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A VHF direction finder (VDF) can determine...

  • A

    slant ranges.

  • B

    magnetic bearings.

  • C

    approach speeds.

  • D

    true courses.

Refer to figure.
VDF (VHF Direction Finding) is a method of measuring the direction from which a VHF signal came. It has been used for many decades now by ground stations, and is particularly useful as the transmitting aircraft only needs a standard VHF radio to ask for a VDF bearing from a suitably equipped Air Traffic Services Unit (ATSU). This can give them:

  • QDM - Magnetic bearing from the aircraft to the station.
  • QDR - Magnetic bearing from the station to the aircraft.
  • QUJ - True bearing from the aircraft to the station.
  • QTE - True bearing from the station to the aircraft.

The system that provides this information to the controller can give all of these values, magnetic and true. All the bearings are measured at the ground station, so therefore the variation used is that of the station.

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