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T E L E –V I S I O N

Derived from the Greek word “tele”, which means at a distance, and “vision”, which means to see. TV literally means to see at a distance.

T E L E V I S I O N

• Derived from the Latin word “videre” that means to see.

•The electrical variations that correspond to changes in light values that is used to reassemble image on the screen of the picture tube at the receiver.

light in

video signal out

Camera Tube

Picture Tube

video signal in

light out

Video Signal

Light image is converted into an electric signal for only one elementary area at a time using a camera tube.

The video signal produced by the camera tube consists of sequential variations in time for the different areas.

The scanning sequence is done dot by dot from left to right and line by line from top to bottom at a very fast rate to cover the entire captured picture then modulated for transmission.

Video Operation

The scanning procedure utilizes timing pulses that can be used with the video signal to synchronize the scanning at the camera tube and picture tube.

The small areas of light or shade and of color are projected to the correct position on the screen to reconstruct the image.

Video Operation

• Derived from the Latin word “audire” that means to hear.

Audio Signal

• The electrical variations that corresponds to aural information.

Microphone

sound in

audio signal out

audio signal in

sound out

Loudspeaker

Audio Operation

Sound signal is transformed into electrical signal using microphones.

The audio signal is demodulated and reconstructed to form a replica of the original sound.

A TV system may be required to reproduce faithfully:

• The shape of each object or structural content.• The relative brightness of each object or tonal content.• The motion or kinematic content.• The color or chromatic content.• The perspective or stereoscopic content.

BASIC TV OPERATION

is a cathode-ray tube (CRT) with an electron gun and a phosphor screen inside the evacuated glass envelope.

the CRT in the receiver performs the opposite functions to the camera tube in the transmitter, converting the electrical video signal into an optical image.

PICTURE TUBEPICTURE TUBE

It performs a synchronized scanning sequence with the camera in projecting the output image on the screen.

has one electron gun for the phosphor screen.

Monochrome Picture Tube

Control Grid, G1 – almost completely covers the cathode cylinder, but a smaller aperture in G1 allows electrons to pass through. The negative bias at the control grid enables G1 to control the space charge of electrons emitted from the cathode.

Screen Grid, G2 – also considered the first anode. It accelerates electrons in the beam to a narrow path. G2 contains internal baffles to restrict the beam to a narrow path.

Ultor – has metallic spring fingers that make contact with the inner Aquadag coating for the anode voltage.

Aluminum Coating – A very thin film that increases the brightness of the screen and ensures that the brightness is even.

Phosphor Screen – emits light when bombarded with an electron beam.

Focus Grid, G3 – forms an electrostatic lens with G2 to force the electrons into paths that come to a point at the phosphor screen.

The screen has red, green and blue phosphors, and three electron beams are used, one for each primary color. The aperture mask, known as the shadow mask, has holes to maintain the separation of colors.

Tricolor Picture Tube

is a perforated thin steel sheet, supported by a heavy internal frame to maintain its rigidity, with about 300,000 holes that is mounted at the back of the phosphor dot screen.

Shadow Mask

Exterior Magnetic Components

Deflection Yoke – has Vertical and Horizontal scanning coils that deflects all three beams to form the scanning raster.

Convergence Yoke – is a magnetic yoke has individual adjustments for each color to make the beams converge through the openings inn the shadow mask. Color Purity Magnetic Rings – These rings are adjusted for bam landing at the screen, to obtain good color purity. The two magnetic rings are moved as a centering adjustment for all three electron beams.

Delta Guns The three electron guns are mounted at the corners of an equilateral triangle, forming a delta. The ability to maintain the three beams at all points on the screen is complicated because there is no combination that the guns are in the same vertical or horizontal plane.

The first shadow mask tubes, produced by Radio Corporation of America (RCA), used the delta-gun arrangement.

Types of Tricolor Gun

In-Line Guns All three guns are in one horizontal plane on a diameter of the tube neck, where green is usually at the center. This system eases the color convergence because one gun is at the center and the other two are in the same horizontal plane.

This requires a wider envelope diameter but the design still enables excellent focus to be maintained with a small spot size for high resolution in the picture.


Sony Trinitron Gun

All the electrodes are contained in a single gun but with three cathodes that produces the three beams. The control and accelerating grids have three holes to accommodate the three beams.


