pratibha report

7/31/2019 Pratibha Report

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REPORT

OnPractical Training At

Submitted To: Submitted By:

Mr.R.S.Tyagi Pratibha Chauhan

(Head of Office) (B.E 2nd Year)

M.B.M Engg. College


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PREFACE

Practical Training is an important constituent of any curriculum and B.E course

is no exception to this general rule. Practical Training helps a student in getting

acquainted with the manner in which his/her knowledge is being practically

used and this is different from what he/she has learnt from books.Hence,when

he/she switcher from the process of learning to that of implementing his/her

finds an abrupt change. This is exactly why a practical training session during

the curriculum becomes all the more important.

The duration of the practical training period prescribed for awarding the B.E

degree is 100 days in our College. This period has been divided in two parts viz.40 days practical training after 2

ndyear ,B.E session and a 60 days Training

after the 3rd

Year ,B.E session.

This report is describes my practical training after the 2nd

Year, B.E session that

I completed at the Doordarshan Kendra, Jaipur. This Training was in the formof, practical study of broadcast station. The report gives an introduction of the

Doordarshan Kendra and its different sections. The whole transmission of a TV

program from production to broadcast is explained in detail in this report. This

complete chain is divided in different segments for clear understanding. This

report consists of the working process of the production unit, Earth stationsatellite and transmitter.


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ACKNOWLEDGEMENT

It gives me immense pleasure to express my gratitude to the family of

Doordarshan Kendra, Jaipur for their prudent response in course of completingmy summer training .I am highly indebted to Mr.A.K.Sundrani, Station

Engineer DDK, Jaipur and Course Coordinator Mr. Harish Chandra (ASE) &

Mr.R.K.Jain (AE) for their guidance and whole hearted inspiration, it has been

of greatest help in bringing out the work in the present shape. The direction,

advice, discussion and constant encouragement given by them has been so

helpful in completing the work successfully.

I am extremely thankful to all the staff members of Doordarshan who have

spend their Valuable time in guiding and providing valuable information and

data required to accomplish this project.

I am extremely grateful to Mr. Arvind Rai(Dean, M.B.M Engg College) and

Head of ECE Department & all the faculty members of ECE Department for

guiding me.

Pratibha Chauhan


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CONTENTS

About DoordarshanDigitizationBasic TV SystemsEarth StationVideo Cassette RecorderVideo TapeMicrophoneLoudspeakerStudio CameraVision MixerConcept Of Satellite communication


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ABOUT DOORDARSHAN

The first television broadcast was viewed by the people of Rajasthan on 1st

August 1975 under the satellite Instructional Television Experiment targeting

the district of Kota, Sawai Madhopur and Jaipur. The footprint of the American

satellite ATS-6 fell on 388 villages in these district which were provided with

direct receiving sets. Special educational programmers were then produced atDelhi.

On 1st

March 1977, Upgrah Doordarshan Kendra (UDK) was set up at Delhi.

The programmes produced at UDK for Jaipur were relayed via high power

transmitters. On 1st

June 1987, Jaipur Doordarshan Kendra was set up. Initially

the Kendra produced only 30 minutes of programming and this was gradually

increased. Presently the Kendra originates about four hours of programming

daily.

The terrestrial channel covers 78%by population and &by area of Rajasthan.

The total numbers of transmitters are:

1) High Power: 8 Nos.2) Low Power: 80 Nos.3) Very low Power: 18 Nos.4) Transposers: 2 Nos

Transmitters in Rajasthan for DD2: 3 Nos (Jaipur, Jodhpur & Kota)

With its vision of Satyam, Shivam and Sunderam, Doordarshan has a mission to

reach every person with reliable news, balanced views, innovative educational

programmes and wholesome entertainment. The Jaipur Kendra Seeks to project

the life and literature, art and culture of Rajasthan in its variegated forms. It

strives not just to portray the resplendent past and the momentous present but to

redesign a human future.


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Doordarshan promotes discussion and dialogue to foster understanding and

goodwill among all sections of society. It endeavors to inculcate scientific

temper among the people. It attempts social reconstruction by waging a war

against casteism and superstition. It aims to wipe out illiteracy and ignorance

and promote health and well-being.

As a public service broadcaster Doordarshan never-even in the midst of the

vicious competition abandon its values and standards of decency. It does not

merely inform but also educates, not merely entertain but also enrich the lives of

all its viewers.

