Television Standards and systems: Components of a TV system –interlacing – composite video signal. Colour TV – Luminance and Chrominance signal; Monochrome and Colour Picture Tubes – Colour TV systems–NTSC, PAL, SECAM-Components of a Remote Control and TV camera tubes, HDTV, LED and LCD TVs, DTH TV.

1. UNIT- II
TELEVISION
Television Standards and systems: Components of a TV system –interlacing – composite video
signal. Colour TV – Luminance and Chrominance signal; Monochrome and Colour Picture
Tubes – Colour TV systems–NTSC, PAL, SECAM-Components of a Remote Control and TV
camera tubes, HDTV, LED and LCD TVs, DTH TV.
INTRODUCTION OF TELEVISION:
 The aim of a television system is to extend the sense of sight beyond its natural limits
and to transmit sound associated with the scene.
 The picture signal is generated by a TV camera and sound signal by a microphone.
 In the 625 lines CCIR monochrome and PAL-B colour TV systems adopted by India, the
picture signal is amplitude modulated and sound signal frequency modulated before
transmission.
 The two carrier frequencies are suitably spaced and their modulation products radiated
through a common antenna.
 As in radio communication, each television station is allotted different carrier frequencies
to enable selection of desired station at the receiving end.
 The TV receiver has tuned circuits in its input section called “tuner”. It selects desired
channel signal out of the many picked up by the antenna.
 The selected RF band is converted to a common fixed IF band for convenience of
providing large amplification to it. The amplified IF signals are detected to obtain video
(picture) and audio (sound) signals.
 The video signal after large amplification drives the picture tube to reconstruct the
televised picture on the receiver screen.
 Similarly, the audio signal is amplified and fed to the loudspeaker to produce sound
output associated with the scene.
Important Blocks for TV transmission and reception are
 Camera tube (transducer light Electrical)
 Picture tube (Electrical light)
 Microphone
 Loudspeaker
Scanning:
Picture Pixels Electricsignals
 Difficult to convert all elements simultaneously.
 Scanning (USING ELECTRON BEAM) is made by element-by-element
one at time in a sequential manner.
 Vertical : process used to move the electron beam across the screen with a continuous
and uniform motion from top to bottom and vice versa
 Horizontal scanning: process used to move the electron beam across the screen with a
continuous and uniform motion from left to right and vice versa.
 Sequential scanning: process in which both horizontal and vertical directions are
scanned simultaneously to provide complete pictures.
 Flicker : If Scanning rate is less-25 frames per second, the time to move one frame to
another frame will be high. This results in alternate bright and darkness in the screen.

2.  Interlaced scanning (Separate odd and even lines,50 frames per second)
 Total lines = 625
 Even lines = 312.5
 Odd lines = 312.5
 Vertical frequency = No of frames per sec = 50 Hz
 Horizontal frequency = no of lines per field x no of times per sec
= 312.5*50
= 15,625 Hz
Sync pulses: Sync pulses are added to provide synchronization between camera tube and
picture tube.
Aspect Ratio:
Aspect Ratio=Width/height 4:3
Most of objects are move in horizontal direction.
Resolution: Ability to reproduce the fine structure and quality of picture
 Vertical Capable of resolving picture details in vertical direction
 Horizontal Capable of resolving picture details in horizontal direction
Positive modulation: Intensity of picture increases then the video signal amplitude increases.
 White level 100%
 Black level-0%
 Disturbance is more.
 Less efficiency.
 More power required.
 High distortion.
Negative modulation: When the intensity of picture increases, the video signal amplitude
decreases.
 Black level-100%
 White level-0%
 Disturbance is less.

3.  More efficiency.
 Less power required.
 Low distortion.
TELEVISION SYSTEMS AND STANDARDS:
Television Standards: There are a number of TV Standards worldwide. Not all television sets
in the world are alike. Countries use one of the three main video standards – PAL, NTSC, or
SECAM. What this means is that a video from a PAL country will not play in a country that uses
the NTSC standard.
Frames: Before we dive deep into the various TV Standards, we shall take a look at a few
basics of TV transmission. A television transmission consists of a set of rapidly changing
pictures to provide an illusion of continuous moving picture to the viewer. The pictures need to
come at a rate of 20 pictures per second to create this illusion. Each of these "rapidly changing"
pictures is a frame. A typical TV transmission is at 25-30 frames per second (fps).
Lines: Each frame consists of several closely spaced lines. The lines are scanned from left to
right and from top to left. A typical TV picture consists of 525 to 625 lines. Considering this large
number of lines, if all were to be written one after another the picture would begin to fade at the
top by the time the last line is written. To avoid this, the first frame carries the odd numbered
lines and the next frame carries the even numbered lines. This provides uniformity in the picture
and this is called interlacing.
Timing: TV receivers require a source to time the rapid succession of frames on the screen.
Designers decided to use the Mains power supply frequency as this source for two good
reasons. The first was that with the older type of power supply, you would get rolling hum bars
on the TV picture if the mains supply and power source were not at exactly the same frequency.
The second was that the TV studio lights or for that matter all-fluorescent, non-incandescent
lights flicker at the mains frequency. Since this flicker is much higher than 16 times per second
the eye does not detect it. However, this flicker could evolve into an extremely pronounced low
frequency flicker on TV screens due to a "beat" frequency generated between the light flicker
and the mains frequency. This would have made programme un-viewable particularly in the
early days of development of TV receivers. Two mains power frequencies worldwide are 50Hz
and 60Hz. This meant that there was an immediate division in the TV standards - the one with
25 frames per second (50 Hz) and 30 frames per second (60 Hz). Most of the compatibility
problems between TV standards across the world stem from this basic difference in
frequencies.
NTSC (National Television Standards Committee) : The majority of 60Hz based countries use a
technique known as NTSC originally developed in the United States by a focus committee
called the National Television Standards Committee. NTSC (often funnily referred to as Never
Twice the Same Colour) works perfectly in a video or closed circuit environment but can exhibit
problems of varying colour when used in a broadcast environment.

