Telephone Communication over Power Lines by High Frequency Currents

Communication is a matter of vital importance in. the operation of large power systems. The difference between ordinary wire communication and communication over high voltage power lines is discussed. The necessity for using energy levels greatly in excess of that commonly used on ordinary wire lines is indicated. The importance of selecting and utilizing only those circuit elements which are inherently stable is discussed. The superior stability of the two frequency system of duplex is brought out. A standard 250-watt communication equipment is described in detail. The great value of the heterodyne principle for calling is noted. The theory of antenna coupling is developed beginning with elementary principles. Several numerical examples are given to show the application of the theory. It is shown that the efficiency of antenna coupling is quite high contrary to the general opinion prevailing at present. A brief description of the propagation of high frequency currents over wires together with some of the principal equations is given. Tests are given which show a close agreement with accepted line theory. A simple method of determining line characteristic resistance and method of determining the effective line resistance is described. This method is applied to ground return circuits and discloses the existence of considerable resistance per mile in the ground return path.