Raster The rectangular area of the picture tube scanned by the electron beam as it is deflected horizontally and vertically.

Line Flyback or Line Retrace A very quick deflection back to the left-hand side to start a new line when the beam reaches the right most side.

SCANNING

SCANNINGField Flyback or Field Retrace A quick deflection back to the top side to start a new field when the beam reaches the bottom most side.Pixel It means picture element. The smallest area of light or shade.

Horizontal Scanning

The movement of the beam from the left-hand side to the right-hand side and quickly deflecting it back from the left-hand side for horizontal retrace.

Vertical Scanning

The movement of the beam from the top to the bottom and quickly deflecting back from the top for vertical retrace.

Linear Scanning

1. Line starts at the top left hand corner of the picture. At this line and the succeeding lines are scanned horizontally; the beam gradually moves downward.

Vertical and Horizontal Scanning Sequence

2. Soon, but not immediately, after the application of the vertical blanking, the vertical scanning generator receives a sync pulse. This causes a vertical retrace to retrace.

3.Vertical retrace continues until the beam reaches the top of the picture and so on.

Interlacing Procedure:1. All the odd lines are scanned from top to bottom, and the even lines are skipped.2. A rapid vertical retrace causes the electron scanning beam to return to the top of the frame.3. All the even lines that were skipped in the first scanning are scanned from top to bottom.

Interlaced Scanning

A sample scanning pattern for 21 lines/frame and 10 1/2 lines/field:

Interlaced Scanning

How many visible horizontal lines are left due to vertical retrace interval?

A. 525 linesB. 485 linesC. 40 linesD. 500 lines

Past Board Exam Question

When the TV camera starts scanning line 1, the receiver must also start projecting line 1 on the CRT output display. Vertical and horizontal tracing and retracing at the camera and CRT must be done at exactly the same time in order to avoid distortion in the receiver output.

Horizontal Blanking and Sync Pulses

SYNCHRONIZATION

Loss of H sync causes picture to break into diagonal bars.

Period Time, µsec

Total line (H) 63.5

H blanking 0.15H-0.18H,or 9.5-11.5

H sync pulse 0.08H,or 4.75 + 0.5

Front porch 0.02H,or1.27 (minimum)

Back porch 0.06H, 3.81 (minimum)

Visible line time 52-54

Details of Horizontal Blanking

For a TV system, the horizontal flyback is 10 percent, this time equals _______.

A. 1.67 msB. 6.4 µsC. 0.167 msD. 0.64 µs


Vertical Blanking and Sync Pulses

Period Time

Total field (V) 1/60 s 0.0167 s

V blanking 0.05V-0.08V, or 0.0008-0.0013s

Each V sync pulse 27.35 µs

Total of six V sync pulse 3H = 190.5 µs

Each equalizing pulse 0.04H = 2.54 µs

Each serration 0.07H = 4.4 µs

Visible field time 0.92V-0.95V, or 0.015-0.016 s

Details of Vertical Blanking

The R, G, and B video voltages provide the picture information and these primary signals are encoded to form separate chrominance and luminance signals.

Addition of Colors

PICTURE INFORMATION ENCODING

● Contrast is the difference in intensity between black parts and white parts of the picture. The peak-to-peak AC video signal amplitude determines contrast.

Assuming it is synchronized to stay still, the reproduced picture also should have high brightness, strong contrast, sharp detail, and the correct proportions of height and width.

● Brightness is the average, or overall, illumination. On the picture tube screen, brightness depends on high voltage and DC grid bias for the picture tube.

Picture Qualities

also known as saturation. is the amount of color in the picture or color intensity.

● Hue is the tint of the color. The hue depends on the phase angle of the chrominance signal.

● Color Level or Chroma Level

● Detail also known as resolution or definition. a measure of how many picture elements can be reproduced. With many fine details, the picture looks sharp and clear.

Picture Qualities

● Aspect Ratio

the width-to-height ratio of the picture frame.

Picture Qualities

Quality Picture Signal

Contrast Range between Amplitude of AC black & white video signalBrightness Background DC bias on picture

illumination tubeResolution Sharpness Frequency response

or details of video signalColor Saturation Intensity or Level Amplitude of 3.58-

of color MHz chroma signalHue Tint of color Phase angle of 3.58-

MHz chroma signal

In Television broadcasting vivid strong colors are often referred as ______.

