ENTERTAINMENT have been provided to the masses. Various programme formats like live phone

in programme, serials, telefilms, variety show, concerts poetic symposiums, quiz features, multi

segmented magazine programmes and programmes for specific target audience like children, youth,

women and physically challenged people have been adopted.

The Kendra has produced special programme on specific themes like socio cultural heritage,

environmental awareness, family welfare, health care, population control, legal awareness, promotion of

tourism, promotion of sports, public grievances and promotion of national integration and communalharmony.

In order to come up to the ever increasing expectations of the public, many reforms have been adopted in

the overall programme pattern through which aspirations of different sections of the society have been

taken care of. The quantum of in-house production has been increased which has raised opportunities for

different scholars, artists and other talented persons to get associated with programmes of their choice

through which their talent is ventilated. Introduction of interactive formats with suitable treatment has

added color to our transmission. Quick response and spontaneous feed back from the public through live

phone in programmes has enhanced access of the viewers which has gone a long way in establishing

credibility of the Kendra. Efforts are continuously made to cast our net as far and wide as possible within

the constraints to net in fresh talent. Instead of restricting our programme activity to the four walls ofstudio, the Kendra has tried to take the TV closer to the door steps of viewers. Various ENG and OB

teams have recorded programmes on natural locations in different formats.

Although the main language of transmission is Hindi, yet programmes in other dialects which are spoken

in the different parts of MP viz. Bagheli, Bundeli, Nimari & Malvi are also included in our telecasts.

FUNDAMENTALS OF MONOCHROME AND

COLOUR TV SYSTEM


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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 andshade 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 andvertical 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 Hert.

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.


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Resolution -The capability of the system to resolve maximum number of pictureelements 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 asgray 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 eyes capability is

much more).

Brightness - Brightness reveals the average illumination of the reproducedimage on the TV screen. Brightness control in a TV set adjusts the voltage between

grid and cathode of the picture tube (Bias voltage).

ContrastContrast 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 DistanceOptimum viewing distance from TV set is about 4 to 8 times the height of the TV

screen. While viewing TV screen one has to ensure that no direct light falls on the

TV screen.


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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 seecontinuous

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 inpractice this problem is solved by scanning method in which information is

converted in one by one pixel line by line and frame by frame .

Colour Composite Video Signal is formed with Video, sync and blanking signals.

The level is standardized to 1.0 V peak to peak (0.7 volts of Video and 0.3 volts

of sync pulse). The

Colour Composite Video Signal (CCVS) has been shown in 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 thefrequency is Zero). In CCIR system B the highest frequency that can be transmitted is5 MHz even though the TV signal can contain much higher frequency components. (Infilm the reproduction of frequencies is much higher than 5 MHz and hence clarity issuperior to TV system.) long shots carry higher frequency components than mid closeups and close ups. Hence in TV productions long shots are kept to a minimum. In factTV is a medium of close ups and mid close ups.


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DC Component of video signal and DC restoration

A TV signal is a continuously varying amplitude signal as the picture elements give riseto varying level which depends on how much of incident light the picture elements canreflect and transmit the light signal to the TV camera. Hence the video signal has anaverage value i.e. a DC component corresponding to the average brightness of thescene to scene.

RF Transmission of Vision and Sound SignalsTV 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 TransmissionIn 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.


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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 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.


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The Colour Television

It is possible to obtain any desired colour by mixing three primary colours i.e. Red,

Blue and green

in a suitable proportion. The retina of human eye consists of very large number of

light- sensitive

cells. These are of two types, rods and cones. Rods are sensitive only to the intensity

of the incident

light and cones are responsible for normal colour vision. The small range of

frequencies to which

the human eye is responsive is known as visible spectrum. This visible spectrum is

from 780 mm(Red) to 380 mm(Violet).