4. PAL (Phase Alternate Lines): This hue change problem is caused by shifts in the colour sub-
carrier phase of the signal. A modified version of NTSC soon appeared which differed mainly in
that the sub- carrier phase was reversed on each second line; this is known as PAL, standing
for Phase Alternate Lines, (it has a wide range of funny acronyms including Pictures At Last,
Pay for Added Luxury etc). PAL has been adopted by a few 60Hz countries, most notably Brazil.
SECAM: Amongst the countries based on 50Hz systems, PAL has been the most widely
adopted. PAL is not the only colour system in widespread use with 50Hz; the French designed a
system of their own -primarily for political reasons to protect their domestic manufacturing
companies -, which is known as SECAM, standing for Sequential Couleur Avec Memoire. The
most common facetious acronym is System Essentially Contrary to American Method.
SECAM ON PAL: Some Satellite TV transmissions (usually Russian) that are available over
India, are in SECAM Since the field (25 frames /sec) and scan rates are identical, a SECAM
signal will replay in B&W on a PAL TV and vice versa. However, transmission frequencies and
encoding differences make equipment incompatible from a broadcast viewpoint. For the same
reason, system converters between PAL and SECAM, while often difficult to find, are
reasonably cheap. In Europe, a few Direct Satellite Broadcasting services use a system called
D-MAC. Its use is not widespread at present and it is trans-coded to PAL or SECAM to permit
video recording of its signals. It includes features for 16:9 (widescreen) aspect ratio
transmissions and an eventual migration path to Europe's proposed HDTV standard. There are
other MAC-based standards in use around the world including B-MAC in Australia and B-
MAC60 on some private networks in the USA. There is also a second European variant called
D2-MAC which supports additional audio channels making transmitted signals incompatible, but
not baseband signals.[1]
Quick Facts:
 NTSC and PAL are video standards that are recorded on the cassette. These videos
send and electronic signal to the television, then only it can be viewed.
 In, India, PAL video format is supported.
 NTSC is the video standard commonly used in North America and most of South
America.
 PAL is the video standard which is popular in most of the European and Asian countries.
 The difference between NTSC and PAL is the transmission of number of frames per
second. In NTSC, 30 frames are transmitted per second. Each frame is constituted up of
525 scan lines.
 In PAL, 25 frames are transmitted per second. Each frame consists of 625 scan lines.
 Second, the power frequency used in NTSC is 60 Hz. While in PAL, the power
frequency is 50 HZ.
REASONS OF TV STANDARDS ARE DIFFERENT:
 Each countries have different main frequency
 American -60 Hz
 European and Asian-50 Hz
 (TV scanning field frequency and main frequency are same).
 INDIA-PAL SYSTEM Comparison between different standards:

5. Parameter NTSC PAL SECAM
Developed/adopted in US Europe(UK) France
Number of lines 525 625 625
Frames/second 60 50 50
Sub-carrier Frequency 3.58 MHz
4.43 MHz
4.25 or 4.4 MHz
Cost Medium Cost Most Expensive Least Expensive
Studio Mixing Easiest Medium Ease Difficult
CAMERA TUBE - VIDICON: Vidicon camera was the first camera tube based on
the photoconductive principle.
Working:
The photo layer has a thickness of about 0.0001cm and behaves like an insulator with a
resistance of approximately 20 X 106
ohms when in dark. With light focussed on it, the photon
energy enables more electrons to go to the conduction band and this reduces its resistivity.
 When bright light falls on any area of the photoconductive coating, resistance across the
thickness of that portion is reduced to about 2 X 106
ohm. Thus, with an image on the
target, each point on the gun side of the photo layer assumes a certain potential with
respect to the dc supply, depending on its resistance to the signal plate.
 As the electron beam scans the target plate, sufficient number of electrons from the
beam is then deposited on the photo layer to reduce the potential of each element
towards the zero potential.
 The remaining electrons are not deposited on the target, return and are not utilised in the
Vidicon.
 However, the sudden changes in the potential on each element, while the beam scans

