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Automatic Direction Finder (ADF)

 Automatic Direction Finder (ADF)

  • Many general aviation-type aircraft are equipped with ADF
  • radio receiving equipment.
  • To navigate using the ADF, the pilot tunes the receiving equipment to a ground station was known as a nondirectional radio beacon (NDB). 
  • The NDB stations normally operate in a low or medium frequency band of 200 to 415 kHz.
  •  The frequencies are readily available on aeronautical charts or in the A/FD.
  • All radio beacons except compass locators transmit a continuous three-letter identification in code except during voice transmissions.
  • A compass locator, which is associated with an instrument landing system, transmits a two-letter identifi cation.
  • Standard broadcast stations can also be used in conjunction
  • with ADF.
  •  Positive identification of all radio stations is extremely important and this is particularly true when using standard broadcast stations for navigation.
  • NDBs have one advantage over the VOR. This advantage is
  • that low or medium frequencies are not affected by line-ofsight.
  • The signals follow the curvature of the Earth; therefore,
  • if the aircraft is within the range of the station, the signals
  • can be received regardless of altitude.

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