The design and implementation of a UHF radio system using distributed antennas, passive reflectors and two-way signal boosters in a room and pillar limestone mine
The Bureau of Mines (BOM) has established a project to demonstrate means for improving underground communications in metal/nonmetal room and pillar mines. The Black River Mine, a large limestone mine near Butler, Kentucky, was selected for conducting propagation tests on 466 and 812 MHz and to develop a practical operating system. Tests of communications between handheld 2 watt ultra high frequency (UHF) transceivers in the mine proved satisfactory for approximately 2,000 feet (610 m) through straight and level haulageways but the range of communication into intersecting crosscuts was quite limited. It was evident that radiation from the transceivers was not being efficiently reflected by limestone pillars into the intersecting crosscuts. Two passive aluminum reflectors, each four feet (1.22 m) square, were installed near the roof and positioned 45° with respect to the axis at an intersection of two haulageways and the range of communications down the intersecting haulageways was significantly extended. Two distributed antenna and base station systems, each feeding four antennas located at principal intersections of haulage and travel roads, were installed and signal or fade margins above 20 dB quieting were measured to determine where reflectors were needed. The reflectors were very effective when they were within direct line of sight and less than 1,000 feet (305 m) from an antenna. The two antenna systems provided satisfactory coverage along the principal travel and haulageways in approximately 70 percent of the central portion of the mine but coverage was unreliable in the active mining areas around the perimeter of the mine. The alternatives of either installing four additional base station and distributed antenna systems or extending the original distributed antenna systems by adding two-way multichannel signal boosters to compensate for cable attenuation were evaluated. The signal booster concept was selected because it is less expensive, simpler to control, avoids hetrodyne interference and communications can be readily extended as the mined area is expanded.
Emergency and quick operational radio communications in Utah Power and Light Company's Deer Creek Coal Mine
An underground radio communications system has been developed and installed in the Deer Creek Coal Mine near Huntington, Utah. The minewide radio communications system provides emergency communications to mine personnel working along the face, belt lines, man and material entries, returns and designated escapeways. The system also provides quick communications between the surface monitoring center and key personnel throughout the mining complex. The radio system utilizes two robust radio signal propagation modes to provide communications throughout the mine. In the first mode, low-conductivity seams of coal, trona, potash, quartzite and gilsonite surrounded by more conductive rock layers form natural waveguides for low-attenuation-rate transmission of radio signals. In the second mode, conductors, AC power distribution cable, conveyer belt structures, steel pipe, rail, etc. form low-attenuation-rate waveguides for distribution of radio signals. The entire radio system meets intrinsic safety requirements and is composed of three basic elements: a base unit (with remote audio capability), transceivers (with different housings which are specific to the application), and repeaters.<<ETX>>
An Analysis of Passive Reflector Antenna Systems
The system gain and radiation pattern of a passive reflector antenna system (with a 45-degree plane rectangular reflector) are developed from aperture field theory. Experimentally determined system gains and a measured radiation pattern substantiate the theoretical analysis. Side-lobe levels and mutual coupling are also discussed.