The use of in-line repeaters in leaky feeder radio systems for coal mines

Leaky feeder techniques are being used increasingly to provide radio communication with men and vehicles in mines and tunnels. A continuing study by the UK National Coal Board has devoted considerable attention to the use of line-powered repeaters in such systems to compensate for line losses as they occur. Several different ways of achieving duplex communication with simple one-way repeaters have been developed or proposed, and these are capable of providing a far more even and reliable performance than was possible with the earlier multiple-base-station operation. The engineered systems described have been developed primarily for coal mines, where considerations of intrinsic safety impose severe restrictions on line-fed power. The resulting need for highest efficiency in the repeaters overrides considerations of linearity, and the threat of intermodulation interference arises in multichannel operation. This in turn may be countered by further system techniques such as time-division-multiplexing and diversity.