Definition
A radio receiver fitted with a directional antenna that determines the bearing from which a radio signal is being transmitted. The pilot or equipment uses the antenna's directional sensitivity to identify the direction toward (or away from) a known ground transmitter, providing a line of position relative to that station.
Plain English
A radio that tells you which direction a signal is coming from, so you can tell where the transmitting station is in relation to your aircraft.
Context Anchor
Seen in radio navigation, older navigation equipment, and lost-position assistance where a radio signal is used to help establish direction.
Derivation
Plain English. Named for what it does: it finds the direction of a radio signal. The term predates modern satellite navigation and reflects an era when bearing-by-radio was the primary navigation method.
Why Pilots Care
It provides reliable directional information when visual references are unavailable, supporting navigation and approach procedures.
Analogy
It is a little like turning your head to tell where a sound is coming from, except the equipment is doing that with a radio signal.
Intuition Check
A direction finder is not just any device that shows direction, like a compass. In this context, it specifically finds direction by using a received radio signal.
Example Sentence 1
Using the direction finder, the pilot tuned the NDB and turned the aircraft until the needle pointed straight ahead, indicating the station was directly off the nose.
Example Sentence 2
Using the direction finder, the crew maintained a steady bearing toward the beacon until the airport came into view.