radio direction finder
Rare technical term for a device that determines the direction of a radio signal; often replaced by simpler terms like 方位測定器 or English loanword RDF in modern contexts.
See also: 方位測定器
An old radio direction finder is on display at the museum.
方位測定器 is a broader term for any direction finder, while 無線方位測定器 specifically refers to a radio-based device.
Compound of 無線 (radio), 方位 (direction), and 測定器 (measuring instrument).