Talk:VHF omnidirectional range

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NPOV dispute[edit]

"VORs are quickly being ignored in favour the much more user-friendly GPS system, and it is generally thought that they will be turned off around 2010. Oddly the airways have become so important to air traffic control that aircraft are forced to follow them even when they are using GPS for navigation."

This is a rather contentious statement, and contains some POV remarks "Oddly...". Nothing odd about it. VOR cannot be "ignored", since as yet GPS is not necessarily actually admitted as a primary means of navigation in many territories. In addition, GPS receivers that are approved for use for aerial navigation are very expensive pieces of kit - the cheap handheld and mobile units are not considered good enough for aircraft use. Thousands of GA aircraft do not have GPS, nor are ever likely to, yet many are fitted with VOR equipment. As a pilot, I have never heard that VOR is likely to be switched off, just as NDB have not been switched off despite being superceded decades ago. Unless you can point to a reliable source for this factoid, I for one am inclined to take it with a very big pinch of salt. Since it's also opinion-laden, I will remove it from the article until it can be verified and reworded.Graham 13:32, 23 Apr 2005 (UTC)

Graham, I've added a point of view template on top of the page as I see what you mean... thanks for the input! -|->TheFSaviator-|-> (talk) 01:25, 10 October 2009 (UTC)

THere is much dispute on the NDB page over wether NDB's are obsolete or being phased out. a few authors contend there is no proof

they are being phased out. -- (talk) 05:51, 7 June 2011 (UTC)

David.lecomte (talk) 00:11, 14 April 2011 (UTC) VORs are being phased out in en-route applications - that is supposed to happen before 2015. They are mandated at airports by many authorities until 2015 - 2020. FAA don't expect complete change-over to satellite based navigation until 2025, thus they expect traditional DME/VOR systems at airports until then. For example see

NDBs are supposed to be phased out by 2012. Here in Australia, though, Air Services just bought (18 months ago) a stack of new ones. I was told by one engineer that he has been told that NDBs would be phased out for the last 20 years - he sees no sign of it happening yet.David.Lecomte

I've reworded the Future section and cited the relative advantages in the Features section. I've also elaborated the operation section to address other issues in this discussion). My hope is to remove the neutrality check from this article. Hopefully helpful, --Grandfatherclok (talk) 21:20, 19 December 2009 (UTC)

After 30d, with 38 watchers, there has been no NPOV discussion. I plan therefore to remove the NPOV tag in approximately 1 week. --Grandfatherclok (talk) 18:16, 18 January 2010 (UTC)

If the article were only focused on VOR usage in the United States this would be true. The VOR system is effectively (if not officially) being phased out by increased GPS usage. But the fact of the matter is that many countries still rely on VORs (and NDBs) almost exclusively. As mentioned here, GPS equipment can be very expensive. Additionally, in order to be safely used for instrument approaches you typically need WAAS (or LAAS) augmentation, which depends upon even more expensive ground facilities and even more expensive receivers installed in the aircraft.

On paragraph in the current version which I find unusual is: "Today VOR has almost entirely replaced the low/medium frequency ranges and beacons in civilian aviation. Due to the higher maintenance cost and siting limitations of VOR transmitters, more airports have NDB and RNAV (GPS) approach procedures than have VOR approach procedures. Due to lower receiver and data update costs, more aircraft are equipped for instrument approach by VOR than by GPS, though the number of aircraft equipped for GPS approaches, and the number of approved GPS approaches is growing significantly."

Do we really know that more airports have NDB approaches than VOR approaches? I'm not as familiar with European and foreign airports, but here in the United States I'm fairly certain that VOR approaches outnumber NDB approaches. Admittedly, this may not be the case in other countries (although the United States maintains a majority, relatively speaking, of the world's airports). Regardless, the paragraph in question is lacking any solid citations and seems poorly constructed. --Matthammer (talk) 21:40, 10 June 2010 (UTC)

