What Is a VOR?

Answer:

VHF Omni Range navigational beacon; uses the VHF band between 108.05 and 117.95 MHz A9W transmission. VOR transmissions are line-of-sight, maximum range in nautical miles is calculated by the VHF max range formula (1.25 x (sqr.root[transmitter height] + sqr.root[receiver height]) in feet. The indication is completely independent of the aircraft’s heading.

The reference signal is an omni directional carrier wave transmission on the VOR’s frequency, and it carries a 9960Hz sub-carrier frequency modulated at 30 Hz. VOR navigation is not possible at low altitudes and great distances from a station. Normally, reception becomes useful from approximately 50nm out and 1000ft above a station.

VOR stations transmit two signals, one by a fixed antenna and one by a rotating antenna which are in phase with magnetic north. As the rotating antenna makes its 360 degree sweep, this signal becomes further out of phase from the static antenna by a different amount for each degree of travel. The receiver in the aircraft detects these phase errors referenced to magnetic north one degree at a time as the receiver passes through the phase radial. Radials are like spokes of a wheel, and are considered to point in a direction from the station. Most VOR stations transmit audio transmissions such as identification (Morse Code) information and weather forecasts.

A position fix can be plotted by the intersection of two or more radials from different stations, and pilots can fly accurately on specific radials or directly along a radial to the station. The range of stations improve with altitude and some VOR’s are specifically stationed to mark flight corridors up to 45 000ft from 130 nm out.