Netherlands-Denmark coaxial-cable system

On the main submarine section, 263 km, two independent solid-polythene-insulated coaxial cables, each with two submerged repeaters, are laid along parallel tracks. Each cable carries 36 channels in both directions, using the frequency band 24-168 kc/s in one direction and 208-352 kc/s in the other. Each submerged repeater employs a single amplifier for both directions, with directional filters, and power is fed over the inner conductor at constant direct current stabilized to plusmn1%. Loop gains can be measured from the terminal stations by means of frequency-doublers and narrow-band filters in each repeater, and intermodulation by a 2-frequency method with corresponding filters. The main overland route across Denmark (total 323 km) is composed of 2-tube and 4-tube coaxial cable sections and employs established techniques, except that the cable is pressurized to 0.5 kg/cm2 with nitrogen, mercury contact manometers being included in every joint and connected across pilot wires for preliminary fault localization. Precision localization is obtained by a G.M. counter above the ground after injection of radium emanation into the cable.