VHF omnidirectional range

A rotating beacon ( abbreviation: BEFORE [ ˌ vi ː ˌ əʊɑ ː ] ) is a beacon for aviation navigation. It sends out a special radio signal to a receiver in the aircraft can take the direction of the beacon. Direction finding system for the aircraft does not need as the direction from the transmitter information is encoded in the signal.

The abbreviation stands for VOR VHF Omnidirectional Radio Range. Means VHF Very High Frequency, the English name for the ultra-short wave (FM ). Omnidirectional radio range in German means "all- radio location ". The German term " VHF omnidirectional radio range " for a VOR is hardly used in the aeronautical practice.

The actual VOR ground station whose signal can be evaluated from the VOR receiver in the airplane and read as directional information on a display device. For simplicity, however, the receiver is called BEFORE.

Knowledge of navigation on VOR be required in the examination for the issue of a flight radio certificate.

  • 9.1 range; Categories of VORs
  • 9.2 container -VOR
  • 9.3 Test VOR ( VOT )
  • 9.4 Combined ground facilities 9.4.1 VOR / DME
  • 9.4.2 VORTAC

Principle of operation

Analogy to the lighthouse

To understand the principle of operation of a VOR, one can imagine a lighthouse that sends out two different light signals:

  • The light signal is white in color and forms a highly collimated beam of clockwise with a period of 6 minutes ( = 360 seconds, which is 1 ° per second) revolves around the lighthouse. So he only lights to the north, 90 seconds later to the east, another 90 seconds later to south and so on.
  • The other light signal is red in color, lights in all directions and always flashes briefly when the rotating white beam points exactly to the north.

An observer on any ship can now from the time difference between the lighting of the red lamp and the appearance of the white light beam, the direction determine the lighthouse. An observer sees, for example, the white light 45 seconds after the red flash, he is located northeast of the lighthouse ( at an angle of 45 ° clockwise ).

This comparison is only for understanding of the principle, such as the direction information is encoded in the signal. In fact, a VOR course sends radio signals and no light signals, and the rotating signal rotates much faster.


In the VOR, this principle has been implemented with radio waves in the VHF range.

The transmitter generates a complex signal consisting of:

In the receiver, the phase difference (0 ... 360 ° ) between the two 30 Hz modulations is measured and as a radial (360 ° azimuth angle 0 ... ) is displayed.

For example, the aircraft east (90 ° ) If the VOR, the phase difference between the directed and undirected the signal is 90 °. The tip of the needle of the radio compass ( RMI Radio Magnetic Indicator = ) points to the angle value 270 °, because the VOR is west. At a position from VOR in West direction ( 270 ° ), the phase difference of 270 °. The tip of the needle of the compass shows on the radio value of the angle 90 °, because the VOR is east.

DVOR ( Doppler VOR)

DVOR is an abbreviation for Doppler Very High Frequency Omnidirectional Radio Range = Doppler VHF omnidirectional radio range. The difference from the VOR is in the form of the generation of the signal. In contrast to conventional BEFORE the 30 Hz AM component (amplitude modulation ) is sent from a stationary omnidirectional antenna, now as a reference signal, while the 9960 Hz sub-carrier by fast forwards between 50 antennas arranged on a circle 13.5 m in diameter is radiated. Thus, a near-continuous rotation of the sub-carrier center is simulated radiation counterclockwise. In the receiver caused by the Doppler effect the required 30 Hz frequency modulation with a frequency deviation of ± 480 Hz, the phase is dependent on the direction (current signal).

The conventional PRIOR than 30 Hz, the reference signal emitted by a stationary FM antenna; the variable signal is generated as a 30 Hz AM by a rotating antenna. When DVOR the roles of reference and variable signals are reversed: the reference signal is 30 Hz AM of a stationary omnidirectional antenna and the variable signal, 30 Hz FM, is generated by the Doppler effect of the surrounding circular array antenna. Because the reference signal and variable signal of DVOR over the conventional VOR are reversed, the signal travels along the circular array antenna counterclockwise.

