FREQUENCY ALLOCATION TABLE.
INTRODUCTION:
For efficiency in transmission of both radio and television waves the should be a standard bandwidth of frequency to be used as guideline. Failure of which is an offence punishable by law. These frequencies are allocated according to use e.g. television channel, radio stations and aeronautical channels,
Broadcasting ,aeronautical radio navigation ,aeronautical mobile ,space navigation and space research , mobile ,amateur and amateur satellite mobile, maritime mobile National Television Standards Committee (NTSC) is the standards that is mostly followed.

CONCLUSION.
Frequencies for different use are allocated as follows.

REFERENCE
www.projects.com
www.digchip.com
www.eporonaelec.com

TELEVISION BLOCK DIAGRAM AND FUNCTIONS:
INTRODUCTION:

A television receiver is made up of several function block which together functions to achieve a good signal reception ,color display, clear sound etc this blocks are shown below plus their functionality.

LCD TV
LCD TV is a digital television system that displays digital video on an LCD (Liquid Crystal Display) and supports digital/analog video broadcasting (cable, satellite, terrestrial), broadband connection, personal video recording (PVR), interactive internet, and wireless connectivity.
Core Subsystem includes:
DSP - performs MPEG encoder/decoder, video, voice/AC3/MPEG audio processing.
RF Demodulation - performs COFDM/QAM/QPSK demodulation, Forward Error Correction (FEC) and video mux.
MCU - controls system electronic, network, and user interface.
Memory - stores executing code and data/parameters.
Video Interface - selects video source to be decoded/encoded by ADC/DAC and DSP.
Audio Interface - allows audio to be digitized by the audio codec and processed by DSP to provide high-quality audio for MPEG/AC3 requirements.
LCD Interface - parallel digital video is converted into serial data for transmitting to the TFT (Thin Film Transistor) controller via the LVDS (Low-Voltage Differential Signaling) transmitters and receivers. The LCD display is controlled by the CCFL (Cold-Cathode Fluorescent Lamp) backlight and the TFT gate/source drivers.
Power Conversion - converts the input power from the AC adaptor to run various functional blocks.

A TV set includes the following functional blocks:

Low voltage power supply (some may also be part of (2).) Most of the lower voltages used in the TV may be derived from the horizontal deflection circuits. Sometimes, there is a separate switching power supply but this would be the exception. Rectifier/filter capacitor/regulator from AC line provides the B+ to the switching power supply or horizontal deflection system. Degauss operates off of the line whenever power is turned on (after having been off for a few minutes) to demagnetize the CRT.
Horizontal deflection. These circuits provide the waveforms needed to sweep the electron beam in the CRT across and back some 15,734 times per second (for NTSC). The horizontal sync pulse from the sync separator locks the horizontal deflection to the video signal.
Vertical deflection. These circuits provide the waveforms needed to sweep the electron beam in the CRT from top to bottom and back 60 times per second (for NTSC). The vertical sync pulse from the sync separator locks the vertical deflection to the video signal.
CRT high voltage (also part of (2).) A modern color CRT requires up to 30 kV for a crisp bright picture. Rather than having a totally separate power supply, nearly every TV on the planet derives the HV (as well as many other voltages) from the horizontal deflection using a special transformer called a 'flyback' or 'Line OutPut Transformer (LOPT) for those of you on the other side of the lake.

Tuner, IF, AGC, video and audio demodulators. Input is the antenna or cable signal and output are baseband video and audio signals. There is usually someplace inside the TV where line level video and audio are present but it may not be accessible from the outside of the cabinet unless you paid for the more expensive model with the A/V option. Very often, the tuner is a shielded metal box positioned on the bottom right (as viewed from the front) separate from the main circuit board. Sometimes it is on the main circuit board. The IF section may be in either place.
On older or cheap TVs with a knob tuner, this is usually mounted to the front panel by itself. There are usually separate boxes for the VHF and UHF tuners.
Chroma demodulator. Input is the baseband video signal. Outputs are the individual signals for the red, green, and blue video to the CRT.

Video drivers (RGB). These are almost always located on a little circuit board plugged directly onto the neck of the CRT. They boost the output of the chroma demodulator to the hundred volts or so needed to drive the cathodes of the CRT.

Sync separator. Input is baseband video. Output is horizontal and vertical sync pulses to control the deflection circuits.

