This document discusses Non-Directional Beacons (NDBs) and Automatic Direction Finders (ADFs). It explains that NDBs transmit low or medium frequency radio signals that can be received by ADFs to determine a bearing to or from the NDB. The document covers the components and concepts of NDBs and ADFs, including types of ADFs, how they indicate relative bearings, and errors that can affect ADF readings like signal interference or obstacles. It also provides a brief history of radio direction finding from early loop antennas to modern ADFs with features like best frequency oscillators.

1. NonDirectional Beacon (NDB)
&
Automatic Direction Finder (ADF)
Sebastián León Serna
Avionics
August 6th, 2022

2. INDEX
2
1.
2.
3.
4.
5.
NDB
RDF
ADF
Modern ADF
Errors

3. Nondirectional Beacon (NDB)
3
ICAO Annex 10
190 – 1750 kHz
Ground wave Sky wave

4. Nondirectional Beacon (NDB)
4
NDB Symbol
NDB Ground
Station

5. Nondirectional Beacon (NDB)
5
Types
Related to an
ILS system
Depends on:
- Radiated Power
- Surface
- Time of day (night effect)
- Obstacles

6. Nondirectional Beacon (NDB)
6
Format
Acceptable precisión: ±5°

7. Nondirectional Beacon (NDB)
7
Night Effect

8. Nondirectional Beacon (NDB)
8
Night Effect

9. Radio Direction Finder (RDF)
9
NDB radio signal
190 – 535 kHz
Morse code

10. 10
Loop Antenna
Radio Direction Finder (RDF)

11. 11
NDB radio signal
Up to MF (1800 kHz)
Morse code
Automatic Direction Finder (ADF)

12. 12
Automatic Direction Finder (ADF)

13. 13
Automatic Direction Finder (ADF)
Types
Relative Bearing
Indicator (RBI) Adjustable cover
Radio Magnetic
Indicator (RMI)
Gyroscope
ADF + VOR
Heading knob

14. 14
Automatic Direction Finder (ADF)
Concepts
QDM: Magnetic heading towards NDB
QDR: Magnetic heading leaving NDB
QDM = QDR ± 180

15. 15
Automatic Direction Finder (ADF)
Concepts
QDR-360°
QDR-090°
QDR-180°
QDR-270°
QDR 060°

16. 16
Automatic Direction Finder (ADF)
Concepts
QDM = 320° + 135° = 455° - 360° = 095°
QDR = 095° + 180° = 275°
QDR 275°

17. 17
Automatic Direction Finder (ADF)
Concepts
QDR 360°
QDR = 360°

18. 18
Automatic Direction Finder (ADF)
Concepts
QDR 360°
QDR = 360°

19. 19
Automatic Direction Finder (ADF)
Modern
BFO: Best Frequency
Oscillator
For NDB without
modulation

20. 20
Automatic Direction Finder (ADF)
Modern

21. 21
Automatic Direction Finder (ADF)
Modern

22. 22
Automatic Direction Finder (ADF)
Errors
1. During turn: ADF Dip error
2. Very sensitive signal near station
3. ADF does not includes signal loss indication
4. Obstacles at mountainous areas
5. Errors in surface changes (earth-water)
6. Interferences due to night effect

23. 23
References
Federal Aviation Administration. (2018). Aircraft Instruments Systems. Aviation Maintenance Technician
Handbook-Airframe, Volume 2 (pp 10-43 – 10-48). Oklahoma City.
Organización de Aviación Civil Internacional (OACI) (Julio, 2016). Anexo 10: Telecomunicaciones
aeronáuticas. Volumen I. Radioayudas para navegación.
Mundo Aeronáutico (2017). NDB | Radioayudas IFR. En línea. Disponible:
https://www.youtube.com/watch?v=9hxa_y20qyY
Mundo Aeronáutico (2017). ADF | Radionavegación. En línea. Disponible:
https://www.youtube.com/watch?v=PajgkXjJw2A