page_title: VHF omnidirectional range
hierarchical_section_title: VHF omnidirectional range
context_page_description: Very high frequency omni-directional range is a type of short-range radio navigation system for aircraft, enabling aircraft with a receiving unit to determine its position and stay on course by receiving radio signals transmitted by a network of fixed ground radio beacons. It uses frequencies in the very high frequency band from 108.00 to 117.95 MHz. Developed in the United States beginning in 1937 and deployed by 1946, VOR is the standard air navigational system in the world, used by both commercial and general aviation. In the year 2000 there were about 3,000 VOR stations operating around the world including 1,033 in the US, reduced to 967 by 2013.
  A VOR ground station uses a phased antenna array to send a highly directional signal that rotates clockwise horizontally 30 times a second. It also sends a 30 Hz reference signal on a subcarrier timed to be in phase with the directional antenna as the latter passes magnetic north. This reference signal is the same in all directions. The phase difference between the reference signal and the signal amplitude is the bearing from the VOR station to the receiver relative to magnetic north. This line of position is called the VOR "radial".
context_section_description: Very high frequency omni-directional range (VOR)  is a type of short-range radio navigation system for aircraft, enabling aircraft with a receiving unit to determine its position and stay on course by receiving radio signals transmitted by a network of fixed ground radio beacons. It uses frequencies in the very high frequency (VHF) band from 108.00 to 117.95 MHz. Developed in the United States beginning in 1937 and deployed by 1946, VOR is the standard air navigational system in the world, used by both commercial and general aviation. In the year 2000 there were about 3,000 VOR stations operating around the world including 1,033 in the US, reduced to 967 by 2013 (stations are being decommissioned with widespread adoption of GPS).
  A VOR ground station uses a phased antenna array to send a highly directional signal that rotates clockwise horizontally (as seen from above) 30 times a second. It also sends a 30 Hz reference signal on a subcarrier timed to be in phase with the directional antenna as the latter passes magnetic north. This reference signal is the same in all directions. The phase difference between the reference signal and the signal amplitude is the bearing from the VOR station to the receiver relative to magnetic north. This line of position is called the VOR "radial". The intersection of radials from two different VOR stations can be used to fix the position of the aircraft, as in earlier radio direction finding (RDF) systems.
  VOR stations are fairly short range: the signals are line of sight between transmitter and receiver and are useful for up to 200 miles. Each station broadcasts a VHF radio composite signal including the navigation signal, station's identifier and voice, if so equipped. The navigation signal allows the airborne receiving equipment to determine a bearing from the station to the aircraft (direction from the VOR station in relation to Magnetic North). The station's identifier is typically a three-letter string in Morse code. The voice signal, if used, is usually the station name, in-flight recorded advisories, or live flight service broadcasts.
caption: DVOR (Doppler VOR) ground station, collocated with DME.
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