VHF Omnirange - VOR

Question 1

A. Introduction:

How does a VOR differ from an ADF/NDB?

Answer 1

Since it is a VHF facility, it is unaffected by static, weather, night effect or other limitations associated with ADF/NDB.

Unlike ADF, the aircraft does not measure the bearing, it simply receives the bearing information and presents to the pilot as one of 360 magnetic tracks.

Question 2

B. Principle:

Basic principle of operation for the VOR

Answer 2

A VOR uses the principle of phase comparison to provide the pilot with bearing information. There are two navigational components transmitted by the VOR:

1. A reference signal;
2. A directional signal

The phase difference between the two signals determines the bearing

Question 3

B. Principle:

What kind of polar diagram does the VOR use?

Answer 3

When the reference and directional signal polar diagrams’ are combined, produces a polar diagram referred to as a “Limacon”

Question 4

C . VOR Phase relationship:

At what direction will the phase difference equal zero?

Answer 4

North

Question 5

D . Presentation:

What is the instrument called used to present the bearing information received from the VOR?

Answer 5

The CDI

Question 6

F. Errors and accuracy:

Explain site error

Answer 6

Reflected energy from building or terrain in the vicinity of the transmitter can affect phase difference, Large errors from this source are published in NOTAMS, AIP or radio facility manuals.

Question 7

F. Errors and accuracy:

Explain propagation error

Answer 7

Multi path refers to two signals, one received directly from the transmitter and the other reflected from a hill or other large obstruction. The two signals arrive at different times and different phase, thus interfering with each other.

Multi path distortion causes a CDI needle to wander, this effect is called scalloping.

Question 8

To which VOR error is “scalloping” related to?

Answer 8

Propagation error, or multi path reception.

Question 9

F. Errors and accuracy:

State the VOR accuracy of both the transmitter and receiver

Answer 9

Transmitter = + - 1 degrees

Receiver = + - 3 degrees.

Aircraft indications must be within 4 degrees.

If the indication is not within 4 degrees, IFR flights should not be attempted

Question 10

F. Errors and accuracy:

Explain Interference error

Answer 10

This is caused by possible VOR interference from another VOR on the same frequency or weak signals when the aircraft is below line of site range.

Question 11

What is the formula for calculating VOR range?

Answer 11

1.25 x the square root of transmitter height AMSL + 1.25 x square root of Receiver heigh AMSL

Question 12

What are the errors that can be experienced when flying over the “cone of ambiguity”?

Answer 12

Weak erratic signals that will cause the indicator to oscillate erratically. The warning flags may appear momentarily and the TO/FROM can also oscillate.

Question 13

F. Errors and accuracy:

Explain equipment error?

Answer 13

Fluctuations of up to 6 degrees may occur in the CDI as a result of certain propeller, or helicopter rotor speeds. Make a small RPM adjustment to fix this

Question 14

The VOR reference signal is?

Answer 14

A 9960 hz sub - carrier frequency modulated at 30hz

Question 15

The VOR directional signal is?

Answer 15

A limacon

Question 16

A VOR is selected and the IDENT is not received but the VOR indications are normal, this means?

Answer 16

The VOR is undergoing maintenance, bearings not to be used.

Question 17

A RMI is both tuned to a VOR and an NDB which are co-located, the pointers will?

Answer 17

Point in different directions due to the difference in variations between the aircraft and the transmitters

Question 18

If a VOR follows a radial a:

Answer 18

great circle track will be flown

Question 19

B. Principle:

Basic principle of operation for the VOR?

Answer 19

A VOR uses the principle of phase comparison to provide the pilot with bearing information.

Question 20

What are the two navigation components transmitted by the VOR?

Answer 20

There are two navigational components transmitted by the VOR:

1. A reference signal;
2. A directional signal

Question 21

What determines the bearing when using a VOR?

Answer 21

The phase difference between the two signals,

1. A reference signal;
2. A directional signal

determines the bearing

Question 22

On an RMI the front end of a VOR pointer indicates the:

Answer 22

radial plus 180º

Question 23

Scalloping(wander of CDI needle) is relevant to which error?

Answer 23

Propagating error

Question 24

VOR signals in elevation radiate up to -

Answer 24

70 degrees

Question 25

Multi-path reception is solved by -

Answer 25

using a DVOR(doppler VOR)