This does indeed seem to be an unsubstantiated statement - while I agree that GPS approaches appear to gradually be replacing VOR and NDB approaches, I don't believe that NDB approaches are more abundant than VOR approaches. In Canada, both seem to be slowly disappearing, although that is strictly from observation, I have not seen any numbers to back this up. Since the last comment was from June of last year and there has been nothing further added, I will change that statement per our comments. — Preceding unsigned comment added by HiFlyChick (talkcontribs) 20:04, 1 February 2011 (UTC)

Possible incorrect link in text of VOR description.[edit]

Thanks for this excellent explanation of VOR (VHF Omnidirectional Range)! However, in the first sentence of the last paragraph of the sub-section titled "Using the VOR", the words "flight director" are intended to refer to a computer on the airplane but they link to a Wikipedia page describing the Chief of Flight Operations for a NASA space mission.

I'm a novice here, so I haven't made any changes regarding this possible incorrect link. Perhaps a more knowlegable contributor can check/fix this.

Thanks for creating and maintaining this excellent encyclopedia!

Steve-vts -- Sept 13, 2005

I have removed the incorrect link to flight director Sfisher 23:08, 13 October 2005 (UTC)

Requested move to VHF Omnidirectional Range[edit]

  • Oppose Capitalization may be a convenient way to clarify the abbreviation VOR, but this is not a proper noun and should remain in lower case. Michael Z. 2005-10-19 18:40 Z
  • Oppose Just because an acronym is often capitalized, that doesn't mean the spelled out version should be. The capitalized acronym in the introductory paragraph as it should be, though it should probably follow rather than precede the spelled out version, which need not be capitalized nor hyphenated. Gene Nygaard 05:19, 21 October 2005 (UTC)

I am a FAA Systems Specialist and I maintain and certify two VOR facilities, one conventional and one doppler. At no time does the FAA ever refer to a VOR facility as a Vor or a vor. Air Traffic Control acronyms are very specific, dictated by a published order. The terms VOR, VOR/DME and VORTAC are always capitalized per Air Traffic Control orders.(FM Guinta 17:35, 26 June 2007 (UTC))

Flight Director[edit]

"Electronics can solve this problem, and the flight director makes such tasks almost foolproof. A flight director is an analog computer..."

The Flight Director is an analogue or digital computer that represents navigational data on the Attitude Indicator as an attitude and angle of bank or rate of turn to fly.

The term you need is "Area Navigation System" which has the slightly bizarre acronym "RNAV": this being an analogue or digital computer system that in its most basic form uses VOR/DME signals to allow direct flight to/from points other than the VORs themselves (these points in the basic equipment are defined as radials and DME distances from VOR/DMEs and are known as 'ghost stations'). Very advanced digital Area Navigation Systems use input from many other navigational sources and do lots more besides and are known as Flight Management Systems.

Corrected, and removed some other related text that was incorrect.

BaseTurnComplete 22:32, 6 January 2006 (UTC)

Operational description in error?[edit]

The article currently says, "The combined signal is fed to an array of four omnidirectional antennas, which rotates the signal at 30 times a second." I've always thought that the carrier signal is radiated in all directions simultaneously and the subcarrier (and only the subcarrier) is rotated as its phase changes. Again, I'm not completely sure of this, thus the discussion rather than an outright edit. However, I would think that, if the article as it stands is correct, there would be a pulsing effect to the received morse identifier (the 30Hz rotation), and this doesn't happen. ChadScott 22:27, 8 June 2006 (UTC)

David.lecomte (talk) 00:11, 14 April 2011 (UTC) The refererence to four omnidirectional antennas is most probably a reference to one of the techniques (not the most common), of designing a Conventional VOR. In a CVOR, the 30HZ variable signal is the "AM" signal as received by the plane. This signal is not modulated onto the carrier. By manipulation of the phase of signals fed to a complex slotted tube antenna, the directivity of the antenna is steered through 360 degrees at 30 times per second. The sub-carrier is amplitude modulated onto the carrier that is fed into these feeds. The aircraft receives the composite signal from all the feeds which combines in space to create the semblance of amplitude modulation. An older less common technique was to use four Alford Loop antennas, with the phase rotation applied to the feeds of all four. Note that the idea is to try and create the semblance of a sinusoidal shape to the signal that combines in space - the result is an approximation that is not too pretty when looked at without a sharp filter. David.Lecomte

