In this video, we will be looking at what is a VOR, the operation of a VOR, how the VOR information is presented in an aircraft, and its uses. What is a VOR? VOR stands for VHF Omnidirectional Range. A VOR is a short-range navigational aid which has been in use since 1960. The VOR can be used during the day or during the night. The VOR may be paired with a DME, which will provide the range and the bearing information for an aircraft.

How does the VOR function? The VOR produces 360 radials at one-degree spacing. These radials are aligned to the magnetic north at the VOR location. The VOR transmits two signals: one signal is the reference signal which is frequency modulated, the other signal is a directional signal which is amplitude modulated. The directional signal will have a phase difference with the reference signal depending on the radial. Let's understand this with a few examples: if an aircraft is north of the VOR transmitter, then it is at the zero-degree radial. The phase difference between the reference signal and the directional signal will be 0 degrees. If the aircraft is east of the VOR, then it is at the 90-degree radial, the phase difference between the reference signal and the directional signal will be 90 degrees. Similarly, if the aircraft is south or west of the VOR, the radials will be 180 and 270 degrees. The phase difference between the signals will be 180 and 270 degrees. So the phase difference between the reference signal and the directional signal will be the same as the corresponding radial. The VOR transmits 360 radials, each at a spacing of 1 degree, so the phase difference will also vary accordingly.

But if we consider an aircraft at a particular radial, let's say 170, how will the aircraft know whether it is flying towards or away from that VOR? To understand this, let's look at how the VOR information is presented in the cockpit. The VOR information is presented on an instrument known as the coarse deviation indicator. To know whether an aircraft is flying towards or away from a VOR, a "To" or a "From" flag will appear on this indicator. "To" means the aircraft is flying towards the VOR, "From" means the aircraft is flying away from the VOR.

Let's look at some other indications and the function of this knob on this instrument. Once a particular VOR frequency is tuned on the navigation radio, the knob is used to select a particular bearing or radial. This knob is called the Omni Bearing Selector. The selected bearing will be shown on the instrument. Depending on the position of the needle, the aircraft may need to fly towards the right or towards the left. If the needle is towards the right, the aircraft has to fly towards the right. If the needle is towards the left, the aircraft has to fly towards the left to capture the selected bearing.

What are the factors that affect the VOR transmission? Since the VOR transmits in the VHF band, it operates in the line-of-sight range. The transmitter power has a direct impact on the range of VOR signals. The terrain around the VOR will also have an impact on the transmission. What is the cone of ambiguity? When flying towards a VOR, the radials will converge, which means the course deviation indicator will become inaccurate. The needle will oscillate rapidly, and an "off" flag may appear for some time. After crossing this cone, the "front" flag will appear and the needle will become steady.

How to identify a VOR? VORs can be identified by three-letter codes which are transmitted by that specific VOR. These signals are transmitted along with the reference signal. A monitoring system at the VOR transmitter location will continuously monitor the identifier signal, the navigation signals, the signal strength, and the status of the monitoring system itself. Nowadays, GPS is the primary navaid that is used in most of the modern aircraft, but VOR is also available as backup or for marking certain airways, for approach procedures, or as a holding point.