DOORDARSHAN - TODAY

Channels 24

Studio Centers 64

Transmitters 1400


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DIGITIZATION

Prasar Bharati, the umbrella organization under which Air and Doordarshanfunction crosses another milestone as its these two media units, enter the digital

era.

The inauguration of a new Broadcasting House and Tower B of Doordarshan in

New Delhi recently is an important milestone in the history of public

broadcasting in India as it marks its entry into the digital era.

Prasar bharati sought to reorient its growth strategies and succeeded in making

its presence felt as a vibrant and socially relevant public broadcasting

organization; Going digital is the latest manifestation of this trend.

Doordarshan has acquired state-of-the-art facilities for production and

transmission of programs. With a network of over 1400 terrestrial transmitters,

Doordarshan covers 90 % of the population and is way ahead of the reach of all

the satellite put together. Moreover, as the Review Committee envisionised,

Doordarshans channels telecast a healthy mix of entertainment and socially

relevant programmes reflecting the varied cultures and languages of the nation.

The Tenth Five-Year Plans proposals for Doordarshan focus on digitization

,Currently 20 out of doordarshans 25 channels are digital. Digital earth stations

have already been set up in Mumbai, Hyderabad, Bangalore, Patna, Jallandhar

Chennai, Thiruvananthpuram, Ahmadabad, Kolkata, Bhubaneswar, Shilling and

Aizawl. Engineers of Doordarshan put up, in record time, the Ku band

transmission facility at Todapur, near New Delhi, for broadcasting DD Direct

Plus, And the Direct TO Home (DTH)broadcast service. Ku band transmission,

which ensures near total coverage, is a cost effective alternative to terrestrial

transmission. Doordarshan has distributed 10,000 DTH receiver systems and

200 cable head ends in select states of north, central and north eastern India,

where television coverage is below the national average. One of the compelling

reasons for introducing DTH is to ensure that programmes of AIR and

Doordarshan reach every household in the country. The DTH service would

help Doordarshan and AIR expand their reach with investment much lower than

that require for increasing the number of transmitters.


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VIDEO CASSETTE RECORDER

Device that records audio and video electrical signals onto magnetic tape. Machine that records on and plays a video tape The video cassette recorder (or VCR, less popularly video tape recorder) is

a type of video tape recorder that uses removable cassettes containing

magnetic tape to record audio and video from TV broadcast so it can be

played back later. Many VCRs has their own tuner and can be

programmed to record the signal on a particular channel during a

particular time interval.

Introduction

The main purpose of the video recorder is recording and replaying video and

audio signals. Although built-in tuners and timers have become integral parts of

the average video recorder, they are not prerequisites for reaching the main goal

audio and video registration and playback.

How the VCR works??

The Helical Scan System in an audio cassette deck, which only registers audio

signals, the tape passes over a static recording/playback head at constant speed.

The higher the speed of the tape , more tape particles pass the head opening and

the higher the frequencies that can be registered. With the extremely narrow

head opening, it is possible to record and play back the entire tone range, up to

18000 or 20000 Hz despite a slow tape speed of no more than 4.75 centimeters

per second.

However, to register video signals, a range of 3.2 MHz is required and so a tape

speed of approximately 5 meters per second is prerequisite. This is over 100

times as fast as the tape speed for an audio cassette deck. The required high

recording speed for video recorders are realized by the helical scan system


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without such a high tape speeds. The system basically consists of a revolving

head drum that has a minimum of two video heads

The head drum has a diameter of approximately 5 cm and rotates at a speed of

1500 revolutions per minute. The (12.65 mm) wide videotape is guided

around half the surface of this drum, in a slightly oblique manner. This is

achieved by positioning the head drum at a slight angle. The tape guidance

mechanism then ensures that the tape is guided through the device at a speed of

approximately 2 cm per second (half of the low speed that is used in audio

cassette decks).

In the meantime, the rapidly revolving video heads write narrow tape tracks of

no more than 0.020 to 0.050 mm wide on the tape, next to each other, diagonaltrack which equals half an images The first head writes one track, i.e., the first

field (the odd numbered scanning lines). The second head writes a second track,

i.e., the other half of the image (the second field; the even numbered scanning

lines), which precisely fits in the first image. This corresponds to the interlacing

principle, as applied in television. One full revolution of both heads results in

two diagonal tracks right next to each other, together forming one entire image

scan (a frame)

. This means that two apparently contradictory requirements can be realized

simultaneously; low tape speed of only 2 cm per second and at the same time a

high registration speed (relative tape speed)

Of no less than 5 meters per second. These two requirements make it possible to

record the high video frequencies up to 3.2 MHz at the same time; the low tape

speed gives a time capacity up to three hours.

