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DHANALAKSHMI SRINIVASANCOLLEGE OF ENGINEERING

(An I SO 9001:2008 Cer ti fi ed In sti tuti on )Coimbatore-641 105

B.E./B.Tech. DEGREE EXAMINATION

VII Semester

Electronics and Communication Engineering

080290057 TELEVISION AND VIDEO ENGINEERING

QUESTION & ANSWER BANK

2013-14

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VII Sem ECE 080290057 Television and Video Engineering

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UNIT - V

PART A (13 2 = 26 Marks)

1. What is a Wobbuloscope? May/June 2013, May/June 2012

A TV Wobbuloscope is an instrument with a combined service facility of a wobbulator or

sweep generator, a cathode ray oscilloscope and a marker generator. It is convenient for bandpass

response alignment of RF/IF and video stages of a TV receiver.

2. State the use of geostationary satellite for TV system? May/June 2013

Geostationary satellites are used for satellite TV system. The satellites are placed well

above the earth in geostationary orbit, which means that they look like stationary upon the horizon.

A dish antenna can be employed to focus on them. Satellite signals are intercepted by the earth,

amplified and downconverted into signals which can be understood by the television through a set-

top.

3. What are the advantages of high definition television systems?4. Mention the advantages of high definition TV. Nov/Dec 2012, Nov/Dec 2011

The advantages of high definition television are

Improved resolution Improved colour reproduction Higher aspect ratio of atleast 5:3

Stereophonic sound

5. What are the advantages of HDTV over standard TV?

6. How does a higher definition television differ from a conventional television?

May/June 2012, May/June 2011

HDTV have twice the vertical and horizontal resolution of conventional television.

HDTV studio equipments have two mega-pixels per frame which is six times the number of pixels as conventional television.

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Viewing angle of HDTV is three times than that of conventional television.

7. How teletext is different from view data? Nov/Dec 2012

Teletext is transmitted using TV signals, but view data is transmitted using the standard

telephone network.

Teletext uses a 3 digit numeric identifier, while view data uses identifiers upto 10 characters.

8. List four merits of digital TV receivers. Nov/Dec 2011

Better picture and sound quality.

No ghosting interference and unwanted noise. Wide screen picture. Multichannel programming.

9. What is teletext? May/June 2010

Teletext is a generic form used to describe any system which makes use of blanked

(inactive) lines in a television system. It convey information which is correspondingly displayed on

the receiver screen in place of or in addition to the normal studio picture.

10. What are the different digital tuning techniques? May/June 2011

The different digital tuning techniques are,

Voltage Synthesized tuning

Frequency Synthesized tuning

11. Give the abbreviations for CATV, MATV and CCTV.

CATV Community Antenna Television System MATV Master Antenna Television System CCTV Closed Circuit Television

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12. How will you classify remote control receivers?

The remote control receivers may be classified into two, namely,

Electromechanical control systems

Electronic systems

13. Name the various digital equipments require in TV studio. May/June 2010

Digitally controlled cameras Electronic character generator Digital art of paint box

PART B

1. (a) Describe in detail the teletext picture with its data lines. How are the teletext

informations coded? Draw and explain the teletext TV receiver. (16 marks)

May/June 2013

Ans:

Teletext is a generic term used to describe any system which makes use of the

blanked (inactive) lines in a television system. It convey information which is correspondingly

displayed on the receiver screen in place or in addition to the normal studio picture.

The teletext picture

In the 625 line television system, a complete picture is made up of two interfaced fields.

Each field is containing 312.5 lines. Out of 312.5 lines, 7.5 lines are used for preequalising, vertical

sync and post equalizing pulses.

Another 12.5 lines are left out for retrace interval. The remaining 292.5 lines are utilized

to carry picture details.

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Out of 574 interlaced lines available for the display of picture details, only 480 lines are

practically used to present teletext picture.

Figure below shows a teletext picture area.

Coding of teletext informations

Out of 12.5 lines allocated for retrace, some are utilized for test and signaling purposes.At

present line numbers 15, 16, 17, 18 of the even numbered fields and line numbers 328, 329, 330

and 331 odd- numbered fields have been standardized for transmitting teletext signals. They are

called teletext data lines.

