Carrier current transmission for underground communication

A report has recently been issued by J. J. Jakosky and D. H. Zellers, both of the Bureau of Mines, on the effect of Metallic Conductors on Underground Communication. This report contains (1) a discussion of the chief factors affecting carrier-current transmission with particular reference in application to underground communication for mines; (2) a description of typical underground circuits used for power and lighting; and (3) description of results obtained in carrier-current experiments in coal mines near Pittsburgh, and conclusions as to power requirements and limitations for mine use.