Audio amplifier/output. The line level audio is amplified to drive a set of speakers. If this is a stereo TV, then these circuits must also perform the stereo demultiplexing.

System control. Most modern TVs actually use a microcontroller - a fixed program microcomputer to perform all user interface and control functions from the front panel and remote control. These are becoming increasingly sophisticated. However, they do not fail often. Older TVs use a bunch of knobs and switches and these are prone to wear and dirt.

conclusion
The vertical yoke is part of the host television set. Two coils make up the vertical yoke. These coils deflect the picture tube's electron beam in an up-and-down direction. The vertical yoke coils flank the sides of the picture tube neck.
The horizontal yoke, like the vertical yoke, is part of the host television set. The horizontal yoke includes two coils. These coils control side-to-side deflection of the electron beam. You'll find horizontal yoke coils above and below the picture tube neck.
Most problems occur in the horizontal deflection and power supply sections. These run at relatively high power levels and some components run hot. The high voltage section is prone to breakdown and arcing as a result of hairline cracks, humidity, dirt, etc.
The tuner components are usually quite reliable unless the antenna experiences a lightning strike. However, it seems that even after 20+ years of solid state TVs, manufacturers still cannot reliably solder the tuner connectors and shields so that bad solder connections in these areas are common even in new sets.

REFERENCE:
www.digchip.com
www.projects.com

UNIVERSITY OF EASTERN AFRICA, BARATON.

SCHOOL OF SCIENCE AND TECHNOLOGY.

SUB- DEPARTMENT OF TECHNOLOGY.

ASSIGNMENT: COLOR TV PICTURE TUBE WITH LABELED PARTS

ASSIGNMENT PRESENTED IN PARTIAL FULLFILMENT OF THE COURSE: CMMT 381 TELEVISION CIRCUIT I.

PRESENTER: KIBARO ISAIAH.

ID. NUMBER: 05S0004.

INSTRUCTOR: PROF. JESSE ROLE

DATE AND PLACE: 14TH FEBRUARY 2008, BARATON UNIVERSITY.

INTRODUCTION.

In a color-television tube, three electron guns (one each for red, green, and blue) fire electrons toward the phosphor-coated screen. The electrons are directed to a specific spot (pixel) on the screen by magnetic fields, induced by the deflection coils. To prevent “spillage” to adjacent pixels, a grille or shadow mask is used. When the electrons strike the phosphor screen, the pixel glows. Every pixel is scanned about 30 times per second.

HISTORY. Crooke’s tube (OLD)

Sir William Crooke’s constructed this forerunner of the modern television picture tube in the 1870s to investigate the properties of cathode rays. When the tube is evacuated and a high voltage applied, one end of the tube glows, caused by cathode rays (now known to be electrons) striking the glass. The modern television picture tube, also known as a CRT (Cathode Ray Tube) is a direct descendant of the Crooke’s tube. The major differences are that a CRT uses a heated cathode to increase the number of electrons, while the Crooke’s tube does not, and the CRT has extra electrodes to focus and deflect the beam as it travels toward the screen. FIGURE 1

Color TV picture tube (MODERN).

A color television picture tube contains three electron guns, one corresponding to each of the three primary colors of light—red, green, and blue. Electromagnets direct the beams of electrons emerging from these guns to continuously scan the screen. As the electrons strike red, green, and blue phosphor dots on the screen, they make the dots glow. A screen with holes in it, called a shadow mask, ensures that each electron beam only strikes phosphor dots of its corresponding color. The glow of all the dots together forms the television picture. FIGURE 2a and FIGURE 2b

Trinitron Cathode Ray Tube.

Many televisions still use cathode ray tubes (CRTs) for receivers. Until the Sony Corporation patented the simplified Trinitron system in the late 1960s, RCA’s original and more complex color tube dominated the market. Today, flat-screen TVs, based on a different technology, are becoming increasingly popular. Electron gun electrode structure that produces and may control, focus, and deflect a beam of electrons, as in a television picture tube, here the beam produces a visual pattern on the tube's screen. The source of the electron beam is the cathode, a flat metal support covered with oxides of barium. Cathode-ray tube Vacuum tube that produces images when its phosphorescent surface is struck by electron beams.

figures

FIGURE 3

FIGURE 2b

FIGURE 2a

REFERENCE:
Encyclopedia Britannica.
Britannica Concise Encyclopedia.
www.digchip.com