"An investigation was made of the feasibility of developing compact transmit antennas and/or other means to efficiently couple very low frequency (VLF) to medium frequency (MF) band radio energy between portable wireless communication units in coal mines. The completely wireless communication range between two portable radios equipped with practical size reference loop antennas in representative coal mine environments was estimated. Antenna technology was assessed with respect to transmit moment, range, intrinsic safety, battery, and wearability requirements to determine the most suitable antenna types for use by miners. It was concluded that aircore bandolier loop antennas, and perhaps ferrite-loaded loop antennas, having peak transmit moments of about 2.5 Ampere/m2 would be the most effective antennas for portable units." - NIOSHTIC-2 NIOSHTIC no. 10001390

National Institute for Occupational Safety and Health