Jzucker From United States of America, joined Nov 1999, 100 posts, RR: 0 Posted (11 years 10 months 1 week 23 hours ago) and read 5691 times:
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...
Dc-10tech From United States of America, joined Jun 2001, 298 posts, RR: 2
Reply 4, posted (11 years 10 months 1 week ago) and read 5467 times:
"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.
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).
The documents also explain the Doppler VOR system (with reversed signal encoding) and ILS, among other things.
Fly2hmo From , joined Dec 1969, posts, RR:
Reply 7, posted (11 years 10 months 5 days 4 hours ago) and read 5325 times:
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).