The additional doppler the DVOR has nothing to do with the Doppler shift due to the flight speed, but the shape of the signal generation.

A DVOR transmitter is typically two to three times more accurate than a conventional VOR station. When DVOR the radial error is rarely more than 1 °, while the radial error in the ordinary VOR can range up to 2.5 °.


The first rotating beacon was the Telefunken compass transmitter ( 1908). The station began with the omnidirectional ( omni-directional ) transmission of its identifier. After reception of the last character of the ID, a special timer is started and stopped again in the receiver for the signal maximum.

In the further development, it proved advantageous to evaluate the minimum of the rotating signal because it can be determined much more accurately than the signal peak.

In Western Europe existed during the First World War stations in Tønder (then Germany ), the island of Sylt, North Wood, Borkum and a station in Belgium Houtave near Bruges (Flanders). These directional transmitters two systems came to Cleveland and Tønder, which radiated omni-directional signals in the time clock. All of these (three ) beacon served the navigation of airships. Aircraft were not equipped with receivers for this system.

During the Second World War greatly enhanced German plants were built under the name Bernhard at the entire Western Front.

The first VOR systems of modern design were taken in Germany in the early 50s in operation. The basic network then consisted of 8 stations.

According to the German Radio Navigation Plan ( DFNP ) of the Federal Ministry of Transport, Building and Urban Development ( BMVBS) the VORs and DVORs be reduced gradually since 2005.


The VOR ground station transmits on a published inter alia in aeronautical charts and in the Aeronautical Information Publication frequency in the range of 108.00 MHz to 117.95 MHz ( according to ICAO Annex 10). The channel spacing is 50 kHz, the channels are so 108.00, 108.05, 108.10 ... 117.95 MHz; However, the frequencies 108.10, 108.30, 108.50 ... 111.90 MHz and 108.15, 108.35, 108.55 ... 111.95 MHz for instrument landing system localizer are reserved.

Azimuth; radial

The VOR system consisting of ground stations and on-board receiver, provides information, namely the azimuth of the aircraft from the VOR transmitter, ie the angle between the ( magnetic ) meridian through the base station and the line connecting the ground station plane. VOR stations are i.d.R. aligned so that the 360 ° radial points to the magnetic north (mis -setting ). VORs in the vicinity of the magnetic poles with high variation, however, are aligned to the geographic North Pole (True ).

A directed away from the VOR transmitter radio base line with a given azimuth is called radial. For the practice of air navigation there are 360 radials. It will not work with decimals, only whole numbers. A radial is therefore a directed vector ( but only with indication of direction, without size) with the direction from the beacon away. In contrast to a light beam from the lighthouse sparks our radio line of position (eg, R -040 ) also over center in the opposite direction (ie the direction of 220 ° = 40 ° 180 °). In this other direction but it is, by definition, referred to as R -220.

Like all course details and compass readings are always written and spoken with three digits and the direction to the radials. All three digits are pronounced separately. The words hundred or ten, twenty, thirty, etc., are not used. Example: 40 ° R -040 and is pronounced: Radial zero - four - zero. Radial 0 ° (ie, north) is usually referred to only as R -360 (radial three - six - zero).

Distance measurement

The distance measurement is not possible with the VOR. But by means of a bearing to two VORs ( cross-bearing ) you can still determine its position and thus its distance from the VOR.

Moreover, often the VOR with a radio navigation system for distance measurement - DME - combined ( about three -quarters of all VOR in Germany have DME). DME ( distance measuring equipment - Distance Measuring Equipment ) indicates the distance to the DME transponder in nautical miles ( NM). The combination, called VOR / DME, gives us a location: azimuth information from VOR, DME distance information from. DME for the display in the aircraft, there is a second device. Conveniently, you have to set just the right frequency for the VOR. Linked to this is automatically the correct setting of the DME frequency. If the VOR stations have no DME, then the DME device remains in the plane without a display.