Azimuth Settings

Compared with early video recorders, modern day video recorders have their

video tracks lying right next to each other. To avoid interference, the two video

heads are angled slightly away from each other. To avoid interference, the two

video heads are angled slightly away from each other. As a result, the video

head openings that transmit the magnetic tracks to the tape, create an angle

between them. The heads are 15 degrees angled in opposite direction, making atotal angle of 30 degrees. This diverted registration angle ensures no problems


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are caused if the heads slightly lose track when playing back and touch the next

track. The heads only register tape information at an angle that precisely

corresponds to the position of the head opening. This system is called the

azimuth recording system. If the video heads stray too far from the track, which

could lead to distorted images, tracking control can correct this.

SYNCHRONIZATION TRACK

The revolutionary speed of the head drum and the video heads needs to

maintain constancy within strict parameters. Moreover, the tracks must be

scanned during playback in precisely the same way as they were recorded. Each

tape track is synchronized at the recording stage by means of field

synchronization pulses. These pulses are generated in the video recorder by a

separate head which are recorded on a separate narrow track at the side of the

video tape. This is called the synchronization, servo or control track.

Video Systems

There are three major video systems in use today:

Video Home System(VHS) Betamax Video Hi8

When the video recorders were first introduced, Philips also developed a system

called V2000. Despite the fact that is a high quality system, it was not

successful in the market. Although Betamax was reasonably successful at first,

its popularity waned and VHS was adopted as the world standard.

Betamax

The Spony Betamax System, launched in 1975, was based on the pre-existing

professional Sony U-matic-system. In the Betamax system, the video tape is

guided along the head drum in aU shape for all tape guidance functions, such as

recording, playback and fast forward/backward. When the cassette is inserted,the tape is guided around the head drum (called threading). Threading the tape


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takes a few seconds, but once the tape is threaded, shifting from one tape to

another can be achieved rapidly and smoothly.

VHS

In VHS, the tape is guided through in an M-shape; so-called M-tape guidance

system. It considered simpler and more compact than the U-shaped system.

Threading is faster and is done every time the tape guidance function is

changed. It is therefore somewhat slower and noisier than the U-system. This

problem is being solved by Quick-start VHS video recorders, which allow

fast and silent changes in tape guidance functions. To avoid excessive wear, M-

tape guidance system recorders are provided with an automatic switch-offfeature, activated some minutes after the recorder is put on hold, which

automatically unthreads the tape. An improvement of the basic VHS system is

HQ(High Quality) VHS.

In the VHS system different starting points were used than in Betamax, such as

track size and relative speed. VHS has rather wide video tracks, but a slightly

lower relative tape speed, and that also counts for the audio tracks. In the end

the result is that there is not too much difference between the sound and image

qualities of both the systems.

SOUND RECORDING

Mono

In case of a mono video recorder, the audio signals which corresponds with the

image is transferred to a separate, fixed audio head.

As in an audio cassette deck, this head writes an audio track in longitudinal

direction of the tape. This is called linear or longitudinal track recording.

The video recorder has two erase heads. One is a wide erase head covering the

whole tape width which automatically erases all existing images,

synchronization and sound information when a new recording is made. The

other erase head is smaller and positioned at the position of the audio track With

this erase head, the sound track can be erased separately, without affecting thevideo information. In this way, separate audio can be added to a video


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recording. This is called audio dubbing, and can be particularly useful when

making your own camera recordings.

The linear audio track does have some restrictions. Due to its low tape speed, it

is not suitable for Hi-Fi recordings. Moreover, the audio tracks are so narrow(0.7 mm for VHS and 1.04 mm for Betamax) that not even stereo sound can be

properly recorded. The frequency range is limited as is the dynamic range

(which relates to the amount of decibels), and the signal-to-noise ratio is not

very high( the signal-to-noise ratio relates to the amount of noise compared to

the total signal. The higher this ratio, less the noise and better the signal will

be).

The sound quality of the mono track can be improved by a noise reduction

system. There is a way to get superior hi-fi stereo sound quality on a video tape

(used in hi-fi video recorders).


