ELF communications system using HVDC transmission line as antenna

Claim 1

In combination with a high voltage direct current power transmission system including first and second distantly spaced electrical power stations and a pair of electrical power transmission lines extending between said stations for conducting electrical current therebetween, said first station at least being provided with means for converting alternating current to direct current for transmission to said second station, and said second station at least being provided with means for inverting said direct current to alternating current for distribution by said second station, the improvement in an extremely low frequency (ELF) communication system utilizing said power transmission lines as an electromagnetic signal radiating antenna, comprising: a. means for generating an electromagnetic communication signal having a carrier frequency in the ELF frequency range; b. means for coupling the output of said generating means to said transmission lines, with said transmission lines having a length which is an appreciable part of the wavelength of said carrier frequency in the ELF range and thereby serving as radiating antenna for propagating said electromagnetic signal into space; and c. electrical isolation means connected with the said transmission lines between said coupling means and said stations for electrically isolating said communication system from said power stations and for electrically isolating said power stations from said communication system and for permitting simultaneous non-interfering operation of said power and communication systems.