Automatic Direction Finder
Chapter 7
(ADF)
QUESTIONS
1. The phenomenon of coastal refraction which affects the accuracy of ADF bearings:
a. is most marked at night.
b. can be minimised by using beacons situated well inland.
c. can be minimised by taking bearings where the signal crosses the coastline at right
angles.
d. is most marked one hour before to one hour after sunrise and sunset.
2. An aircraft is intending to track from NDB ‘A’ to NDB ‘B’ on a track of 050° (T), heading 060° (T).
If the RBI shows the relative bearing of ‘A’ to be 180° and the relative bearing of ‘B’ to be 330°
then the aircraft is:
a. Port of track and nearer ‘A’.
b. Port of track and nearer ‘B’.
c. Starboard of track and nearer ‘A’
d. Starboard of track and nearer ‘B’.
3. ADF Quadrantal Error is caused by:
a. static build up on the airframe and St. Elmo’s Fire.
b. the aircraft’s major electrical axis, the fuselage, reflecting and re-radiating the incoming
NDB transmissions.
c. station interference and/or night effect.
d. NDB signals speeding up and bending as they cross from a land to water propagation
path.
4. The overall accuracy of ADF bearings by day within the Promulgated Range (DOC) is:
a. ± 3°
b. ± 5°
c. ± 6°
d. ± 10°
5. In order to Tune, Identify and Monitor NON A1A NDB emissions the BFO should be used as
follows:
Tune Identify Monitor
a. On On Off
b. On On On
c. On Off Off
d. Off Off Off
6. The magnitude of the error in position lines derived from ADF bearings that are affected by
coastal refraction may be reduced by:
a. selecting beacons situated well inland.
b. only using beacons within the designated operational coverage.
c. choosing NON A2A beacons.
d. choosing beacons on or near the coast.
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7. An aircraft is tracking away from an NDB on a track of 023°(T). If the drift is 8° port and
variation 10° west, which of the RMIs illustrated below shows the correct indications?
a b
c d
8. The BFO facility on ADF equipment should be used as follows when an NDB having NON A1A
type emission is to be used:
a. BFO on for tuning and identification but may be turned off for monitoring.
b. BFO on for tuning but can be turned off for monitoring and identification purpose.
c. BFO off during tuning, identification and monitoring because this type of emission is
not modulated.
d. BFO should be switched on for tuning, ident and monitoring.
9. The Protection Ratio of 3:1 that is provided within the Promulgated range/Designated
Operational Coverage of an NDB by day cannot be guaranteed at night because of:
a. Long range skywave interference from other transmitters.
b. Skywave signals from the NDB to which you are tuned.
c. The increased skip distance that occurs at night.
d. The possibility of sporadic E returns occurring at night.
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10. An aircraft has an RMI with two needles. Assume that:
i) The aircraft is outbound from NDB Y on a track of 126°(M) drift is 140° Port.
ii) A position report is required when crossing a QDR of 022 from NDB Z.
Which of the diagrams below represents the RMI at the time of crossing the reporting point?
a b
c d
11. Each NDB has a range promulgated in the COMM section of the Air Pilot. Within this range
interference from other NDBs should not cause bearing errors in excess of:
a. day ±5
b. night ± 10
c. day ±6
d. night ±5
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12. The range promulgated in the Air Pilot and flight guides for all NDBs in the UK is the range:
a. Within which a protection ratio of 3:1 is guaranteed by day and night.
b. Up to which bearings can be obtained on 95% of occasions.
c. Within which bearings obtained by day should be accurate to within 5°.
d. Within which protection from skywave protection is guaranteed.
13. In order to resolve the 180° directional ambiguity of a directional LOOP aerial its polar diagram
is combined with that of a SENSE aerial ................................ to produce a............... whose single
null ensures the ADF needle moves the shortest distance to indicate the correct................
a at the aircraft, cardioid, radial.
b. at the transmitter, limacon, bearing.
c. at the aircraft, limacon, bearing.
d. at the aircraft, cardioid, bearing.
14. The protection ratio afforded to NDBs in the UK within the Promulgated range(DOC) applies:
a. by day only.
b. by night only.
c. both day and night.
d. at dawn and dusk.
15. The phenomena of coastal refraction affecting ADF bearings is caused by the signal _______
when it reaches the coastline and bending _______ the normal to the coast:
a. accelerating towards
b. decelerating towards
c. accelerating away from
d. decelerating away from
16. In an ADF system, night effect is most pronounced:
a. during long winter nights.
b. when the aircraft is at low altitude.
c. when the aircraft is at high altitude.
d. at dusk and dawn.
17. When the induced signals from the loop and the sense antenna are combined in an ADF receiver,
the resultant polar diagram is:
a. a limacon
b. a cardioid
c. figure of eight shaped
d. circular
18. When flying over the sea and using an inland NDB to fix position with a series of position lines,
the plotted position in relation to the aircraft’s actual position will be:
a. further from the coast.
b. closer to the coast.
c. co-incident.
d. inaccurate due to the transmitted wave front decelerating.
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19. An aircraft on a heading of 235°(M) shows an RMI reading of 090° with respect to an NDB. Any
quadrantal error which is affecting the accuracy of this bearing is likely to be:
a. a maximum value.
b. a very small value.
c. zero, since quadrantal error affects only the RBI.
d. zero, since quadrantal error affects only the VOR.
20. The principal propagation path employed in an NDB/ADF system is:
a. skywave
b. surface wave
c. direct wave
d. ducted wave
21. The ADF of an aircraft on a heading of 189°(T) will experience the greatest effect due to
Quadrantal Error if the NDB bears:
a. 234°(T)
b. 279°(T)
c. 225°(T)
d. 145°(T)
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