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MICROPHONE

Microphone is a transducer, in which sound waves are translated intomechanical vibrations in a thin, flexible DIAPHRAGM these sound vibrations

are then converted by various methods into an electrical signal which varies inamplitude, frequency and phase according to the sound waves.

Characteristics of microphone:

Sensitivity Signal to noise ratio Frequency response Distortion Directivity Output impedance

SENSITIVITY: It is defined as output in milli volts for the sound pressure of1 Microbar.

SIGNAL TO NOISE RATIO: It is define to be ratio in dB of the output tothe output in the absence of sound.

FREQUENCY RESPONSE: It is define by the bandwidth of audio

frequencies in the output of microphone within 1dB of the output at 1000Hz.

DISTORTION: Two types of distortions in microphones

1. Non linear distortion.

2. Phase distortion.

DIRECTIVITY: The angle of the half power points in a polar diagramrepresents Directivity of a microphone.

Three types of directivity:-

1. Omnidirectional.2. Bidirectional.3. Cardioids or heart shaped4. Varieties of microphone: Capacitor microphone Ribbon microphone

Electrets microphone Carbon microphone


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Crystal microphone Laser microphone

LOUD SPEAKER

Loud speaker performs an opposite function to a microphone i.e. it converts

electrical signal into sound wave.

Two types of loud speaker:

Moving coil type. Horn type.MOVING COIL TYPE :(direct radiating loud speaker)

Principle:Interaction between the magnetic field and the current ,resulting ina force working on the movable coil. This force is proportional to the audio

current and hence causes vibratory motion in the coil,which makes a

diaphragm to vibrate and produce pressure variations in air, resulting in

sound waves.

Advantages-

1. Low cost .2. Compact size.

Applications: Radio receiver,TV receiver and in cassette players.

HORN TYPE : ( Indirect Radiating loud speaker)

Principle: same as in moving coil type loud speakerbut instead ofradiating power directly in open space of listenersarea, the power is firstdelivered to the air flared horn and from there to the air in the listeners

area.

Advantages-

1. Better impedance matching.2. High efficiency.Applications: Used in PA system and music concerts.


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EARTH STATION

INTRODUCTION

Communication using conventional technique like coaxial cable and microwave

relay link involves a large number of repeaters and is a costly affair. A better

option for transmission was introduced in 1945 by Arthur C Clark that

worldwide coverage can be obtained by using 3 microwave repeaters placed in a

geostationary.

Orbit at the height of about 36000Km with the period of 24 hrs Satellites

communication.

A satellite communication system consists of a number of earth stations

interconnected through a satellite serving as a microwave relay repeater. At

transmitting earth station, incoming signal modulated an incoming carrier

frequency. The modulated signal is uncovered using a local oscillator to a

microwave radio frequency. RF signal is amplified in a HPA (High Power

Amplifier) and transmitted to the satellite repeater through a transmittingantenna. The signal is received through a satellite antenna and after

amplification is converted to the downlink frequency using a translation

frequency provided by a local oscillator. After amplification to a high power

stage, the signal is down linked through a transmit satellite antenna to the

ground coverage area. At the receive earth station, signal received through the

antenna, after amplification by a sensitive low noise amplifier (LNA) is down

converted and de modulated to recover the base band signal.

EARTH STATION

Pat loss in a satellite system is much higher as compared to terrestrial radio

relay systems and therefore, earth station should have high transmit and receive

antenna.

Gains, high power amplifier on transmit side and more sensitive low noise

amplifier on the receive side.


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A simplified block diagram is shown in fig. information signal, received

through a terrestrial end link, are multiplexed and amplified in a base band

amplifier. Base band amplifier. Base band signals modulate a carrier at an

intermediate frequency. Modulated output is uncovered to a radio frequency. RF

signal in amplified in a HPA.

EQUIPMENT USED IN EARTH STATION

The earth station is generally equipped with following equipments:-

1. High power amplifier.2. Low noise amplifier.3. Up and down converter4. Power system.5. Antenna.6. End links


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BASIC TV SYSTEMS

The most commonly used color TV systems are:

1. NTSC

2. PAL

3. SECAM

NTSCThe work of ntsc was built on the basis of earlier attempts. The ntsc laid

foundations that made television a reality in the united states. At the dawn of

color tv it seemed at first that it was not going to compatible with

monochrome tv& would need special recievers.

a.R, G, B signals are combined in the suitable proportion to obtain Ysignals.

b.Luminance signals & two color signals are combined to obtain two colorsignals.

c. These are quadrature modulated & only sidebands are transmitted withsync signal

d.Color burst is transmitted on a black porch of the lines sync pulse.

