Читать книгу Introduction To Modern Planar Transmission Lines - Anand K. Verma - Страница 16

The telegraph is the first coded point‐to‐point electrical communication system. As early as 1747, William Watson showed the possibility of transmitting an electrical current on a wire using the earth as a return conductor. Thus, overhead single‐wire with the earth as a return conductor is the first transmission line. It is to be noted that even the voltaic pile, i.e. the chemical battery of Volta was nonexistent at that time. The Leiden jar, a capacitor to store the static electrical charges, was invented just two years before in 1745. However, much earlier in the year 1663, Otto Von Guericke studied the phenomenon of static electricity and designed a machine to produce it. Thus, the charged Leiden jar became a source of electricity, and single‐wire transmission was the communication medium. These were two important ingredients to establish the telegraph link. The third ingredient of telegraphy, the electroscope, invented by William Gilbert around 1600, acted as the receiver for the coded signals. It is interesting to note that the telegraph was conceived without any theoretical investigations on electricity. Even Coulomb's law was discovered later in 1785. However, the proper telegraphy could be developed only after the invention of voltaic pile, i.e. a chemical battery by Volta in 1799. Further development of the telegraph has an involved history. In 1837, Morse patented his telegraph in the United States, and on January 6, 1838, the first telegram was sent over 3 km distance. Cooke commercialized the telegraph in England and established the 21 km link on April 9, 1839. Thus, an era of electrical communication heralded. In 1844, long‐distance Morse's telegraph between Washington, DC, and Baltimore, Maryland was established. Before further reviewing the growth of the classical transmission lines, it is useful to have a quick look at the theoretical developments related to electricity [B.5].