Open file report (United States. Bureau of Mines) ; 68-73

"A prototype electromagnetic (em) location system consisting of six miniature transmitters, six miniature receivers, and one multichannel receiver was developed by westinghouse georesearch laboratory and is described in this report. The equipment was designed to operate in a deep coal mine of relatively high overburden conductivity. One mine having these characteristics is the genevea coal mine operated by the U.S. Steel Corp. Near dragerton, Utah. The equipment was tested there. The system consisted of six manpack transmitters and six manpack receivers covering the frequency band from 900 hz to 2,900 hz as well as a six- channel receiver designed for use in a helicopter. Tests showed that em signals from lightweight (3/4 lb) transmitters could be detected both on the surface and from a helicopter through as much as 1,650 feet of relatively high conductivity (2 x 102 mhos/m) overburden. Furthermore, the resulting field strength profiles could be used to determine source location to within 150 feet of the actual surveyed location in the mine." - NIOSHTIC-2

NIOSH no. 10001481

National Institute for Occupational Safety and Health

Contract H0232049