Advantages:a. Higher frame rateb. Atomic color editsc. Less inherent picture noise

Disadvantages:

a. Lower number of scan linesb. Smaller luminance signal bandwidth


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c. lower gamma rated. Undesirable automatic featuresPAL

This system is a refinement of NTSC system. It has adopted in our country.

This system was developed in the federal republic of Germany & was

introduced in year 1967.

The three color signals i.e. R , G , B signals are combined to obtain Cr & Y

signals.

Advantages:

Greater number of scan lines.Wider signal bandwidth.

Stable hues.

Higher gamma ratio.

Disadvantages:

More flicker.

Lower signal to noise ratio

Loss of color editing accuracy variable color saturation

SECAM SystemIt is the abbreviation of French term Sequential Colors AMemoroire.

This system is also refinement of NTSC system & entirely different fromPAL system.

Transmission of only one of two signals at a time.

A difference weightage factor is used.

The sub carrier is frequency modulated by color difference signals.

Advantages:

Stable hues & constant saturation.

Higher number of Sean lines.


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Concepts of satellite communication

1. GEOSTATIONARY SATELLITEA geostationary satellite is any satellite which is placed in a geostationary

orbit. Here satellites maintain a constant position relative to the surface of the

earth. Geostationary satellites do this by orbiting the earth approximately 22,300

miles above the equator. This orbital path is called the Clarke Belt. In contrastto geostationary satellites are commonly used for communications & weather

observation. The typical life expectancy of a geostationary satellite is ten to

fifteen years. Because satellites circle the earth at the equator, they are not able

to provide coverage at the Northernmost & Southernmost latitudes.

Geostationary orbits are often referred to as geosynchronous.

2. MEDIUM EARTH ORBITMedium Earth Orbit (MEO) refers to a satellite which orbits the earth at an

altitude below 22,300 miles & above the altitude of low earth orbit(LEO)

satellites. Medium earth orbit terrestrial terminals can be of lower power & use

smaller antennas than the terrestrial terminals of geostationary satellite systems.

However they cannot be as low power or have as small antennas as Low

Earth Orbit terrestrial terminals. Medium Earth systems better round trip time

than geosynchronous orbit systems, but not as low as LOW EARTH ORBIT

systems.

3. LOW EARTH ORBITLEO refers to satellite which orbits the earth at altitudes between 200 miles &

930 miles. low Earth Orbit satellites must travel very quickly to resist the pull

of gravity approximately 17,000 miles per hour because of this, low earth orbit

satellites can orbit the planet in as little as 90 minutes .low earth orbit satellitesystems require several to provide coverage of the entire planet .


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Low earth orbit satellites typically operate in polar orbits.

Low earth orbit satellites are used for applications where a short round trip time

(Rtt) is very important , such as mobile satellite services

Low earth orbit satellites have a typical service life expectancy of five to seven

years.

4. ROUND TRIP TIME

In a satellite network, round trip (RTT)is the time required for a single to travel

from a terrestrial system up to the satellite and back ,or for a signal to travel

from a satellite down to a terrestrial system and back up to the satellite again.

Round trip time is limited by the speed of light .Round Trip TIME will beshortest for a low earth orbit (LEO) satellite and longest for a geostationary

satellite.

An LNB- Low noise Block (also called an LNC-Low Noise Converter), is used

for communication (broadcast) satellite reception .the LNB is usually affixed

either in or on the satellite dish.

5. LNB

The purpose of the LNB is to utilize the super heterodyne effect ; and amplify

and convert a wide block (band) of frequencies. This helps compensate the

signal loss associated with typical coaxial cable at relativety high frequencies.

The term low noise relates to the quality of the 1st

stage input amplifier

transistor ,measured in either called noise temperature units or noise factor

units.Both noise factor and noise figure are easily converted into noise

temperature units .a lower Noise temperature rating is always better (i.e. an

LNB with a noise temperature of 100k is 2x as good as one rated 200k).

