04 VHF Omnidirectional Range (VOR) Flashcards
What frequency range does VOR operate in?
108 MHz to 117.95 MHz
Describe the basic operation of a VHF Omnidirectional Range (VOR) system
- 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
Are the radial directions from a VOR in true or magnetic?
Magnetic
For a VOR where does variation need to be accounted for?
Variation needs to be applied at the station
What are the two types of VOR;
- What type of modulation is used where?
- What direction does the centre antenna rotate?
Conventional VOR (CVOR)
- Variable Phase: AM, Reference Phase: FM
- Rotates clockwise
Doppler VOR (DVOR)
- Variable Phase: FM, Reference Phase: AM
- Rotates anti-clockwise
When is the signal from a Conventional VOR (CVOR) strongest?
When the antenna and AC are pointed directly at each other
What are the benefits of using a DVOR over a CVOR?
- Requires less space
- More accurate
- Less susceptible to sitting errors
Why does a DVOR rotate in the opposite direction from a CVOR?
- To ensure the phase differences produced are the same as a CVOR.
- This means the same equipment on the AC can use either system
How does a VOR system self-check?
- 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
What conditions must be met by a VOR self-check for it register as functioning correctly?
- 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
What is the typical and maximum size of a VOR’s cone of silence?
- 35 degrees
- Max 50 degrees
What are the three types of VOR?
- En-route VOR
- Terminal VOR (TVOR)
- Test VOR (VOT)
What equipment for a VOR is found on the AC?
- Antenna
- VOR receiver and control unit
- Indicator system
To what level of accuracy does VOR work to?
+- 5 degrees
Describe the scalloping error
- 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
For a VOR on an OBI instrument, how are the To and From indicators determined?
- 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
For a VOR on an OBI instrument, how are the Left and Right indicators determined?
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
By what principle does VOR operate?
Reference Phase Comparison
What is the equation for calculating the maximum distance between two VORs for a given airway width and VOR accuracy?
Distance(nm) = (((Airway width / 2) / Tan (VOR accuracy)) x 2
When tracking towards a VOR, what is the equation for the distance off track?
Distance Off-Track(nm) = (Angular displacement x Distance to VOR) / 60
Using a VOR beyond it’s published protection range, errors could be caused by?
Interference from other transmitters on a similar frequency
What frequency does a TVOR operate in?
- Same as an ILS
- 108 to 112 MHz