Binary pulse encoding is used for coding teletext informations. The digital pulses utilizedto convey teletext information which form a teletext lines are arranged in a specially coded groups.

The individual pulses within and every group are binary digits called bits. They represent

one or other of numbers 0 or 1. The number 0 represents the pulse absent state and 1

represents the pulse present state.

Every coded group of pulses is called word.

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Teletext TV receiver

A simplified block diagram of a teletext TV receiver is shown below. The pages of

information are converted into digital form. They are transmitted along with picture video signal

sequentially and during allotted line numbers.

A special circuit with the receiver retriever decodes these signals. The teletext decoder

suppresses normal picture signals being given to the picture tube. It supplies teletext signals

recalled from the data store and after conversion to suitable video signal by the character generator.

The teletext signals are sent with the same standards as for normal TV programmes so

that the viewers receiver can accept either of these without any extra circuitry.

2. (b)(i) Describe the application of satellite communication in the domestic broadcasting

systems? (8 marks)

May/June 2013

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Ans:

For a large number of TV owners living in rural areas served poorly by the cable

operators, broadcasting satellites remain the only choice. Today, millions of dish antenna are in

operation and the users are increasing rapidly.

For broadcasting TV signals three sets of frequency bands have been used namely

S, C and U bands. STAR TV and CNN are received on the C band using dishes ranging in

size from 2.5m to 5m in diameter.

To receive satellite TV in C band and S band, a satellite TV receiver system has to be

available. The satellite TV receiver system consists of a parabolic dish antenna with an azel mountlow noise block converter and a satellite video receiver. An azel mount permits the antenna to

point to various satellites beaming programmes like CNN, STAR, MTV.ZEE, BBC etc.

Tracking of different satellites is either motorized or manual. A low noise block

converter is employed at the head of the receiver chain and is connected to the feed output of the

antenna system.

A satellite receiver interfaces with the motor controlling the dish of the antenna.

Hence when a viewer selects a station through remote control, the dish turns to the appropriate

part of the sky to receive the signal.

3. (b)(ii) Write a detailed note on HDTV. (8 marks)

May/June 2013

4. (a)(ii) Explain the characteristic features of HDTV systems. (6 marks)Nov/Dec2012

Ans:

HDTV is usually defined as a system having twice the horizontal spatial and vertical

spatial resolution of the current television systems. The HDTV system is an extremely complex

collection of digital, communication, and computer techniques. The characteristic features of

HDTV systems are,

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Fine picture quality. Wide screen format and a fineness of definition. HDTV system allows viewing at about 3 times the picture height. The system implies large screen display of cinema quality, using more than 1000 lines. Improved colour rendition by separate colour difference. Includes one or more stereophonic channels that provide quality comparable to that of compact

disc.

HDTV broadcasting system consists of the basic three parts:

Program generating studio equipment. Transmitters and transmission links. Large screen TV receivers sets, projection TV equipment.

The program generating studio equipment consists of cameras and VCRs. Transmitters

and transmission links include microwave and satellite.

5. (a)(i) Describe the features of a satellite television system. (10 marks)

Nov/Dec2012

6. (b)(i) Write detailed notes on satellite television systems. (8 marks)


Ans:

One of the most common methods of TV signal distribution is via communication

satellite. A communication satellite orbits the equator about 22,300 mi out in space. It rotates in

synchronism with the earth and therefore appears to be stationary. The satellite is used as a radiorelay station as in figure below.

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The TV signal to be distributed is used to modulate a microwave carrier, and then it is

transmitted to the satellite. The path from earth to the satellite is called the uplink. The satellite

translates the signal to another frequency and then retransmits it back to earth. This is called thedownlink.

A receive site on earth picks up the signal. The receive site may be a cable TV company

or an individual consumer. Satellites are widely used by the TV networks, the premium channel

companies, and the cable TV industry for distributing signals nationally.

A newer form of consumer satellite TV is direct broadcast satellite (DBS) TV. The DBS

systems are designed specifically for consumer reception directly from the satellite. The new DBS

systems feature digitally encoded video and audio signals, which make transmission and reception

more reliable and provide outstanding picture and sound quality.

The features of a satellite television system are,

i. The picture quality from satellite systems is surprisingly good comparing to the conventional

land based TV transmissions.

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ii. It is free from picture ghosting.

iii. The range of propagation is more.

iv. Capacity to accommodate large number of users due to broadband.

v. Satellite communication is not prone to sabotage as there is no cable running through long

distances.

vi. Satellite communication is distance insensitive.

vii. 24 hours of music, videos, news, features etc are available on satellite TV.

viii. A variety of entertainment programmes, sports, childrens programs, foreign language

broadcasts and cultural programmes are available.

ix. Some of the channels are free to watch.

7. (b)(i) Explain the basic functions of a TV receiver remote control circuits. (10 marks)Nov/Dec2012

8. (a) With block diagram explain the working of infrared remote control unit of a TV

receiver. (16 marks)

Nov/Dec 2011

Ans:

The remote control unit consists of a small portable handset containing a keypad on thefront. Inside the set, there is a digital IC which generates and encodes pulses and a driver amplifier

for driving a light emitting diode (LED). The LED generates invisible infrared light. Every key

acts as a on-off switch.

The usual functions performed by the unique codes are channel selection (CS), fine

tuning (FT), brightness control, contrast control, colour saturation and audio volume control. Each

control has two positions: up and down.

The controlling function of the signals sensed from the remote control unit and decoded

by the microcomputer in the receiver is illustrated in figure below.

The advanced remote control units may also have teletext selection, bass control,

treble control etc.

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Fig: Controlling in TV receiver acting on remote signal

The infrared light from the LED travels in a straight line to the TV receiver. At the

receiver, the infrared light pulses are intercepted by a photodiode sensor, located in front panel of

the TV receiver.

The photodiode converts the light pulses into electrical pulses, which are amplified by a

high gain amplifier and are clipped to a constant level before feeding them to a microprocessor

unit.

The microcomputer used is a dedicated programmed microprocessor. The function of the

microprocessor is to decode the pulses and feed them through a data bus to the relevant circuits as

well as to display the control function on the screen. All controls are voltage operated.

An example for selecting channel 2 is given below. Key no. 2 on the keypad of the

handset is pushed, IC of the handset comes to life. It generates an appropriate pulse train which is

amplified to activate the LED to give chopped light pulses at about 38KHz.

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The photodiode at the receiver converts these pulses into electrical pulses. A preamplifier

IC amplifies these pulses which are fed to the microprocessor chip. The arrival of the first pulse

interrupts whatever the microprocessor was doing and sends the data into the decoder where the

code word is decoded. The decoded word operates the relevant tuner circuit.

The decoded word is stored in the memory of the microprocessor. A memory address is

generated and sent to the ROM device which generates the desired character matrix for displaying

the function on the screen.

9. (b)(ii) Describe briefly the teletext of videotext systems. (6 marks)

Nov/Dec 2012

Ans:

Teletext is a generic term used to describe any system which makes use of the

blanked (inactive) lines in a television system. It convey information which is correspondingly

displayed on the receiver screen in place or in addition to the normal studio picture.

Teletext is a one way service based on broadcast or cable TV system. A teletext

provides the technique of transmitting blocks of digital data containing alphanumeric or graphicinformation, which the teletext decoder in a home TV receiver into a series of displays called pages

of an electronic magazine.

Each magazine contains hundreds of pages containing information on such topics as

news headlines, weather forecasts, program airline schedules, stock exchange and so on. The

viewer can select on a specially adapted receiver with teletext decoder, the normal programs or

teletext pages or a combination of both, by a remote control key pad.

In teletext mode, an index page provides the key to select the desired information and

on entering the appropriate page number through the keypad, the wanted page can be accessed in a

matter of seconds.

