A PAL colour TV transmitter consists of following three main sections.
1. Production of Luminance (Y) and Chrominance (U and V) signals
2. PAL encoder
3. Video and Audio modulators and transmitting antenna
Production of Luminance (Y) and Chrominance (U and V) signals:
* Colour camera tube produces R, G and B voltages pertaining to the intensity of red, green and blue colours respectively in pixels. The luminance signal Y is obtained by a resistive matrix, using grassman's law. Y=0.3R+0.59G+0.11B. * For colour section Y is inverted colours R&B obtained from the colour camera tubes are added to it to get (R-Y) and (B-Y) colour difference signal. These signals are weighted by two resistive matrix network which gives U & V signals as U=0.493 (B-Y) & V=0.877(R-Y)
PAL encoder:
* PAL switch which operates electronically at 7812.5Hz with the help of bistable multivibrator and feeds the sub-carrier to balanced modulator with phase difference of +90 degree on one line and -90 degree on the next line. * The PAL encoder consists of a subcarrier generator and two balanced modulator with filters to produce modulated subcarrier signal. These signals are added vertically to give Chroma signal (C). Then Chroma signal is mixed with Y signal along with sync. And blanking pulses to produce Colour Composite Video Signal (CCVS)
Video and Audio modulators and transmitting antenna:
* CCVS amplitude modulates the main video carrier. It is followed by a sharp VSB filter to attenuate the LSB to give AMVSB signal for transmitter. Audio signal modulates separate carrier. This modulation is FM type. * AMVSB video signal along with audio signal passes to the transmitting antenna through Diplexer Bridge which is a wheatstone's bridge.