Review of the earth mode communication program at AFCRL

Leon A. Ames, John W. Frazier, Arnold S. Orange, Air Force Cambridge Research Laboratories (U.S.)

The program in earth mode communications research at the U.S. Air Force Cambridge Research Laboratories is reviewed. Emphasis is placed on geological and geophysical problems encountered in the course of the program. Communications modes studied include: (1) 'deep-strata', wherein radio frequency electromagnetic waves are propagated between buried antennas over a path entirely within rock strata, and (2) 'conduction current', consisting of ULF conduction field communications between long, grounded dipoles. Deep-strata studies were carried out utilizing both loops and linear antennas immersed in the rock medium. Antenna and transmission path characteristics were studied under a variety of conditions and over paths up to 4.5 km in length. It was found that two of the greatest problems facing the communicator are the complexity of the earth's crust and its low values of electrical...