SUMMARY
I have completed my training of 4 weeks from Doordarshan Kendra, Indore. There
I have learned practical knowledge. As, you all know Doordashan is a public
broadcaster of India. So all the things are related to signal transmission and
reception.
In Doordarshan there is a perfect balance between theory classes and practical
classes. In the 1st week they have arranged all the practical classes. They
showed us their studio, where they judge the picture quality of a signal. Then, we
moved to the transmitter section of Doordarshan from where all the signals are
transmitted to different centers of Doordarshan. And then we moved to the
receiver section of Doordarshan from where all the signals from different centers
are received. In Doordarshan we seen that there is a back-up arrangement for
every task. In theory classes they teach us the theoretical aspects of signal
transmission and reception.
My summer training at Doordarshan is very wonderful. The employees of
Doordarshan is very co-operative and humble. They are very experienced and
their experience can be seen in their body-language and teaching. In the last
day of our training they arranged motivational seminar for us and to bid all the
best for our future.
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INTRODUCTION:
Process of sending information to a distant place is called Broadcasting. Broadcasting
started in India in the year 1923. AIR was formed in the year 1936. 1 st T.V. station was
established in Delhi in 1959. T.V. was separated from AIR in 1976.
Means of Broadcasting in India:
1. Terrestrial
2. Satellite
3. Internet
Both AIR & DD make use both Terrestrial & Satellite mode of broadcasting.
Doordarshan is a Division of Prasar Bharati, a public service broadcaster nominated by
the Government of India. Doordarshan kendra serving an individual organization which
plays an important role in TVs cinema. It provides free to air channels DD-1, DD-NEWS
and many more. It originates the programs and telecast on the channel.
Doordarshan is one of the Largest broadcasting organization in the world in terms of
the infrastructure of studios and transmitters. Recently, it has also started Digital
Terrestrial Transmitters. On September 15 2009, Doordarshan celebrated its 50th
anniversary.
Doordarshan has contributed significantly towards Creation of awareness, acceleration
of socioeconomic change, promotion of national integration, & stimulation of scientific
temper in the country.Doordarshan Networks in India is divided into 5 zones.
Presently more than 90 % of the India population can receive Doordarshan (DD
National) programs through a network of nearly 1400 terrestrial transmitters & about 46
Doordarshan Studios produce TV programs today & about more than 75 % of India area
wise.
Doordarshan has a three-tier programs service –National, Regional & local.
30 Channels : This includes regional Language Satellite Channels ; State Network ,
International channel:- DD1, DD News, DD Bharti, DD Sports & DD Urdu.
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Company Profile:
Prasar Bharti is statutory autonomous body established under the Prasr Bharti act and
came into existence on 23/11/1997. It is the public service broadcaster of the country.
Doordarshan is the public television broadcaster of India and is a division of Prasar
Bharti , a public service broadcaster nominated by the government. It is one of the largest
broadcasting organizations of the world in terms of infrastructure of the studios and
transmitter.
Recently it has also started digital transmitters. On 15/09/2009 doordarshan celebrated
its 50th anniversary.
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Height penetration
Position
Channel
Reach ( No. of people )
1.
DD 1
233 Million
2.
DD Metro
133 Million
3.
Star Plus
54 Million
4.
Sony
41 Million
5.
Zee TV
36 Million
Regional language Satellite channels DD North.East, DD Bengali, DD Gujarati, DD
Kashmir, DD Malayam, DD Oriya, DD Rajasthani, DD Punjabi, DD Lock Sabha and DD
Gyandarshan.Not only in India It also wants to International Broadcasting. International
Channel- DD India, DD News, DD Sports, DD Bharti. DD-India is broadcast internationally
via satellite. It is available in 146 countries worldwide.
HISTORY:
Doordarshan, the national television service of India is devoted to public service
broadcasting. Doordarshan had a modest beginning with the experimental telecast starting
in Delhi on 15 September 1959 with a small transmitter and a make shift studio. The
regular daily transmission started in 1965 as a part of All India Radio. The television
service was extended to Bombay (now Mumbai) and Amritsar in 1972. Up until 1975, only
seven Indian cities had a television service and Doordarshan remained the sole provider of
television in India. Television services were separated from radio in 1976.
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Each office of All India Radio and Doordarshan were placed under the management of two
separate Director Generals in New Delhi. Finally Doordarshan as a National Broadcaster
came into existence.
National telecasts were introduced in 1982. In the same year, color TV was introduced in
the Indian market with the live telecast of the Independence Day speech by then Prime
Minister Indira Gandhi on 15 August 1982.
Followed by the 1982 Asian games which were held in Delhi. Now more than 90 percent
of the Indian population can receive Doordarshan (DD National) programs through a
network of nearly 1,400 terrestrial transmitters. There are about 46 Doordarshan studios
producing TV programs today.