That whole paragraph might need a bit of rewording. page 81 of 126 has a brief description:
"A VOR transmits two 30 Hz modulations resulting in a relative electrical phase angle equal to the azimuth angle of the receiving aircraft. A cardioid field pattern is produced in the horizontal plane and rotates at 30 Hz. A nondirectional (circular) 30 Hz pattern is also transmitted during the same time in all directions and is called the reference phase signal. The variable phase pattern changes phase in direct relationship to azimuth. The reference phase is frequency modulated while the variable phase is amplitude modulated." (PD-US-GOV)
I'm pretty sure the 1020 Hz ident (and sometimes voice ident) is/are transmitted periodically on the carrier output, along with the reference signal (which is omni-directional, non-rotating and equal amplitude in all directions). The electronically rotated pattern is transmitted via the same four antennas and fed via a sideband 1 and sideband 2 signal. Don't ask me for a source for that or how to incorporate any of the above into the article. I'll try to find something on the net later. -Dual Freq 03:06, 9 June 2006 (UTC)
I've reworded the article a bit to make this clearer to the reader. ChadScott 05:57, 13 June 2006 (UTC)
I think it's worse now, from above: "The reference phase is frequency modulated while the variable phase is amplitude modulated." (PD-US-GOV) FM is the 9960 Hz which is the reference, AM is the cardioid / rotating pattern. --Dual Freq 11:10, 13 June 2006 (UTC)
I believe I've fixed the paragraph, bottom line from the FAA source above is the reference is 30Hz FM and the variable is 30 Hz AM. Right now all I can cite as a source is the above paragraph and what's in my head (which may not be an acceptable source). I'll look for a net source, but I don't know if I can find one. However, I'd rather pull the whole paragraph than leave it with something that's not correct, what's in there now is as correct as I can be with no other sources. --Dual Freq 00:33, 14 June 2006 (UTC)
I think this is close, but I'm still not sure it's totally correct. The variable signal is on the subcarrier, isn't it? In other words, the morse-code ID and reference 30Hz tone are omnidirectional FM and the variable rotating signal is AM on a 9660 subcarrier? ChadScott 07:13, 14 June 2006 (UTC)
I think this backs me up, the 9960 Hz if FM modulated by 30Hz ref. Then that is AM to the carrier. "A 30-Hz fixed-phase reference signal (0°-Magnetic North) is frequency modulated on a 9960-Hz subcarrier and then amplitude modulated to the operating rf frequency of the station. A 30-Hz variable phase signal (representing 0° to 360°) is directly amplitude modulated to the same rf frequency. The two audio tones are detected from the received VOR rf; the phase of the reference signal Is corrected for a selected course other than 0°, and the two signals compared. The difference between the two indicates the angular deviation of the aircraft from the selected course."TM-11-1510-213-34 (PD-USGov-Military-Air Force) Lower font size in browser if the linked page is hard to read because of overlapping text. The ref says directly AM to the RF carrier, but I've always heard it described as space-modulation via the sideband signals meaning the modulation occurs somewhere other than the transmitter, but to the aircraft receiver it still modulates the carrier amplitude, so I guess it is AM. If this modulation were visualized, it would look like a cardioid pattern rotating at 30 Hz. The phase of the two 30 Hz signals is what is compared, not the amplitude. --Dual Freq 11:12, 14 June 2006 (UTC)
In the case of a conventional VOR, the 30Hz omnidirectional FM signal is the reference signal to which the 30Hz rotating AM signal is referred. In the case of a Doppler VOR (DVOR) transmitter, the 30Hz AM signal is transmitted from a single omnidirectional antenna and the other signal is frequency modulated by the doppler effect as the transmitter scans around a ring of antennas 30 times per second. So in the case of a DVOR the 30Hz AM is regarded as the reference signal to which the 30Hz FM is referred -- just the opposite of the conventional VOR. Since the roles of the reference signal and the rotating signal are reversed, the DVOR ring antenna array is scanned counterclockwise. Dulciana 11:01, 9 October 2007 (UTC)

David.lecomte (talk) 00:11, 14 April 2011 (UTC) I'm not sure what the conclusion is, but I can write with absolute certainty that the IDENT information is modulated onto the reference signal of a DVOR. Thus the reference signal is modulated with an audio signal that consists of three inputs - the 30Hz reference signal (nominally 30% modulation index), a voice signal (usually at a maximum of 30% modulation) and the Ident (10%). This is radiated from the centre antenna of the DVOR ring.

