Cost-effective leaky-feeder radio systems

Leaky-feeder systems for artificially propagating VHF radio signals underground are highly developed in the UK for application in coal mines. Techniques now in regular use provide two-way communication using one-way repeater-amplifiers or ´signal boosters´ in conjunction with small linepowered frequency converters. Examples of these devices are described. Although of low power and designed to be intrinsically safe for coal mine use, the equipment and techniques are applicable to other fields of application such as underground passenger transportation.