Passive reflectors as a means for extending UHF signals down intersecting cross cuts in mines or large corridors

Abstract

Tests of communication between hand held two watt UHF transceivers in a room and pillar limestone mine were satisfactory for several thousand feet through straight haulage ways but the range of communication at right angles to the haulage way into intersecting cross cuts was quite limited. It was evident that the radiation from the transceivers was not being reflected by the limestone pillars into the intersecting cross cuts. Two passive aluminum reflectors, each four feet square were installed near the ceiling and positioned 45° with respect to the axis at an intersection of a main haulage way and a cross cut. The range of communications down the intersecting cross cut was significantly extended. Propagation measurements on 450 and 850 MHz in the same mine demonstrated that passive reflectors are a practical and inexpensive means for extending communications into intersecting cross cuts. The same formulae and nomograms which are used for microwave passive reflectors can be used for UHF reflector design.