With a VOR receiver and a stopwatch can estimate the distance to the VOR follows: One turns from the radial side through 90 °, so flies tangentially to the sender, and the time that you, up to a specific file, for example 2 ° needed. The distance is then given by elementary geometric consideration using the small angle approximation to (in radians ) or ( in degrees).

Does one need, for example, at a speed of 80 knots () for 25 seconds, so the distance to the VOR about

Cone of silence

If you find yourself with the aircraft directly over the VOR station, you can indeed receive the transmitted radio waves, the evaluation of the phase difference does not succeed because the procedure is optimized for the horizontal plane. This cone of silence (english cone of silence or cone of confusion ) also exists in the NDB and has an opening angle of about 10 °. With high-flying airliners he can reach a diameter of several miles.

Since the display of the VOR instrument in silence cone is not reliable, which is indicated by a red warning flag to the VOR receiver.

VOR name

VORs have a real name and a three letter code. For example: Gardermoen -VOR or GRD (which is the international airport of Oslo / Norway). The three letters are i.d.R. derived from real names. You speak the three letters usually in the international flyer alphabet ( ICAO alphabet) - in other words Golf Romeo Delta. In flight radiotelephone is always simply told VOR and not VOR / DME or VORTAC. If it is clear that there is a VOR, the name is usually simply said - without the " VOR". Example: "cleared to Frankfurt via Nienburg and Warburg ."

The name of Intersections is specified with 5 letters in order to be clearly distinguished from VORs. For example, the route BUDDA - DERFA - visla -PRG - Werla so via exactly one BEFORE: PRG -VOR.

Namensdoppelungen occur only rarely, and then usually only on different continents. This is therefore only an issue when you create routes from global databases of navigation systems. Then, usually, an interim query by the type and the coordinates of the two radio systems of the same name are displayed. There are also name clashes with NDBs.

Map display

On aeronautical charts, there are separate symbols for

  • VOR with DME

No distinction is made between VOR, DVOR, etc..

In the compass roses around VORs on the aviation map the magnetic declination is already included ( if required).

In Germany, the following FM radio beacon: 14 VOR systems; 37 VOR / DME; 9 VORTAC; 38 DME ( without VOR); 21 TACAN (without VOR) (as of December 2012).

Ground facilities

Reach; Categories of VORs

VORs are ordered by their distance ( engl. service volume ) divided in the U.S. into three categories, depending on how far the Guaranteed clear signal reception without interference.

  • High Altitude VOR ( hvor ) - Range up to 130 NM at 45,000 ft
  • Low Altitude VOR ( LVOR ) - Range 40 NM at 18,000 ft
  • Terminal VOR ( TVOR ) - Range 25 NM at 12,000 ft, is generally used as an approach aid.

Here are followed by the breakdown of ranges based on the altitude.

  • Hvor: 1000-14500 ft - 40 NM
  • 14500-18000 ft - 100 NM
  • 18000-45000 ft - 130 NM
  • 45000-60000 ft - 100 NM

From a TVOR station can be received often the ATIS.

Container BEFORE

If a longer period of time BEFORE fails ( eg remodeling, renovation ), is situated by the DFS, a container -VOR, which takes over the operation during the downtime. The Container BEFORE usually gets its own frequency and therefore does not transmit on the frequency of the replaced VORs. The replacement frequency and duration of replacement as well as any limitations in range and accuracy will be published by NOTAM.

Test VOR ( VOT )

The performance of the VOR receiver must be checked at regular, prescribed intervals. This can be on the one hand more frequently performed on airfield positions whose coordinates are known. It can also be checked by the frequency of a VOR test is set at the VOR receiver. The VOR instrument is then constant radial 360 and the measured deviation may not exceed 1 °.

For the VOT testing a signal is sent which indicates to the receiver 360 ° FROM ( or 180 ° TO). At the bottom of the deviation shall not exceed ± 4 °. In the air, the deviation shall not exceed ± 6 °. In two VOR receivers in the aircraft, the display difference between two receivers must not exceed 4 °.