DDK INDORE
Primary coverage area-65-70 kms radial
Type of cooling-liquid cooled
Cost of transmitter-Rs 1,10,87,854
Height of towers-150mtr
Year of erection-28/01/1985
Type of mast- steel self supported
Weight of structure-450 tonnes
Range of FM= 88Mhz – 110Mhz
For TV Signal < 800 Mhz
Exciter-ATV exciter (SH700)
Power Amplifier – Broadband
Cooling Pump - Type ZK610 R&S
Tower – 150M
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Television studio:
A television studio is an installation in which video productions take place, either for
the recording of live television to video tape, or for the acquisition of raw footage for
post-production. The design of a studio is similar to, and derived from, movie studios,
with a few amendments for the special requirements of television production. A
professional television studio generally has several rooms, which are kept separate for
noise and practicality reasons. These rooms are connected via intercom, and personnel
will be divided among these workplaces.
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TELEVISION TRANSMITTER
A television transmitter is a device which broadcasts an electromagnetic signal to
the television receivers. Television transmitters may be analog or digital An oversimplified
block diagram of a monochrome TV transmitter is shown in Fig. 1.4. The luminance signal
from the camera is amplified and synchronizing pulses added before feeding it to the
modulating amplifier. Synchronizing pulses are transmitted to keep the camera and picture
tube beams in step.
The allotted picture carrier frequency is generated by a crystal controlled oscillator. The
continuous wave (CW) sine wave output is given large amplification before feeding to the
power amplifier where its amplitude is made to vary (AM) in accordance with the
modulating signal received from the modulating amplifier. The modulated output is
combined (see Fig. 1.4) with the frequency modulated (FM) sound signal in the combining
network and then fed to the transmitting antenna for radiation.
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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 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.
 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.
 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 slant 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 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. (Since 625 lines are scanned at
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the rate of 25 Hz i.e. 25 cycles per second, the number of lines scanned in one second
is 625 multiplied by 25 which yield 15,625. So the horizontal frequency is 15,625 hertz
and hence each line takes 64 micro seconds).
Similarly there is vertical blanking period and 25 TV lines are blanked out 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 and the resolution
factor (also known as Kell factor).
 GREY SCALE
In black and white (monochrome) TV system all the colours appear as gray on a 10step gray scale chart. TV white corresponds to a reflectance of 60% and TV black 3 %
giving rise to a Contrast Ratio of 20:1 (Film can handle more than 30:1 and eye’s
capability is much more).
 BRIGHTNESS
Brightness reveals the average illumination of the reproduced image on the TV screen.
Brightness control in a TV set adjusts the voltage between grid and cathode of the
picture tube (Bias voltage).
 CONTRAST
Contrast is the relative difference between black and white parts of the reproduced
picture. In a TV set the contrast control adjusts the level of video signal fed to the
picture tube.
 VIDEO SIGNAL
Video is nothing but a sequence of picture .The image we see is maintained in our eye
for a 1/16 sec so if we see image at the rate more than 16 picture per sec our eyes
cannot recognize the difference and we see the continuous motion. In Tv cameras
image is converted in electrical signal using photo sensitive material.
Whole image is divided into many micro particle known as Pixels. These pixels small
enough so that our eyes cannot recognize pixel and we see continuous image ,thus at
any instant there are almost an infinite no. of pixel that needs to be converted in
electrical signal simultaneously for transmitting picture details. However this is not
practicable because it is no feasible to provide a separate path for each pixel in practice
this problem is solved by scanning method in which information is converted in one by
one pixel line by line and frame by frame.
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 COLOUR COMPOSITE VIDEO SIGNAL (CCVS)
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.
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).
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VISION MIXING AND SWITCHING
Unlike films, television media allows switching between different sources simultaneously
at the video switcher in Production control room operated by the Vision Mixer on the
direction of the program producer.
The producer directs the cameramen for proper shots on various cameras through
intercom and the vision mixer (also called VM engineer) switches shots from the
selected camera/cameras with split second accuracy, in close cooperation with the
producer.
The shots can be switched from one video source to another video source,
superimposed, cross faded, faded in or faded out electronically with actual switching
being done during the vertical intervals between the picture frames. Electronics special
effects are also used now days as a transition between the two sources.
The vision mixer provides for the following operational facilities for editing 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.
CAMERA CONTROL UNIT (CCU)
The television cameras which include camera head with its optical focusing
lens, pan and tilt head, video signal pre-amplifier view finder and other associated
electronic circuitry are mounted on cameras trolleys and operate inside the
studios.
The output of cameras is pre-amplified in the head and then connected to the
camera control unit (CCU) through long multi-core cable (35 to 40cores), or triax cable.