6. cause a current flow in the signal electrode producing a varying voltage across the
resistance RL.
 The current in the RL voltage across the RL are directly proportional to light intensity
variations on the screen.
 The video signal developed across the load resistance is very small in amplitude. It is
therefore amplified by the conventional amplifiers before it leaves the camera unit.
Advantages:
 Small in size
 Low cost
 Long life
 High resolution
 By varying the target voltage, it can be operated at different levels of sensitivity.
 Gamma cancellation circuit is not necessary.
Disadvantages:
 High dark current
 Poor sensitivity
 Image lag is more
MONOCHROME PICTURE TUBE:
Construction:
Electron gun motion:
 The electron gun unit has a cathode, control grid and accelerating anode. The cathode
(K) is a small metallic oxide disk placed at the end of a narrow tube that covers the
heater. It is heated to produce thermionic emission and thus serves as source of
electrons for the beam current.
 The control grid (G1) is used to control the flow of electrons from the cathode (K). The
control grid (G1) is maintained at negative potential with respect to cathode (K).
 The grids that follow the control grid are the accelerating grid (or) screen (G2) and
focusing grid (G3).these are maintained at different positive potentials with respect to
cathode (K).
 All the grids, cathode, heater elements of the electron gun are connected to the base
pins. Through this base pins only necessary voltages are applied.
Focusing anode section:
 Electrostatic focusing method is used here, to focus the electron beam. This section also
brings all the electrons in the stream into small spot. It is considered as first electrostatic
lens action.
 The second lens system consists of screen grid are so selected that the second
convergence point is on the screen of the picture tube.
Deflection coil section:
 Here we are using electromagnetic system to deflect the electron beam in horizontal and
vertical direction.one pair of deflection coils is placed left and right side neck of the
picture tube to produce vertical deflection and one pair is placed top and bottom side of
the neck to produce horizontal deflection.
 The two pairs of coils are collectively called deflection yoke. The magnetic field in the
coil reacts with the electron beam to make the deflection.

7.  In the deflection yoke centering magnet and pin cushion magnet are also provided for
centering the electron beam and adjusting the movement of the electron beam at the
corners.
Monochrome picture tube
Deflection coil: (Deflection angle)
 This is the angle through which the beam can be deflected without striking the side of
the picture tube (or) bulb.
Final anode section:
 A final anode is included in the tube, to provide sufficient velocity and energy for the

8. electron beam. Here a black graphite material coating called aquadag, it is used as final
anode. It is connected through a specially provided pin at the top or side of the glass bell
to a very high potential of over 15kv. The secondary electrons emitted from the screen
are attracted by these aquadag coating.
Phosphor screen:
 The phosphor chemicals are generally light materials such as zinc and cadmium in the
form of sulphate and phosphate compounds. This material is proceeded to produce very
fine particles, which are then applied on the inside of the glass plate. The high velocity
electrons of the beam on hitting the phosphor excite its atoms with the result that
corresponding spot fluoresces and emit light.
External conductive coating:
 Aquadag is also coated on the outer surface of the glass bell. A spring clip is used to
connect this coating with the chasis ground. This coating is used to filter the AC ripples
in high voltage and to provide a perfect higher voltage.
Working:
 An AC supply of 6.3V is given to the heater. This filament heats the cathode (K) and the
cathode emits electrons. The control grid (G1) controls the flow of electrons. By varying
the control grid voltage, the number of electrons in the beam is also controlled.
 The accelerating anode (G2) increases the velocity of the moving electrons. The
focusing anode (G3) merges the electron beam so that they merge at a point and strike
the phosphor coating on the screen.
 The aquadag coating inside the tube is given a high voltage in the order of about 10kv to
15kv. This high voltage coating accelerates the electrons and collects the secondary
emissions.
 Using the deflection coils, we can deflect the electrons in both vertical and horizontal
directions. A sawtooth current is used for this, when the electron beam strikes the
phosphor coating it emits light. Depending on the video signal voltage, the emitted light
is bright (or) dark.
COLOR PICTURE TUBE – DELTA GUN PICTURE TUBE:
In this color picture tube, the three guns are arranged in a rectangular form and hence the name
delta gun tube. Radio Corporation of America developed it.
Main sections:
1. Electron gun section
2. Screen and shadow mask section
Electron gun section:
 The three guns are spaced equally at 120 degree with one another. They are tilted
inward with respect to axis of the tube. The three guns are in the three corners and
found delta shape.
 The three independent electron beams for each primary color come out of the three
guns. Each gun has a heater filament, cathode, control grid and accelerating anode. The
accelerating anodes are supplied EHT of about 25 kV. While the focussing grids are
provided an adjustable potential of about 5 to 75 kV for optimum focus.

9.  The deflection yoke design is more complex, since, we have to deflect three electron
beams at a time. The purity magnets are used to adjust the axis of electron beams so
that they can strike the correct phosphor dot at the screen.
Screen and shadow mask section:
In the screen, the three colour phosphor dots are arranged in a group called trials.it forms the
delta shape.
Gun structure b) Screen and shadow mask c) colour picture tube
 Each dot represents one primary colour. Depending on the screen size, nearly 3 lacs to
4 lacs triads are formed over the screen. The diameter of the each dot is about mm and
each spaced some 0.72 mm apart triangularly.
 Shadow mask is a thin perforated metal sheet. It is placed behind the screen. Shadow
mask has one hole for each triad on the screen. This arrangement moves the electron
beam passing through a hole and hit only one triad on the screen.
Working:
 The video signals corresponding to each primary colour are to three electron guns.
Necessary acceleration and focusing are done for each electron beam by its
accelerating and focusing anodes.
 Here purity magnet adjusts the axis of each electron beam. Convergence coil assembly
will converge the electron beams. Due to these arrangements the three electrons beams
will strike the corresponding colour phosphor dots in each of the triads.

10.  The shadow mask arrangement makes only one triad to energize by electron beam at a
time. The mask hides the other triads.
Advantages:
 Better focusing, if best possible ratio of gun-to-neck diameter is achieved.
Disadvantages:
 Shadow mask absorbs 80% of beam current.
 Beam convergence is a complex process.
BLACK AND WHITE TRANSMISSION:
Monochrome transmitter
Picture Transmission
 An oversimplified block diagram of a monochrome TV transmitter is shown in Fig.
 The luminance signal from the camera is amplified and synchronizing pulses added
before feeding it to the modulating amplifier.
 Synchronizing pulses are transmitted to keep the camera and picture tube beams in
step.
 A crystal-controlled oscillator generates the allotted picture carrier frequency.
 The continuous wave (CW) sine wave output is given large amplification before feeding
to the power amplifier where its amplitude is made to vary (AM) in accordance with the
modulating signal received from the modulating amplifier.
 The modulated output is combined with the frequency modulated (FM) sound signal in
the combining network and then fed to the transmitting antenna for radiation.
Sound Transmission
 There is no difference in sound transmission between monochrome and colour TV
systems.
 The microphone converts the sound associated with the picture being televised into
proportionate electrical signal, which is normally a voltage

11. Black and white transmitter
 This electrical output, regardless of the complexity of its waveform, is a single valued
function of time and so needs a single channel for its transmission.
 The audio signal from the microphone after amplification is frequency modulated,
employing the assigned carrier frequency.
 In FM, the amplitude of carrier signal is held constant, whereas its frequency is varied in
accordance with amplitude variations of the modulating signal as shown in Fig.
 Output of the sound FM transmitter is finally combined with the AM picture transmitter
output, through a combining network, and fed to a common antenna for radiation of
energy in the form of electromagnetic waves.
Black and white reception:
 A simplified block diagram of a black and white TV receiver is shown in Fig.
 The receiving antenna intercepts radiated RF signals and the tuner selects desired
channels frequency band and converts it to the common IF band of frequencies.
 The receiver employs two or three stages of intermediate frequency (IF) amplifiers.
 The output from the last IF stage is demodulated to recover the video signal.
 This signal that carries picture information is amplified and coupled to the picture tube,
which converts the electrical signal back into picture elements of the same degree of
black and white.
 The picture tube shown in Fig. is very similar to the cathode-ray tube used in an
oscilloscope.
 The glass envelope contains an electron-gun structure that produces a beam of
electrons aimed at the fluorescent screen.
 When the electron beam strikes the screen, light is emitted.

12. Monochrome receiver
 The beam is deflected by a pair of deflecting coils mounted on the neck of picture tube in
the same way as the beam of camera tube scans the target plate.
 The amplitudes of currents in the horizontal and vertical deflecting coils are so adjusted
that the entire screen, called raster, gets illuminated because of the fast rate of
scanning.
 The video signal is fed to the grid or cathode of picture tube.
 When the varying signal voltage makes the control grid less negative, the beam current
is increased, making the spot of light on the screen brighter.
Black and white reception
 More negative grid voltage reduces brightness. If the grid voltage is negative enough to
cut-off the electron beam current at the picture tube, there will be no light. This state
corresponds to black.

13.  Thus the video signal illuminates the fluorescent screen from white to black through
various shades of grey depending on its amplitude at any instant.
 This corresponds to brightness changes encountered by the electron beam of the
camera tube while scanning picture details element by element.
 The rate at which the spot of light moves is so fast that the eye is unable to follow it and
so a complete picture is seen because of storage capability of the human eye.
Sound Reception
 The path of sound signal is common with the picture signal from antenna to video
detector section of the receiver.
 Here the two signals are separated and fed to their respective channels.
 The frequency modulated audio signal is demodulated after at least one stage of
amplification.
 The audio output from the FM detector is given due amplification before feeding it to the
loudspeaker.
VHF and UHF tuner
 VHF tuner must cover the frequency range from 54 to 216MHz.
 Yagi-Uda antenna is used.

14.  UHF tuner must cover the frequency range from 470 to 890MHz.
 Log-periodic antenna is used.
 IF amplifier section is to amplify the modulated IF signal over its entire BW.
 Video detector is used to recover the original vidoe signal from the modulated IF signal.
 Video amplifier is used for further amplification.
 Video detector divides the picture and sound information.
AGC circuit
The AGC circuit provides a constant voltage at the output of video detector.
Horizontal and vertical sync pulses
 Contrast in the reproduced picture does not change.
 AGC permits increase in gain for weak signals.

15. Horizontal and vertical sync pulses
 The horizontal and vertical sync pulses are separated in the sync separator.
 A sync separator is a clipper circuit, which is biased to produce output, only during sync
pulses.
Color transmission and reception:
Picture Transmission
 A colour TV transmitter is essentially the same as the monochrome transmitter except
for the additional need that colour (chroma) information is also to be transmitted.
 Any colour system is made compatible with the corresponding monochrome system.
 Compatibility means that the colour TV signal must produce a normal black and white
picture on a monochrome receiver and a colour receiver must be able to produce a
normal black and white picture from a monochrome TV signal.
 For this, the luminance (brightness) signal is transmitted in a colour system in the same
way as in the monochrome system and with the same bandwidth.
 However, to ensure compatibility, the colour camera outputs are modified to obtain (B-Y)
and (R-Y) signals.
 These are modulated on the colour sub-carrier, the value of which is so chosen that on
combining with the luminance signal, the sidebands of the two do not interfere with each
other i.e., the luminance and colour signals are correctly interleaved.
 A colour sync signal called „‟colour burst‟‟ is also transmitted for correct reproduction of
colours.

