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Electromagnetic Retransmission System for Locating Trapped Mine Workers.
Raab FH; Hansen PK
NTIS: PB/81-215329 :268 pages
The electromagnetic retransmission system is a new, automated method of locating trapped mine workers. This technique overcomes many limitations inherent in electromagnetic direction finding by reducing the effects of the conducting ground to an acceptable maximum, by finding position accurately in the presence of antenna tilt, and by eliminating the need for the receiver to be located directly above the subsurface transmitter. Three transportable three-axis magnetic-dipole transmitters on the surface create a system of electronic grids in which the phases of the downlink signals convey position information. The subsurface retransmitter modulates the uplink carrier of the existing beacon transmitter with the received downlink signal; the coal-pillar loop antenna is used for both receiving and transmitting. The uplink receiver uses a three-axis antenna and extensive digital signal processing. A small computer integrates data, estimates position, and controls system operation through VHF-FM communications. Both coal-mine and deep- mine operations are possible by selecting appropriate transmitting power and signal frequencies.
CP; Final Contract Report;
NTIS Accession No.
Polhemus Navigation Sci. Inc.
Page last reviewed: October 29, 2021Content source: National Institute for Occupational Safety and Health Education and Information Division