DECLARTION
I hereby declare that work entitled "summer training report" submitted towards completion of
summer training after 2nd year B.tech(E.C.E) at school of engineering and technology, ITM
UNIVERSITY GWALIOR , comprises of my original work pursed under the guidance of
The results embodied in this report have not been submitted to any other institute or university
for any award.
Tribhuwan Bhatt
B.tech. 2nd year
Branch:- E.C.E
1
CERTIFICATE
This is to certify that Mr. Tribhuwan Bhatt , a candidate of school of engineering and
technology , ITM UNIVERSITY GWALIOR completed 4 week vocational training program at
Doordarshan Gwalior under my guidance and directions.
Signature of guide
Mr. H.K Verma
2
ACKNOWLEDGEMENT
"It is not possible to prepare a summer training report without the assistance and
encouragement of other people. This one is certainly no exception."
On the very outset of this report, I would like to extend my sincere and heartfelt obligation
toward all the personage who have helped me in this endeavor.
Without their active guidance, help ,cooperation and encouragement , I would not have made
headway in the project.
First and foremost , I would like to express my sincere gratitude to my project guide
Mr.
Verma.
I was prevail edged a sustained enthusiastic involved interest from his side. This is fuelled may
enthusiasm even further and encouraged me boldly step into what was the totally dark and
unexplored expanse before me. He always fuelled my thoughts to think broad and out of the
box.
I would like to thank Mr.
Verma (Head vocational training) to given me a chance to do this
training and the stuff member for motivation guidance and support throughout the training.
"Thanking You "
3
TABLE OF CONTENTS
1) Preface
01
2) Introduction of Doordarshan Gwalior
02
3) Fundamentals of Monochrome & colour TV systems
03
4) Colour Composite Video Signal (CCVS)
05
5) TV Camera
08
6) TV Lighting
12
7) Microphone
16
8) Principle of Video tape Recording
18
9) Vision Mixing
19
10) 3-D GRAPHICS
23
11) Television Transmission
25
12) TV Transmitter Antenna Systems
29
13) OV VAN
31
14) DTH (Direct-To-Home)
32
15) Future scope
34
16) Conclusion
35
4
PREFACE
Training is important phase of student life. During these period students gets theoretical as well
as practical knowledge of the subject. Training also impresses student overall approach his to
life and impress his personality and confidence.
Our training was in Doordarshan kendra Gwalior.
This report contains a detail study of Doordarshan kendra Gwalior.
There are two divisions in Gwalior:-
 Studio
 Transmitter
1) Studio:Doordarshan is leading broadcasting service provider in India. DD Gwalior fullflathead broadcast setup. Many serial & program are being made here like
etc Recorded in studio.
2) Transmitter:Here is 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 done here .
5
INTRODUCTION OF DOORDARSHAN
GWALIOR
Doordarshan Kendra, Gwalior foundation stone laid by Hon’ble Madhav Raw Scindia
(Member of Parliament) , Hon’ble K.P Singh (DEO Union Ministry of State Information and
broadcasting ) preceded over the function Date. 16 June 1994.
Doordarshan Kendra, Gwalior is part of DD India, the large stele vision network in the world.
Doordarshan with over five high power terrestrial transmitters, 62 low power, 5 very low
power transmitters and three production centers serve M.P inaugurated on 28 may 2000
by the broadcast minister Mr. Arun Jately . Doordarshan Kendra, Gwalior currently produces
and telecast 168 hrs of local program per week. Now more than 85% of 60,385,118
populations of M.P, with the introduction of the DTH almost cent percent of the
population can now receive D.D.K Gwalior programmed with cable connection.
Doordarshan studios have been established at Gwalior, Bhopal and Indore to foster regional
diversit . People all over India are watching Doordarshan’s programmers. It also received in
64 continents of Asia, Africa, Europe, Australia and America.
6
FUNDAMENTALS OF MONOCHROME AND
COLOUR TV SYSTEMS
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 pickup 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 frames divided into 2 fields
the flicker reduces. The field rate is 50 Hertz. The frame rate is 25 Hart.
Number of TV Lines per Frame If the number of TV lines is high larger band width 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.
7
Resolution The capability of the system to resolve maximum number of picture elements along scanning
lines determines the horizontal resolution. It means how many alternate black and white
elements can be there in a line. The vertical resolution depends on the number of scanning
lines and the resolution factor (also known as Kill factor)
Grey ScaleIn black and white (monochrome) TV system all the colours appear as gray on a10-step gray
scale chart. TV white corresponds to a reflectance of 60% and TV black 3 % giving rise to a
Contrast Ratio of 20:1 (Film can handle more than 30:1 and eye’s capability is much more).
Brightness Brightness reveals the average illumination of the reproduced image on the TV screen.
Brightness control in a TV set adjusts the voltage between grid and cathode of the picture tube
(Bias voltage).
Contrast:Contrast is the relative difference between black and white parts of the reproduced picture. In
a TV set the contrast control adjusts the level of video signal fed to the picture tube.
