Topic Author
Posts: 99
Joined: Sat Nov 13, 1999 6:16 am

Principles Of VOR

Sun Apr 11, 2004 2:08 pm

Can anyone explain exactly how VOR's work?
I am tired of hearing the lighthouse analagy, and am really concerned with where the "phase difference" actually occurs between the reference and variable...
Posts: 532
Joined: Fri Oct 26, 2001 7:09 am

RE: Principles Of VOR

Sun Apr 11, 2004 2:22 pm

Well if you understand the lighthouse analagy... the real thing isn't much different:

The variable signal (the rotating 'beacon') rotates round at 1800RPM, your equipment only 'sees' it when it is shining right toward it.

The reference signal is sent out everytime the variable signal moves through north (360*).

Your VOR reciever just measures the difference between the two signals, and therefore can figure out what radial you're on:

Posts: 800
Joined: Tue May 18, 1999 2:41 am

RE: Principles Of VOR

Sun Apr 11, 2004 10:24 pm

Skyguy11 this has got to be the best (and yet the simplest) graphical presentation of VOR. Thanks!
I seriously think I just creamed my pants without any influence from any outside variables.
Posts: 532
Joined: Fri Oct 26, 2001 7:09 am

RE: Principles Of VOR

Mon Apr 12, 2004 12:12 am

Thanks! I agree it is very good, got it from a friend.
Posts: 291
Joined: Fri Jun 15, 2001 6:40 pm

RE: Principles Of VOR

Mon Apr 12, 2004 1:00 pm

"Skyguy11 this has got to be the best (and yet the simplest) graphical presentation of VOR. Thanks!"

Great post skyguy11. That is the same graphic that was in our Air Force training manuals at Com/Nav Technical Training.

To simplify: The VOR receiver measures the phase difference of the two signals it is recieving, which then tells it where it is in relation to the station, it then inverts this signal to represent the azimuth to the VOR station. (ok, not that simplified  Smile )

In the diagram. Lets say your aircraft is east of the station. ( 90* relative to the station) and heading north. The aircraft VOR rcvr sense a 90* phases difference, inverts this and position the needle on the RMI to point to 270*. This is the direction to the VOR station.
Posts: 4698
Joined: Thu Mar 14, 2002 5:39 pm

RE: Principles Of VOR

Mon Apr 12, 2004 8:00 pm

Sorry for the double post, but hey, Skyguy11, great great explanation. Thanks.

Posts: 20713
Joined: Wed Jul 11, 2001 7:41 am

RE: Principles Of VOR

Mon Apr 12, 2004 8:16 pm

I´ve had trouble understanding exactly how the signal encoding would work to transmit both the reference and the variable-phase signal...

I´ve finally found an excellent source here:


The section that deals with VOR/DME/ILS is "Aviation - en route" with the long explanation here:


The respective overhead sheets provide a good illustrated summary as well (can´t link to them due to the freakin´ a.net HTML conversion.  Angry)

Apparently, both signals are transmitted on the same carrier, with the variable-phase signal being amplitude-modulated on the main carrier at 30 Hz, and the reference signal FM-encoded with a 9960Hz sub-carrier on the same signal. (In between, there´s still space for audio transmission of the beacon´s ID).

Pretty neat!  Big thumbs up

The documents also explain the Doppler VOR system (with reversed signal encoding) and ILS, among other things.
Posts: 7184
Joined: Sat Jan 24, 2004 12:14 pm

RE: Principles Of VOR

Wed Apr 14, 2004 9:26 am

Get yourself a scanner and you can hear the funny alien-like-antimatter-gun sound they make and the Morse code, some even have voice, like ATIS. You need to get close to them though, at ground level their range for crystal clear sound is less than 3 miles (from my own experience). It's best when you have them in direct line-of-sight (no obstructions) for hearing them. You can distinguish the two tones mentioned if you listen closely. A fast repeating cyclical tone (reference signal) in the foreground and a constant tone in the background (rotating beacon signal).

cheers  Smile

[Edited 2004-04-14 02:34:37]

[Edited 2004-04-14 02:37:03]

Who is online

Users browsing this forum: AA737-823, CanadianNorth, Goodbye, Google [Bot] and 19 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos