Navigation and Seamanship

6.6.2.1. Working of Radio Direction Finder

Radio Direction Finder (RDF) often referred as ‘Radio Compass’, is an important electronic radiolocation instrument for navigation of both aircraft and ships. It used for finding the direction of a radio signal transmitting source. It is one of the long range and reliable radio navigation system. RDF was introduced in 1930s and extensively used in air traffic. The RDF is still used in air and marine crafts, because of its simplicity. Fixing the vessel’s position by radio bearing is very simple when compare to visual bearings.

The RDF is basically a radio receiver fixed onboard a vessel or aircraft, which has display unit and directional aerial (antenna) system. The directional antenna determines the direction of the incoming radio signal in relation to the ship’s head. The radio signal in a particular frequency will be transmitted from a transmitter kept in coast station, radio beacon, light house beacon in the vicinity whose position is known. Establishment of radio bearing is possible from a vessel to a transmitting station. The established line of position is plotted on the appropriate chart. Similarly, a second line of bearing can be established from another radio transmitting station of known frequency .These two bearings are plotted to obtain vessel’s position at particular time. It is also possible to take third line of bearing from yet another transmitting station to make the fix the vessel’s position very accurately.