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10. (a) Draw a neat block diagram to represent cable TV system and explain its working

principle. Explain the scrambling and descrambling employed in it. (16 marks)

May/June 2012

11. (a) Write notes on cable TV. (10 marks), (8 marks)


Ans:

Cable TV, sometimes called CATV, is a system of delivering the TV signal to home

receivers by way of a coaxial cable rather than over the air by radio wave propagation. The cable

TV system is an extension of the master antenna TV system. It covers not only the TV receivers

located in shadow zones or fringe areas, but even the receivers which are well within a clear line of

sight and which would otherwise receive excellent signal strength direct from the telecast.

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Inputs from various antennas and from VCR or digital video discs are combined in a

mixer. The mixer is called head-end. The head-end converts all radio frequency signals into VHF

channels.

The outputs from the head-end are fed to a broadband distribution amplifier from where

these are fed to the trunk cables. The trunk cables feed the signal to the branch lines from which

signal is trapped to be sent to homes. Line amplifiers are used at suitable points on the line to

overcome progressive loss of signal.

Various elements of CATV system are shown in figure above. Description of their

functions are as follows:

Head-end: The broadcast signals picked up by the respective antennas are processed. They are

amplified by a low noise amplifier and adjusted for correct level.

Trunk line cables: It consists of a coaxial cable which is an efficient wideband line.

Branch line cable: Small diameter (about 10mm) is used because the length is not too long.

Drop line: It is the line running from the branch to the subscribers home TV. It generally uses a

coaxial cable of about 6mm diameter.

Trunk amplifier: Trunk amplifiers are used to eliminate losses in the cable such as DC loss (I^2R

loss), skin effect loss and dielectric loss.

Bridge amplifier: It acts as a bridge between the trunk line and the branch line. It takes care ofimpedance mismatch and compensates the loss in the trunk line.

Line amplifiers: When a branch line is to be extended, line amplifiers are used.

Directional coupler: To ensure that each branch line extracts only a small energy from the trunk

line, directional couplers are used.

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Besides the normal programmes, some premium services like uncut movies, current

movies, special sports events, rainbow channel etc. are offered by the cable TV system on payment

of a premium channel fee. To allow access to such programmes to the authorized customer only,

the signal is scrambled. The authorized customer will have a descrambler unit supplied by the

cable operator.

Scrambling

In scrambling, the RF signal modulated by the composite video signal does not have the

sync pulses. Without sync pulses, the receiver cannot lock in with the sync suppressed signal. Also

the AGC voltage is locked, which cause reversal of black and white portions, ie., picture becomes

negative picture. Thus the scrambled picture will not be seen to ordinary subscribers.

Descrambling

For those subscribers who pay extra premium for seeing pay TV programmes, the

scrambled channels have to be descrambled. The descrambler restores sync pulses to the radio

frequency signal. For this, a pilot carrier of frequency lower than the RF channel frequency is sent

by the cable operator.

The descrambler unit at the subscribers end consists of a narrow band receiver, whichselects the pilot, amplifies it and filters out the spurious components. The filtered pilot carrier

passes through an AM detector. The detectors output consists of puls es which pass through a

pulse-shaping circuit to get clean pulses. The pulses are added to the sync suppressed signal at the

right place.

Fig: Descrambling with the help of a pilot carrier

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12. (a)(ii) Explain digital television systems. (8 marks)


13. (b) Explain the elements of a digital TV receiver. (16 marks)

Nov/Dec 2011

Ans:

The television system in which analog audio and video signals are converted into

digital binary pulses for transmission and after detection at the receiver are reconverted into analog

signals for being reproduced asoriginal sound and picture, is called digital television or simply

DTV.

Advantages

Picture quality: It is superb in all respects. Special features:

i. Picture in picture

ii. Freezing of frame

iii. TV games can be operatediv. All the processing functions can be software controlled and can be achieved by the

remote control unit

v. Teletext reception can be incorporated in the TV receivers

vi. Viewdata can be provided

vii. The DTV systems are able to provide interaction between the end user and the

broadcaster for pay TV through the use of a return path

viii.

