Analysis of the Dedicated Communication Line in a Mine Tunnel for a Shunt-Loaded Trolley Wire

The theory of transmission in a semicircular tunnel containing two axial conductors is simplified for the case of radio frequencies. It is shown that the effect of ohmic losses in the wall can be represented as series impedances per unit length in the equivalent coupled transmission line circuits. This opens the way for a systematic calculation of the mode conversion phenomena that occur when one of the axial conductors has a discrete shunt load to the ground plane. Explicit formulas are obtained for the modal conversion coefficients. These are used to discuss the effect of a shunt load on the trolley wire on the performance of a radio frequency communication system. It is confirmed that the unloaded dedicated communication line provides for a low loss mode that is hardly affected by the shunt load on the adjacent trolley wire in the tunnel.