Color TV transmitter
Sound Transmission
 There is no difference in sound transmission between monochrome and colour TV
systems.
 The microphone converts the sound associated with the picture being televised into

16. proportionate electrical signal, which is normally a voltage.
 This electrical output, regardless of the complexity of its waveform, is a single valued
function of time and so needs a single channel for its transmission.
 The audio signal from the microphone after amplification is frequency modulated,
employing the assigned carrier frequency.
 In FM, the amplitude of carrier signal is held constant, whereas its frequency is varied in
accordance with amplitude variations of the modulating signal.
 The sound FM transmitter is finally combined with the AM picture transmitter output,
through a combining network, and fed to a common antenna for radiation of energy in
the form of electromagnetic waves.
Receiver
 A colour receiver is similar to the black and white receiver as shown in Fig.
 The main difference between the two is the need of a colour or chroma subsystem.
 It accepts only the colour signal and processes it to recover (B-Y) and (R-Y) signals.
 These are combined with the Y signal to obtain VR, VG and VB signals as developed by
the camera at the transmitting end.
 VG becomes available as it is contained in the Y signal.
Color TV receiver
 The three colour signals are fed after sufficient amplification to the colour picture tube to
produce a colour picture on its screen.
 As shown in Fig., the colour picture tube has three guns corresponding to the three pick-
up tubes in the colour camera.
 The screen of this tube has red, green and blue phosphors arranged in alternate stripes.
 Each gun produces an electron beam to illuminate corresponding colour phosphor
separately on the fluorescent screen.
 The eye then integrates the red, green and blue colour information’s and their luminance
to perceive actual colour and brightness of the picture being televised.
 The sound signal is decoded in the same way as in a monochrome receiver.

17. Parameter NTSC PAL SECAM
Developed/adopted
in
US Europe(UK) France
Number of lines 525 625 625
Frames/second 60 50 50
Color info
transmission
U & V or I & Q are
used
U & V are used Db & Dr are used
Sub-carrier
Frequency
3.58 MHz 4.43 Mhz 4.25 or 4.4 MHz
Color Burst
9 cycles of sub-
carrier frequency
10 cycles of sub-
carrier frequency
burst cycles of red and blue
sub-carrier frequency
Variants 4.43, J, M
B, D, G, H, I, N, M &
Nc
B, G, D, K, K1, L
Cost Medium Cost Most Expensive Least Expensive
Studio Mixing Easiest Medium Ease Difficult
NTSC: (National Television System Committee)
Features of NTSC:
 Developed in the US.
 Compatible with the 525 line, 60 field per second, 2:1 interlaced monochrome system.
 To transmit color information, we use I & Q signals derived as follows:
 I=Vcos33 -Usin33 &
 Q=Vsin33 +Ucos33 where,
 U=0.492(B-Y) &
 V=0.877(R-Y)Note-(B-Y) & (R-Y) are the color signals that contain the real color
information. Furthur, U & V are weighted color signals and I & Q are then obtained from
U & V.
 I & Q are used to modulate a color sub-carrier of frequency 3.58 Mhz using two
balanced modulators.
 Variants of NTSC are NTSC 4.43 (VCRs), NTSC J (Japan) & NTSC M (same as J but
includes blanking pulses)
Advantages of NTSC:
 Higher frame rate – reduces visible flicker
 Less inherent picture noise – better S/N ratio
 Simpler circuits than PAL & SECAM
 Easy studio mixing
 Less costly than PAL
Disadvantages of NTSC:
 Small luminance signal bandwidth (3.85 MHz) – increased likelihood of interference
 Susceptible to hue fluctuations

18.  Lower gamma ratio (2.2 as opposed to 2.8 in PAL systems)
 More costly than SECAM
 Lower number of scan lines – means reduced quality on large TV screens

PAL (Phase Alternating Line)
Features of PAL:
 Adopted by Europe.
 Compatible with Europe’s 625 line, 50 fields per second, 2:1 interlaced monochrome
standard.
 It is a modification of NTSC to overcome high order of phase and amplitude integrity
requirements to avoid color distortion. It implements this by line-by-line reversal of the
phase of one of the color components. U & V signals (defined above) are used in
transmission and the modulation is phase quadrature balanced modulation. The phase
of the V is reversed on every other line so any color sub-carrier phase errors are
cancelled. Hence, hue errors are corrected by phase alternation. The color sub-carrier
frequencies are different for different versions of PAL as defined below.
 PAL B, D, G, H, I, N (color sub-carrier frequency = 4.43 MHz), PAL M (3.57 MHz) &
PAL Nc (3.58 MHz)
Advantages of PAL:
 Greater number of scan lines – more picture detail.
 Wider luminance signal bandwidth (4.43 MHz in most PAL variants)
 Stable hues – due to error correction by phase alternation
 Higher gamma ratio (2:8) – hence, higher level of contrast than NTSC
 Easy studio mixing compared to SECAM
Disadvantages of PAL:
 Costliest receivers due to complex circuits for electronic switching
 Lower frame rate – hence, more flicker
 Lower S/N ratio than NTSC
 Variable color saturation – cancelling out phase differences by alternation holds hue
stable but at the same time, it can change (reduce) color saturation.
SECAM (Sequential Color with Memory)
Features of SECAM:
 Developed in France
 625-line system, 50 fields per second, 2:1 interlaced system.
 Instead of transmitting R & B information together, they are sent one by one (hence,
sequential) and information about the color from the preceding line is used (hency,
memory). Transmits Db signal (blue color information) on one line and Dr signal (red
color information) on the next line while Y is transmitted on each line.Here,

