Comparison of medium frequency propagation characteristics of a transmission line measured from both ends in a coal mine entry

An underground coal mine medium frequency (MF) communication system generally couples its electromagnetic signals to a long conductor in a tunnel (entry). The entry plus the conductor acts as a transmission line (TL). Transceivers exchange signals along the line. The propagation characteristics of the TL, which is generally the longest signal path, play a major role in determining the system performance. In this paper, we present MF measurements of TL characteristics as measured from both ends of the TL in a coal mine entry. The characteristic impedances from both ends have some significant differences, but the other propagation parameters are very similar.