Offshore floating radio relay station

Abstract

A rapid increase in demand for larger capacity communication systems in Japan in recent years has brought the Nippon Telegraph and Telephone Public Corporation to develop a new offshore microwave transmission system. This new system will be remarkable in that it is the first attempt to adopt the combination of coaxial cables and microwave transmission among onshore and offshore stations. Coaxial cables of large transmission capacity have an advantage of sending electric waves for a long distance over deep waters where disturbance or damage to the cables due to various human activities in the sea is not seriously expected. On the other hand, in the shallow waters of continental shelves, coaxial cables are apt to be considerably exposed to danger of being damaged and cut off by anchors and dragnets of fishing boats, etc. To solve the problem in shallow waters, an offshore floating radio relay station should be installed at the edge of continental shelves, by heavy anchor chains, to receive microwave transmission from an onshore station and to transmit it to the next offshore station, or vice versa, through coaxial cables connecting the offshore station network. The antenna to receive the microwave signal on the floating station is automatically adjustable to keep the correct direction in spite of motions of the offshore station in waves. On October, 1973, a full scale test station was installed in 200 metres of water at a location five kilometers offshore of Izu-Ohshima Island off Tokyo. This test station is 135 m tall and afloat in an upright condition with 100 m draft. Its mooring system consists of four sets of 3 inch chain of 600 meters in length to keep the station in a workable condition in max. 15 meter waves and 60 m/see wind. The test has just started and will he continued for two years. It is the intent of this paper to describe the outline of the designing and construction of the newly developed offshore floating radio relay station.