Viewing Distance:Optimum viewing distance from TV set is about 4 to 8 times the height of the TV screen. While
viewing TV screen one has to ensure that no direct light falls on the TV screen.
8
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 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 particles 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.
Colour Composite Video Signal is formed with Video, sync and blanking signals. The level is
standardized to 1.0 V peak to peak (0.7 volts of Video and 0.3 volts of sync pulse). The Colour
Composite Video Signal (CCVS) has been shown in figure.
Frequency Content of TV Signal:The TV signals have varying frequency content. The lowest frequency is zero. (when we are
transmitting a white window in the entire active period of 52 micro seconds the frequency is
Zero).In CCIR system B the highest frequency that can be transmitted is 5 MHz even though the
TV signal can contain much higher frequency components. (In film the reproduction of
frequencies is much higher than 5 MHz and hence clarity is superior to TV system.) long shots
9
carry higher frequency components than mid close ups and close ups. Hence in TV productions
long shots are kept to minimum. In fact TV is a medium of close ups and mid close ups.
DC Component of video signal and DC restoration
A TV signal is a continuously varying amplitude signal as the picture elements give rise to
varying level which depends on how much of incident light the picture elements can reflect and
transmit the light signal to the TV camera. Hence the video signal has an average value i.e. a DC
component corresponding to the average brightness of the scene to scene.
RF Transmission of Vision and Sound Signals:TV Transmission takes place in VHF Bands I and III and UHF Bands IV and V. Picture is amplitude
modulated and sound is frequency modulated on different carriers separated by 5.5 MHz Also
for video amplitude modulation negative modulation is employed because of the following
main advantages.
Pictures contain more information towards white than black and hence the average power is
lower resulting in energy saving. (Bright picture points correspond to low carrier amplitude and
sync pulse to maximum carrier amplitude).
Interference such as car ignition interfering signals appears as black which is less objectionable.
Picture information is in linear portion of modulation characteristic and hence does not suffer
compression. Any compression that may take place is confined to sync pulse only.
The design of AGC circuit for TV Receiver is simpler.
AM produces double side bands. The information is the same in both side bands. It is enough to
transmit single side band only. Carrier also need not be transmitted in full and a pilot carrier can
help. However, suppressing the carrier and one complete side band and transmitting a pilot
carrier leads to costly TV sets. A compromise to save RF channel capacity is to resort to vestigial
side band system in which one side band in full, carrier and a part of other side band are
transmitted.
Sound Signal Transmission:In CCIR system B sound carrier is 5.5 MHz above the vision carrier and is frequency modulated.
The maximum frequency deviation is 50 KHz. Also the ratio of vision and sound carriers is 10:1
(20:1 is also employed in some countries) If we assume maximum audio signal is 15 KHz the
band width is 130 KHz. According to Carson’s Rule the bandwidth is 2 x (Maximum frequency
10
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.
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 lightsensitive 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 Color Mixing:The figure shows the effect of projecting red, green, blue beams of light so that they over lapin
screen. Y= 0.3 Red + 0.59 Green + 0.11 Blue
11
TV Camera
INTRODUCTION:
A TV Camera consists of three sections.
a) A Camera lens & Optics:- To form optical image on the face plate of a pick up device.
b) A transducer or pick up device:- To convert optical image into a electrical signal.
c) Electronics: - To process output of a transducer to get a CCVS signal.
TYPES OF PICK - UP DEVICES:There are three types of pick up devices based on:
a) Photo emissive material:This material emits electrons when the light falls on them. Amount of emitted electrons
depends on the light. Monochrome cameras used in Doordarshan were based on this material.
These cameras were called Image Orthicon Cameras. These cameras were bulky and needed lot
of light. These are no longer in use at present.
12
b) Photo conductive material:The conductivity of these material changes with amount of light falling on them. Such material
with variable conductivity is made part of a electrical circuit. Voltage developed across this
material is thus recovered as electrical signal. Earlier cameras based on this principle were
Videocon Cameras. Such cameras were often used in the monochrome televise chain. These
cameras had serious Lag & other problems relating to dark currents. Improvement in these
cameras leads to the development of Plumb icon and Sat icon cameras.
c) Charge coupled devices:These are semiconductor devices which convert light into a charge image which is then
collected at a high speed to form a signal. Most of the TV Studios are now using CCD cameras
instead of Tube cameras. Tube cameras have become obsolete & are not in use.
Camera sensors – CCD basics
The CCD is a solid-state device using special integrated circuitry technology; hence it is often
referred to as a chip camera. The complete CCD sensor or chip has at least 450 000 picture
elements or pixels, each pixel being basically an isolated (insulated) photodiode. The action of
the light on each pixel is to cause electrons to be released which are held by the action of a
positive voltage.
The Charge held under electrode can be moved to electrode by changing the potential on the
second electrodes. The electrons (negative charges) follow the most positive attraction. A
repeat of this process would move the charges to next electrode, hence charge-coupled device.
A system of transfer clock pulses is used to move the charges in CCDs to achieve scanning.