A. saturationB. hueC. chrominanceD. luminance


Luminance or Y signal

A combination of R, G, and B that contains the brightness variations, corresponding to a monochrome video signal. It is formed by taking 30% of the R video, 59% of the G video, and 11% of the B video.I signal It is formed by taking 60% of the R video, -28% of the G video and -32% of the B video. (Note: The minus sign indicates the addition of video voltage of negative polarity.) Its positive polarity is orange, and the negative polarity is cyan. These colors are chosen as best for the I signal in showing details of color.


Q signal It is formed by taking 21% of the R video, -52% of the G video, and 31% of the B video. Its positive polarity is purple; the negative polarity is yellow – green.


Y = 0.30R + 0.59G + 0.11B

I = 0.60R - 0.28G - 0.32B

Q = 0.21R - 0.52G + 0.31B

R

G

B

MATRIX

Video Signals from the Camera

Chrominance Modulation The I and Q signals are transmitted as the modulation sidebands of a 3.58 MHz subcarrier signal, which in turn modulates the main picture carrier wave.

90°90°

3.58MHzColor oscillator


Q Modulator

color sync

Q

I

I Modulator

3.58MHzCarrier signal

RCC

Adder or color

multiplexerTransmitter

color sync

CY

Y + C + color sync

Colorplexed Composite Video Signal

Y and C signals are separated from a colorplexed video then using synchronous demodulators for 3.58 MHz to provide B – Y and R – Y video, which are combined for G – Y video.

PICTURE INFORMATION DECODING

Monochrome Receiver Circuit

Y Video Amplifier0–3.2MHz

Chrominance BPA

3.58 MHz

colorplexed video

Y signal

C signal

R – Y = +0.62 Q + 0.95 I

90°90°



R-Y Demodulator

B-Y Demodulator

G-Y Amplifiercolor

sync

C

C

R-Y

G-Y

B-Y

video

video

video

MatrixAdder

R-Y

G-Y

B-Y

red

green

blue

Y signal

G – Y = -0.64 Q – 0.21 I B – Y = +1.73 Q – 1.11 I

A TV transmission where the modulating signal is applied in the polarity that reduces the RF carrier amplitude for peak white in the video signal.

TELEVISION TRANSMISSION

Relative amplitude for the AM RF picture signal:Tip of sync = 100%

Blanking level = 75% Black setup = 67.5%

Maximum white = 10 to 15% or 12.5% (typical)

The carrier signal does not go below 10% because there is distortion when the amplitude becomes zero.



Also known as negative-polarity modulation.


The carrier signal does not go below 10% because there is distortion when the amplitude becomes zero.


1. Noise pulses in the transmitted RF signal increase the carrier amplitude toward black, instead of white, thus, the noise streaks in the picture becomes less obvious.2. It uses less power since pictures are mostly white, thus the carrier amplitude is low most of the time when the picture information is transmitted.

3. The tip of sync is the reference of the carrier strength that can easily provide DC voltage that is proportional to the amount of the RF carrier signal. This DC voltage is used for bias in the automatic gain control (AGC) system of the receiver.

The advantages are:

The AM picture signal is not transmitted as a normal double sideband signal, only a part of the lower sideband is filtered out before transmission and vestige of sideband remains.

The purpose is to reduce the frequency band needed for the video modulation in the picture signal while keeping the low video frequency signal that contain the most important luminance information for large areas in the picture.

Vestigial Sideband Transmission

FM Sound Signal

Frequency Modulation is used for the associated sound signal in order to gain the advantages for less noise and interference.

This is practically the same with FM broadcast radio except that the maximum frequency swing is + 25 kHz, instead of 75 kHz. The audio modulating frequency range is from 50 Hz to 15 kHz.

NTSC (National Television System Committee) It was formed by the Electronic Industries Association (EIA) to prepare the standards for monochrome TV in the United States in 1941 and later the color TV standard in 1954.

PAL (Phase Alteration by Line) Similar to the NTSC system, but for each successive line one component of the chrominance signal is reversed in polarity so that any error in the hue phase can be averaged.

SECAM (Sequential Chrominance and Memory) It is a French system with a sequential technique and memory storage. In this method, two chrominance signals are transmitted one at a time for successive lines.