The sideband antennas only broadcast the carrier signal +/- 9960Hz. This is only amplitude modulated according to the manufacturer's preferred method of blending. The phase of the upper and lower sidebands are referenced to the phase of the carrier. This way the two sideband signals are kept in phase. The relative phase of their phase centre can (usually) be adjusted so that distortions caused by coupling can partially compensate distortions caused by blending. No signals are modulated onto the sub-carriers.

Note that the IDENT is transmitted usually every 10 seconds when there is no co-located DME, or every 7.5 seconds when there is. In the latter case, every 4th Ident signal is not transmitted by the VOR, but instead by the DME. As both audio paths are combined in an RNAV receiver in the aircraft, the pilot (should he be listening) just here the ident every 7.5 seconds. Ident synchronisation is done by setting up either the DME as master (and VOR as slave) or vice-versa. David.Lecomte

I elaborated the operation section in the hope of making it clearer. The ICAO (as cited above) requires that the phase angle by which the AM signal lags the FM signal be equal to the azimuth. For the sake of common language, the ICAO (as cited above) arbitrarily (or historically) identifies the signals by reception. The received leading (i.e. FM) signal is reference, and the lagging (i.e. AM) signal is variable, regardless of generation. Between conventional and doppler signals, testing and monitoring procedures necessarily differ by what must me checked anisotropically and what can be checked more simply. Ideally, receivers cannot discern (within accuracy limits) whether rotation/revolution is electronic or mechanical. --Grandfatherclok (talk) 02:47, 20 December 2009 (UTC)
Grandfatherclok - This is not correct. I believe that it would be much more logical to always refer to the FM signal as REF and the AM signal as VAR regardless of generation method but unfortunately it is not so. ICAO Annex 10 Chapter says [referring to 9960 Hz FM subcarrier] "For the conventional VOR the 30 Hz component of this FM subcarrier is fixed without reference to azimuth and is termed the 'reference phase'. For the doppler VOR, the phase of the 30 Hz component varies with azimuth and is termed the 'variable phase' ". The Annex continues on to state the equivalent concept with the 30 Hz AM signal. -- (talk) 08:04, 4 August 2010 (UTC)


I added the accuracy standard ARINC 711 reference. This standard is the most difficult to obtain but it is possible and can be far better using an optimal receiver algorithm. --bloublou 18:03, 7 August 2006 (UTC)

As stated in the article. 1.4 degree system accuracy per FRS that is cited. That probably includes the .4 ARINC specifies for reciever equipment and 1.0 FAA uses for ground based transmitter equipment. Ground based VORs are monitored with a +/- 1 degree tolerance and will shutdown if they exceed it. Dual Freq 22:14, 7 August 2006 (UTC)

ILS subsection[edit]

I removed the ILS subsection as VORs and ILS work completely differently. Calling an ILS a "narrow" VOR is an inaccurate simplification. ChadScott 01:40, 13 January 2007 (UTC)

Their only overlap is that the share the 108-112MHz band David.Lecomte


I've pruned quite a bit of US-specific stuff and internationalized other stuff accordingly. To our American friends: you're not the only English speakers in the world, nor does the world end at your borders. Please try to bear this in mind when editing articles that are not inherently US-specific!BaseTurnComplete 09:25, 31 January 2007 (UTC)

Creation of Rotating Field[edit]

I've deleted the work "electronic" from the sentence: "A second, amplitude modulated 30 Hz signal is derived from the rotation of a directional antenna array 30 times a second." (previously: "...derived from the electronic rotation...").

