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

### Principles Of VOR

Hi..
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...

SkyGuy11
Posts: 532
Joined: Fri Oct 26, 2001 7:09 am

### RE: Principles Of VOR

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:

.

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

### RE: Principles Of VOR

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.

SkyGuy11
Posts: 532
Joined: Fri Oct 26, 2001 7:09 am

### RE: Principles Of VOR

Thanks! I agree it is very good, got it from a friend.
.

DC-10Tech
Posts: 291
Joined: Fri Jun 15, 2001 6:40 pm

### RE: Principles Of VOR

"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   )

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.
Forums.AMTCentral.com

707CMF
Posts: 4698
Joined: Thu Mar 14, 2002 5:39 pm

### RE: Principles Of VOR

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

707

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

### RE: Principles Of VOR

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:

http://wwwtvs.et.tudelft.nl/P&N/education/et4-022/et4-022.htm

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

http://wwwtvs.et.tudelft.nl/P&N/education/et4-022/notes/h7.pdf

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

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!

The documents also explain the Doppler VOR system (with reversed signal encoding) and ILS, among other things.

Fly2HMO
Posts: 7184
Joined: Sat Jan 24, 2004 12:14 pm

### RE: Principles Of VOR

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

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

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

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