An Automatic Direction Finder (ADF) system comprises which components?

• A. Sense antenna and loop antenna
• B. Transponder and GPS
• C. Localizer and glideslope
• D. Antenna array and satellite link

Answer: (A)

An Automatic Direction Finder relies on two antennas to determine the bearing to the station: a loop antenna and a sense antenna. The loop antenna provides a directional pattern that helps the receiver compute where the NDB is relative to the aircraft, but it has a 180-degree ambiguity because it can’t tell front from back. The sense antenna resolves that ambiguity by providing information about whether the station is in front or behind, allowing the system to establish the true bearing. Together with the ADF receiver and indicator, these two antennas make up the core of the ADF system.

The other options describe components from different navigation or surveillance systems (transponder/GPS, ILS localizer and glideslope, or antenna array with satellite link) and are not part of a basic ADF.