TELEVISION SYSTEMS

Specifies the rules governing radio broadcast services and television broadcast stations in the United States whose rules were adopted in the Philippines.

Each TV station is assigned 6 MHz wide channel with a specific carrier frequency.

FCC (Federal Communications Commission)

Television Broadcast Channels

Specific Frequencies for Channel 3 (60 to 66 MHz)

P = 61.25


P = 61.25

4.5 MHz

S = 65.75


P = 61.25

4.5 MHz

S = 65.75

C = 64.833.58 MHz


Television Channel Frequency Assignment

Channel Frequency Band DescriptionNumber (MHz)

1 Not used 2 54 - 60 3 60 - 66 Low Band VHF 4 66 - 72 Channels 5 76 - 82 6 82 - 88

88 – 108 FM Band

7 174 - 180 8 180 - 186 9 186 - 192 10 192 - 198 High Band VHF 11 198 - 204 Channels 12 204 - 210 13 210 - 216

14 – 83 470 – 890 UHF Channels

Which band does channel 14 of the television Channel belong?

A. high VHF bandB. EHF bandC. UHF bandD. low VHF band


Using NTSC standard, (PhilippineTV Standard), in what frequency isthe color sub-carrier found when tuned to channel 7?

A. 178.83 B. 182.13C. 184.83D. 175.13


Broadcast means “to send out in all directions.” The transmission of sound and images over a broad area.

TV Transmitter It operates on encoded visual and aural transmission where both AM picture signal and FM sound signal are emitted from a common radiating antenna. The typical service area of about 74 miles (121 km) in all directions.

TELEVISION BROADCASTING

Scanning And Sync

Scanning And Sync

Video Amplifier

Video Amplifier

Audio Amplifier

Audio Amplifier

Sound Signal Transmitter

Sound Signal Transmitter

Picture Signal Transmitter

Picture Signal Transmitter

TV Transmitter

microphone

antenna

TV Receiver It intercepts both the modulated audio and video, amplifies them for easy detection, demodulation and decoding and recovers the audio and video information.

