18/05/2024
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What is VOR ? VHF Omni-Directional Radio Range

Empowering pilots with direction: Imagine flying through the clouds, unsure of your exact position. That’s where VOR steps in, using radio signals to guide you. This air navigation marvel, aptly named the VHF Omni-directional Radio Range, shines in the avionics systems category.
Unraveling direction through radio magic: VOR works its magic by comparing phases of ground-broadcasted signals. IT reveals your direction from the station like a secret whisper in the sky.



VOR Working Principle

The VOR operates in the 108 – 117.95 MHz band with 50 kHz channel steps. The ground station emits an electromagnetic pattern of 30 cycles/second. This signal generates a 30 Hz sinusoidal wave at the VOR receiver on the aircraft.

The ground station also broadcasts an FM modulated signal into space on a 30 Hz reference mark in all directions. The phase difference between the two aforementioned 30 Hz signals gives the angle of the aircraft relative to the ground station.

The VOR system works with the Line of Sight (LoS) principle due to the characteristic of the VHF band, in other words, there should be no obstacle between the VOR station and the air platform, and they should be in direct sight of each other.

VOR devices are mostly used together with the DME (VOR/DME). DME indicates the distance to the station, and the frequency selected for the VOR is also connected to the DME station. Thus, both radial tracking and distance information are provided.

VOR - VHF Omnidirectional Range
VOR – VHF Omnidirectional Range

VOR General Information

All VOR stations make it easy to navigate! They use 000 degrees as their north reference, giving you precise magnetic bearing information (radials) through your HSI or CDI instruments. Whether you want to know your location relative to the station (like being due east on the 090 radial). Or the exact heading to reach it, these handy devices have you covered!

TO and FROM information

An aircraft can be located in one of two different sectors relative to a selected VOR radial (relative to the ground station):

FROM: If the aircraft is within the selected radial +/- 90 degree area, it is in the FROM (from station) sector.

TO: The aircraft is in the TO (to station) sector if it is “not” within the selected radial +/- 90 degree area.

For example, if 110 radial is selected in the device on the aircraft -regardless of the head of the aircraft- when the aircraft is within the sector from 020 degrees to 200 degrees according to the station, FROM is read on the display, otherwise the phrase TO is read. VOR information is independent of the direction and the position of the CDI and TO/FROM information do not change regardless of the head of the aircraft.

While passing over the VOR station, information cannot be received or the information received cannot be trusted. This area on the VOR stations is called the cone of silence. And when the device is in this region, where the phrase TO FROM is, the phrase FLAG (flag), indicating that the information cannot be received or is not reliable, is seen. After the station is passed -as the sector changes- TO information returns to FROM and FROM to TO.

Cone of Silence instagram

Further Reading Links:

VOR VHF Omni-Directional Radio Range
VHF Omni-Directional Radio Range