There are three types of CCD device:. Frame transfer (FT)
. Interline transfer (IT)
. Frame interline transfer (FIT)
Size of the chip used for broadcast cameras varies from ½ inch to 2/3inch.
Frame transfer (FT):Frame transfer was the first of the CCDs to be developed and it consists of two identical areas,
an imaging area and a storage area. The imaging area is the image plane for the focused optical
image; the storage area is masked from any light. The electrical charge image is built up during
one field period, and during field blanking this charge is moved rapidly into the storage area. A
mechanical shutter is used during field blanking to avoid contamination of the electrical charges
during their transfer to the storage area. The storage area is „emptied‟ line by line into a readout register where, during line –time, one line of pixel information is „clocked‟ through the
register to produce the video signal.
Interline transfer (IT):Interline transfer CCDs were developed to avoid the need for a mechanical shutter The storage
cellist placed adjacent to the pick-up pixel; during field blanking the charge generated by the
13
pixel is shifted sideways into the storage cell. The read-out process is similar to the frame
transfer device, with the storage elements being „clocked‟ through the vertical shift register at
field rate into the horizontal shift register, then the charges read out at line rate. Earlier forms
of IT devices suffered from severe vertical smear, which produced a vertical line running
through a highlight. This was caused by excessive highlights penetrating deeply into the
semiconductor material, leaking directly into the vertical shift register. Later IT devices have
improved the technology to make this a much less objectionable effect.
Frame interlines transfer (FIT):Frame interline transfer CCDs are a further development of the interline transfer device to
overcome the problem of vertical smear. As its name suggests, it is a combination of both types
.The FIT sensor has a short-term storage element adjacent to each pixel (as IT) and a duplicated
storage area (as FT). During field blanking the charges are moved from the pixels into the
adjacent short-term storage element and then moved at 60 times field frequency into the
storage area. This rapid moving of the charge away from the vulnerable imaging area
overcomes the vertical smear problem.
Development in CCD technology has seen the introduction of:The hole accumulated Diode (HAD) sensor which enabled up to 750 pixels/line, with increased
sensitivity and a reduction in vertical smear
The hyper HAD sensor, which included a micro lens on each pixel to collect the light more
efficiently (this gave a one stop increase in sensitivity over the HAD sensor)
The power HAD sensor with improved signal-to- noise ratio which has resulted in at least half
an ƒ-stop gain in sensitivity; in some cases a full ƒ-stop of extra sensitivity has been realize.
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.
14
The signal system in most of the cameras consists of processing of the signal from red, blue and
green CCD respectively. The processing of red and blue channel is exactly similar. Green
channel which also called a reference channel has slightly different electronic concerning
aperture correction. So if we understand a particular channel, the other channels can be
followed easily. Soled us trace a particular channel. The signal picked up from the respective
CCD is amplified in 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 preamplifier. 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 provides 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 colour bar/camera switch. This switch can select R, G and B from the camera or
from the R, G, and Signal from colour bar generator. In the encoder section these R, G, B signals
are modulated with Scot 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.
15
TV LIGHTING
GENERAL PRINCIPLES: Lighting for television is very exciting and needs creative talent. There is always tremendous
scope for doing experiments to achieve the required effect. Light is a kind of electromagnetic
radiation with a visible spectrum from red to violet i.e., wave length from 700nm to 380 nm
respectively. However to effectively use the hardware and software connected with lighting it is
important to know more about this energy.
Light Source:Any light source has a Luminance intensity (I) which is measured in Candelas. One Candela is
equivalent to an intensity released by standard one candle source of light.
Luminance flux (F):It is a radiant energy weighted by the photonic curve and is measured in Lumens. One Lumen is
the luminous flux emitted by a point source of 1 Candela.
Illumination (E):It is a Luminous Flux incident onto a surface. It is measured in LUMENS/m2, which is also called
as LUX. A point source of 1 candela at a uniform distance of 1meter from a surface of 1 square
meter gives illumination of 1 LUX.
Luminance (L):It is a measure of the reflected light from a surface. Measured in Apostils. A surface which
reflects a total flux of 1 lumen/m2 has a luminance of 1 Apostils .Elementary theory of light also
says that:
Colour temperature:
One may wonder, how the light is associated with colour . Consider a black body being heated;
you may observe the change in colour radiated by this body as the temperature is increased.
The colour radiated by this body changes from reddish to blue and then to white as the
temperature is further increased. This is how the concept of relating colour with temperature
became popular. Colour temperature is measured in degree Kelvin i.e., 0C +273). The table
below gives idea about the kind of radiation from different kinds of lamps in terms of colour
temperature.
a) Standard candle 19300K
b) Fluorescent Lamps range 3000-6500oK
c) HMI lamp 5600+- 400oK (H=Hg, M=Medium arc, I=Metal Iodide}
d) CSI (Compact Source Iodide) 4000+- 400oK
e) CID (Compact Iodide Daylight) 5500+- 400o Colour TV Display, white 6500oK
f) Monochrome TV 9300oK
g) Blue sky 12000 – 18000oK
16
h) Tungsten Halogen 3200oK
I) Average summer sunlight (10am –3pm) 5500oK
It can be noted that as the temperature is increased, the following things happen:
1) Increase in maximum energy released
2) Shift in peak radiation to shorter wavelengths (Blue)
3) Colour of radiation is a function of temperature
Hence by measuring the energy content of the source over narrow bands at the red and blue
ends of the spectrum, the approximate colour temperature can be determined. The entire color
temperature meter is based on this principle.
