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Principles
2. Receiver
– The receiver and associated control panel
are used to tune the ADF to the required
NDB.
Principles
General ADF modes:
• OFF = Switch ADF off
• ADF = Normal position for bearing information
• ANT = Only sense antenna is used. No bearing
information but enhanced audio reception
• BFO = Beat frequency oscillator, rarely used in
Australia
• TEST = deflects needle to right wing. Pressing
ADF again points needle to NDB
Principles
3. Cockpit Display
– The needle always points directly TO the
station
038º M
Principles
038º M
HDG + RB = TO Station
038 + 226 = 264
Principles
• Fixed Card ADF
– The needle indicates relative bearing of the
station from the aircraft
Principles
• Rotatable-Card ADF
– The needle indicates a magnetic bearing TO
the station. Any change in HDG requires realignment
of the ADF card.
Principles
• Radio Magnetic Indicator (RMI)
– Is a gyro-stabilised ADF which automatically
aligns the card, and indicates magnetic
bearings.
Considerations
• The ADF/NDB system has various limitations
and errors that must be considered. These are:
N – Night
C – Coastal
T – Terrain
T – Thunderstorm
T – Tuning / Co-channel
H – Height
M – Mountain
Q – Quadrantal
Considerations
• Night effect
– Radio waves take two paths; ground waves
(along the Earth’s surface) and sky waves.
– During the day the sky waves are absorbed
by the lower ionosphere. At night the
ionosphere reflects the sky wave back, mixing
with the ground wave, causing errors.
Considerations
Extract from ERSA (Darwin INTL)
FAC D – 114 Not for operational use
Considerations
• Coastal refraction
– When passing from land to sea at an oblique
angle, NDB radio waves may be refracted
(bent) due to different conducting and
reflecting properties of land and water. Always
refracts towards the land (away from the
normal).
Considerations
• Terrain effect
– Radio signals have greater range over water
than over sandy or mountainous country
where the range is considerably reduced.
Considerations
• Terrain Effect
Extract from ERSA (Darwin INTL)
FAC D – 114 Not for operational use
Considerations
• Thunderstorm
– Thunderstorms generate a lot of radio energy,
and the ADF needle may point towards it; a
poor mans weather radar.
Considerations
• Incorrect tuning
– The receiver must be correctly tuned.
Incorrect tuning will cause false bearing
indications, restricted range, reversed sensing
indication and possible co-channel
interference from adjoining frequencies.
Considerations
• Co-channel interference
– signals received from other NDBs operating
on the same frequency, may give false
bearing information. (eg: SHT and BNS)
Generally NDBs of similar frequencies are
spaced well apart geographically.
Extract from ERSA FAC S – 324, FAC B – 30, Not for operational use
Considerations • Height
– The range of an NDB over the sea is relatively
independent of aircraft height.
– However, over land, and particularly over
unfavourable terrain, range can be improved
considerably as the aircraft climbs higher.
Extract from ERSA (Darwin INTL)
FAC D – 114 Not for operational use
Considerations
• Mountain effect
– fluctuating bearings may result from the mixing of
radio waves reflected from the surfaces of mountains.
– higher frequencies minimise this effect.
Extract from ERSA
(LATROBE
VALLEY)
FAC L – 197 Not for
operational use
Consideration
Extract from ERSA (WONTHAGGI)
FAC W – 400 Not for operational use
Considerations
• Quadrantal
– Results from the metal construction of the
aircraft.
– The Needle of the ADF will align itself to the
cardinal points of aircraft. (ie: N, E, S, W)
when station in between these quadrants.
Air Exercise
T
I
T
- Tune to NDB using receiver
- Identify using Morse code
- Test by depressing TEST switch
Airmanship
• Always use NDB within it’s rated coverage
• TIT checks before use
• AM stations not to be used for navigation
　
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