airborne radio compass

An airborne radio compass, also known as an automatic direction finder (ADF), is a navigational tool used in aviation. It continuously displays the bearing of a designated radio beacon, helping pilots determine their direction relative to a radio transmitter.1

This technology evolved from earlier direction-finding techniques used in marine navigation. By rotating a loop antenna, pilots could identify the direction of radio waves from a transmitter. This allowed them to plot bearings on a chart, and by using signals from two different transmitters, they could fix their position. The airborne direction finder became a valuable aid to air navigation, especially as aviation grew. While modern navigation systems have advanced, the ADF was an important step in guiding aircraft toward their destinations.2