Leaky-feeder radio communication: A historical review

Problems of radio communication in mines, tunnels and other confined spaces are being increasingly solved by the use of leaky-feeder techniques. As first described in 1956 these comprised a simple open-braided coax or a twin-lead connected to one or more standard VHF base stations: nowadays they incorporate remarkably simple and inexpensive line-powered signal boosters or ´repeaters´ to compensate for line losses as they occur and can provide virtually unlimited range without dependence on linking land-lines. For use in coal mines the entire system can be made intrinsically safe, since the power drawn by a typical present-day signal booster need be only a few milliwatts of DC.