Some characteristics of a leaky feeder in a tunnel

Details are given of how magnetic field strength varies throughout a short section of a 1500 m long tunnel fed by a leaky feeder. Both phase and amplitude are examined. A second series of measurements examines in detail the phase variation along a single line down the tunnel over a distance of 500 m. The results enable judgments to be made about the potentiality for postion fixing in a tunnel using phase information.