Additive Colour MixingThe figure shows the effect of projecting red, green, blue beams of light so that theyoverlap

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

TV Camera

INTRODUCTION:A TV Camera consists of three sections.

a) A Camera lens & Optics: To form opticalimage on the face plate of a pick up device


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b) A transducer or pick up device: To convert optical image into a electrical signalc) Electronics: To process output of a transducer to get a CCVS signal

Camera sensors - CCD basicsThe CCD is a solid-state device using special integrated circuitry technology, hence it is oftenreferred to as a chip camera. The complete CCD sensor or chip has at least 450 000 pictureelements or pixels, each pixel being basically an isolated (insulated) photodiode. Theaction of thelight on each pixel is to cause electrons to be released which are held by the actionof a positivevoltage.

The Charge held under electrode can be moved to electrode by changing the potential on thesecond electrodes. The electrons (negative charges) follow the most positiveattraction. A repeat of this process would move the charges to next electrode, hencecharge-coupled device. A system of transfer clock pulses is used to move the chargesin 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 inch to 2/3inch

Frame transfer (FT)

Frame transfer was the first of the CCDs to be developed and it consists of twoidentical areas, animaging area and a storage area. The imaging area is the image plane for the focusedoptical image,the storage area is masked from any light. The electrical charge image is built upduring one field

period, and during field blanking this charge is moved rapidly into the storage area. Amechanicalshutter is used during field blanking to avoid contamination of the electrical chargesduring theirtransfer to the storage area. The storage area is emptied line by line into a read- outregisterwhere, during line -time, one line of pixel information is clocked through theregister to produce the video signal.

Interline transfer (IT)Interline transfer CCDs were developed to avoid the need for a mechanical shutter

The storage cellis placed adjacent to the pick-up pixel; during field blanking the charge generated bythe pixel isshifted sideways into the storage cell. The read-out process is similar to the frametransfer device,with the storage elements being clocked through the vertical shift register at fieldrate into thehorizontal shift register, then the charges read out at line rate. Earlier forms of ITdevices sufferedfrom severe vertical smear, which produced a vertical line running through ahighlight. This wascaused by excessive highlights penetrating deeply into the semiconductor material,

leaking directly into the vertical shift register. Later IT devices have improved thetechnology 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 toovercome the problem of vertical smear. As its name suggests, it is a combination ofboth types .


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The FIT sensor has a short-term storage element adjacent to each pixel (as IT) and aduplicatedstorage area (as FT). During field blanking the charges are moved from the pixels intothe adjacentshort-term storage element and then moved at 60 times field frequency into thestorage area. Thisrapid moving of the charge away from the vulnerable imaging area overcomes thevertical smearproblem.

Optical block for Video Cameras

Development in CCD technology has seen the introduction of:

The hole accumulated Diode (HAD) sensor which enabled up to 750pixels/line, with

increased sensitivity and a reduction in vertical smear;

The hyper HAD sensor, which included a microlens on each pixel to collectthe 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 hasresulted in at least

half an -stop gain in sensitivity; in some cases a full -stop of extra sensitivityhas been

realized.

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.

Greenchannel 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


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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.

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 ofelectromagnetic radiation with a visible spectrum from red to violet i.e., wavelength from 700 nm to 380 nm respectively. However to effectively use thehardware and software connected with lighting it is important to know more aboutthis energy.

Light Source: Any light source has a Luminance intensity (I) which is measured inCandelas. 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 photoniccurve and is measured inLumens. One Lumen is the luminous flux emitted by a point source of 1 Candela.


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Illumination (E): It is a Luminous Flux incident onto a surface. It is measured inLUMENS/m2, which is also called as LUX. A point source of 1 candela at a uniformdistance 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 inApostilbs . A surface which reflects a total flux of 1 lumen/m2 has a luminance of 1Aposilbs .Elementary theory of light also says that:

Colour temperature:

One may wonder, how the light is associated with colour . Consider a black bodybeing heated;you may observe the change in colour radiated by this body as the temperature isincreased.

The colour radiated by this body changes from reddish to blue and then to whiteas thetemperature is further increased. This is how the concept of relating colour withtemperaturebecame popular. Colour temperature is measured in degree Kelvin i.e., 0C +273) .

