Electronic Television Set / Receiver - Technology Evolution

Monochrome (Black &White) CRT Television

The Picture Tube heart of a television set. The picture tube is made up with a cathode ray tube; It consists of an evacuated glass bulb  which has an electron gun and phosphor screen. Screen is coated with a luminescent material that produces light when electrons strike the screen. The narrow neck contains the electron gun that produces the beam of electrons. A black and white TV receiver has one electron gun and a screen with continuous phosphor coating that produces a black and white picture..

Picture Tube

The Picture Tube heart of a television set. The picture tube is made up with a cathode ray tube; It consists of an evacuated glass bulb  which has an electron gun and phosphor screen. Screen is coated with a luminescent material that produces light when electrons strike the screen. The narrow neck contains the electron gun that produces the beam of electrons. A black and white TV receiver has one electron gun and a screen with continuous phosphor coating that produces a black and white picture. 

The neck of the picture tube contains the electron gun assembly. The election gun assembly consists of filament, cathode, control grid, accelerating grid (for 1^st anode) and a focusing anode. These electrodes are generally made of nickel or nickel alloy, mounted on ceramic insulator or supports inside the glass neck. The control grid is kept at a negative potential with respect to cathode and controls the flow of electrons from the cathode. The accelerating and focus anodes are given positive voltage. The final anode is kept at very high potential. The inside of the screen has a fluorescent material coating

Working Principle

When cathode is heated up it emits electrons. The control grid controls the number of electrons and the accelerating anode provides a high speed to the electrons. The focusing anode focuses the electrons in the form of a beam so that this beam of electrons is sharply focused at the screen. When this beam strikes the screen, a dot of bright light is formed there. These electrons can be deflected from the centre of the screen to any point of the screen. The deflection of electrons is achieved by deflection yoke placed on the neck of the CRT.

Two pairs of deflection coils are placed at the neck of the picture tube. One pair of coils is placed at the neck of the picture tube. One pair of coils placed above and below the electron beam produces horizontal deflection. The pair of coils placed left and right of the beam produces vertical deflection. The deflection of beam is possible only when required current is given to horizontal and vertical pairs of coils. As soon as current is given to these coils, a magnetic field is produced which causes the movement of electrons in horizontal and vertical directions. These movements of electrons form the complete scanning raster and it results a picture frame

 Signal Receiver Circuitry

 

            Picture tube is known as Heart while receiver circuit is the brain of a receiver. Antennas are treated as the integral part (Hand) of a television receiver unit. Antenna receives signals from the transmission medium and fed to TV circuit.  There are several types of antennas that we will discuss later on. Evolution of cable TV and digital broadcast replaces individual home antennas widely.

By the way RF tuner circuit is the input port of TV signal. This receives the signal then amplifies and covert the signals in to intermediate Frequency . Band selection and channel selection are occurring here. Common IF amplifies both video IF frequency and audio IF frequency and feeds its output to a video detector. Video detector separates video signals and its corresponding sync signals. Sync signals are used synchronize the picture to its corresponding raster rate or simply to help picture tube produce a regulated electron flow to produce the picture illusion.  Video amplifier amplifies the signal then feeds to the picture tube . tube mechanism coverts all this electrical singles as picture on its screen using its gun and deflection plates ( Horizontal and vertical plates with the help of sync signals )

The output of the tuner consists of all the signals in the desired channel, but the intermediate channel is fixed in the frequency band from 41 to 47 MHz, no matter what channel is tuned in.

Television audio is frequency modulated and is added to the video signal. FM sound demodulator separates audio signals from modulated carrier and gives to audio amplifier. Audio amplifier amplifies the signals to produce sound using a speaker

Other Inputs:

AV Input : Here clean audio and video is feeding directly to the video detector and detector separates video signal and sync signals and fed corresponding  succeeder  circuits . Audio feeds to the audio amplifier and then to loud speaker.