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.
Microwave System Engineering Using Large Passive Reflectors
This paper will provide the microwave engineer with the basic techniques of microwave system engineering using large passive reflectors and will outline the many advantages of their use. Small passive reflectors of the "periscope type" have been used for many years on microwave systems. Large passive reflectors have also been used but to a much lesser degree. Large passives may be used at intermediate points on long (200 miles or more) microwave links in lieu of active repeaters. Most microwave engineers have little knowledge of system engineering using these reflectors. This paper describes their use in both the "near" and "far fields" in line-of-sight systems and describes how they may be used on non-line-of-sight systems (tropospheric scatter and diffraction systems). Formulas are developed and graphs provided which will enable the microwave engineer to determine the path loss of multihop passive reflector systems. Large passive reflectors should be considered as another tool which can be used by the microwave engineer for planning and engineering communications systems. When used effectively with line-of-sight, diffraction and tropospheric scatter modes of propagation, communication systems may be engineered more economically, with more reliability and with a decrease in the operating and maintenance problems.
A Theoretical Study of an Antenna-Reflector Problem
This paper gives the results of a theoretical investigation of an antenna used with a plane reflector. This finds application in microwave relay stations, where the antenna is placed at ground level facing up and the reflector is located some distance above it. The results given show that there are certain values of X, separation distance, reflector and antenna size for which the received power is greater than for the same antenna alone at the elevated location.