The tablebelow gives idea about the kind of radiation from different kinds of lamps in terms

of colourtemperature.

a) Standard candle 19300Kb) Fluorescent Lamps range 3000-6500oKc) HMI lamp 5600+- 400oK(H=Hg, M=Medium arc, I=Metal Iodide}d) CSI (Compact Source Iodide) 4000+- 400oKe) CID (Compact Iodide Daylight) 5500+-400o Colour TV Display,white 6500oKf) Monochrome TV 9300oK

g) Blue sky 12000 - 18000oKh) Tungsten Halogen 3200oK

i) Average summer sunlight (10am -3pm) 5500oKIt 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


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Hence by measuring the energy content of the source over narrow bands at thered and blue ends of the spectrum ,the approximate colour temperature can bedetermined. 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 colourtemperature for cameras while shooting with different colour temperature. These filters

change the colour temperature at the cost of reduction in light transmission. Colourtemperature filters are also introduced in the optical path of cameras to facilitate cameraelectronics to do the white balance without loading the amplifier chain. Cameraselectronics is generally optimized for a colour temperature of 3200K, hence it usesreddish filter whileshooting at higher colour temperatures.Generally it is normal to correct daylight to produce tungsten quality light, becauseit is usually easier to do and saves lot of power, otherwise blue filters are going toreduce lot of light thus requiring the use of higher wattage lamps.. However, whenthe amount of tungsten to becorrected 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 typesof filter :-i) One which is orange in colour and converts Daylight to

Tungsten Light. ii) One which is blue in colour and convertsTungsten to Daylight.

Day Light:The sun does not changes its colour temperature during the day it is only itsappearance from a fixed point on earth. It is because the sunlight gets scatteredbecause of the medium , shorter wavelengths like blue gets more effected.Certain situations like, sunrise and sunset causes the light to be more yellow thanmidday, because the light has to travel the long distance so acareful note should be made of the Transmission factor of each of the filters. Oftenacompromise has to be reached in terms of correction and light loss.

NEUTRAL DENSITY FILTERSIn addition to colour temperature correction sometimes it may be necessary toreduce theintensity of daylight at an interior location. Neutral density filters available toattenuate the

light are of:0.3 Density which has a transmission of 50%= 6dB=1 f stop0.6 Density which has a transmission of 25%= 9dB=2 f stop0.9 Density which has a transmission of 13%= 12dB=3f stop

COMBINATION OF CTC FILTERS AND NEUTRALDENSITY FILTERS:Single filters exist which are a combination of full colour temperature orangeand neutral density as follows:-Full Orange + 0.3 N.D. with a transmissionof 50%Full Orange + 0.6 N.D. with a transmissionof 38%

The HMI light source has a colour temperature of about 60000K and can be used withexterior

daylight without the need for a colour temperature correction filter.


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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


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- Kickkar light, Extra light on shadow side of the face at an angle behind and tothe side of theactor- 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 givethe desiredeffect. In order to assist in setting up a particular lighting plon, a consoleshould 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.

DIMMERSThree basic methods for dimming are :-1. Resistance

This is the simplest and cheapest form of dimmer. It consists of a wire woundresistor 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 withthe

lamp.

LIGHTING THE SET FOR DRAMA:--Openings such as windows within a setshould 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:

1. If there is a choice in the direction of the 'sun'(Key) take the shortest routeinside the set to a wall, and if possible throw the shadow of window bars onto adoor - 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 projectedonto a wall to produce a suitable window effect.4. Roof and Ceiling Pieces - if they make lighting impossible, check if they can beremoved at the planning state. Light any ceiling pieces from outside, use a softsource at ground level. If theceiling has plaster moulding or ornamentation, a hard source may be used.Indoor night time:


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- The outside of the window should be dark, except for a possible dim skyline if theroom is well above adjacent streets, or lit by an outside practical lamp i.e. streetlighting.- 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 hedirection of lighting in the set compared to that used for day.


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- 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 arenormally achieved by back lighting to give a more softer, romantic mood than would be achieved than afrontal key.

In colour, to obtain a night effect, blue cinemoid is used over the luminaries. This gives a stylisedeffect. An alternative is to use much more localised lighting than for daylight and light only the

artists and odd parts of the set.

