VOR NAVIGATION

      This is a short-range navigation aid. A VOR system determines the position of the aircraft with respect to a ground navigation station. The ground station can be compared to a lighthouse.VOR provides only bearing information.A more precise navigational information is obtained when DME is operated as a complement with VOR.                                    

 The signals radiate outwards like spokes of a wheel and known as radials.The signals received by the VOR system are processed by a navigation receiver and passed to an instrument called a Radio Magnetic Indicator (RMI).VOR ground navigation stations are located along aircraft airways permitting the pilot when he selects the correct VOR bearing radial to fly from station or to station.The selected radial bearings can serve other navigation systems such as the flight director and automatic pilot.

  During VOR operation a horizontal situation indicator is used to indicate course deviation.A VOR system operates in the 108 to 117.95 Megahertz range.All the frequencies between 108.00 to 111.95 MHz. with the exception of those frequencies allocated for localiser operation, are allocated to Category B VOR.All the frequencies 112.00 to 117.95 MHz. are allocated to category A VOR.Category A VOR is used for normal enroute navigation.This has a carrier RF output of 200 watts providing a service range of upto 200 nm.Category B VOR is used for providing approach information o airport (sometimes called Terminal VOR).

VOR PRINCIPLE

VOR radiated VHF energy modulated with Reference signal (omni directional flash) and Variable phase signal (rotating beam) and the bearing of the VOR station is the phase difference between reference and variable phases (time difference between flash and beam).

                                            The principle of VOR navigation involves a comparison of phase difference between the two transmitted signals.One of the signals is termed as the reference signal and the other one is variable signal.The use of AM and FM with a wide frequency separation between them prevents cross modulation between the signals which would otherwise cause bearing errors in the system.VOR transmitter radiates both unidirectional and omni directional signals.

                                               The transmitter is crystal controlled and is amplitude modulated by A 30 Hz AM referred to as variable phase signal (directional signal) and A sub carrier AM of 9960 Hz with a deviation of plus minus 480 Hz which is frequency modulated at 30 Hz. (omni directional signal).A 1020 Hz AM is also transmitted for the station identification(morse code of 2 or 3 letters).The VOR beacon transmits a signal in all directions (omni directional).We call these signals “Radials”.The transmitted radials contain different information to separate the radials from each other.The VOR beacon radiates the first radial in the direction of magnetic north of the station (called zero radial).

                                The radial is measured from the difference in phase between the reference and variable signal.The 30 Hz reference signal always has the same phase whatever  aircraft’s position with respect to the station.The phase of the variable signal varies with the aircraft’s position.VOR receiver receives the ground signal, detects and separates the phase and compares the phase of the two signals. The receiver is able to gives the magnetic and relative bearing of the transmitter,Deviation of the aircraft from a selected course andTo-From information.

VOR radiated VHF energy modulated with Reference signal (omni directional flash) and Variable phase signal (rotating beam) and the bearing of the VOR station is the phase difference between reference and variable phases (time difference between flash and beam).

                                            The principle of VOR navigation involves a comparison of phase difference between the two transmitted signals.One of the signals is termed as the reference signal and the other one is variable signal.The use of AM and FM with a wide frequency separation between them prevents cross modulation between the signals which would otherwise cause bearing errors in the system.VOR transmitter radiates both unidirectional and omni directional signals.

                                               The transmitter is crystal controlled and is amplitude modulated by A 30 Hz AM referred to as variable phase signal (directional signal) and A sub carrier AM of 9960 Hz with a deviation of plus minus 480 Hz which is frequency modulated at 30 Hz. (omni directional signal).A 1020 Hz AM is also transmitted for the station identification(morse code of 2 or 3 letters).The VOR beacon transmits a signal in all directions (omni directional).We call these signals “Radials”.The transmitted radials contain different information to separate the radials from each other.The VOR beacon radiates the first radial in the direction of magnetic north of the station (called zero radial).

                                The radial is measured from the difference in phase between the reference and variable signal.The 30 Hz reference signal always has the same phase whatever  aircraft’s position with respect to the station.The phase of the variable signal varies with the aircraft’s position.VOR receiver receives the ground signal, detects and separates the phase and compares the phase of the two signals. The receiver is able to gives the magnetic and relative bearing of the transmitter,Deviation of the aircraft from a selected course andTo-From information.