Reduced bandwidthix. It permits multiplexing of two or more programmes on the same channel

Special effects

i. Editing can be done by processing the signals through a computer

ii. Two zoom features can be provided

iii. Blasting: Camcorders fitted with a digital field memory storage can zoomany part of the

picture chosen for recording and subsequent display. It is called blasting.

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iv. Pixelation: Mosaic like look can be provided to the picture by slowing the clock rate

progressively. The effect is called pixilation.

v. Wide Dimension TV (WDTV): WDTV gives special cinema like effect.

High reliability: Reliability is high as component count is lowered.

Digital TV receiver

The block diagram of digital TV receiver is shown below ,

Fig: Block diagram of a digital TV receiver

It is a superheterodyne receiver. The bundle of bits pertaining to sound and vision beats

with the local oscillator and produces IF signals (video IF and audio IF).

The tuner selects the desired channel. A sharp filter separates the cideo IF and audio IF.Video bits are detected and decoded to give the original samples after decompression. These are

converted into analog signal using a DAC. For audio, IF is converted into intercarrier frequency and

the sampled audio pulses are obtained by using a DQPSK demodulator. The demodulated pulses

passes through a decoder and a DAC circuit to get the original audio signal.

14. (b)(ii) Explain video disc system. (8 marks)

May/June 2011

Ans:

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Video disc system was developed to record video and associated audio information on a

disc with the help of laser beams, to eliminate the disadvantages of magnetic recording tapes.

The video disc was very much superior to tape and has the following advantages.

i. As it is covered by a transparent plastic or transparent lacquer, the tracks and recordings

remain safe and are not affected by dust, grease and scratches.

ii. Signal to noise rtio is high as 90dB.

iii. Dynamic range is high.

iv. Channel separation is high.

v. Wow and flutter do not exist and total distortion is low.vi. Frequency response is excellent.

vii. Size is quite small.

viii. Dropouts only upto 2.5nm of disc are felt due to error correction codes and distortion dur

to scratched is also automatically corrected.

ix. As the audio signals are converted into binary digits, the system has all the advantages of a

digital system.

x. The video discs are more economical than magnetic tapes.

15. (a)(ii) Describe VCR. (6 marks)

May/June 2010

Ans:

The main purpose of the video recorder is recording and replaying video and audio signals.

The video signal can be recorded on a magnetic tape for picture reproduction in a similar way as

the audio tape is used for reproduction of sound. Figure below shows the elements of a magnetic

tape recorder.

The tape consists of very fine particles of magnetic iron oxide on a plastic base. The

transport mechanism pulls the tape past the record-playback head. As the head consists of many

turns of fine wire, its magnetic field reacts with the magnetic tape. At the recording position,

signal current magnetizes the tape with the same variations as the signal.

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On playback, the moving tape induces current in the head. The record-playback switch

decides whether the machine records or playback. To increase tape speed, rotating heads can be

used. The relative head to tape speed is the writing speed. One more technique is helical scan in

which the head records diagonally across the width of the tape.

16. (b)(i) Write notes on 3DTV. (8 marks)

May/June 2010

Ans:

Normal television receiver pictures are two dimensional (2D) in nature. They have length

and breadth dimensions and lack depth, hence look flat. In three dimensional (3D) televisions,

viewing depth is also depicted on the screen. Therefore, the picture appears to have all the qualities

of a live scene as viewed with normal vision.

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3D Transmission

3D picture transmission is invaluably provided along with stereo sound. To accomplish

this, the left (L) channel and right (R) channel audio signals are independently frequency modulated

with the 5.5 MHz sound carrier. Then they are combined with the corresponding side video signal as in

figure below.

Thus the left and right channel signals formed together with the sync pulses. They are

amplitude modulated with the station channel carrier in separate modulators. From the output of right

channel modulator, the upper sideband (USB) is chosen while from the left channel modulator the

lower sideband (LSB) is removed. On combining they look like as shown in figure below.

It can be observed that, a total channel bandwidth of nearly 12 MHz is required for 3D

picture and stereo sound TV system. Therefore special channel width allocation equal to nearly twice

the normal channel width is required for such transmitting stations.

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