MICROPHONES

IntroductionMicrophone plays a very important role in the art of sound broadcasting. It is a device whichconverts accoustical energy into electrical energy. In the professional broadcasting fieldmicrophones have primarily to be capable of giving the highest fidality ofreproduction over audio bandwidth.

Microphone ClassificationDepending on the relationship between the output voltage from a microphoneand the sound pressure on it, the microphones can be divided into two basicgroups.

Pressure Operated TypeIn such microphones only one side of the diaphragm is exposed to the sound wave. The outputvoltage is proportional to the sound pressure on the exposed face of the diaphragmwith respect tothe constant pressure on the other face. Moving coil, carbon, crystal and condensermicrophonesare mostly of this type. In their basic forms, the pressure operated microphones are


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omni-directional.

Velocity or Pressure Gradiant TypeIn these microphones both sides of the diaphragm are exposed to the sound wave.Thus the outputvoltage is proportional to the instantaneous difference in pressure on the two sides ofthediaphragm. Ribbon microphone belongs to this category and its polar diagram isfigure of eight.

Types of MicrophonesThere are many types of microphones. But only the most common types used in

broadcasting have been described here.Dynamic or Moving Coil MicrophoneThis is common broadcast quality microphone which is rugged and can becarried to outsidebroadcast/recording etc. It consists of a strong permanent magnet whose poleextensions form aradial field within a round narrow gap. A moving coil is supported within this gapand a domeshaped diaphragm usually of aluminium foil is attached to the coil. The coil isconnected to amicrophone transformer whose secondary has sometimes tapings to select properimpedance formatching. With sound pressure changes, the diaphragm and coil move in themagnetic field,therefore, emf is induced in the speech coil, which is proportional to the incomingsound. Theprimary impedance of the matching transformer is generally high (5 to 6 times ofthe speech coilimpedance so that low frequencies are not lost and rising impedance frequencycharacteristic isavoided as best as possible. The resonant frequency is generally damped with specialarrangementsof absorption in acoustic cavity, Bass/boost arrangements are provided by an

equalising tubeconnecting the rear side of diaphragm i.e. inside of microphone with the atmosphere.The diameterand length of the tube is critically adjusted for achieving good frequency response.

Ribbon/ Velocity Microphone


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Corrugated aluminium foil about 0.1 mm thick forms a ribbon which is suspendedwithin twoinsulated supports. The ribbon is placed within the extended poles of a strong horseshoe magnet.The ribbon moves due to the difference in pressure (at right angles to its surface) i.e.from the frontor rear of the mike. There exists the maximum pressure difference between thefront and rear of ribbon because of maximum path difference. The sound does not develop anypressure gradientwhen it comes from the sides of the microphones because there is no path difference.

It reaches thefront and rear of ribbon at the same time, hence no movement of ribbon. Thus, thismicrophone isbi-directional and follows figure of eight directivity pattern with no pick up fromsides. Such amicrophone has a clarity filter. This is a series resonant circuit at low frequenciesacross theprimary of microphone transformer. When switched to the Talk or Voice position,the responseis modified cutting down low frequencies by about 8 dB at 50 Hz. This filter shouldtherefore not bein circuit during music performances. All the other types of microphones arepressure operatedwhereas ribbon mike operates on pressure gradient which results in the change invelocity of theribbon. Thus it is also called the Velocity microphone. This microphone is very goodfor balancingof programmes. In case of Orchestra, instruments with strong output are positionedtowards thedead side and week voices or instruments are arranged on the front and rear ofthe mike. Thedistance and location with respect to microphone are considered against loudnessof voice or

musical instrument during balancing. Ribbon Microphone Output MagnetsCorrugated ribbonTransformer N S

VISION MIXING


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IntroductionVision mixing is a process of creating composite pictures from varioussources. 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 thevision mixers.


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MixingTwo input sources are mixed in proportion in a summing amplifier asdecided by the position of control fader. Two extreme position of the fadergives either of the sources at the output. Middle of the fader gives mixedoutput of the two sources; control to the summing amplifier is derived fromthe fader.

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

KeyIn the Key position between two sources i.e. foreground (FG) and

background (BG) the

control derived from one of the source itself (overlay), or by the third source(external

key). This keying signal can be generated either by the luminance, Hue or

chrominance of

the source input. The keyed portion can be filled with the same or with matte

or external

source. Matte means internally generated BG with choice of colors from the

vision mixer

itself.

