The bicoaxial leaky line and its applications to underground radio communication

The bicoaxial leaky line comprises two separate leaky cables spaced closely parallel so that the two outer braids or conductors form a bifilar transmission line. The type of construction was developed first as a research tool in the study of mode-conversion processes in leaky coaxial cables and to test previously developed theories; the single-wire modes of the two constituent cables combine to form a bifilar mode which can be more accurately predicted and measured. As well as serving this purpose, the new cable lends itself to a new configuration of leaky cable radio communication system in which line repeaters are bridged between the constituent coaxial cables in alternate directions instead of being connected simply in series; midspan filters ensure system stability. Such a system provides duplex communication from a unified base station using simple one-way repeaters and is particularly adaptable to spurs and branching. The inherent “tailback” feature also provides a particularly consistent level of coupled signal through the system. The overall system of bicoaxial cable and line repeaters will accommodate several separate radio channels simultaneously and thus constitutes a bidirectional “communications highway” for mining use.