VOR (VHF Omnidirectional Range) Navigation System Overview

VOR image download

VOR Navigation System 

One of the  oldest  and  most  useful  navigational  aids for aircraft  is the VOR  system. The system was constructed after WWII and is  still  in  use  today.  It consists of thousands of land-based transmitter stations that are called VORs. The ground VOR stations  communicate  with radio receiving  equipment  on board aircraft. 

How VORs Works?

The position of all VOR stations is marked on aeronautical charts along with the name of the station, the frequency of the station which an airport can tune to use, and also a Morse code designation for the station.

VOR uses VHF (Very High Frequency) radio (frequency range 108–117.95 MHz) with a 50 kHz separation between each channel. This keeps atmospheric interference  to a minimum  but limits  the VOR to line of sight usage. To receive VOR  VHF  radio waves, generally a  V-shaped,  horizontally  polarized,  bi-pole  antenna  is used by aircraft. Other types of antennas are also certified. The manufacturer’s instructions for installation location must be followed. 

The signals emitted by a VOR transmitter travel 360 degrees around the unit and are used by aircraft to navigate to and from the station using an onboard VOR receiver and display equipment. Because the signal from a VOR station propagates in all directions, a pilot does not need to fly a pattern to intersect it. The radio waves are received regardless of the aircraft's direction of travel as long as it is within range of the ground unit.

vor dme image download
VOR/DME Ground Station

vor antenna image download

A VOR transmitter sends out two signals that a plane's receiver uses to figure out where it is in relation to the ground station. One of the signals is a reference signal. The second is made by electronically spinning a variable signal. The variable signal is in phase with the reference signal when it is at magnetic north, but as it rotates to 180°, it becomes increasingly out of phase. As it spins to 360° (0°), the signals become increasingly in phase, until they are once again in phase at magnetic north.The aircraft's receiver decodes the phase difference and calculates the aircraft's position in degrees from the VOR ground station. Most planes have two VOR receivers.

Types of VORs Receivers

vor receiver image download
VOR Receiver

VOR receivers are sometimes found in the same avionics unit as the VHF communication transceiver (s). NAV/COM radios are what they're called. Internal components are shared since their frequency bands are close together.  Larger aircraft may have two dual receivers, as well as two antennas. Normally, one receiver is chosen for usage, while the other is tuned to the conditions encountered along the way. There is a button for selecting the active or standby frequency, as well as a way to switch between NAV 1 and NAV 2.

Instrument landing systems (ILS) and glideslope receivers are also used in conjunction with VOR receivers. The bearing in degrees to (or from) the VOR station where the signals are generated is interpreted by a VOR receiver.  It also generates Dc power, which is used to power the display indicating the deviation from the planned course centerline to (or from) the chosen station. In addition, the receiver determines whether the aircraft is flying toward or away from the VOR.

VOR Display Function

VOR image download
VOR Signal Propagate in all Direction

These things can be exhibited in a variety of ways on a variety of instruments. An older aircraft may be fitted with a VOR gauge that displays just VOR information. 

An omni-bearing selector (OBS) or a course deviation indication is another name for this device (CDI). The CDI linear indicator is essentially vertical, but it moves left and right across the graduations on the instrument face to reflect deviation from the target. Each degree is represented by a graduation. The azimuth ring is rotated by the OBS knob. The pilot spins the OBS until the course deviation indication centres when in range of a VOR. The OBS can be rotated to two settings where the CDI will be centred on each aircraft location.

 One causes an arrow to appear in the TO window of the gauge, indicating that the plane is approaching the VOR station. The other possible bearing is at an angle of 180 degrees to this one. When this option is selected, an arrow appears in the FROM window, showing that the aircraft is travelling away from the VOR on the set course. To fly directly to or from the VOR, the pilot must guide the aircraft to the heading with the CDI centred. The phase connection between the two simultaneously broadcast signals from the VOR ground station is used to create the displayed VOR information. A NAV warning flag appears when power is lost or the VOR signal is poor or interrupted.

VOR Cockpit Display

HSI EHSI VOR image download
VOR Display on HSI/EHSI

VOR HSI EHSI image download
VOR Dispaly

A separate  gauge  for the  VOR information  is not always used. As flight instruments and displays have evolved, VOR navigation information has been integrated into other instrument displays, such as the radio magnetic indicator (RMI), the HSI, an EFIS display or an electronic attitude director indicator (EADI). Flight  management  systems  and automatic  flight  control  systems are  also made  to integrate VOR  information  to automatically  control the aircraft  on its planned flight segments. Flat panel MFDs integrate VOR information into moving map presentations and other selected displays. 

The basic information of the radial bearing in degrees, course deviation indication, and to/from information remains unchanged, however. At large  airports,  an  instrument  landing  system  (ILS) guides the aircraft to the runway while on an instrument  landing approach. 

The radio signals are decoded using the aircraft's VOR receiver. On the same instrument display as the VOR CDI display, it produces a more sensitive course deviation signal. The localizer is a component of the ILS that is detailed in the previous article. The VOR circuitry of the VOR/ILS receiver remains dormant while tuned to the ILS localizer frequency. At VOR stations, the VOR transmitter is frequently combined with distance measuring equipment (DME) or a nondirectional beacon (NDB), such as an ADF transmitter and antenna. Pilots can use the VOR and DME together to achieve a precise fix on their location when combined with a DME.

The pilot is relieved of needing to fly over the station to know with certainty his or her location because the VOR shows the aircraft's bearing to the VOR transmitter and a co-located DME indicates how far away the station is. The next sections go through each of these navigational aids independently. The operational precision of VOR technology is crucial to flight safety. VOR receivers are put through their paces utilising VOR test facilities (VOT). These can be found at a number of airports, which can be found in the Airport Facilities Directory for the area in question.

VOR Testing

To conduct the test, specific points on the airport's surface are designated. Most VOTs necessitate adjusting the VOR radio to 108.0 MHz and focusing the CDI. On the indicator, the OBS should show 0° when showing FROM and 180° when showing TO. The test heading should always indicate 180° if an RMI is utilised as the indicator. although not on 108.0 MHz. 

Also Read

May Like to Watch on YouTube

Post a Comment