6. Linear- LNB

LNB stands for low noise blocker and it is essentially an amplifier on the end

of your small satellite tv dish or communications dish .the linear portion of


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linear LNB stands for the charecterstics of the radio waves that are transmitted

via the satellite in space to your dish (LNB).

7. Types OF Polariization

7.1. Circular polarization

Circular polarization is a characterisitic of radio waves that are transiitted

from a satellite in actual space ,in which the actual radio waves rotate in a

spiral .the spiral of radio waves either rotates clockwise or counters clockwise

.a great analogy of how circular radio waves approach your satellite dish

(LNB)is by picturing an airplane propeller.the airplane propeller follows a

specific path ,but as it approaches the radio wave is spinning vertically.

7.2.Linear polarization

Linear polarization is the characteristic of radio wave in which the radio wave

in which the radio wave rotates on a single horizontal plane.a great analogy is

instead of an airplane propeller the radio wave approaches your satellite dish in

the form of a helicopter .the radio waves spin horizontally .

Besides the direction of the wave being either horizontal or vertical ,satellite

receivers usually only are able to work with one type of polarization .however

,they are able to pick up both signals ,the difference is about 50% loss in signal

strength(-3dB).

8. Fixed Satellite Service(FSS)

Fixed Satellite services (FSS)refers to a satellite services which uses fixed

terrestrial terminals .In other words ,FSSis any satellite service where the

ground station does not change locations frequently .

Consumer satellite television is the most popular application of fixed Satellite

service.

The opposite of FSS is mobile satellite services (MSS).


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9. Mobile Satellite services

Mobile satellite service (MSS)IS A Satellite system which uses portable

terrestrial terminals. MSS terminals may be mounted on a ship , an airplane ,or

an automobile . MSS terminals may be carried by an individual .

The most promising application of Mobile satellite service is portable satellite

telephones which will enable phone services anywhere on the globe.

10. Uplink

Uplink is the signal path from an earth station to a satellite.

Uplink Frequencies

Satellite band Uplink frequencies

C Band 5.925 -6.425

Ku band 14-14.5ghz

Ka band 27.5-31 ghz

11. Downlink

Downlink is the signal path from a satellite towards the earth .

Downlink frequencies

Satellite band Downlink frequency

C Band 3.7-4.2 ghz

Ku band 11.2 -12.7 ghz

Ka band 18.3-20.2 ghz


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12. Elevation

Elevation is the angular measurement of a satellite above the horizion .it is

measured in degrees .A satellite which is higher in the sky will have a greater

elevation than one which is close to the horizon .

A satellite exactly level with the horizon would have an elevation of 0 degrees

.a satellite with an elevation of 90 degrees would be directly overheaded .

Knowing the elevation of a satellite from your location is critical to being able

to successfully point a satellite antenna to it.


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STUDIO CAMERA

It is fited on the tripod.it has a cable known as the triaxial cable ,both videoand audio signal pass through this cable.15 V supply is required .

Camera has three parts:

1. Lens2. Transducer3. ElectronicsLENS:- use to form optical image in shooting .

TRANSDUCER:-is used to convert the video signal into the electrical

signal.

ELECTRONICS:-is used to convert the electrical signal into the

complete composite video signal.

MAIN CONTROLS ON CAMERA:-

Focus Zoom Iris

General process of the shooting from studio camera:-

Filter AWB Focus and zoom Electronic shutter speed VTR

The studio camera is the backbone of the television industry. It is mounted on a

dolly pedestal so the camera operator may wheel it to different locations withrelatives ease during shot changes. Television techniques monitor and adjust the

video levels of the studio camera with the camera control unit.

Video Noise increases in proportion to the video gain previously described.Even the best cameras will deliver noisy pictures under low-light levels. A

noisy picture has a great amount of snow, or white vibrating spots, in the

picture. This occurs when the video signals produced by the pickup tube are not

strong enough to override the electronic interference the system usuallygenerates .At 12dB gain, the system is generating more electronic interference-


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and more videos camera noise. Having covered the basic operation and

electronic characteristics of a video camera, we now examine the types of video

cameras you will work with at NBS detachments.


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VIDEO TAPE

Tape Characteristics

There are three different characteristics which contribute to total tape quality:

mechanical, magnetic and electro-acoustical characteristics.

