04 VHF Omnidirectional Range (VOR)

Question 1

What frequency range does VOR operate in?

Answer 1

108 MHz to 117.95 MHz

Question 2

Describe the basic operation of a VHF Omnidirectional Range (VOR) system

Answer 2

• Comprises of a ring of antenna surrounding another antenna
• Each antenna in the ring broardcasts a specific direction (or Radial)
• This is done by the signal from the centre antenna being at different phases with each signal of the antennas surrounding it
• Therefore the combination of each signal (centre and surrounding ring) produces a different signal for each radial

Question 3

Are the radial directions from a VOR in true or magnetic?

Answer 3

Magnetic

Question 4

For a VOR where does variation need to be accounted for?

Answer 4

Variation needs to be applied at the station

Question 5

What are the two types of VOR;

• What type of modulation is used where?
• What direction does the centre antenna rotate?

Answer 5

Conventional VOR (CVOR)

• Variable Phase: AM, Reference Phase: FM
• Rotates clockwise

Doppler VOR (DVOR)

• Variable Phase: FM, Reference Phase: AM
• Rotates anti-clockwise

Question 6

When is the signal from a Conventional VOR (CVOR) strongest?

Answer 6

When the antenna and AC are pointed directly at each other

Question 7

What are the benefits of using a DVOR over a CVOR?

Answer 7

• Requires less space
• More accurate
• Less susceptible to sitting errors

Question 8

Why does a DVOR rotate in the opposite direction from a CVOR?

Answer 8

• To ensure the phase differences produced are the same as a CVOR.
• This means the same equipment on the AC can use either system

Question 9

How does a VOR system self-check?

Answer 9

• Using a ‘pick-up’ antenna positioned at specific radial

- Since the radial the antenna is placed up is constant and known, it is able to detect any drift in the signal

Question 10

What conditions must be met by a VOR self-check for it register as functioning correctly?

Answer 10

• Bearing must not be out by more than +- 1 degree
• Power output must be no less than a drop of 15%
• Monitor itself must be working

Question 11

What is the typical and maximum size of a VOR’s cone of silence?

Answer 11

• 35 degrees

- Max 50 degrees

Question 12

What are the three types of VOR?

Answer 12

• En-route VOR
• Terminal VOR (TVOR)
• Test VOR (VOT)

Question 13

What equipment for a VOR is found on the AC?

Answer 13

• Antenna
• VOR receiver and control unit
• Indicator system

Question 14

To what level of accuracy does VOR work to?

Answer 14

+- 5 degrees

Question 15

Describe the scalloping error

Answer 15

• Caused by the signal being reflected and refracted
• Generates small oscillations of bearing information
• Auto pilot may be disconnected if it is not capable of following the rapidly changing flight path

Question 16

For a VOR on an OBI instrument, how are the To and From indicators determined?

Answer 16

• If the AC is +- 10 degrees from the selected course then it is a From reading
• If the AC is +- 10 degrees from the reciprocal of the selected course then it is a To reading

Question 17

For a VOR on an OBI instrument, how are the Left and Right indicators determined?

Answer 17

If the AC is positioned to the right of the selected course (relative to the same direction) then its a turn left, otherwise a turn right

Question 18

By what principle does VOR operate?

Answer 18

Reference Phase Comparison

Question 19

What is the equation for calculating the maximum distance between two VORs for a given airway width and VOR accuracy?

Answer 19

Distance(nm) = (((Airway width / 2) / Tan (VOR accuracy)) x 2

Question 20

When tracking towards a VOR, what is the equation for the distance off track?

Answer 20

Distance Off-Track(nm) = (Angular displacement x Distance to VOR) / 60

Question 21

Using a VOR beyond it’s published protection range, errors could be caused by?

Answer 21

Interference from other transmitters on a similar frequency

Question 22

What frequency does a TVOR operate in?

Answer 22

• Same as an ILS

- 108 to 112 MHz