COLOUR FILTERS AND THEIR USE:Colour filters are used to modify the colour temperature of lights and to match colour
temperature for cameras while shooting with different colour temperature. These filters
change the colour temperature at the cost of reduction in light transmission. Colour
temperature filters are also introduced in the optical path of cameras to facilitate camera
electronics to do the white balance without loading the amplifier chain. Cameras electronics is
generally optimized for a colour temperature of 3200K, hence it uses reddish filter while
shooting at higher colour temperatures.
Generally it is normal to correct daylight to produce tungsten quality light, because it is usually
easier to do and saves lot of power, otherwise blue filters are going to reduce lot of light thus
requiring the use of higher wattage lamps.. However, when the amount of tungsten to be
corrected is small it may be more practical to convert it to daylight, but with a considerably
reduced light output from the luminaries.
There are two basic types of filter:i) One which is orange in colour and converts Daylight to Tungsten Light.
ii) One which is blue in colour and converts Tungsten to Daylight.
Day Light:The sun does not change its colour temperature during the day it is only its appearance from a
fixed point on earth. It is because the sunlight gets scattered because of the medium , shorter
wavelengths like blue gets more effected. Certain situations like, sunrise and sunset causes the
light to be more yellow than midday, because the light has to travel the long distance so careful
note should be made of the Transmission factor of each of the filters. Often compromise has to
be reached in terms of correction and light loss.
NEUTRAL DENSITY FILTERS:In addition to colour temperature correction sometimes it may be necessary to reduce the
intensity of daylight at an interior location. Neutral density filters available to attenuate the
light are of:
0.3 Density which has a transmission of 50%= 6dB=1 f stop
17
0.6 Density which has a transmission of 25%= 9dB=2 f stop
0.9 Density which has a transmission of 13%= 12dB=3f stop
COMBINATION OF CTC FILTERS AND NEUTRAL DENSITYFILTERS:Single filters exist which are a combination of full colour temperature orange and neutral
density as follows:Full Orange + 0.3 N.D. with a transmission of 50%
Full Orange + 0.6 N.D. with a transmission of 38%
The HMI light source has a colour temperature of about 60000K and can be used with exterior
daylight without the need for a colour temperature correction filter
.DIFFERENT LIGHTING TECHNIQUES:- Eye light Low intensity light on camera itself to get extra sparkle to an actor’s eye.
-Rim light to highlight actors outline, it is an extra back on entire body at camera level.
- Kicker light Extra light on shadow side of the face at an angle behind and to the side of the
actor
- Limbo lighting only subject is visible, no back ground light- Silhouette lighting, No light on
subject, and BG is highly lit.
LIGHTING CONSOLE
In a television production, each scene will require its own lighting plan to give the desired
effect. In order to assist in setting up a particular lighting plan, a console should provide:a) One man operation and a centralized control desk with ability to switch any circuit.
b) Facilities to obtain good balance with flexibility to have dimming on any circuit.
c) With all controls for power at low voltage and current.
Modern 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 consoles also
provide Mimic panels to show which channels are in use and which memories or files have
been recalled.
DIMMERS
Three basic methods for dimming are:1. Resistance this is the simplest and cheapest form of dimmer. It consists of a wire wound
resistor with wiper .It is used in series with the load.
2. Storable Reactor (System SR) The basic principle of the storable reactor is to connect an iron
cored choke in series with the lamp.
18
LIGHTING THE SET FOR DRAMA:-Openings such as windows within a set should be highlighted without overstating them. Where
the walls having such feature should be lit to reveal these features but care must be taken to
ensure that there is only one shadow. The top of the set should be darkened off by using the
barn doors, 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) takes the shortest route inside the set to
wall, and if possible throws the shadow of window bars onto a door - it usually is in shot.
2. A patch of light on the floor inside the set, backlight from outside using a soft source at steep
elevation adds realism.
3. When a set does not have a window, a window pattern can be projected onto a wall to
produce a suitable window effect.
4. Roof and Ceiling Pieces - if they make lighting impossible, check if they can be removed at the
planning state. Light any ceiling pieces from outside, use a soft source at ground level. If the
ceiling has plaster molding or ornamentation, a hard source may be used.
Indoor night time:The outside of the window should be dark, except for a possible dim skyline if the room is well
above adjacent streets, or lit by an outside practical lamp i.e. street lighting- The wall with the
window in it should be lit at night to be brighter than for the day condition. Subjectively the
walls appear brighter at night than at daytime.
