VOR

The VOR (VHF Omnidirectional Range) is the most widely used radio aid in IFR navigation. It provides a magnetic azimuth (radial) from the station.

Operating principle

The VOR transmits two signals:

1. An omnidirectional signal (reference)
2. A directional signal that rotates at 30 revolutions per second

The onboard receiver measures the phase difference between the two signals, which gives the radial on which the aircraft is located.

Using the CDI (Course Deviation Indicator)

The CDI is the primary instrument for reading VOR information:

1. Select the radial by turning the course knob (OBS — Omni Bearing Selector)
2. Read the deviation on the center needle:
   • Needle centered = on the selected radial
   • Each dot of deviation = 2° of offset
   • Full-scale deflection = 10° of offset

TO/FROM indicator

• TO: The selected radial leads towards the station
• FROM: The selected radial leads away from the station

Note: The CDI indicates a position relative to a radial, not a direction to follow. Interpretation depends on the aircraft's heading.

Intercepting a radial

To intercept a VOR radial:

1. Set the desired radial on the CDI
2. Determine which side you are on (direction of needle deflection)
3. Take an intercept heading (typically 30° to 45° relative to the radial)
4. Monitor the needle — when it starts to center, turn to track the radial

Technical characteristics

Limitations

• Range limited by altitude (VHF line-of-sight reception)
• Cone of silence above the station (zone with no reliable signal)
• Site errors in mountainous terrain (reflections)