Mumbai university > Electronics and telecommunication Engineering > Sem 6 > Television Engineering

Marks: 05

Years: Dec 2016

• Regular colour TV broadcast could not be started till 1954 because of the stringent requirement of making colour TV compatible with the existing monochrome system.

• Compatibility implies that -

1. The colour television signal must produce a normal black and white picture on a monochrome receiver without any modification of the receiver circuitry.
2. A colour receiver must be able to produce a black and white picture from a normal monochrome signal. This is referred to as reverse compatibility.

• To achieve this, that is to make the system fully compatible, the composite colour signal must meet the following requirements:

1. It should occupy the same bandwidth as the corresponding monochrome signal.
2. The location and spacing of picture and sound carrier frequencies should remain the same.
3. The colour signal should have the same luminance (brightness) information as would a monochrome signal, transmitting the same scene.
4. The composite colour signal should contain colour information together with the ancillary signals needed to allow this to be decoded.
5. The colour information should be carried in such a way that it does not affect the picture reproduced on the screen of a monochrome receiver.
6. The system must employ the same deflection frequencies and sync signals as used for monochrome transmission and reception.

• In order to meet the above requirements, it becomes necessary to encode the colour information of the scene in such a way that it can be transmitted within the same channel bandwidth of 7MHz and without disturbing the brightness signal.

• Similarly at the receiving end a decoder must be used to recover the colour signal back in its original form for feeding it to the tricolour picture tube.