ASYS 310 – Aircraft Navigation SystemsSAIT PolytechnicBelinda Gonzales

VOR – VHF OMNIDIRECTIONAL RANGE

Introduction

VOR is an accurate short/medium range navigation system that is used. It gives “TO” and “FROM” information in reference to the ground station. This “TO” and “FROM” information tells pilots which radial the aircraft is sitting on in reference to the ground station.

Frequencies

Frequencies used for VOR is in the range of 108 – 117.95MHz.
Certain Frequencies between 108 – 112.00, every odd tenth are used for ILS and cannot be used for VOR navigation.

Inputs

A valid frequency must be inputted, between 108 – 117.95 MHz expect for frequencies between 108 – 112MHz every odd tenth. If an ILS frequency is inputted, the needle on the RMI will park.

control_panel.jpg
VOR control head

Another input needed for this system to work at its best is a course selection. The pilot enters the course they want to travel on through the OBS knob on the CDI.

OBS_knob_on_CDI.jpg
The OBS on this CDI is set to 300

Inputs needed to allow the RMI to work is the correct VOR frequency, and one of the needles on the indicator selected on VOR

Basic Navigation Principles

The VOR ground station propagates three signals modulated into the carrier signal, an omnidirectional reference signal, a variable directional signal, and a Morse code or voice identification that provides the name of the station.

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When the VOR system in the aircraft sees this rotating signal, it converts the signals and displays which radial the aircraft is sitting on in reference to the station.

A receiver picks up the signal and sends the information to a manual and automatic converter, which converts the signals and sends the information to an indicator where the pilot can read it.

The manual converter compares the received signals to the selected course that the pilot has chosen and gives the pilot To, From, Left and Right information. The pilot must input a desired course through the OBS knob on the CDI to give any kind of to/from/left/right information. The signals in the manual converter are filtered and phase shifted to allow proper readable information on the CDI.

The automatic converter takes the information from the VOR receiver and compass information and sends the signals to the RMI, which to information is only displayed.

The information sent to the manual converter gives to and from information, and the information sent to the automatic converter converts the signal into relative bearing information.

The Morse code is modulated at 30% into the carrier wave as 1020 Hz that lets the crew know what station they have locked into.

Outputs

Audio
VOR does have an audio tone, some stations provide only Morse code, or voice identification that alternates with Morse code.
CDI
When the right information is inputted into the VOR (Frequency and Selected Course), the CDI will display To/From and Left/Right information

CDI_with_information.jpg
The indicator tells us that the aircraft is flying on radial 255 away from the station

RMI
When the information is inputted (Frequency and Compass information) the RMI will display TO information only. It will display the heading of the aircraft and To
information to the VOR station.

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This RMI tells us the aircraft is flying TO the station on the radial 77



Equipment

Ground station
VOR systems require a ground station to tell the aircraft where it is.
VOR_ground_station.jpg
Typical VOR station

Aircraft
In order for VOR to work on an aircraft, it requires a half-wave dipole antenna horizontally polarised, a control panel, indicators, and a receiver, which is usually combined with other navigation systems.



If you are interested in seeing how this system would work, check this link out, you can change where the aircraft is sitting, the heading, and move the OBS around




References

http://www.navfltsm.addr.com/vor-nav.htm

Aircraft Communications and Navigation Systems;
Mike Tooley and David Wyatt,
2007 first edition