-Often a completely different feel to the set can be obtained by reversing He direction of
lighting in the set compared to that used for day.
- General for night effects it is not a good plan to just simply dim the set lighting when changing
from day to night. This is because the excessive change in colour temperature of the light
source and the apparent increase in saturation of surfaces at low luminance.
Outdoor daylight and Moonlight:The direction of the light is dictated by the position of the sun or moon. As a general principle
one should remember that sunlight (hard source) is accompanied by the reflected "skylight"
(soft source) whereas moonlight is a single hard source. One of the biggest problems when
lighting exteriors is the maintenance of “single shadow" philosophy - double shadows on a long
shot will quickly destroy the apparent realism created in the set. Very large area filler light is
ideal for exterior daylight scenes. This can be achieved by using a suspended white screen 12 x
8 where the filler would be positioned then lighting it with hard light.
The exact lighting treatment will depend on the situation but as a general rule, moonlight
effects are normally achieved by back lighting to give a softer, romantic mood than would be
achieved than a frontal key
19
MICROPHONES
Introduction
Microphone plays a very important role in the art of sound broadcasting. It is a device which
converts acoustical energy into electrical energy. In the professional broadcasting field
microphones have primarily to be capable of giving the highest fidelity of reproduction over
audio bandwidth.
Microphone Classification
Depending on the relationship between the output voltage from a microphone and the sound
pressure on it, the microphones can be divided into two basic groups.
Pressure Operated Type
In such microphones only one side of the diaphragm is exposed to the sound wave. The output
voltage is proportional to the sound pressure on the exposed face of the diaphragm with
respect to the constant pressure on the other face. Moving coil carbon, crystal and condenser
microphones are mostly of this type. In their basic forms, the pressure operated microphones
are Omni-directional.
Velocity or Pressure Gradient Type
In these microphones both sides of the diaphragm are exposed to the sound wave. Thus the
output voltage is proportional to the instantaneous difference in pressure on the two sides of
the diaphragm. Ribbon microphone belongs to this category and its polar diagram is figure of
eight.
Types of Microphones
There are many types of microphones. But only the most common types used in broadcasting
have been described here.
Dynamic or Moving Coil Microphone
This is common broadcast quality microphone which is rugged and can be carried to outside
broadcast/recording etc. It consists of a strong permanent magnet whose pole extensions form
radial field within a round narrow gap. A moving coil is supported within this gap and a dome
shaped diaphragm usually of aluminum foil is attached to the coil. The coil is connected to
20
microphone transformer whose secondary has sometimes tapings to select proper impedance
for matching. With sound pressure changes, the diaphragm and coil move in the magnetic field,
therefore, emf is induced in the speech coil, which is proportional to the incoming sound. The
primary impedance of the matching transformer is generally high (5 to 6 times of the speech
coil impedance so that low frequencies are not lost and rising impedance frequency
characteristic is avoided as best as possible. The resonant frequency is generally damped with
special arrangements of absorption in acoustic cavity, Bass/boost arrangements are provided
by an equalizing tube connecting the rear side of diaphragm i.e. inside of microphone with the
atmosphere. The diameter and length of the tube is critically adjusted for achieving good
frequency response.
This microphone delivers – 80 dav with a very good frequency response. The output impedance
of this microphone is high. The popular method of providing d.c. voltage to the condenser is
known as “Phantom Powering‟. Variable directivity capacitor microphones are becoming
popular these days. Fig. 3 Condenser Microphone Output Phantom power Head Amplifier
Output Transformer Very high resistance Insulator Phantom power DC blocking capacitor
Earthed back-plate Diaphragm
Electrets ‘Microphone:It is a modified form of condenser microphone in which the polarizing voltage is avoided. In fact
plastic polymer containing metallic dust keeps the metal particles permanently charged within
the plastic insulation and such a polymer within the diaphragm foil or fixed plate delivers the
electrical signal on the principle of the condenser mike. The hissing noise gets avoided since
there is no external polarizing resistor as a load. The microphone has high impedance and is
generally having FET pre-amplifier. The microphone costs very little but develops excellent
quality designs in many forms.
21
PRINCIPLES OF VIDEO TAPE
RECORDING
Introduction
Video tape recorder is a most complex piece of studio equipment with analog and digital
processing servo system, microprocessors, memories, logic circuits and mechanical devices etc.
Also these recorders have been the main limitation so for as the quality output from studio is
concerned. Right from fifties, continuous efforts are being made to improve its performance so
as to reproduce cameras faithfully by improving S/N ratio and resolution. Designer for video
tape recorders had to consider the following differences in the video and audio signals:
Magnetic Principle
Magnetic field intensity H = NI / L
Magnetic flux density B = H
Magnetic Flux Ø= BA
( is of the order of 100 to few 10,000 for ferromagnetic materials)
Property of the ferromagnetic materials to retain magnetism even after the current or the H is
removed is called retentively and is used for recording electrical signals in magnetic form on
magnetic tapes. This relationship can also be represented by a curve called BH curve. Magnetic
tapes are made of ferromagnetic materials with broader BH curve than the material used for
video heads as the heads are not required to retain information.
