"This report describes magnetic field measurements in the Helvetia Coal Co. Lucerne No. 8 Mine for purposes of deriving a mapping of the magnetic field strength covering the major haulageways which contain conductors. The results of the testing at medium frequency show that coverage of the entire mine area containing conductors can be achieved employing wireless radio techniques whereby radio signals are coupled into and are carried by these conductors. These results confirm earlier qualitative testing of the Collins Mine Wireless Radios in this mine. These results, performed over the frequency range 71-2890 kHz, illustrate the effect of frequency on the radio propagation with the conclusion that the best overall coverage is obtained at frequencies approximating 1000 kHz. This report presents all the raw data and the reduced data in the form of magnetic field strength contour maps. Sufficient information is provided to enable independent reduction of the data. A summary of observations which can be made directly from the contour maps is given." - NIOSHTIC-2 NIOSH no. 20030898

National Institute for Occupational Safety and Health