Ground Direction Finding and ADF/NDB
NDB transmits in the LF/MF band (typically 190-535 kHz) and the ADF receiver in the aircraft provides a relative bearing to the station. Candidates must understand relative bearing, magnetic bearing (QDM/QDR) and the relation: magnetic bearing to station = magnetic heading + relative bearing (mod 360). Know the fixed-card versus rotating-card ADF, and the meaning of the ADF needle during turns.
Ground direction finding uses a DF station to take bearings on the aircraft transmission and pass a QDM (magnetic bearing to the station) or a position fix from two or more stations. Understand that DF bearings are subject to errors from coastline, night effect, and station interference.
ADF errors to know: quadrantal error, night effect (skywave on LF/MF), coastal refraction, mountain effect and station interference. Traps include mixing QDM (to station) with QDR (from station), and forgetting that relative bearing is measured clockwise from the aircraft nose, not from magnetic north.
Worked example: heading 090M, relative bearing 045. Magnetic bearing to station = 090 + 045 = 135M (QDM 135). To home, turn right to 135M.