PAL DECODER | DE COLOUR | PAL ENCODER

PAL -D RESIVER

 Runner 

• It is very important to keep the correct value of the frequency of the local oscillator to produce different colors in the picture. This is called automatic tuning (AFT) and the function of this circuit is to control the frequency of the local oscillator, so that the 38.9 MHz picture comes. F . (I.F) can be obtained at the output of the converter
• A.F.T  The discriminator of the circuit measures the intermediate frequency and D.C . The control produces a voltage that is proportional to the frequency deviation and the error voltage it receives is applied to the reactance section of the local silter. So that the frequency is kept to the correct value 

Sound strip

• The sound strip of the color television system is similar to the sound strip of black and white television. Frequency Modulated Sound I. M . The signal is processed or produced with the help of a sound signal. In which the volume and tone controls are controlled by the audio amplifier and the output of the audio amplifier is connected to the loudspeaker

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 PAL CODER |PAL ENCODER

A.G.C. Sink Seperator and deflection circiut 

• The function of automatic gain control is to control gain. Since the signals from the antenna are highly variable, the function of automatic gain control is to adjust the gain of the receiver system according to the received signal. The sink seperator circuit consists of differantial and integrator. And the vertical signal has to be separated from the composite video signal so that synchronization can be established between the transmitter and receiver. The function of the deflection circuit is to provide scanning in the picture tube. So that the electron beam can be deflected in the horizontal and vertical direction on the raster.

Luminance channel

• The output of the luminance channel receives a composite vedio signal. And this inverted video signal is provided at the junction of the three cathodes of the picture tube. This part of the circuit is the drive adjustment by which the black lavel is saved. And the color can be reproduced correctly.

Colour signal processing

• This unit is a mixed network of Blanking Circuit, Chrominance Band Pass Amplier, Pal Dille Line, Eder, Substator, Secrets Demodulator, Color Metrican and Color Difference Amplifier. Which is used for the generation of color difference signals

Subcarrier Generation and Control

• The main function of this section is to generate subcarriers of the correct frequency. Generated subcarrier It should be of just the right frequency but also in the same phase as the subcarrier. A crystal oscillator is used in the receiver and with the help of automatic frequency and face control, it is also operated at the right phase and frequency and this circuit is called A.P.C. The circuit says 
• A.P.C. The circuit compares burst and local generated subcarrier and with its help generates control voltage.

Benefit

• The problem of differential phase error can be overcome.
•  Hue error can be easily eliminated.

disadvantages

• The controlling circuit requires careful drive
• The cost is high
• The structure of the receiver ckt is complex
• In this system, color signal recording is difficult to do on Magnetic tape as compared to other systems because it requires eight fields for color coding. T. s . C . (N.T.S.C) requires four (four) fields. Question 13. Write advantages of PAL color system over NTSC color system