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COLOUR TEMPERATURE
One may wonder how the light is associated with colour. Consider a black body being
heated; you may observe the change in colour radiated by this body as the temperature
is increased.
The colour radiated by this body changes from reddish to blue and then to white as the
temperature is further increased. This is how the concept of relating colour with
temperature became popular. Colour temperature is measured in degree Kelvin i.e.,
(0°C +273).
It can be noted that as the temperature is increased, the following things happen:
1) Increase in maximum energy released
2) Shift in peak radiation to shorter wavelengths (Blue)
3) Colour of radiation is a function of temperature
Hence by measuring the energy content of the source over narrow bands at the red and
blue ends of the spectrum, the approximate colour temperature can be determined. The
entire color temperature meter is based on this principle.
SYNC PULSE GENERATOR (SPG)
It is essential that all the video sources as input to the switcher are in synchronism i.e.,
start and end of each line or all the frames of video sources is concurrent.
This requirement is ensured by the sync pulse generator (SPG). SPG consists of highly
stable crystal oscillator. Various pulses of standard width and frequency are derived
from this crystal electronically which form clock for the generation of video signal.
These pulses are fed to all the video generating equipment to achieve this objective of
synchronism. Because of its importance, SPG is normally duplicated for change over in
case of failure.
It provides the following outputs:
 Line drive
 Field drive
 Mixed blanking
 Mixed sync
 colour subcarrier
 A burst insertion pulse
 PAL phase Indent pulses
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ANTENNA:
“An antenna is any device that converts electronic signals to electromagnetic waves
(and vice versa)” effectively with minimum loss of signals as shown below
An antenna is used to radiate electromagnetic energy efficiently and in desired
directions. Antennas act as matching systems between sources of electromagnetic
energy and space. The goal in using antennas is to optimize this matching.
Properties of antennas:
1) Field intensity for various directions (antenna pattern).
2) Total power radiated when the antenna is excited by a current or voltage of known
intensity (or Power Flux Density).
3) Radiation efficiency which is the ratio of power radiated to the total power (Radiation
Pattern).
4) The input impedance of the antenna for maximum power transfer (matching).
5) The bandwidth of the antenna or range of frequencies over which the above
properties are nearly constant.
Antennas can also be classified as electrical devices which convert electric currents into
radio waves and vice-versa. They are generally used with a radio transmitter and
receiver. They are broadly classified in two categories:
 Transmitting antennas
 Receiving antennas
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a) Power amplifier is transmitter as PT watts. Feeder connects to this antenna and the
new power reaching to this antenna will be PT – Losses at the feeder. Further loss is
seen in the antenna and thus the radiated power is shown as PRAD.
b) Power PRec is transferred to the antenna from a passing radio wave. Again the
losses in the antenna will reduce the power at the feeder. Giving only PIN to the feeder.
Receiving feeder looses further reduce the power to PR.
ANTENNA FUNDAMENTALS
Antennas for wireless devices are as varied as the devices themselves. Possibilities
include external versus embedded, printed on flex printed-circuit boards (PCBs), formed
from thin sheet metal, created on the product housing using sprayed-on conductive
paint, embedded in materials with a high-dielectric constant for size reduction, and so
forth. Regardless of the type and configuration of the antenna, performance can be
characterized by the same metrics:







Radiation Pattern
Directivity
Input impedence
Antenna efficiency
Antenna gain
Polarization
Bandwidth
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RADIATION PATTERN
Radiation pattern shows that the gain of an antenna varies with direction. At a fixed
distance r, gain will vary with θ and Φ and is written as G (θ, Φ) as shown in figure.The
Radiation Pattern is the gain normalized at a maximum value.
Let the maximum gain be G. thus Radiation Pattern is denoted as g is given by:
g (θ, Φ) = G(θ, Φ) / G
The Radiation Pattern gives directional properties of the antenna normalized to the
maximum value (maximum gain). A three-dimensional representation of this shows a
lobe.
Radiation Pattern
Figure shows the following:
• HPBW: The half power beam width (HPBW) can be defined as the angle subtended by
the half power points of the main lobe.
• Main Lobe: This is the radiation lobe containing the direction of maximum radiation.
• Minor Lobe: All the lobes other then the main lobe are called the minor lobes. These
lobes represent the radiation in undesired directions. The level of minor lobes is usually
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expressed as a ratio of the power density in the lobe in question to that of the major
lobe. This ratio is called as the side lobe level (expressed in decibels).
• Back Lobe: This is the minor lobe diametrically opposite the main lobe.
• Side Lobes: These are the minor lobes adjacent to the main lobe and are separated by
various nulls. Side lobes are generally the largest among the minor lobes.
In most wireless systems, minor lobes are undesired. Hence a good antenna design
should minimize the minor lobes.
