Electronics - Television

Television Points : Television, Television network, Television transmission, Image formation, Formation of voltage pulses, Modulation, Transmission of carrier signals, Reception and conversion of carrier signals into picture & sound Definition It is an electronic device, which utilizes electromagnetic waves of very high frequency for simultaneous transmission and reception of sound as well as picture. Television network In a television network images of objects are transmitted along with sound by electromagnetic carrier waves from one place and are received at another distant place. Television transmission: Transmission through television network can be divided into following steps.
• Formation of image
• Formation of voltage pulses (Video and audio signals)
• Modulation of Video and audio signals to carrier signals
• Transmission of carrier signal.
• Reception and conversion of carrier signals into picture and sound 1. Image formation: A T.V camera is focused on the object to be televised. The convex lens of the camera produces an image of the object on a thin photo — sensitive plate called mosaic screen which emit electrons when light strike it. Electron beam scans the rear surface of the mosaic screen by magnetic deflection system. 2. Formation of voltage pulses: These electrons after repulsion from the positive charge area, converted into voltage pulses.
• Voltage pulses of the picture called video signals.
• Voltage pulses of the sound called audio signals. 3. Modulation: These video and audio signals now modulate to high frequency carrier signals. 4. Transmission of carrier signals: These carrier signals now transmitted through an antenna in the form of electromagnetic waves. 5. Reception and conversion of carrier signals into picture & sound: When these carrier signals strike the antenna of TN set, produce fluctuating A.C current in it. T.V set circuit separate video and audio signals and send them to the electron gun and loud speaker respectively which convert them into picture and sound respectively.