اجهزة التلفزيون الحديثة .. كتاب التلفزيون الملون والعادي

In the old television, it had more than thirty vacuum valves, the receiver performed various functions such as rectification - amplification - oscillators - mixing - sound and image detectors, etc.. and since its work was only accomplished by the presence of heating fuses inside it, it used to consume a lot of energy And it releases high heat, in addition to its large size and weight. As for modern devices, they use semiconductors, such as diodes, transistors, and integrated circuits, which are smaller in size, consume less energy, and spread less heat, Figure (1)-(1). The digital system (DIGITAL) was used in the automatic tuning channel elector, in the remote control circuits, in the timing, and other things that we will discuss in the coming chapters.

1-1 Modern TVs:

B

Figure (1-1)
A - A 9-inch black and white transistor TV that operates on network current (220 V) and DC battery 12 V.
B - Color TV (19) inch transistor with automatic picture light.
C - 25-inch color TV with electronic tuning, with the channel number displayed on the screen

The digital system:

It depends on the two numbers (zero) - (one) (0-1). Zero represents the OFF state. And one is the operating state (ON). The state of zero represents a low voltage close to zero (volts and one voltage is (+) 5 volts). The digital system works on the principle of logical circuits using diodes, transistors, or integrated circuits (IC). Among the common circuits is the (TTL) circuit, i.e. (transistor - logical transistor). The use of this system and integrated circuits makes electronic devices less expensive, smaller in size and weight, and lower energy consumption.

Applications of the digital system in the color television set: 1- Replacing the manual rotary channel elector with the electronic elector with touch tuning or pistons. The screen can show the channel number, time, etc. 2- Tuning and fine tuning of the channel, and controlling the vertical and horizontal tuning signal. (H.H.C), (V.H.C)

.

_0 Antenna and time programming Figure (1-2). Automatic correction of colors and their saturation using the (VIR) system. As for the transmission process, the digital system was applied in transmitting the visuals signal by spacecraft, and one of its important features is the reduction of noise on the clarity of the image, which appears as snow spots. This system requires wide frequency bands, which made it difficult to use in the range of current television frequencies. This problem was solved by making the carrier frequency (12000 MHz, or 12 GHz).

- Programming the device to pick up the station according to a prior timing of the required program

- Possibility of using computers and microprocessors to select and direct channels

Core circuits

Matrix x one fasting bladder

Voltage stabilized richer and vertical circuits

RANDOM-ACCESS TUNING

Keyboard (A) PROGRAMMER KEYBOARD

Figure (2-1) A - A 25-inch color TV with digital circuits showing the channel number and the correct time. B - An open TV showing a large number of integrated circuits and its computer circuits and remote control C - Audio and high voltage circuits appear - Programming circuits and moving the antenna CIRCUIT BOARD The station according to

Circuit board AUTOMATIC PROGRAMMING ROTOR CONTROL Automatic control of antenna rotation ANTENNA

PROGRAMMER

remote control

REMOTE

CONTROL

(B)

Characteristics of a Good Picture in Color Television The picture is the basic component on which most television receiver circuits end up functioning. In order for the image to be good and acceptable, it must be achieved

The following: 1 - The image is visible to the viewer from the usual distance, so that it is no less clear than a good photograph.
2- The colors of the image are as close as possible to real life. - That it does not contain any noticeable convulsions, and for this reason the image is made up of (50 or 60 fields per second) and every two fields overlap to form one image, so the frequency of the image is (25) or 30 times per second (one, depending on the system used). The image is suitable so that it can be viewed from a suitable place and by several people together, and its dimensions are not large so that its components and lines appear clear.

6 - The contrast of the image is good (Contrast), which is the ratio of the highest brightness to the lowest in the screen. In practice, the ratio is 100 to 1. This called for a contrast switch. As for the details of the image, it is like a photograph, consisting of a large number of dots graded between black and white. As for the color image, it is composed of a very large number. Tricolor dots (Red - Green - Blue) (RGB). These points must not be visible to the naked eye, so the smaller and larger the number, the clearer and better the image. from