19. Db=1.505(B’-Y) &
Dr=-1.902(R’-Y)
 The color sub-carrier frequencies for Blue & Red signals are 4.25 MHz and 4.4 MHz
respectively and FM is used as color modulation.
 Variants of SECAM are SECAM B, G, D, K, K1, & L. (B & G use a video bandwidth of
5 MHz while others use a video bandwidth of 6MHz.
Advantages of SECAM:
 Use of FM makes system free of phase errors.
 No crosstalk between color signals since they do not exist on the same line.
 Hue control not needed. (needed in NTSC but not needed in PAL & SECAM)
 Saturation control not needed (needed in both NTSC & PAL)
 Lower cost than both NTSC & PAL
 Higher number of scan lines than NTSC
Disadvantages of SECAM:
 Half color information is lost on each line since only one color signal is transmitted on
each line.
 Not suitable for studio use – studios use PAL and then transcode to SECAM for
SECAM markets.
 Incompatibility between different versions of SECAM (due to political influence)
DIGITAL TELEVISION:
 Digital television technology emerged to public view in the 1990s.
 Digital Television (DTV) is an advanced broadcasting technology that has transformed
the television viewing experience.
 DTV enables broadcasters to offer television with better picture and sound quality, and
multiple channels of programming.
 The switch from analog to digital broadcast television is known as the Digital Television
Transition.
 An important benefit of the switch to all-digital broadcasting is that parts of the valuable
broadcast spectrum have been freed up for public safety communications by groups
such as police, fire departments and rescue squads
Digital TV types: There is more than one type of digital television service.
Digital terrestrial: Digital terrestrial TV is received via your existing TV aerial, ensuring minimal
disruption to your TV viewing and little extra cost.
Digital satellite TV
 Digital television is received via a satellite dish and is a popular option for those whose
property already has such a dish fitted
 There are no geographical restrictions on this service as the digital TV signal is beamed
directly from satellites orbiting overhead.
 Free sat is the satellite equivalent to Free view and requires a one off payment for a free

20. sat box and satellite dish.
 Digital cable TV: Digital cable TV is delivered via a network of high-speed fibre optic
cables.
 Telephone line digital TV: This simply refers to digital television delivered to a user via a
telephone line. BT Vision is a prime example of this, although this service is only offered to
existing BT phone or broadband customers.
 Internet protocol television: Otherwise known as IPTV, internet protocol television uses a
broadband connection to provide digital television services to home.
DIGITAL TV RECEIVER:
 Digital television means the digital processing of TV signals both the transmitter and at
the receiver.
 But in the receiver side the digital signal should be converted into analog after
processing. Because of some technical problems and cost of the equipment digital
pictures cannot be televised.
 Both the picture and sound signal received from the antenna are analog in form. Then
this signal is fed into IF amplifier. After the amplification process, all the processes are
done in digital.
 At the final stage of processing these signals are converted into analog form and fed into
the respective picture tube and speakers.
 The luminance and chrominance signal process are in digital form.
 The central control unit is a microcomputer-based device used to control and co-
ordinate all circuits in this receiver.

Digital television receiver
The main blocks in this digital receiver are,
 Video codec: Video coder/decoder is used to convert the amplified analog IF signal into
digital form.
 Video processor: The signal received from the codec is fed into the video processor for
separating the luminance and chrominance signals.
 Luminance signal is separated and fed into multiplier stage to produce required contrast

21. and brightness.
 In chrominance section, chroma band pass filter and amplifier, reference oscillator, U&V
signal separator and the matrix formation are done.
 Deflection processing unit: In this section, the sync pulse from composite video signal
is separated and it is fed into integrator and differentiator for separation of vertical and
horizontal sync pulse respectively. These are used to trigger the horizontal and vertical
oscillators. This is done by counting the colour subcarrier and locking to it.
 Audio codec: Audio codec is used to separate the sound IF and to convert the analog
signal into digital signal.
 Audio processor: Audio processor is used to demodulate the frequency-modulated
signal and this signal is passed to filters for control stereo, tone and other functions.
 Central control unit: It is microprocessor-based device to control all circuit in the
receiver. It translates the user’s instruction and also signals from remote transmitter. The
unit contains 8-bit processor with EPROM, timer and other necessary circuits.
Merits of digital receiver:
 Resolution is high.
 No interference of electrical appliances.
 Synchronizations is better.
 Picture-in-picture is possible.
Colour receiver of new generation:
 Employing digital ICs and microprocessor. The keyboard located on the receiver itself or
through a remote keypad conveying instructions to the microprocessor by the infrared
radiation exercises control of available functions by the user.
 Thus the user can select the any of the available UHF and VHF channels and also
adjust the contrast, brightness, degree of saturation and the volume. Colour receiver
design is changing fast to include many more innovations
 Alternatively, the viewer can, with the keyboard, switch ON the VCR and adjust its
picture or call for the time of the day to be displayed on the small area of the screen.