Picture andSoundCircuits

Picture andSoundCircuits

Sound Signal

Sound Signal

Video signalfor the Picture

Video signalfor the Picture

Scanning And Sync

Scanning And Sync

antenna

loudspeaker

TEST YOUR KNOWLEDGE

1. In all standard television broadcast channels, the difference between the picture and sound carrier frequencies is

A. 0.25 MHzB. 1.25 MHzC. 4.50 MHzD. 6.00 MHz

TEST YOUR KNOWLEDGE

2. The number of lines scanned per frame in the raster on the picture tube screen is

A. 525 B. 262.5 C. 20 D. 10

TEST YOUR KNOWLEDGE

3. The difference between the sound carrier frequencies in two adjacent channels is


TEST YOUR KNOWLEDGE

4. Brightness variations of the picture information are in which signal

A. IB. QC. YD. R - Y

TEST YOUR KNOWLEDGE

5. What is the range of Baseband Frequencies in audio systems?

A. 0 – 4 MHzB. 20 – 20 kHzC. 30 – 300 kHzD. 3 – 30 kHz

TEST YOUR KNOWLEDGE

6. A _____ represents one set of 262.5 scanning lines.

A. fieldB. frameC. cycleD. interface set

TEST YOUR KNOWLEDGE

7. Picture frames are repeated at the rate of _____ per second.

A. 25B. 30C. 40D. 50

TEST YOUR KNOWLEDGE

8. Vestigial sideband is known as _____ type of emission.

A. CF3B. C3FC. B8ED. 83E

TEST YOUR KNOWLEDGE

9. The field rate in the NTSC television system.

A. 30 HzB. 120 HzC. 60 HzD. 15.75 Hz

TEST YOUR KNOWLEDGE

10. For NTSC TV system, the image is scanned from

A. top to bottomB. left to rightC. right to leftD. choices A and B

TEST YOUR KNOWLEDGE

11. What are the three separate signals derived from a matrix in a color TV transmitter?

A. Y, I and QB. T, D and QC. M, N and OD. R, S and T

TEST YOUR KNOWLEDGE

12. Range of UHF television transmitter

A. 470 – 670 MHzB. 470 – 770 MHzC. 470 – 890 MHzD. 470 – 980 MHz

TEST YOUR KNOWLEDGE

13. What is the chroma subcarrier signal frequency for color television?


TEST YOUR KNOWLEDGE

14. Under FCC standards, the black level is reached at

A. 75% of maximum amplitudeB. 85% of maximum amplitudeC. 95 % of maximum amplitudeD. 100% of maximum amplitude

TEST YOUR KNOWLEDGE

15. A material that glows when struck by the energetic electrons in a CRT.

A. aquadagB. SiliconC. GermaniumD. Phosphor

TEST YOUR KNOWLEDGE

16. The modulation used for the chroma signal in a standard NTSC color TV receiver.

A. SSBB. vestigial sideband AMC. suppressed-carrier AMD. FM

TEST YOUR KNOWLEDGE

17. In a TV signal (Negative Polarity), percentage modulation for white level is _____ that of synchronizing pulse level.

A. equal toB. greater thanC. less thanD. none of the above

TEST YOUR KNOWLEDGE

18. What signal is sent by the TV transmitter to ensure correct scanning at the receiver?

A. syncB. chromaC. luminanceD. video

TEST YOUR KNOWLEDGE

19. Which subcarrier leads by 90° in TV system?

A. IB. QC. YD. R

TEST YOUR KNOWLEDGE

20. In TV receiver, what is the horizontal sync frequency?

A. 60 HzB. 15,750 HzC. 525 HzD. 30 Hz

TEST YOUR KNOWLEDGE

EXCHANGE

PAPERS

1. In all standard television broadcast channels, the difference between the picture and sound carrier frequencies is


a n s w e r s

2. The number of lines scanned per frame in the raster on the picture tube screen is

A. 525B. 262.5C. 20D. 10

a n s w e r s

3. The difference between the sound carrier frequencies in two adjacent channels is


a n s w e r s

4. Brightness variations of the picture information are in which signalA. IB. QC. YD. R - Y

a n s w e r s

5. What is the range of BasebandFrequencies in audio systems?

A. 0 – 4 MHzB. 20 – 20 kHzC. 30 – 300 kHzD. 3 – 30 kHz

a n s w e r s

6. A _____ represents one set of 262.5 scanning lines.

A. fieldB. frameC. cycleD. interface set

a n s w e r s

7. Picture frames are repeated at the rate of _____ per second.

A. 25B. 30C. 40D. 50

a n s w e r s

8. Vestigial sideband is known as _____ type of emission.

A. CF3B. C3FC. B8ED. 83E

a n s w e r s

9. The field rate in the NTSC television system.

A. 30 HzB. 120 HzC. 60 HzD. 15.75 Hz

a n s w e r s

10. For NTSC TV system, the image is scanned from

A. top to bottomB. left to rightC. right to leftD. choices A and B

a n s w e r s

11. What are the three separate signals derived from a matrix in a color TV transmitter?

A. Y, I and Q B. T, D and QC. M, N and OD. R, S and T

a n s w e r s

12. Range of UHF television transmitter.

A. 470 – 670 MHzB. 470 – 770 MHzC. 470 – 890 MHzD. 470 – 980 MHz

a n s w e r s

13. What is the chroma subcarrier signal frequency for color television?


a n s w e r s

14. Under FCC standards, the black level is reached at

A. 75% of maximum amplitudeB. 85% of maximum amplitudeC. 95 % of maximum amplitudeD. 100% of maximum amplitude

a n s w e r s

15. A material that glows when struck by the energetic electrons in a CRT.

A. aquadagB. SiliconC. GermaniumD. Phosphor

a n s w e r s

16. The modulation used for the chroma signal in a standard NTSC color TV receiver.

A. SSB

D. FM

B. vestigial sideband AM C. suppressed-carrier AM

a n s w e r s

17. In a TV signal (Negative Polarity),percentage modulation for white levelis _____ that of synchronizing pulselevel.

A. equal toB. greater thanC. less thanD. none of the above

a n s w e r s

18. What signal is sent by the TVtransmitter to ensure correctscanning at the receiver?

A. syncB. chromaC. luminanceD. video

a n s w e r s

19. Which subcarrier leads by 90° in TV system?

A. IB. QC. YD. R

a n s w e r s

20. In TV receiver, what is the horizontal sync frequency?

A. 60 HzB. 15,750 HzC. 525 HzD. 30 Hz

a n s w e r s

GOOD LUCK…

THANK YOU…

copy of tv

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