Abstract :
The paper discusses the present use of the Decca Navigator radio position-fixing system as a marine and aircraft navigational aid. The permanent navigational service currently comprises 12 chains and some 4000 ship and aircraft installations; in addition, mobile chains are used for surveying and exploration. The absence of modulation permits close spacing of the chain frequencies. The receivers contain a reference system giving a common phase datum for all users. The system is a c.w. hyperbolic one in which, in ships, the fixing co-ordinates are normally indicated as phase-meter (Decometer) readings. Aircraft normally use an automatic plotter driven from the receiver by an impulse-motor servo system. There are several different types of airborne receiver, and for certain airborne applications a servo system imparting an inertial characteristic to the displayed data is employed. The system can be combined with a navigational aid of the Doppler type to form the Dian system, and the Dectra long-range aid, also part of Dian, has common ground and airborne equipment with the parent Decca Navigator system. A recent development includes a zone-identification facility and employs a new form of transmission that substantially increases the range at which lane identification is effective at night.