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. Usingsuch 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.


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DesignAll the TV transmitters have the same basic design. They consist of an exciterfollowed by power amplifiers which boost the exciter power to the required level.

ExciterThe exciter stage determines the quality of a transmitter. It contains pre-correctorunits both atbase band as well as at IF stage, so that after passing through all subsequenttransmitter stages, anacceptable signal is available. Since the number and type of amplifier stages, maydiffer according tothe required output power, the characteristics of the pre-correction circuits can bevaried over awide range.

Vision and Sound Signal AmplificationIn HPTs the vision and sound carriers can be generated, modulated and amplifiedseparately and then combined in the diplexer at the transmitter output.In LPTs, on the other hand, sound and vision are modulated separately but amplifiedjointly. This is common vision and aural amplification.A special group delay equalization circuit is needed in the first case because of errorscaused by TV diplexer. In the second case the intermodulation products are moreprominent 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 requiresfewer amplifierstages.

IF ModulationIt has following advantages

Ease of correcting distortions

Ease in Vestigial side band shaping

IF modulation is available easily and economically

Power Amplifier StagesIn BEL mark I & II transmitters three valve stages (BEL 450 CX, BEL 4500 CX and BEL15000 CX)are used in vision transmitter chain and two valves (BEL 450 CX and BEL 4500 CX) inauraltransmitter chain. In BEL mark III transmitter only two valve stages (BEL 4500 CX andBEL 15000CX) are used in vision transmitter chain. Aural transmitter chain is fully solid state inMark III

transmitter.

Constant Impedance Notch Diplexer (CIND)Vision and Aural transmitters outputs are combined in CIN diplexer. Combined power isfed to main feeder lines through a T-transformer.


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BEL 10 kW TV TRANSMITTER (MARK-II)

Block Diagram of BEL 10kW TV Transmitter (Mark-II)

TRANSMITTER CONTROL SYSTEMThe transmitter control unit performs the task of transmitter interlocking and control. Also itsupports operation from control console. The XTR control unit (TCU) has twoindependent system

viz.

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


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Functions performed by MCS (Main Control System)- XTR control

- Interlocking

- RF monitoring- Supporting operation from control console

- Three second logic for protection against sudden fluctuation.

- Thermal protection for 1 kW and 10 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/OInterlock 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.

TV TRANSMITTERANTENNA SYSTEM


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AntennaSystemis thatpart ofthe

Broadcasting Network which accepts RF Energy fromtransmitter and launches electromagnetic waves in space. The polarization of theradiation asadopted by Doordarshan is linear horizontal. The system is installed on asupporting tower andconsists of antenna panels, power dividers, baluns, branch feeder cable, junctionboxes and main

feeder cables. Dipole antenna elements, in one or the other form are common at VHFfrequencieswhere as slot antennae are mostly used at UHF frequencies. Omni directionalradiation pattern isobtained by arranging the dipoles in the form of turnstile and exciting the same inquadraturephase. Desired gain is obtained by stacking the dipoles in vertical plane. As aresult of stacking,most of the RF energy is directed in the horizontal plane. Radiation in vertical plane isminimized.The installed

Antenna system should fulfill the following requirements :


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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 theplanned area of interest. The radiation pattern should be omni directional if thelocation of the transmitting station is at the center of the service area and directionalone, if the location is otherwise.c) It should offer proper impedance to the main feeder cable and thereby to thetransmitter so that optimum RF energy is transferred into space. Impedance mismatchresults into reflection of power and formation of standing waves. The standard RFimpedance at VHF/UHF is 50 ohms.