22
VISION MIXING
Introduction
Vision mixing is a process of creating composite pictures from various sources. Vision mixing
involves basically three types of switching or transitions between various sources. These are
mixing, wiping and keying. These transitions can also be accompanied by special effects in some
of the vision mixers.
Mixing
Two input sources are mixed in proportion in a summing amplifier as decided by the position of
control fader. Two extreme position of the fader gives either of the sources at the output.
Middle of the fader gives mixed output of the two sources; control to the summing amplifier is
derived from the fader.
Wipe
In this case the control for the two input sources is generated by the wipe pattern generator
(WPG), which can either be saw tooth or parabola at H, V or both H & V rate. Unlike in MIX,
during WIPE, one source is present in one side of the wipe and the second source on other side
of the wipe. A very simple to very complex wipe patterns can be generated from the WPG.
Key
In the Key position between two sources i.e. foreground (FG) and background (BG) the control
derived from one of the source itself (overlay), or by the third source (external key). This keying
signal can be generated either by the luminance, Hue or chrominance of the source input. The
keyed portion can be filled with the same or with matte or external source. Matte means
internally generated BG with choice of colors from the vision mixer itself.
23
NON LINEAR EDITING & 3-D GRAPHICS
INTRODUCTION
Fundamentally editing is a process where one places Audio video clips in an appropriate
sequence and mainly used in video post production. Linear editing is tape based and is
sequential in nature. It has various problems like long hours spent on rewinding of tapes in
search of material, potential risk of damage to original footage, difficult to insert a new shot in
an edit, difficult to experiment with variations, quality loss is more, limited composting effects
and color correction capability. On-linear editing (NLE) is a video editing in digital format with
standard computer based technology. NLE can also be extended to film editing. Computer
technology is harnessed in Random-access, computational and manipulation capability,
multiple copies, multiple versions intelligent search, sophisticated project and media
management tools, standard interfaces and powerful display.
ADVANTAGES OF NLE
NLE has various advantages over tape based (linear) editing.
Flexibility in all editing functions
Easy to do changes, undo, copy, duplicate and multiple version
Easy operation for cut, dissolve, wipes and other transition effects
Multi-layering of video is easy. Powerful integration of video and graphics, tools for filtering,
color correction, key framing and special 2D/3D effects.
Equally powerful audio effects and mixing
Possible to trim ; compress or expand the length of the clip.
Intelligent and powerful 3D video effect can be created and customized.
Efficient and intelligent storage
24
BREAKOUT BOXVarious video sources like VTR, CD player, camera and other playback/recording devices are
connected to NLE machine through breakout box. The NLE machine takes input from various
video sources for editing and gives output for monitoring and recording through break out box.
INPUTS
Video Inputs
There are three analog inputs (1) Component Video (2) S-Video (3) Composite video
Audio Inputs
To capture synchronized audio with your video, you must connect audio out from the VTR or
other play back device to the audio inputs. You can also connect audio only devices for sound
track production etc. the dps reality board (NLE hardware) has three analog audio options;
balanced, unbalanced and Aux.
25
Time Code
Time code is simply a series of labels attached to a recording at timed intervals, generally
fractions of sounds. Each label contains a time of recording. Time code is used for editing; in
order to be able to return repeatedly to a selected time, and for synchronization among audio
and video recorders and players. The two versions of time code that is available with dps.
OUTPUTS
Video Output
Component (CAV) Video has three connectors, labeled Y, B-Y, R-Y. A cable connects each of
these three outputs to your video monitor or VTR.
Audio Output
Choose what type of video to output based on whether you’re VTR and other video and audio
equipment can receive balance or unbalance audio. Audio out is connected to speakers for
playback or to a VTR or other audio recording device during recording.
26
3 –D GRAPHICS
THE FIVE MODULES OF SOFTIMAGE
Softimage 3 D Extreme has given different modules that correspond to different phases of the
workflow process you use to create animation. Each of the modules replaces some of the menu
cell son the left and right menu columns, while leaving other menu cells that are applicable in
all modules. The modules are listed along the top right corner of the screen: Model, Motion,
Actor, Matter, and Tools. You can enter these modules either by clicking the text labels in the
top right corner or by pressing the supra keys that represent them: F1 for Model, F2 for Motion,
F3 for Actor, F4 for Matter, and F5 for Tools.
MODEL
You start your workflow in the Model module, where you construct all your scene elements.
Model’s tools enable you to create objects from primitive shapes, draw curves, and develop
surfaces from those curves.
MOTION
You then move to animate some parts of your scene, using the animation tools found in the
Motion module. The Motion module allows you to set animation key frames for objects, assign
objects towpaths, and to see and edit the resulting animation on screen. After you have refined
your animation using the F Curve tools, you move to the next module, Actor.