As I wrote under the discussion heading 'Operational description in error?', this sentence is true as it applies to conventional VORs, where the rotating field is created by mechanically rotating a directional antenna. If you talk about electronic rotation of an antenna array, then you're talking about a DVOR and here it's the 30Hz FM signal that's created by electronically scanning (rotating) the array, not the AM signal. Dulciana 11:12, 9 October 2007 (UTC)

CVOR blokk.jpg

It is my understanding that the ICAO differentiates by whether the F3 reference signal is isotropic (CVOR) versus anisotropic (DVOR), primarily as to the difference in certification and inspection procedures. I believe the first conventional VOR stations used an antenna on a physically rotating platform as developed for WWII radar. The rotating platform also turned a variable capacitor to F3 modulate the reference signal. In the early 1970s, transistors reduced the cost of bandwidth relative to vacuum tubes, and FFT software made more complex and precise antenna design practical. Electronic trim, rotation, and revolution of antenna "arrays" became less expensive than mechanical for radar, direction finding, beaming, etc. If ~250 m2 (2000 ft2) of lateral room was available, electronically revolving twin upper and lower sideband antennae fed from a single centrally located antenna required little manufacturing precision. If there was no room at an existing site, an electronically rotated array of 4 elements (as diagrammed) fit in ~1 m2 (10 ft2) but required much more precise manufacture. I understand the cost of lateral room was usually less than precision manufacture, so most VOR stations are now DVOR, and the cost of precision manufacture was usually less than lifetime mechanical maintenance, so most CVORs now use electronic rotation. --Grandfatherclok (talk) 01:39, 20 December 2009 (UTC)


I see how the VOR works?

How does DME work? —Preceding unsigned comment added by Jokem (talkcontribs) 17:04, 13 March 2008 (UTC)

See the separate article on DME. Electronically speaking, VOR and DME are two completely separate systems; although the ground stations are often co-located. -- Dulciana (talk) 10:54, 19 March 2008 (UTC)

Thx, I will put DME questions on the DME Page. I will also add this link to the VOR page if there is not one already. Jokem (talk) 20:54, 4 April 2008 (UTC)

David.lecomte (talk) 00:11, 14 April 2011 (UTC) DME & VOR are co-located at airports because an RNAV receiver tunes to both. Most pilots refer to DME/VOR as "VHF Navs", being unaware that DME operates in the UHF band. This is because the VOR channel is directly associated with the DME channel. The pilot selects the VHF channel for the VOR, and that automatically selects the ICAO defined DME channel associated with that VOR channel - hence their confusion. In most airports the DME antenna is located about 20 metres from a CVOR, or right on the edge of the counterpoise of a DVOR. They are synchronised with respect to their Ident, with the DME transmitting every fourth IDENT burst. If one listens to the VOR IDent bursts, one will hear three bursts and then a pause, and then three bursts. In the pause, the DME transmits its burst. The pulse train that encodes the Morse code sequence in the DME is converted to audio by the DME receiver, and its audio output is combined with the audio signal sent by the VOR. If everything is OK, the pilot can hear the Morse burst every 7.5 secs typically. If the DME is out, he will notice the pauses on every 4th code. If the VOR is out there will be long gaps between hearing the one Morse code.

-- Each should refer to the other -- [User:David.Lecomte|David.Lecomte]]

VOR = VHF Omnidirectional Radio Range[edit]

An unregistered user edited the introduction, suggesting VOR = VHF Omnidirectional Radio. He or she apparently misunderstood the word "range"; it doesn't mean range in the sense of distance between the ground facility and the aircraft, rather "range" should be understood in the sense of an area of land that is served by the facility (cf. rifle range, testing range etc.). It's easier to understand the derivation of "omnidirectional range" if you're acquainted with the much older MF bidirectional radio range -- see the last paragraph of

Dulciana (talk) 15:02, 9 April 2009 (UTC)

"zero-zero" weather[edit]

I changed the Future section so that one sentence that previously said (practically speaking, landings in "zero-zero" weather) to now say "zero visibility weather" as it makes more sense to the layman, and is more accurate. —Preceding unsigned comment added by (talk) 22:42, 8 October 2009 (UTC)

