Presented by: Amany Mohamed Yara Naguib May Mohamed Sara Mahmoud Maha Ali Supervised by: Dr.Mohamed Abd El Ghany

Analogue Terrestrial TV.

No satellite Transmission

Digital Satellite TV.

Uses satellite and provides wide channel range.

Cable TV or (CAT).

Distributes audiovisual content using co-axial cables.

New Technologies:

Digital Terrestrial TV.

HD TV.

Uses NTSC, PAL, SECAM.

Web-TV.

IP TV.

The cathode ray tube (CRT) is a vacuum tube containing one or more

electron guns, and a phosphorescent screen used to view images. It has a

means to accelerate and deflect the electron beam onto the screen to create

the images.

Color television is a television transmission technology that includes

information on the color of the picture, so the image can be displayed in

color on the television screen. It is an improvement on the earliest

television technology, monochrome or black and white television, in which

the image is displayed in grey scale.

A cathode-ray tube (CRT) television displays an image by scanning a beam

of electrons across the screen in a pattern of horizontal lines known as a

raster. At the end of each line the beam returns to the start of the next line;

the end of the last line is a link that returns to the top of the screen. As it

passes each point, the intensity of the beam is varied.

A color television system is identical except that an additional signal

known as chrominance controls the color of the spot.

The chrominance is the signal used in video systems to convey the color

information of the picture

When analog television was developed, the luminance signal has to be

generated and transmitted at the same time (displayed on CRT).

It is therefore essential to keep the raster scanning in the device generating

the signal in exact synchronization with the scanning in the television.

The human eye has a characteristic called Phi phenomenon.

Quickly displaying successive scan images will allow the apparent illusion

of smooth motion.

The quick movement of the image can be partially solved using a long

persistence phosphor coating on the CRT, so that successive images fade

slowly.

The maximum frame rate depends on the bandwidth of the transmission

system and the number of horizontal scan lines in the image.

A frame rate of 25 or 30 Hz is a satisfactory compromise, while the process

of interlacing two video fields of the picture per frame is used to build the

image.

Plasma screens and LCD screens have been used in analog television

sets. These types of display screens use lower voltages than older CRT displays.

Many dual system television receivers, equipped to receive both analog transmissions and digital transmissions have analog tuner receiving capability and must use a television antenna.

A TV channel usually consists of 2 signals.

The picture information is transmitted using amplitude modulation.

The sound information is transmitted using frequency modulation.

Different methods of modulation are used to minimize interference between the picture and sound signals.

The picture information is transmitted on a separate carrier located 4.5 MHz lower in frequency than the sound carrier.

Vestigial sideband modulation technique is used in Television system.

The video signal is most often generated by a TV camera.

TV camera is used to convert the scene to an electric

signal this is done by transmitting a voltage of 1 V for

black and 0 V for white.

The scene is divided into smaller segments that can be

transmitted serially over a period of time.

Scanning is a technique that divides a rectangular scene

into individual lines.

the scene is subdivided into many fine horizontal lines

called scan lines.

Each line represents a very narrow portion of light

variations in the scene.

TV standards call for the scene to be divided into a

maximum of 525 horizontal lines.

The greater the number of scan lines, the

higher the resolution and the greater the detail that can be

observed.

The RF Tuner consists of an RF amplifier, mixer, and local

oscillator.

The tuner is used to select the TV channel to be viewed by

choosing an appropriate intermediate frequency (IF).

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.

The signal that carries picture information is amplified and

coupled to the picture tube

The picture tube converts the electrical signal back into picture

elements of the same degree of black and white.

The picture tube 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.

When electron beam strikes the screen, This beam is

deflected by a pair of deflecting coils.

The video signal is fed to the grid or cathode of the

picture tube.

Relation between signal voltage and the control grid.

IF signal consists of a video carrier wave and the sound carrier

A demodulator recovers the video signal

New carrier frequency is sent to an FM demodulator

Advantage of intercarrier sound

So the FM sound carrier is then demodulated, amplified, and used to drive a loudspeaker.

Color signal conveys picture information for each of the

RGB components of an image

Not simply transmitted as three separate signals, because

• Monochrome receivers

• Three times the bandwidth of existing television

• Problems with signal transmission

The RGB signals are converted into YUV form

Y signal represents the lightness and darkness

(luminance) of the colors in the image.

The Y signal is ideal for transmission as the luminance

signal.

The U and V signals are

"color difference" signals

The U signal is the difference

between the B signal and the

Y signal

The V signal is the difference

between the R signal and the

Y signal

Advantage of this scheme

Two demodulators

• X demodulator

• Z demodulator

Color difference signals are further matrixed into

three color difference signals.

R, G, B signals in the receiver are electronically derived

by matrixing

Low resolution portion of the Y signal cancel out

The higher resolution portions of the Y signals do not

cancel out

U and V are transmitted by using quadrature amplitude

modulation

Before transmission, the subcarrier, a 3.58 MHz sine

wave, is removed from the active portion of the video

Subcarrier sidebands that carry all the information of U

and V signals are produced

The subcarrier sidebands are known as "Chroma" or "chrominance".

It is a 3.58 MHz sine wave which changes phase as compared to the subcarrier according to the changing values of U and V representing hue of the color

It also changes amplitude which represents the approximate saturation of a color

The chrominance signal represents only the U signal, after 70 ns V signal, 70 ns later –U and 70 later –V

To extract U, a synchronous demodulator samples the Chroma every 280 nanoseconds

The output is a train of discrete pulses having amplitude same as original U(discrete time analog samples)

The pulses are low-pass filtered (analog continuous time signal)

To extract V, a 90 degree shifted subcarrier samples the Chroma signal every 280 nanoseconds

The mentioned process uses the subcarrier HOW?!! The receiver must reconstitute the subcarrier.

Color burst, is transmitted during the back porch of each scan line

Phase-locked loop (oscillator) locks onto the signal to achieve a phase reference

Such a process causes poor color reproduction due to phase errors in the received signal

Synchronizing pulses added to the video signal at the end of every scan line

video frame remains locked to reconstruct the image

The Sync signal separator circuit separates the composite signal into

2 signals.

a sync separator circuit detects the sync voltage levels

Loss of horizontal synchronization results in an unwatchable picture

Loss of vertical synchronization produces an image rolling up or

down the screen.

Signals the beginning of each new video line.

A back porch, which is used as a reference level to remove any DC

components from the floating (AC-coupled) video signal.

For composite color signals, the clamping occurs during the

horizontal sync pulse

It is a series of pulses that occur between fields to signal the monitor

and prepare to scan the next field.

Some lines contain only HSYNC pulses, while others contain

VSYNC pulses

Changes to the image are kept in step with the vertical

synchronization pulse to avoid visible discontinuity of the image.

If the image is updated with a new one while being transmitted, the

display shows a mishmash of both frames

Vertical synchronization times frame buffer to ensure that only

whole frames are seen on screen.

the program has to wait until the video controller finishes

transmitting the image

Triple buffering reduces this latency significantly.

Channel selector switch

The fine tuning control

The hold control

The brightness control

The contrast control

The volume and tone controls

http://www.tecnicontrol.pt/en/wiki/item.html?id=81-the-various-methods-of-tv-transmission

http://www.daenotes.com/electronics/communication-system/tv-television-transmitter

https://en.m.wikipedia.org/wiki/Analog_television