Communication with moving trains in tunnels

This paper describes tests conducted in the North River tunnel of the Pennsylvania Railroad to determine a practical means for communicating with moving locomotives and trains in tunnels. It is shown that frequencies between about 25 and 1500 megacycles per second are not suitable for such communication over any substantial distance when employing conventional radio techniques. Tests are described utilizing other means of transmission, including the use of a series of antennas bridged onto a transmission line extending through the tunnel, and a closely-spaced two-wire line without antennas acting as a radiating and pick-up device. It is concluded that satisfactory transmission in tunnels can be obtained for a distance up to approximately 6,000 feet using the frequencies and equipment ordinarily employed in railroad mobile systems and twin-lead cable such as RG-86/U suitably located within the tunnel.