Paragutta, A New Insulating Material for Submarine Cables

*ORMERLY deep sea cables were used exclusively for telegraph purposes but in recent years there has been an increasing use of this type of cable for telephone service. Telephonic communication requires cables of very much superior transmission quality to that needed for telegraph. At the higher frequencies of voice transmission the energy losses in the insulating material become a serious factor and a radical improvement in submarine insulation is called for. The longest existing deep sea cables operating at voice frequency only slightly exceed 100 miles and the construction of a transoceanic telephone cable with standard materials has been regarded as beyond the practical limits of feasibility. The installation and rapid expansion of transatlantic radio telephony during the past few years have created a need for a deep sea telephone cable to supplement this service, particularly during periods of atmospheric disturbances. In addition the development of carrier telephony offers possibilities for increasing the traffic over shorter submarine cables. For the shorter cable, the still higher frequencies of carrier telephony make demands upon the insulating material similar to those of long cables operating at voice frequency. In view of these circumstances an extended study was undertaken of the causes of losses and other electrical weaknesses of submarine insulation and a search has been made for better materials. As a * Jour. Franklin Institute, Jan., 1931. 132 PARA GUTTA, A NEW INSULATING MATERIAL 133 result of this investigation an insulation called paragutta has been developed which, as the name suggests, is derived essentially from rubber and gutta percha.