Outdoor Broadcasting van

O B Van (Outdoor Broadcasting van )- OB van is used for live broadcastinglike 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


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Inner View of OB van


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Inner View of OB van

Earth Station

SATELLITE COMMUNICATIONSatellite Communication is the outcome of the desire of man to achieve the concept of

global village. Penetration of frequencies beyond 30 Mega Hertz through 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.Clarkes 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


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STATSIONAR, GORIZONT, Russian Satellites

Architecture of a Satellite Communication System

The Space SegmentThe space segment contains the Satellite and all terrestrial facilities for the controland monitoringof the Satellite. This includes the tracking, telemetry and command stations (TT&C)together withthe Satellite control centre where all the operations associated with station-keepingand checking

the vital functions of the satellite are performed. In our case it is Master ControlFacility (MCF) atHassan.

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.


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The Ground SegmentThe ground segment consists of all the earth stations ; these are most often

connected to the endusers equipment by a terrestrial network or, in the case of

small stations (Very Small Aperture Terminal, VSAT), directly connected to the end-users 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.

Space Geometry

Types of OrbitThe orbit is the trajectory followed by the satellite in equilibrium between twoopposing forces.These are the force of attraction, due to the earths gravitation, directed towards thecentre of theearth and the centrifugal force associated with the curvature of the satellitestrajectory. Thetrajectory is within a plane and shaped as an ellipse with a maximum extension at theapogee and aminimum at the perigee. The satellite moves more slowly in its trajectory as thedistance from theearth increases .

Most favourable Orbits

Elliptical orbits inclined at an angle of 64o with respect to the equatorial plane. Thisorbit enables the satellite to cover regions of high latitude for a large fraction of theorbital period as it passes to the apogee. This type of orbit has been adopted by


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the USSR for the satellites of the MOLNYA system with a period of 12 hours. Pleasenote that the satellite remains above the regions located under the apogee for aperiod of the order of 8 hours. Continuous coverage can be ensured with threephased 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 typeof orbit guarantees that the satellite will pass over every region of the earth. Severalsystems with world wide coverage using constellations of satellite carries in lowaltitude circular orbits are for e.g. IRIDIUM, GLOBAL STAR, ODYSSEY, ARIES, LEOSAT,STARNET, etc.

Circular orbitswith zero inclination (Equatorial orbits). The most popular is the geo stationarysatellite orbits ; the satellite orbits around the earth at an altitude of 35786 km, and inthe same direction as the earth. The period is equal to that of the rotation of theearth and in the same direction. The satellite thus appears as a point fixed in the skyand ensures continuous operation as a radio relay in real time for the area of visibilityof the satellite (43% of the earths surface).

Factors deciding the selection of OrbitThe choice of orbit depends on the nature of the mission, the acceptableinterference 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.

InterferenceThe performance of launchers

TVRO System

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


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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)andenergy dispersal signal (25 Hz). After modulation (70 MHz) and upconversion (6 GHz)the carrier is amplified and uplinked through Solid Parabolic Dish Antenna (PDA). Downlink 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.

Satellite TransponderAs shown in fig, the uplinked signal (6 GHz) at satellite is received, amplified and downconverted to4 GHz band and sent back through filter and power amplifier (TWT). The localoscillator frequency of down converter is 2225 MHz for C band and Ex-C bandtransponders.

Block diagram of Satellite Transponder


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Receiving Satellite SignalFor 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

Azimuth and Elevation

For receiving a satisfactory signal from the satellite the dish antenna should bepointed towards the satellite accurately. For that we need to know the azimuth andelevation of a particular satellite from our place. The azimuth and elevation areangles which specify the direction of a satellite from a point on the earth's surface. Inlayman terms the azimuth is the east west movement and the elevation can bedefined as the north south movement of the dish. Both the azimuth and elevation of adish can be affected by three factors for geo-stationary satellites.

They are1. The longitude of the satellite.


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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 UnitsThe indoor unit contains two units.They are :1. System unit

2. Satellite Receiver Unit

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


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frequency correction

through a low pass filter. Thus the VCO works in a phase locked loop mode.

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. Satellitebroadcasting, 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 alevel 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 highpowered 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.


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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), Setup Box (Integrated Receiver Decoder, IRD) with CAS (Conditional Access

System). A bouquet of 40 to 50 video programs can simultaneously be received in DTH

mode.

UPLINK CHAIN


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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 dishantenna 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-Bandtransmission 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 inDoordarshan, 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.


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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).

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.


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report doordarshan

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