USA only information?[edit]

Last time I looked on the political map the USA is not equivalent to The World. As far as I know the FAA has no authority outside the USA. The developments in the USA are not always applicable to the rest of the world. I see the same approach on many, if not all, aviation pages on the Wiki. There is life outside the USA. — Preceding unsigned comment added by (talk) 12:24, 14 September 2011 (UTC)

Life outside the USA? Don't be ridiculous! (talk) 02:24, 11 November 2012 (UTC)


This article currently states that "An "ambiguity" (TO-FROM) indicator shows whether following the selected course would take the aircraft to, or away from the station." This is not entirely accurate since the VOR system has no way of knowing which direction you are flying along the radial. I am currently studying PPL and my instructor showed me a practical example of this the other day. All radials come From the station and it's perfectly possible to fly towards a VOR beacon with the FROM indicator showing. It is equally possible to fly away from the VOR on a TO radial, which is the cause of much confusion to pilots unfamiliar with the system. Again, the beacon or the equipment in the aircraft doesn't know which direction you are flying. — Preceding unsigned comment added by (talk) 14:40, 31 January 2012 (UTC)

The "VOR system" consists of the transmitter and your receiver. Yes, your system does know if you are on flying to/from a radial provided you are referencing the correct radial. and not the line that runs through the radial an out the other side of the transmitter (On a course of 000 flying directly north at a VOR, your instruments can certainly show a FROM indication. It isn't wrong, you just have your equipment set up on a reciprocal heading. Put it on 180 and that TO/FROM indicator will show what you are expecting). I think this article explains it quite well, but if you think it can be improved, feel free to contribute and make a change! Buffs (talk) 23:50, 31 January 2012 (UTC)

Simulator link not working?[edit]

I've tried the online VOR simulator referenced in the External Links section with Flash version 11.8.800.175 but it doesn't seem to be working. I am unable to update my flash due to system administrator settings. Can anyone else confirm that the simulator works? -- (talk) 00:30, 10 July 2014 (UTC)

Works for me (talk) 00:58, 10 July 2014 (UTC)

Who knew?[edit]

VOR signal strength is enhanced by reflections from clouds? Much of the "Features" paragraph is nonsense, what happened here? Did not have time to fix today. Altaphon (talk) 01:28, 30 September 2014 (UTC)

Never mind, fixed. Added some references to balance the GPS-averse assertions made some time ago. Altaphon (talk) 07:16, 1 October 2014 (UTC)


Sentence in question: "By comparing the phase of the secondary signal with the master, the angle (bearing) to the aircraft from the station can be determined."

Original edit: [1] (Unnecessary bolding: the bearing to the station can be determined just as easily)

Revert: [2] (The bearing "to" the station would not be a correct description of a VOR radial.)

But the sentence doesn't use the phrase "VOR radial". It just makes a statement which is equally true whether the word "to" or "from" is used, so the heavy emphasis on "from" is misleading. The term "radial" is introduced a couple of sentences later, and that's the place where the distinction should be made. – Smyth\talk 17:07, 22 August 2015 (UTC)

May edits[edit]

In reviewing the large chunk of edits made in May [3], I have found a significant number of factual errors and inappropriate material. For example:

  • The FAA Pilots Handbook of Aeronautical Knowledge says, "a radial is defined as a line of magnetic bearing extending outward from the VOR station". The repeated usage of the term "radial" to refer to the bearing TO the station is therefore incorrect.
  • No WP:Reliable source has been provided to support use of the term "VOR Head", yet the above edit suggests it is preferred terminology.
  • The statement "Live voice can also be received on VOR frequencies, to which the pilot must reply on a COM frequency (such as 122.100R)." is unsourced and presumably specific to a certain location.
  • Other expanded explanations of principles are largely correct, but made longer and more complicated.

On balance, I do not feel this series of edits improve the article, so I have reverted them. Any specific suggestions for improving the article can be discussed on this page in order for them to gain WP:CONSENSUS. Burninthruthesky (talk) 09:33, 13 July 2016 (UTC)