NDB

Question 1

What is an NDB?

Answer 1

A non directional beacon (NDB) is a simple ground based radio signal that transmits an omnidirectional radio wave using LF and MF bands.

NDB, as in the name, bears no directional information.

Question 2

What freq range does an NDB use?

Answer 2

190 to 1750kHz

NDB is a Class B non precision approach.

Question 3

How is an NDB identified?

Answer 3

Normally 2 or 3 letters transmitted in morse code.

Question 4

What are the disadvantages of using an NDB?

Answer 4

The lack of failure flags, so when the NDB is faulty there is no indication of this.

Only aviation specific NDBs are monitored and when it’s faulty/out of use it will be published in the NOTAM.

Question 5

What equipment is required for NDB?

Answer 5

NDB on the ground

On the aircraft: 
Automatic DF (ADF)
Loop antenna
Sense antenna
An indicator

Question 6

Why is a loop and a sense antenna required?

Answer 6

Because a loop antenna is not good at informing you of direction, and so a sense antenna is added to null out a point (cancelling out the ‘wrong’ beacon) to give you a direction.

Question 7

Where is the variation applied for an NDB?

Answer 7

Variation is applied at the A/C

Question 8

Name the 2 types of NDBs and it’s range.

Answer 8

1. Locator beacon (LCT) - 10 to 25 NM
   Suitable for approach procedures
2. NDB - range of 50NM or more
   Suitable for en-route navigation and approach procedures

Question 9

The display needle for an ADF points at….

Answer 9

The pointer indicates QDM; to the beacon while

The tail indicates QDR; from the beacon

Question 10

What does the BFO or TONE selection switch on an ADF receiver do?

Answer 10

By selecting BFO or TONE on the ADF receiver it will ident the NDB’s interrupted (pulse) signals. That is, the receiver will pick up the ident morse code from the NDB.

Specifically the N0N A1A NDB

Question 11

What does the ANT switch on the ADF receiver do?

Answer 11

By selecting the ANT switch, the loop antenna is disconnected and the receiver will only pick up on AM LF/MF radio waves.

As the loop antenna has been disconnected, no bearing info can be obtained and so the display ADF display needle/pointer is parked.

Only when ADF is enabled can bearing to the station can be obtained.

Question 12

When an NDB signal cannot be properly and clearly ident, what must you do?

Answer 12

Not use it!

Question 13

What is an NDB’s cone of confusion (silence)

Answer 13

As NDB’s are designed to send out signals horizontally, there is an area above the NDB (40˚ either side of the vertical) that has a weak or no signal at all. This is called the COC.

Question 14

What is the COC formula for an NDB?

Answer 14

Diameter of COC =
Height above the NDB x tan 40˚ x 2 ÷ 6080 (ft/nm)

If only want radius then do NOT ‘x2’

Question 15

There are 2 types of NDB ident transmission. What are they?

Answer 15

A0A A1A : (CW) Continuous wave
NDBs using interrupted carrier (pulse) to ident
So BFO/TONE must be selected on the receiver to.
ident

A0A A2A: (MCW) Modulated continuous wave
NDBs using AM to ident
So ADF must be disconnected on the receiver to ident

Question 16

What are the 4 RBI?

Answer 16

Fixed card ADF (radio compass)
Moving card ADF
Remote magnetic indicator (RMI)
Symbols on an electronic nav display (EFIS ND)

Question 17

Identify the 4 elements that make up the airborne part of the NDB system:

Answer 17

Loop antenna
Sense antenna
ADF
Indicator

Question 18

What is the formula for RB?

Answer 18

Relative bearing = magnetic bearing - magnetic heading OR

RB = QDM - MH

Question 19

What is the difference between the fixed and moving card ADF compared to the RMI display?

Answer 19

The RMI auto aligns the A/C magnetic HDG using inputs received from a remote indicating ˚M.

Question 20

You are homing and flying towards the beacon, you drift right, what will happen to the compass?

Answer 20

The compass will decrease.

Question 21

You are homing and flying towards the beacon, you drift left, what will the compass do?

Answer 21

Compass will increase

Question 22

What will happen to the compass when you are homing and flying away from the beacon drifting left, and then right?

Answer 22

Away from beacon, drift right, compass will increase.

Away from beacon, drift left, compass will decrease.

Question 23

What is the biggest drawback with the ADF?

Answer 23

The lack of failure flags

Question 24

What is static interference?

Answer 24

What electrical charges in the atmosphere interferes with a signal. This happens largely in CB

Question 25

What is night (twilight) effect?

Answer 25

This is where at night the ionosphere extends upwards and D layer disappears while the E and F layers remains.

Due to the increase in ionosphere depth, the signals can travel further and so interfere with other signals.

Question 26

What is costal refraction?

Answer 26

Where signal changes direction due to the angle at which it travels over different terrain. Apart from parallel or perpendicular, the signal will alter course.

The greatest refraction is where the beacon is far in land and/45˚ angle. The refraction makes you think you’re closer inland than you really are.

Question 27

What is multi path propagation?

Answer 27

Aka mountain effect. This is where radio waves reflects off the terrain and follow several different paths between the NDB and A/C.

Question 28

What is quadrantal error?

Answer 28

A/C structure bends incoming waves as it receives it. Therefore the min quadrantal error occurs at the cardinal points, max error at 45˚.

Question 29

What are the 6 major errors suffered by DME?

Answer 29

• lack of failure flags
• static interference (think CB and lightning strikes too!!!!)
• night/twilight effect
• quadrantal error
• coastal error
• multi path propagation - refraction of signals

Question 30

How does an A/C locate an NDB? Once located how do you then use the NDB?

Answer 30

BFO button needs to be pressed to ident the NDB, but then you have to press button again to switch it off so you can navigate with it.