Q. Explain about Communication Systems?

Even though most modern communication systems have only been invented and developed during the eighteenth and nineteenth centuries, it is difficult to imagine aworldwithout telephones, radio, and television. After the invention of the electric battery by Alessandro Volta in 1799, Samuel Morse developed the electric telegraph and demonstrated it in 1837. Morse devised the variable-length binary code, in which letters of the English alphabet are represented by a sequence of dots and dashes (code words). In this code, more frequently occurring letters are represented by short code words, whereas letters occurring less frequently are represented by larger code words.

Morse code (variable-length binary code), developed in 1837, became the precursor to variable- length source coding methods. Telegraphy, the earliest form of electrical communication, was a binary digital communication system in which the letters of the English alphabet were efficiently encoded into corresponding variable-length code words having binary elements. In the baudout code, developed in 1875, the binary code elements were of equal length, and each letter was encoded into fixed-length binary code words of length 5.

With the invention of the telephone, telephony came into being and the Bell Telephone Company was established in 1877. Transcontinental telephone transmission became operational in 1915. Automatic switching was another important advance, and a digital switch was placed in service in 1960. Numerous significant advances have taken place in telephone communications over the past four decades. For example, fiber-optic cables have replaced copper wire, and electronic switches have come into use in place of electromechanical devices.

Marconi is credited with the development of wireless telegraphy in the late 1890s, after Maxwell's theory of electromagnetic radiation was verified experimentally by Hertz in 1887. The invention of the vacuum tube was particularly instrumental in the development of radio communication systems. Amplitude modulation (AM) broadcast was initiated in 1920, while frequency modulation (FM) broadcastwas developed commercially by the end ofWorldWar II. Commercial television broadcasting began in 1936 by the BBC (British Broadcasting Corporation), and the FCC (Federal Communications Commission) authorized television broadcasting five years later in the United States.