Automatic Direction Finding
An automatic direction finder (ADF) is an aircraft radio-navigation instrument that automatically and continuously displays the relative bearing from the aircraft to a suitable radio station. ADF receivers are normally tuned to aviation NDBs (Non-Directional Beacon) operating in the LW band between 190 – 535 kHz. Like RDF (Radio Direction Finder) units, most ADF receivers can also receive medium wave (AM) broadcast stations, though these are less reliable for navigational purposes.
The operator tunes the ADF receiver to the correct frequency and verifies the identity of the beacon by listening to the Morse code signal transmitted by the NDB.
