6. VDF, ADF & NDB - N2

Question 1

Direction finding accuracies

Answer 1

CLASS A: +/- 2 degrees
CLASS B: +/- 5 degrees
CLASS C: +/- 10 degrees
CLASS D: worse than class C

2, 5, 10, CRAP

Each unit will have a classification for their own equipment.

Question 2

What is QTE?

Answer 2

QTE
TRUE bearing of an aircraft in relation to the
direction-finding station or other specified point.

Question 3

What is QDR?

Answer 3

QDR
MAGNETIC bearing of an aircraft in relation to the direction-finding station or other specified point.

Question 4

What is QDM?

Answer 4

QDM
MAGNETIC HEADING to steer, with no wind, to make for the direction-finding station or other specified point. (aka Homing)

Question 5

What is a radio bearing?

Answer 5

The angle between the apparent direction of a definite source of emission of radio waves and a reference direction, as determined at DF station.

Question 6

What is triangulation?

Answer 6

Pilots can establish their approximate position by obtaining two or more bearings from separate DF stations, and plotting the point at which the bearings intercept.

Question 7

What is Homing?

Answer 7

The procedure of using the DF equipment at your radio station with the radio bearing of an aircraft transmission, whereby the aircraft proceeds continuously towards the station following bearings obtained from your DF equipment.

Question 8

What is ADF?

Answer 8

Automatic Direction Finding

Also known as a Radio Compass

Operates on 300KHz - 3MHz

Question 9

How does ADF work?

Answer 9

Is a tuneable receiver fitted inside an aircraft

The ADF works on the directional properties exhibited by a loop aerial, receiving signals from a ground-based transmitter. (It is effectively an airborne DF unit)

Displays a Relative Bearing in relation to the aircraft’s heading using a pointer on an RBI

Question 10

What can a DF station refuse to give bearings? (4)

Answer 10

• Conditions are unsatisfactory.
• When bearings do not fall within the calibrated limits of the station.
• When to do so would monopolise the frequency due to the priority given to messages relating to
  DF. (lower than, say, Emergencies))
• When the above occurs state the reason at the
  time of refusa

Question 11

What is an NDB?

Answer 11

Non-Directional Beacon
The ground based NDB is an omni-directional transmitter. Continuously transmits and Audio tone with a morse signal identifier.
Operates on MF band – 190 to 1750KHz

Can operate in LF (not in UK)

Question 12

How does an NDB work and its range?

Answer 12

Continuously transmits an audio tone with a morse signal identifier.
Average radius of coverage is between 10 and 500 nm.

High powered NDBs are used for long range
navigation on or off airways.

Low powered NDBs are used as airfield approach aids, known as locator beacons. They have a limited range

Question 13

What errors do NDBs suffer from? (7)

Answer 13

Static Interference - (TS & CB)
Station Interference - (TXs on similar freqs)
Mountain Effect - (Reflected Waves)
Night Effect - (ionosphere)
Coastal Refraction -
Quadrantal Error - (AC Fuselage)
System Malfunction

Question 14

NDB range

Answer 14

MAXIMUM range is experienced from a high
powered NDB at night when flying over the sea.

MINIMUM range is experienced from a low
powered NDB’s used as locator beacons at airfields.

Question 15

What are the ADVANTADGES of NDB?

Answer 15

• Reception is not limited to line of sight.
• The MF waves follow the curvature of the earth.
• The maximum range is dependent on the power of the NDB.

Question 16

DISADVANTADGES of NDB?

Answer 16

The NDB is subject to
- Atmospheric interference (electrical storm)
- Coastal and night refraction which affects bearing accuracy.

It is not as accurate as the VOR.

Question 17

What is Direction Finding?

Answer 17

Direction finding (DF), or radio direction finding (RDF), is the measurement of the direction from which a received signal was transmitted

Question 18

What is a true bearing?

Answer 18

TRUE radio bearing. A radio bearing for which the reference direction is True North.

Question 19

What is a magnetic bearing?

Answer 19

MAGNETIC radio bearing. A radio bearing for which the reference direction is Magnetic North.

Question 20

What is the difference between an a/c’s heading and its bearing?

Answer 20

• Heading is: Which way its nose is pointing
• Bearing is a direction to or from the aircraft.

Question 21

What are the Q codes associated with VDF?

Answer 21

QDM, QTE, QDR

Question 22

The Q-code expression QDR is the true bearing of the aircraft from the station?

Answer 22

False

Question 23

For a pilot to make use of VDF equipment what airborne equipment must be fitted to an AC?

Answer 23

VHF Radio

Question 24

What is an RMI?

Answer 24

An arrow is superimposed onto the compass rose so that a QDM can be read straight
from the pointer. The instrument can house more than one arrow to simultaneously display bearing
information to more than one beacon

Question 25

What is an RBI?

Answer 25

A relative bearing in relation to the aircraft’s heading is continuously displayed on the
Relative Bearing Indicator (RBI). To obtain a bearing to the NDB, the aircraft’s heading must be added to
the RBI reading.
E.G Ac Hdg 135ºM, RBI 145º = QDM 280º