ABSTRACT
This chapter looks at the historical background to radio navigation, reviews typical automatic direction finder (ADF) hardware and conclude with some practical aspects associated with the operational use of ADF. The early airborne navigation systems using ground-based navigation aids consisted of a fixed-loop antenna in the aircraft tuned to an amplitude modulation (AM) commercial radio broadcast station. Navigation based on ADF became an established method of travelling across country. With the growth of air travel, dedicated radio navigation aids were installed along popular air transport routes. These radio stations, known as non-directional beacons (NDB), gradually supplemented the commercial radio stations and a network of NDBs sprang up in the nations developing their aeronautical infrastructure. The evolution of digital electronics, together with integration of other systems, has led to the introduction of the flight management system (FMS) control display unit (CDU) which is used to manage the ADF system.
