VOR

VOR is short for Very High Frequency (VHF) Omni-directional Range. When VOR was invented it replaced the Low-Frequency Range, which had only four legs. Thus the term “Omni-directional”, indicates that a VOR generates courses in all directions, which is its distinctive characteristic.

VOR is also distinct from Non-directional Beacons (NDB) in that the directional signal is embedded in the VOR signal. With an NDB there is no directional information embedded in the signal thus the airborne radio must have direction finding abilities.

I have created a computer animation, shown below, that explains in pictures better than I can do it in words how a VOR station works.

Basically the VOR transmits two signals. The “phased signal” is transmitted outward in a spiral, shown in blue in the animation. A second signal is transmitted simultaneously with each revolution of the spiral. This second signal acts as a timing reference. Your VOR receiver picks up both signals and acts like an oscilloscope creating a standing wave of both signals. The phase difference between the signals represents the radial you are on. A radial is simply your bearing awayt from the VOR.

In the animation I have slowed the process down so that you can see it. In a real VOR the signals are transmitted 30 times per second and move out at the speed of light.

For more details of how VOR works here is an article on Wikipedia.