Combined ground facilities


A VOR is often associated with a radio navigation system for distance measurement - the DME ( distance measuring equipment - Distance Measuring Equipment ) - combined (about three quarters of the VOR in Germany have DME). BEFORE indicates the direction of the ground station to the aircraft; DME shows the distance to the DME transponder in nautical miles ( NM). The combination of VOR and DME allows the positioning of a single ground station.


TACAN ( Tactical Air Navigation ) is a military omnidirectional radio and works similar to a VOR, but is more accurate by a factor of 1.2 to 2. In addition, integrated functionality in TACAN signal always the DME. TACAN transmits ( 962-1213 MHz) in the UHF range. If there are VOR and TACAN ground station at the same location, the combination is called a VORTAC.

Board system

The on-board system is to power supply and cabling of the following components. Depending on the installation situation, several modules can be combined in a single housing.

Operating unit

Here the frequency of the desired VOR ground station is set. Some BEFORE devices offer the possibility to set two frequencies: the current active frequency and a preselected frequency ( stand-by frequency). By pressing a button you exchange the two frequencies.

If the airplane is equipped with ILS, at the same time the frequency of the Gleitwegsenders ( 329.15 335.00 MHz frequency band ... ) is also hereby set.

Is the aircraft equipped with DME, usually be at the same time with this, the transmission and reception frequencies of the DME ( 960 ... 1215 MHz frequency band ) is set.


Various types of display devices can be used:

  • Radio Magnetic Indicator ( RMI). A pointer rotates on a compass card and points towards the VOR ground station; the compass card in turn is rotated by the gyro and shows the ill -looking heading. The pilot can read the RMI both the magnetic bearing to the VOR ground station ( QDM ) and the relative bearing of the VOR ground station ( left / right).
  • Course Deviation Indicator (CDI - Course deviation indicator). Depending on the design, the display needle rotates around the top point, or it wanders through parallel shift to the right or left. The needle indicator points to a scale of an intermediate point and the five points on the right and left. Each point corresponds to a deviation of 2 ° from the set course.
  • Cross pointer instrument. If the airplane is equipped with ILS, is used instead of the CDI a cross pointer instrument used. The vertical needle (rash left / right) has the function as in the CDI. The horizontal needle (rash top / bottom) indicates the deviation from the glide path.
  • Electronic Flight Instrument System ( EFIS ). Information from the VOR receiver can be displayed in the navigation screen of the EFIS. Often conventional electromechanical instruments, such as RMI and CDI are mimicked in the EFIS.

Comparison with other navigation systems

VOR, due to their limited reach in densely populated countries in very good used with flat landscapes. In narrow valleys VORs are unsuitable because of the strong reflection of the FM signals to the mountains, where one is dependent on NDBs such as the Innsbruck airport.

For cost reasons, the convenient, but expensive VOR navigation highly developed countries is reserved, in sparsely populated ( developing) countries are NDBs mandatory for flight navigation. Islands such as Tuvalu are not found without NDB, there will probably be no future BEFORE.

The Global Positioning System (GPS) gradually supplanted the VOR / DME. In Germany VOR / DME are still required by law for instrument navigation primary instruments.


Airways were originally mainly via radio navigation facilities, including VOR beacon and its course was defined by them. The branching of airways was often on VORs. Since the introduction of area navigation ( RNAV ) airways and trigger points ( intersections ) are increasingly defined independently of ground -based radio navigation systems like VORs, which increases the capacity of the airspace clear. The line connecting the two radio range (VOR, NDB, etc.) is given by their fixed position necessarily a course that is also called OBS course. In the ticket you will find this course located next to the airway, it is not to be confused with the radial of the VOR (eg R -345 ), which indicates the opposite course ( ± 180 ° ) to the actual course.

If you move to an air street to a radio fire, this is called "inbound ", one moves away from it, so it is called an "outbound ".

List of VORs in Germany

List of VORs in Austria

List of VORs in Switzerland