Definition

Radio direction finding. Radiodetermination using the reception of radio waves for the purpose of determining the direction of a station or object.

Source: ICAO Annex 10, Volume II

Note: Radio direction finding is a general term encompassing various applications using the same principle of operation. The definition above was initially introduced by the International Telecommunication Union (ITU) and then adopted by ICAO. As VHF is the primary means of communication in civil aviation, the term VDF is most recognizable among aviation professionals.

Description

The VHF direction finder (VDF) is a ground based radio aid that consists of a directional antenna system and a VHF radio receiver, tuned to the operating frequency of an air traffic services unit. Thus, when a transmission is received from an aircraft, the VDF provides the direction that transmission came from (i.e. azimuth relative to the receiver).