The Mechanical characteristics are related to the carrier, the thickness of the

tape, the slack resistance and especially the tape guidance system behavior. The

latter is a matter of cassette housing, the precision of which should meet the

highest requirements, just like the tape itself. The tape guidance should always

be tight but flexible, without friction, but also without getting tangled. The

vulnerable edges of the thin tape should not wear, even at the microscopic levelor after many hours of use. Damage at the edges will have a negative effect on

the sound production right next to the edges. Some tapes have a thin layer o

coating on the back, to reduce the friction to an absolute minimum.

Close-up of the Video Tape

As far as the magnetic characteristics are concerned, the tape should be resistant

to demagnetize i.e. should have a high coercive force. The reminisce, which is

the magnetism that remains on the tape after the magnetism generating field is

taken away, is another essential characteristic. For audio tapes a high reminisceis a pre requisite in order to produce a wide dynamic range, but in case ofvideotapes high reminisce is not required, because of the high registration

speed for five meters per second. The reminisce of an average normal

videotape has more or less the same value as that of a conventional Ferro-oxide

audio cassette.

The electro-magnetic characteristics largely determine the quality of the tape.

These Characteristics are:

Signal to noise ratio(S/N) Color reproduction Sound Quality

The Quality of the color reproduction (chrominance:C) is expressed by the color

signal to noise ratio(color S/N).The higher this value, the better the hues arereproduced and the deeper the colors are. Here too, dB is the standard, but the

latest tapes also achieve higher values, up to +5 dB. The video and color S/N

relate directly to how equally the particles are spread on the tape surface.


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Hf or high frequency output level, also called Sensitivity, express the capability

of the tape to register the high video frequencies. If this is not done properly, it

reference standard. The HF level relates to the size of the particles.

Tape and Purpose

Different applications require tapes of different quality. It makes sense to use

the right tape for the right purpose. There is no need to purchase a high quality

tape, if the application does not require it. For almost all normal application the

standard(or High Standard)tape will suffice.


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VISION MIXER

A Vision Mixer (also called video switcher, video mixer or production switcher)is a device used to select between several different video sources and in some

cases composite (mix) video sources together and add special effects. This is

similar to what a mixing console does for audio.

Explanation

Typically a vision mixer would be found in a professional television production

environment such as a television studio, cable broadcast facility, commercial

production facility, remote truck/OB van or linear video editing bay. The term

can also refer to the person operation the device.Vision mixer and video mixer are most exclusively European terms to describeboth the equipment and operators. In the United States, the common name for a

device of this kind is (video) production switcher and the common name for the

operator of the device is known as technical device.

Software vision mixers are also available.

Capabilities usage in TV Productions

Besides hard cuts (switching directly between two input signals), mixers canalso generate a variety of transmissions, from simple dissolves to pattern wipes.

Additionally, most vision mixers can perform keying operations and generate

color signals(called mattes in this context).Most vision mixers are targeted atthe professional market, with newer analog models having component video

connection and digital ones using SDI. They are used in live and videotaped

television productions and for linear video editing, even though the use of

mixers in video editing has been largely supplanted by computer based non-

linear editing.

Older professional mixer worked with composite video inputs. There is still a

number of consumer video switchers with composite video, S-Videos or evenFireWire available. These are often used for VJing, presentations, and small

multi-camera productions.

Operation

The main concept of a professional vision mixer is the bus,basically a row of

buttons with each button representing a video source.Pressing such a button will

set the video out of the bus.Older video mixers had two equivalentbusses(called the A and B bus,such a mixer is known as an A/B mixer).One of


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these busses could be selected as the main out(or program)bus. Most Modern

mixers, however, have one bus that is always the program bus,the second main

bus being the preview bus. These mixers are called flip-flop mixers, since the

selected source of the preview and the program buses can be exchanged. Both

preview and program bus usually has their own video monitor.

Another main feature of a vision mixer is the transition lever, also called a T-bar

or Fader Bar. This lever, similar to an audio fader, creates a transition betweentwo buses. Note that in a flip-flop mixer, the position of the main transition

lever does not indicate which bus is active, since the program bus is always the

active or hot bus. Instead of moving the lever by hand, a button (commonlylabeled mix auto or auto Trans) can be used, which performs the

transition over a user-defined period of time.

The Third bus on a vision mixer is the key bus. A mixer can actually have morethan one of these, but they usually share only one set of buttons. Here, a signal

can be selected for keying into the program. The image that will be seen in theprogram is called the fill, while the mask used to create the keys translucence is

called the source.

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