ACTORT
He Actor module contains the special Softimage tools for setting up virtual actors, assigning
inverse kinematic skeletons, assigning skin, adjusting skeletons deformations, and weighting
the skin to the IK skeletons. Actor also contains the controls for physical-based animation –
Dynamics, Collisions, and Stretch – which is an automatic squash-and-stretch feature.
MATTER
When your modeling, animation, and acting are complete, you move to the fourth module:
27
Matter. In the Matter module, you assign color and material values to the objects in your scene,
determining how they will look in the final render.
At any time in the first four modules, you can create lights and adjust their effect on the scene.
The Matter module is also where you perform the last step in the workflow process, rendering.
TOOLS
Tools contain a variety of utility programs for viewing, editing and exporting your work. You
may view individual images, sequences of images, and line tests. You may bring in images
created in other programmers as image maps or import objects created in other programs as
geometry. You can composite sequences of images together, reduce colours in sequences of
images for reduced colour games systems, and move your finished work to video disk recorders
and film recorders.
28
TELEVISION TRANSMISSION
VESTIGIAL SIDE BAND TRANSMISSION If normal amplitude modulation technique is used for picture transmission, the minimum
transmission channel bandwidth should be around 11 MHz taking into account the space for
sound carrier and a small guard band of around 0.25 MHz Using such large transmission BW will
limit the number of channels in the spectrum allotted for TV transmission. To accommodate
large number of channels in the allotted spectrum, reduction in transmission BW was
considered necessary. The transmission BW could be reduced to around 5.75MHz by using
single side band (SSB) AM technique, because in principle one side band of the doublewide
band (DSB) AM could be suppressed, since the two side bands have the same signal content.
Design
All the TV transmitters have the same basic design. They consist of an exciter followed by
power amplifiers which boost the exciter power to the required level.
Exciter
The exciter stage determines the quality of a transmitter. It contains pre-corrector units both
abase band as well as at IF stage, so that after passing through all subsequent transmitter
stages, inacceptable signal is available. Since the number and type of amplifier stages, may
differ according to the required output power, the characteristics of the pre-correction circuits
can be varied over a wide range.
29
Vision and Sound Signal Amplification
In HPTs the vision and sound carriers can be generated, modulated and amplified separately
and then combined in the diplexer at the transmitter output.
In LPTs, on the other hand, sound and vision are modulated separately but amplified jointly.
This is common vision and aural amplification.
A special group delay equalization circuit is needed in the first case because of errors caused by
TV diplexer. In the second case the intermediation products are more prominent and special
filters for suppressing them is required.
As it is difficult to meet the intermediation requirements particularly at higher power ratings,
separate amplification is used in HPTs though combined amplification requires fewer amplifier
stages.
IF Modulation
It has following advantages
· Ease of correcting distortions
· Ease in vestigial side band shaping ·
IF modulation is available easily and economically
·Power Amplifier Stages
In BEL mark I & II transmitters three valve stages (BEL 450 CX, BEL 4500 CX and BEL 15000
CX)are used in vision transmitter chain and two valves (BEL 450 CX and BEL 4500 CX) in aural
transmitter chain. In BEL mark III transmitter only two valve stages (BEL 4500 CX and BEL
15000CX) are used in vision transmitter chain. Aural transmitter chain is fully solid state in Mark
III transmitter.
Constant Impedance Notch Diplexer (CIND)
Vision and Aural transmitter’s outputs are combined in CIN diplexer. Combined power is fed to
main feeder lines through a T-transformer.
BEL 10 kW TV TRANSMITTER (MARK-II)
30
TRANSMITTER CONTROL SYSTEM
The transmitter control unit performs the task of transmitter interlocking and control. Also it
supports operation from control console. The XTR control unit (TCU) has two independent
system viz.
1. Main control system. (MCS)
2. Back-up Control System (BCS)
Functions performed by MCS (Main Control System)
- XTR control
- Interlocking
- RF monitoring
- Supporting operation from control console
- 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
keyboard. The control elements are controlled in accordance with the programmed fused in
thee PROMS.
Only while operating from the MCS (Main Control System), the interaction with TCU is
supported through a LCD display unit. The LED bar display board showing the status
information is used by both the MCS and BCS (Back up Control Unit).
Main Control System (MCS)
The MCS consists of the following:
1. Mother Board with the following PCBs.
CPU
BIT I/O
Interlock Interface Board (IIB).
Analog I/O Board (AIO)
Control Interface Board (CIB)
Analog Receiver Board (An Rx)
Rectifier and Regulator Board (RRB MCS)
31
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.
