Automatic Directional Finder (ADF) intended fornavigation for compass locator and broadcast radiostations. ADF received amplitude-modulation signals from ground station and determines directions to radio signals (fig. 70). Usually equipment ADF intended for take bearing of radio signals in range 190-1750 kHz. ADF determines angles of radiostations – angle between longitudional axis of aircraft and direction to radio beacon.
Board equipment ADF consist of panel control, receiver and antens systems. ADF antenna consist of with direct and all direct antennas which are located together. Through comparing signal from two antennas, direct antenna goes to the ground radio stations and determines course angle of radio stations. Throught panel control pilot exposes the frequency of radio beacon, which will be defined direction..In modern on-board computer systems ADF is adjusted automatically with FMS according to a given flight plan.
Fig. 70. Heading angle of radio beacon
In the case of bearing two radio beacons ADF can be used to determine the location of the aircraft. In addition to performing navigation functions, ADF can be used for recognition of airports and waypoints through the listening of call.
Fig. 71. Automatic direction finder ADF-462 (RocwellColins)
Range ADF depends from the altitude and power of radiostations; when power is 500 W – range is 200-300 km.