Navigation and Seamanship

6.6.4. Automatic Direction finder

                                                                                

Automatic direction finding (ADF) is  an improved version of  basic radio direction finder.  In ADF ,the automatic  rotation of  the loop antenna will ensure that the signal is always a maximum. Two loop antennas, set up at a right angle to each other, and measure the ratio of the signals from each antenna to get the angle to the beacon. ADF is the  radio navigation system still in use radio signals in the low to medium frequency band of 190 Khz. to 1750 Khz. The curvature of the earth is not a limiting factor for ADF. The range of operation mainly depends on the  power of the beacon. Commercial AM radio stations broadcast on 540 to 1620 Khz. Non-Directional Beacon operate in the frequency band of 190 to 535 Khz. The  following are the merits of Radio Direction Finder over other radiolocation systems

 1)    It is simple to use.

2)    It can be used in any part of the world.

3)    Bearing of any radio transmitter can be independently taken on board ship or aircraft..

4)    Signal reception from the desired transmitter is possible  by turning the loop antenna (or the goniometer)

5)    If there is no radio beacons in the vicinity of vessel, navigator will request the nearest port tot transmit radio signals. Any one of the coast station  or pilot vessels to transmit signals and thus act as radio beacons.

6)    Signals from transmitting  stations are usually very strong, so that a good bearing and position line can be obtained