Navigation Systems: ADF/NDB - University of Salford PDF

Navigation Systems: Automatic Direction Finder (ADF) and Non Directional Beacon (NDB) Dr. Marta Camps Santasmasas, based on material by Eur Ing Peter Bradbury 1  Learning o...

Navigation Systems: Automatic Direction Finder (ADF) and Non Directional Beacon (NDB) Dr. Marta Camps Santasmasas, based on material by Eur Ing Peter Bradbury 1  Learning objectives Uses of the ADF/NDB navigation system. Components of the ADF/NDB. Principle of operation of the ADF/NDB. Interpret ADF/NDB readings using Relative Bearing Indicator (RBI) Radio Magnetic Indicator (RMI) Factors affecting ADF accuracy 2  ADF / NDB Provides the bearing of the NDB station relative to the aircraft longitudinal axis. 3  Uses of the ADF/NDB ⚫ En route Navigation Bearings ⚫ Homing to or flying from the NDB when maintaining an airway centre line ⚫ Holding overhead at an assigned level ⚫ Runway approach procedures 4  Automatic Direction Finder Non Directional Beacon (NDB) (ADF) Ground-based transmitter Aircraft equipment Emits omnidirectional signal Loop aerial LF / MF band Sense aerial Control unit Receiver Display unit Presentation 4 Principles of ADF 5  Principle of operation of an ADF Loop antenna Maximum received signal No received signal 6 Source: Video by An huynh thai 7 https://youtu.be/CQv2lRUdrpI?si=6voFGxi_AH8MjxXw  NDB A NDB B Presentation 4 Principles of ADF 8 Loop antenna Sense antenna Radiation diagrams in the horizontal plane 9  Sense antenna emits an omnidirectional signal in phase with one element of the loop aerial. Sense + loop = carotid radiation pattern Null of carotid does not match null of loop antenna. 10  Control unit Logic circuit which defines the correct null in the loop antenna as the one after which the carotid signal strength increases when the loop is rotated clockwise. Strength increase 11 The Fixed Loop ADF 12  Receiver Frequency in use Frequency in standby Timer Mode: ADF or Antenna Tune (select) (ANT). Antenna is used Switch from the freq in use standby freq to identify the station to the freq in standby Beat Frequency Oscillator: hear the Morse code identification of the station 13  Display unit OR Relative Bearing Indicator Radio Magnetic Indicator (RBI) (RMI) 14 Source: Video by Evan Luft 15 https://youtu.be/XJ6IwjkyHr0?si=5vH2MkqiAfW-baeR  Relative Bearing Indicator (RBI) Aircraft’s front longitudinal axis 136 deg 16  Radio Magnetic Indicator (RMI) Aircraft’s Magnetic bearing Mag VOR needle (not North relevant for ADF) 136 deg 76 deg 300 deg ADF needle 17  Frequencies and Types of NDB’s ⚫ NDB’s operate in the band 190 – 1750 kHz ⚫ Mode of Propagation – Surface Wave / Sky wave ⚫ Most NDB’s in the range 250 – 450 kHz ⚫ Two general types of NDB – Locator Low powered NDB’s Used for airfield approach procedures Range 10 – 25 nm – En Route High powered NDB’s Used for homing, en-route navigation Range > 50 nm 18  Factors affecting ADF accuracy ⚫ Static Interference ⚫ Station Interference ⚫ Mountain Effect ⚫ Coastal Refraction ⚫ Quadrantal Error ⚫ Angle of Bank ⚫ Lack of Failure Warning 19  Coastal Refraction Presentation 4 Principles of ADF 20  Quadrantal Error Presentation 4 Principles of ADF 21  Summary Uses of the ADF/NDB navigation system: Locator NDB’s are used for holding overhead during approach procedures and for runway approaches. En route NDB’s are used as route navigation bearings. Components of the ADF/NDB: ADF: Loop aerial: Directional antenna that detects the angle of incoming NDB signals, since the signal received from NDB is 0 when the loop antenna is perpendicular to the direction of the NDF signal. Sense aerial: A non-directional antenna a signal in phase with one element of the loop aerial. Control unit: Logic circuit which defines the correct null in the loop antenna. Receiver: The interface where the pilot tunes the ADF to a specific NDB frequency and adjusts frequencies. It also processes the signals received by the antennas. Display unit: Displays the directional information calculated by the ADF. Relative Bearing indicator Radio Magnetic Bearing indicator NDB: Ground based transmitter. Emits an omnidirectional signal in the LF/MF band 22  Summary Principle of operation of the ADF/NDB: An ADF (Automatic Direction Finder) receives signals from a Non-Directional Beacon (NDB) using two aerials: a loop aerial for directional signal detection and a sense aerial to resolve any directional ambiguity. The control unit processes these signals, and the display units display the bearing to the NDB relative to the aircraft’s heading, allowing the pilot to navigate toward or away from the beacon. Interpret ADF/NDB readings using Relative Bearing Indicator (RBI) Radio Magnetic Indicator (RMI) Factors affecting ADF accuracy: Static Interference, Station Interference, Mountain Effect, Coastal Refraction, Quadrantal Error, Angle of Bank, Lack of Failure Warning. 23