Automatic direction finding (ADF) is an electronic aid to navigation that identifies the relative bearing of an aircraft from a radio beacon transmitting in the MF or LF bandwidth.
In Infinite Flight it can be used to tune to Non-directional beacons (NDB) and can be found in the NAV/Avionics menu. You’d tune the same way you would tune to a VOR station.
ADF equipment determines the direction or bearing to the NDB station relative to the aircraft by using a combination of directional and non-directional antennae to sense the direction in which the combined signal is strongest.
References: SKYbrary
