AN INTRODUCTION TO A MEDIUM FREQUENCY PROPAGATION CHARACTERISTIC MEASUREMENT METHOD OF A TRANSMISSION LINE IN UNDERGROUND COAL MINES

An underground coal mine medium frequency (MF) communication system generally couples its electromagnetic signals to a long conductor in a tunnel, which acts as a transmission line, and exchanges signals with transceivers along the line. The propagation characteristics of the transmission line, which is usually the longest signal path for an MF communication system, play a major role in determining the system performance. To measure the MF propagation characteristics of transmission lines in coal mine tunnels, a method was developed based on a basic transmission line model. The method will be presented in this paper along with the propagation measurements on a transmission line system in a coal mine using the method. The measurements conflrmed a low MF signal power loss rate, and showed the in∞uence of the electrical properties of surrounding coal and rock on the MF propagation characteristics of the line.