T.V.ENGINEERING TEXT BOOK BY R.R GULATI

T.V.Engineering Textbook :

                          

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Development of Television

Television* means ‘to see from a distance’. The desire in man to do so has been there for ages.
In the early years of the twentieth century many scientists experimented with the idea of
using selenium photosensitive cells for converting light from pictures into electrical signals
and transmitting them through wires.

The first demonstration of actual television was given by J.L. Baird in UK and C.F.
Jenkins in USA around 1927 by using the technique of mechanical scanning employing rotating
discs. However, the real breakthrough occurred with the invention of the cathode ray tube and
the success of V.K. Zworykin of the USA in perfecting the first camera tube (the iconoscope)
based on the storage principle. By 1930 electromagnetic scanning of both camera and picture
tubes and other ancillary circuits such as for beam deflection, video amplification, etc. were
developed. Though television broadcast started in 1935, world political developments and the
second world war slowed down the progress of television. With the end of the war, television
rapidly grew into a popular medium for dispersion of news and mass entertainment.

Television Systems

At the outset, in the absence of any international standards, three monochrome (i.e. black and
white) systems grew independently. These are the 525 line American, the 625 line European
and the 819 line French systems. This naturally prevents direct exchange of programme between
countries using different television standards. Later, efforts by the all world committee on
radio and television (CCIR) for changing to a common 625 line system by all concerned proved
ineffective and thus all the three systems have apparently come to stay. The inability to change
over to a common system is mainly due to the high cost of replacing both the transmitting
equipment and the millions of receivers already in use. However the UK, where initially a 415
line monochrome system was in use, has changed to the 625 line system with some modification
in the channel bandwidth. In India, where television transmission started in 1959, the 625-B
monochrome system has been adopted.

The three different standards of black and white television have resulted in the
development of three different systems of colour television, respectively compatible with the
three monochrome systems. The original colour system was that adopted by the USA in 1953
on the recommendations of its National Television Systems Committee and hence called the
NTSC system. The other two colour systems–PAL and SECAM are later modifications of the
NTSC system, with minor improvements, to conform to the other two monochrome standards.