DIRECTIVITY
The directivity of an antenna has been defined as “the ratio of the radiation intensity in a
given direction from the antenna to the radiation intensity averaged over all directions”.
In other words, the directivity of a non isotropic source is equal to the ratio of its
radiation intensity in a given direction, over that of an isotropic source.
Where D is the directivity of the antenna
U is the radiation intensity of the antenna
Ui is the radiation intensity of an isotropic source
P is the total power radiated
INPUT IMPEDANCE
The input impedance of an antenna is defined as “the impedance presented by an
antenna at its terminals or the ratio of the voltage to the current at the pair of terminals
or the ratio of the appropriate components of the electric to magnetic fields at a point”.
Hence the impedance of the antenna can be written as:
Zin = Rin + jXin
Where Zin is the antenna impedance at the terminals
Rin is the antenna resistance at the terminals
Xin is the antenna reactance at the terminals
The imaginary part, Xin of the input impedance represents the power stored in the near
field of the antenna. The resistive part, Rin of the input impedance consists of two
components, the radiation resistance Rr and the loss resistance Rl .
The power associated with the radiation resistance is the power actually radiated by the
antenna, while the power dissipated in the loss resistance is lost as heat in the antenna
itself due to dielectric or conducting losses.
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ANTENNA EFFICIENCY
The antenna efficiency is a parameter which takes into account the amount of losses at
the terminals of the antenna and within the structure of the antenna. These losses are
given as:
• Reflections because of mismatch between the transmitter and the antenna.
• I 2R losses (conduction and dielectric).
Hence the total antenna efficiency can be written as:
et=ereced
where e t = total antenna efficiency
= (1− Γ2 ) e r = reflection (mismatch) efficiency
e c = conduction efficiency
e d = dielectric efficiency
ANTENNA GAIN
Antenna gain is a parameter which is closely related to the directivity of the antenna.
We know that the directivity is how much an antenna concentrates energy in one
direction in preference to radiation in other directions.
Hence, if the antenna is 100% efficient, then the directivity would be equal to the
antenna gain and the antenna would be an isotropic radiator.
Since all antennas will radiate more in some direction that in others, therefore the gain
is the amount of power that can be achieved in one direction at the expense of the
power lost in the others.
The gain is always related to the main lobe and is specified in the direction of maximum
radiation unless indicated.
It is given as:
G(θ ,φ ) e cd = D(θ ,φ )
(dBi)
POLARIZATION
Polarization of a radiated wave is defined as “that property of an electromagnetic wave
describing the time varying direction and relative magnitude of the electric field vector”.
The polarization of an antenna refers to the polarization of the electric field vector of the
radiated wave.
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In other words, the position and direction of the electric field with reference to the earth’s
surface or ground determines the wave polarization. The most common types of
polarization include the linear (horizontal or vertical) and circular (right hand polarization
or the left hand polarization).
If the path of the electric field vector is back and forth along a line, it is said to be linearly
polarized. Above figure shows a linearly polarized wave.
In a circularly polarized wave, the electric field vector remains constant in length but
rotates around in a circular path.
A left hand circular polarized wave is one in which the wave rotates counterclockwise
whereas right hand circular polarized wave exhibits clockwise motion as shown in
Figure below,
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BANDWIDTH
The bandwidth of an antenna is defined as “the range of usable frequencies within
which the performance of the antenna, with respect to some characteristic, conforms to
a specified standard.” The bandwidth can be the range of frequencies on either side of
the center frequency where the antenna characteristics like input impedance, radiation
pattern, beam width, polarization, side lobe level or gain, are close to those values
which have been obtained at the center frequency.
The bandwidth of a broadband antenna can be defined as the ratio of the upper to lower
frequencies of acceptable operation. The bandwidth of a narrowband antenna can be
defined as the percentage of the frequency difference over the center frequency.
According to these definitions can be written in terms of equations as follows:
Where,
f H= upper frequency
f L= lower frequency
f C= center frequency
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CONCLUSION
Doordarshan, the national television service of India, is devoted to public service
broadcasting.It is one of the largest terrestrial networks in the world. In my Industrial
training at Doordarshan Kendra, Indore, I have gained useful knowledge which will surely
be of great help in future.
This training gave me an opportunity to learn the practical aspects of the knowledge of my
field of interest, Electronics and communication
I have learned how science and engineering can interact in useful ways and how
remarkable research can occur even when it is ‘profit driven’; at DD, while deadlines and
budgets are important, creativity is not limited and true innovation occurs.I was lucky
enough to work with a group of enthusiastic and communicative people, who for whatever
reason share in enjoying what they are doing; the atmosphere at DD is unique and hope
that it says that way.
It has been a unique opportunity and one that I will not soon forget; I am looking forward to
continuing work there as a thesis student. My time there has been eye opening and I
thoroughly recommend the experience to any other student who is thinking of applying.
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