Very High Frequency Omni-directional Range (VOR)
A VOR is a radio station that transmits radio navigation signals in the very high frequency (VHF) band. The station transmits radio signals, called radials, in every direction away from the station. Pilots use 360 radials, one for each degree in a circle, to determine position. If the equipment in the airplane says the airplane is on the 360 degree radial, then the airplane is north of the VOR. An airplane on the 90 radial is east, while one on the 180 degree radial is due south of the station.
Since pilots rely on the compass for directional guidance, the radials transmitted by VORs are aligned with magnetic north.
A VOR station is referred to as terminal (T), low (L), or high (H). Each has a different standard service volume. The signal received from a terminal VOR is valid between 1,000 and 12,000 feet AGL to a distance of 25 nm. A low VOR signal is good up to 40 nm and 18,000 feet AGL. A high VOR signal is good up to 60,000 feet AGL at varying distances. From 1,000 to 14,500 feet, that distance is 40 nm. Above 14,500 feet, it is 100 nm. High VORs are designed to be used in conjunction with the high altitude airways. These J routes extend from 18,000 MSL, the base of the Class A airspace, up to 45,000 feet. At these altitudes, a high VOR signal is good out to 130 nm.
Tuning and Identifying a VOR
Before using a VOR for navigation, it must be tuned and identified. Tuning in the VOR is a simple matter of selecting the proper frequency on the receiver. Next, configure the airplane's audio system so that you can monitor the audible Morse code identifier, which is broadcast by the VOR station. Each VOR has a unique three letter identifier. By hearing the Morse code for this three letter identifier, you have positively identified that the signal on your display is being received from the intended VOR.
If no three letter identifier is heard, it indicates maintenance is being performed on the station, and the VOR signal may not be reliable.
Finding Your Location from a VOR
Turn the omni-bearing selector (OBS) knob on the VOR receiver display until the needle centers and the TO-FROM flag displays "FROM". Once the needle is centered, your magnetic bearing, or radial, from the VOR is shown on the top of the display. For example, if the reading was 135, this tells you the airplane is located over the 135 radial. In other words, the airplane is southeast of the VOR.
One thing that can be very confusing when learning VOR navigation: The radial you are on has nothing to do with your heading. You could be on that 135 radial and be heading north, south, or any direction.
Finding the Direction to a VOR
Rotate the OBS until the needle is centered with a "TO" indication. The number shown on the top of the display is the bearing from your airplane to the VOR. This is exactly the opposite of the direction from the station to the airplane. Therefore, your bearing, or radial, from the station is also shown, on the bottom of the display.