TELEVISION - 2

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EC 326 COMMUNICATION SYSTEMSUNIT - III

T Srinivasa RaoT Srinivasa RaoDept. of ECE

Bapatla Engineering College

Part 1

Vision characteristics and scanning systems, Composite video signal.

Part 2 Camera tubes: Principle of operation, Image

Orthicon, Vidicon, Plumbicon.

Part 3Block diagram of broad cast TV transmitterBlock diagram of broadcast TV receiver.

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Simplified cross-sectional view of a Vidicon TV camera tube

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Elements of a picture tube

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Signal transmission paths illustrating compatibility between colourand monochrome TV systems.R, G and B represent three camera tubes which develop video signals corresponding to the red, green and blue contents of the scene being televised

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A Rectangular Picture Tube

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Monochrome Picture Tube One Electron Gun Continuous phosphor coatingColour Picture Tube Three electron beams Three phosphors.

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Electron Gun Control Grid Accelerating Grid Focusing Grid

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Vidicon camera tube cross-section

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Circuit for output signal from a Vidicon camera tube

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Leaky Capacitor Concept

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THE PLUMBICON

Target Details Output Signal Current Characteristics

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A sync generator driving

several camera units

Switcher for selecting any camera output to one monitor.

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Block diagram of a drive and sync pulse generator

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Block Diagram of a Television Transmitter

Rear view of a black and white receiver with the back removed

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Block diagram of a monochrome television receiver

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CHOICE OF INTERMEDIATE FREQUENCY IN TV

(i) Image Rejection Ratio(ii) Pick-up Due to Local Oscillator Radiation from TV

Receivers(iii) Ease of Separation of Modulating Signal from IF

Carrier at the Demodulator(iv) Image Frequencies Should Not Lie in the FM Band(v) Interference or Direct Pick-Up from Bands Assigned

for other Services(vi) Gain

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V S B CORRECTION

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VIDEO DETECTOIN

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Detector and filter circuit of a radio receiver

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REQUIREMENTS

(a) The detector load must provide a suitable impedance as seen through the diode, at input of the detector to tune and damp secondary of the last IF coupling circuit correctly.

(b) The detector load must remove from the output, the IF content in the signal as much as possible. For this purpose the load usually includes one or two low-pass filter sections.

(c) The detector load should have a trap circuit (a series rejector circuit) for separating the intercarrier sound signal.

(d) The detector load must also include a provision to boost the higher video frequencies to compensate for the loss due to input capacitance of the video amplifier.

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FUNCTIONS OF THE COMPOSITE VIDEO SIGNAL

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SOUND SIGNAL SEPARATION

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Block diagram of AGC system

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High Voltage (EHT) Supply

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Deflection Circuits

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Operating Controls of a T V Receiver

Channel Selector Fine Tuning Volume Tone Contrast Brightness Vertical Hold Horizontal Hold.

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Next…

Colour

Television…

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