22. Colour receiver of new generation
EDTV (Enhanced Definition Television)
 EDTV is a common name for a particular subset of the DTV (Digital Television)
standards, but is considered specifically a part of the HDTV format.
 EDTV operates as 480p
 EDTV also offers the benefits of digital surround sound.
 EDTV supports only progressive scan displays
 EDTV has less clarity
All TV programs, DVDs, and DVD players are compatible with an EDTV.
EDTV Minimum Performance Attributes:
 Receiver: Receives ATSC terrestrial digital transmissions and decodes all ATSC Table
3 video formats
 Display Scanning Format: Has active vertical scanning lines of 480 progressive (480p)
or higher
 Aspect Ratio: None Specified
 Audio: Receives and reproduces, and/or outputs Dolby Digital audio
HDTV
 High-Definition Television, a new type of television that provides much better resolution
than current televisions based on the NTSC standard.
 Types of HDTV displays include direct-view, plasma, rear screen, and front screen
projection.
 HDTV is a digital TV broadcasting format where the broadcast transmits widescreen
pictures with more detail and quality than found in a standard analog television, or other
digital television formats.
 HDTV requires an HDTV tuner to view and the most detailed HDTV format is1080i.
 DTV (high definition television) is a television display technology that provides picture
quality similar to 35 mm.
 HDTV generally uses digital rather than analog signal transmission.
 HDTV provides a higher quality display with a vertical resolution display from 720p to
1080i.
 The p stands for progressive scanning, which means that each scan includes every line
for a complete picture, and
 The i stands for interlaced scanning which means that each scan includes alternate lines
for half a picture.
 These rates translate into a frame rate of up to 60 frames per second, twice that of
conventional television.
 HDTV preserves extra clarity.
 All TV programs, DVDs, and DVD players are incompatible with HDTV.

23. HDTV Minimum Performance Attributes:
 Receiver: Receives ATSC terrestrial digital transmissions and decodes all ATSC Table
3 video formats
 Display Scanning Format: Has active vertical scanning lines of 720 progressive
(720p), 1080 interlaced (1080i), or higher
 Aspect Ratio: Capable of displaying a 16:9 image1
 Audio: Receives and reproduces, and/or outputs Dolby Digital audio
HDTV tuner: A device capable of receiving and outputting HDTV signals for display. HDTV
tuners can be a stand-alone device or it can integrate in the HDTV display. HDTV has many
different consumer names including HDTV decoder, HDTV receiver, and set-top box.
Integrated HDTV: A high-definition television or display that has the HDTV tuner built into the
set. It does not need a separate set-top box to receive over-the-air HDTV signals.
HDTV TRANSMITTER
Colour receiver of the future:
 The advent of satellite relay stations and ease with which complex control and memory
functions can be manipulated with the aid of microprocessors, together open up exciting
possibilities for television in the future.
 While digital processing of TV signal is being adopted in the new generation receivers,
the real breakthrough will come when a standard system will enable anyone anywhere in
the world to pick up a TV signal from a geostationary satellite and to display the
programme contained in the signal on his own receiver with no need for conversion from
one operating standard to another.
 It is even possible that such satellite pictures will be accompanied with electronically
generated sub-titles with possibility of simultaneous on-line translation from and into any
reasonably widely used language in the world.


24. Colour receiver of the future
INTRODUCTION TO MODERN TV CAMERAS, LCD AND PLASMA
DISPLAYS
It contains three camera tubes (vidicons) where each pick-up tube receives light of only one
primary colour.
 Light from the scene falls on the focus lens and through that on special mirrors.
 Colour filters that receive reflected light via relay lenses split it into R, G and B colour
lights. Thus, each vidicon receives a single colour light and develops a voltage
proportional to the intensity of one of the primary colours.
 If any primary colour is not present in any part of the picture, the corresponding vidicon
does not develop any output when that picture area is scanned.
 The electron beams of all the three camera tubes are kept in step (synchronism) by
deflecting them horizontally and vertically from common driving sources.
 Any colour light has a certain intensity of brightness. Therefore, light reflected from any

25. colour element of a picture also carries information about its brightness called
luminance.
 A signal voltage (Y) proportional to luminance at various parts of the picture is obtained
by adding definite proportions of VR, VG and VB.
 This then is the same as would be developed by a monochrome (black and white)
camera when made to scan the same colour scene.
 This i.e., the luminance (Y) signal is also transmitted along with colour information and
used at picture tube in the receiver for reconstructing the colour picture with brightness
levels as in the televised picture.
LCD Displays
 The liquid-crystal display has the distinct advantage of having low power consumption
than the LED.
 It is typically of the order of microwatts for the display in comparison to the some order of
mill watts for LEDs.
 Low power consumption requirement has made it compatible with MOS integrated logic
circuit. Its other advantages are its low cost, and good contrast.
 The main drawbacks of LCDs are additional requirement of light source, a limited
temperature range of operation (between 0 and 60 C), low reliability, short operating life,
poor visibility in low ambient lighting, slow speed and the need for an AC drive.
Basic structure of an LCD
 A liquid crystal cell consists of a thin layer (about 10 u m) of a liquid crystal sandwiched
between two glass sheets with transparent electrodes deposited on their inside faces.
 With both glass sheets transparent, the cell is known as transmitter type cell.
 When one glass is transparent and the other has a reflective coating, the cell is called
reflective type.
 The LCD does not produce any illumination of its own. It, in fact, depends entirely on
illumination falling on it from an external source for its visual effect