32
TV TRANSMITTER ANTENNA SYSTEM
Antenna System is that part of the Broadcasting Network which accepts RF Energy from
transmitter and launches electromagnetic waves in space. The polarization of the radiation as
adopted by Doordarshan is linear horizontal. The system is installed on a supporting tower and
consists of antenna panels, power dividers, balloons, branch feeder cable, junction boxes and
main feeder cables. Dipole antenna elements, in one or the other form are common at VHF
frequencies where as slot antennae are mostly used at UHF frequencies. Omni directional
radiation pattern is obtained by arranging the dipoles in the form of turnstile and exciting the
same in quadrature phase. Desired gain is obtained by stacking the dipoles in vertical plane. As
a result of stacking, most of the RF energy is directed in the horizontal plane. Radiation in
vertical plane is minimized. The installed
Antenna system should fulfill the following requirements:
a) It should have required gain and provide desired field strength at the point of reception.
b) It should have desired horizontal radiation pattern and directivity for serving the planned
area of interest. The radiation pattern should be Omni directional if the location of the
33
transmitting stations at the center of the service area and directional one, if the location is
otherwise.
c) It should offer proper impedance to the main feeder cable and thereby to the transmitter so
that optimum RF energy is transferred into space. Impedance mismatch results into reflection
of power and formation of standing waves. The standard RF impedance at VHF/UHF is 50 ohms.
34
Outdoor Broadcasting van
O B Van (Outdoor Broadcasting van )OB van is used for live broadcasting like any match or any event. It consist all the equipments
that is present in the studio for telecasting. It also referring as mini studio .
It has mainly 3 parts :
1) Power supply unit
2 )Production control unit
3) Audio console and VTR
35
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 gigantic task and expensive affair to run and maintain the large number
of transmitters. Satellite broadcasting, came into existence in mid sixties, was thought to
provide the one-third global coverage simply by up-link and down-link set-ups. In the beginning
of the satellite broadcasting, up-linking stations (or Earth Stations) and satellite receiving
centers could had only been afforded by the Governments organizations. The main physical
constraint was the enormous size of the transmitting and receiving parabolic dish antennas
(PDA). In the late eighties the satellite broadcasting technology had undergone a fair
improvements resulting in the birth of cable TV. Cable TV operators set up their cable networks
to provide the services to individual homes in local areas. It rapidly grew in an unregulated
manner and posed a threat to terrestrial broadcasting. People are now mainly depending on
cable TV operators. Since cable TV services are unregulated and unreliable in countries like
India now, the satellite broadcasting technology has ripened to level where an individual can
think of having direct access to the satellite services, giving the opportunity to viewers to get rid
of cable TV. Direct-to-Home satellite broadcasting (DTH) or Direct Satellite Broadcasting (DBS) is
the distribution of television signals from high powered geo-stationary satellites to a small dish
antenna and satellite receivers in homes across the country. The cost of DTH receiving
equipments is now gradually declining and can be afforded by common man. Since DTH
services are fully digital, it can offer value added services, video-on-demand, Internet, e-mail
and lot more in addition to entertainment. DTH reception requires a small dish antenna (Dia60
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
40to 50 video programs can simultaneously be received in DTH mode.
UPLINK CHAIN
DTH broadcasting is basically satellite broadcasting in Ku-Band (14/12 GHz). The main
advantage of Ku-Band satellite broadcasting is that it requires physically manageable smaller
size of dish antenna compared to that of C-Band satellite broadcasting. C-Band broadcasting
requires about 3.6m 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 9dB coding gain in the digital broadcasting. Requirement of transmitter
power (about 25 to 50Watts) is less than that of analog C-band broadcasting. The major
drawback of Ku-Band transmission is that the RF signals typically suffer 8 to 9dB rain
attenuation under heavy rainfall while rain attenuation is very low at C-Band. Fading due to rain
can hamper the connectivity of satellite and therefore rain margin has to be kept for reliable
36
connectivity. Rain margin is provided by operating transmitter at higher powers and by using
larger size of the dish antenna (7.2m PDA).Fig.1 shows schematic of uplink chain proposed to
broadcast bouquet of 30 video programs in Doordarshan, Prasar Bharati, India. 30 video
programs may either be down-linked from satellites or taken from other sources like video tape
recorders.
Video cameras etc. in digital format. These sources are fed to Router whose outputs are
divided in three groups A, B and C. Each group contains 10 video sources multiplexed in a
Multiplexer. These three multiplexed streams are digitally (QPSK modulation) modulated
individually at 70 MHz Intermediate Frequency (IF). Each group is further doubly up-converted,
first conversion at L-Band (950-1450 MHz) and second conversion at Ku-Band (12-14 GHz).
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
building or house. RF waves (12.534GHz, 12.647GHz, 12.729 GHz) from satellite are picked up
by 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.
37
FUTURE SCOPE
Doordarshan the national television service of India is devoted to public service broadcasting.
It is one of the largest terrestrial networks in the world.
Doorarshan is the first ISO certified channel in India. The largest viewers of India, watching
Doordarshan. It has good future scope in communication world. Because largest network
converted by the Doordarshan only.
 As now a days there is a huge competition and everything is getting digitized there is a
wide scope for electronics and communication engineers to show their skills and keep the
technology up to date.
 In Doordarshan, all the electronics devices used are to be operated by skilled engineers.
 It provides with good pay scales.
 The selection for the posts is through UPSC & SSC examination.
38
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, Gwalior 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 my knowledge of my field of interest, electronics & communication.
39