Types of LCD (Liquid Crystal Displays.)
 Two types of display available are dynamic scattering display and field effect display.
 When dynamic scattering display is energized, the molecules of energized area of the
display become turbulent and scatter light in all directions. Consequently, the activated
areas take on a frosted glass appearance resulting in a silver display. Of course, the
energized areas remain translucent.
 Field effect LCD contains front and back polarizers at right angles to each other. Without
electrical excitation, the light coming through the front polarizer is rotated 90 in the fluid.

26. Working of LCD
 The main principle behind liquid crystal molecules is that when an electric current is
applied to them, they tend to untwist.
 This causes a change in the light angle passing through them. This causes a change in
the angle of the top polarizing filter with respect to it.
 So little light is allowed to pass through that particular area of LCD. Thus, that area
becomes darker comparing to others.
 For making an LCD screen, a reflective mirror has to be setup in the back. An electrode
plane made of indium-tin oxide is kept on top and a glass with a polarizing film is also
added on the bottom side.
 The entire area of the LCD has to be covered by a common electrode and above it
should be the liquid crystal substance.
 Next comes another piece of glass with an electrode in the shape of the rectangle on the
bottom and, on top, another polarizing film. It must be noted that both of them are kept at
right angles.
 When there is no current, the light passes through the front of the LCD it will be reflected
by the mirror and bounced back.
 As the electrode is connected to a temporary battery, the current from it will cause the
liquid crystals between the common-plane electrode and the electrode shaped like a
rectangle to untwist.
 Thus the light is blocked from passing through. Thus, that particular rectangular area
appears blank.

27. PLASMA DISPLAY
 Two plates of glass are taken between which millions of tiny cells containing gases like
xenon and neon are filled.
 Electrodes are also placed inside the glass plates in such a way that they are positioned
in front and behind each cell.
 The rear glass plate has with it the address electrodes in such a position that they sit
behind the cells.
Plasma display
 The front glass plate has with it the transparent display electrodes, which are surrounded
on all sides by a magnesium oxide layer and also a dielectric material. They are kept in
front of the cell.
 As told earlier when a voltage is applied, the electrodes get charged and cause the
ionization of the gas resulting in plasma.
 This also includes the collision between the ions and electrons resulting in the emission
of photon light.
 The state of ionization varies in accordance to colour plasma and monochrome plasma.
 For the latter a low voltage is applied between the electrodes. To obtain colour plasma,
the back of each cell has to be coated with phosphor.
 When the photon light is emitted they are ultraviolet in nature. These UV rays react with
phosphor to give a coloured light.
 Working of Plasma display
 The working of the pixels has been explained earlier. Each pixel has three composite
coloured sub-pixels. When they are mixed proportionally, the correct colour is obtained.
 There are thousands of colours depending on the brightness and contrast of each. This
brightness is controlled with the pulse-width modulation technique.
 With this technique, it controls the pulse of the current that flows through all the cells at a
rate of thousands of times per seconds.

28. Characteristics of Plasma Display
 Plasma displays can be made up to large sizes like 150 inches diagonal. Very low-
luminance “dark-room” black level.
 Very high contrast.
 The plasma display panel has a thickness of about 2.5 inches, which makes the total
thickness not more than 4 inches.
 For a 50 inch display, the power consumption increases from (50-400) watts in
accordance with images having darker colors.
 All displays are sold out in shop mode, which consumes more power than the above
described. It can be changed to home mode.
 Has a lifetime of almost 100,000 hours. After this period, the brightness of the TV
reduces to half.
Advantages of Plasma Display
The slimmest of all displays
 Very high contrast ratios [1:2,000,000]
 Weighs less and is less bulky than CTR‟s.
 Higher viewing angles compared to other displays [178 degrees].
 Can be placed even on walls.
 High clarity and hence better colour reproduction. [68 billion/236 vs
 16.7 million/224]
 Very little motion blur due to high refresh rates and response time.
 Has a life span of about 100,000 hours.
Disadvantages of Plasma Display
 Cost is much higher compared to other displays.
 Energy consumption is more.
 Produces glares due to reflection.
 These displays are not available in smaller than 32 inches.
 Though the display doesn’t weigh much, when the glass screen, which is needed to
protect the display, is included, weighs more.
 Cannot be used in high altitudes. The pressure difference between the
 Gas and the air may cause a temporary damage or a buzzing noise.
 Area flickering is possible.
COMPARISON BETWEEN LCD AND PLASMA:
Specification LCD PLASMA
Thickness Minimum 1 inch Minimum 1.2 inches
Power
consumption
Requires less power Consumes more power
Screen size 13 - 57 inches 32 inches and above

29. Cost Much cheaper Cheaper
Life span 50,000 - 100, 000 hours Around 20, 000 – 60,000 hours