06vhf Omnidirectional Range

7/31/2019 06vhf Omnidirectional Range

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VHF OMNIDIRECTIONAL

RANGE

VOR


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GROUND BASED EQUIPMENT

Rotating antenna transmits a directional signal.(rotates at 30 rps)

Stationary antenna transmits reference pulse

each time the rotating antenna passes throughmagnetic north. (true north in areas of compass

unreliability.)

The aircraft set measures the phase difference

between the reference signal and rotating signal

resulting in accurate track information. (radials)


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AIRCRAFT EQUIPMENT

Receiver

Receive VOR and ILS transmitters.

Control Head

Indicator

Course Deviation Indicator (CDI)

Radio Magnetic Indicator (RMI)

Horizontal Situation Indicator (HSI)

Antenna usually on vertical stabilizer.


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OPERATION

The desired frequency is tuned.

The OBS knob ( omni bearing selector) sets referencedirection on the CDI, or the track needle on an HSI.

The station is identified.

The CDI needle or track bar (HSI) shows deviation fromselected course.

Each VOR instrument incorporates a TO/FROMindicator. This is a TO/FROM window on a CDI and anarrow on a HSI.

The TO/FROM indicator simply displays direction tostation.

Signal warning flags are incorporated so frequencymonitoring is unnecessary.


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TESTING

VOT: VOR Receiver Test Facility: Transmits a 360 radial on all azimuths of an

assigned frequency.

Tune VOT frequency. Set 360 on CDI. Confirm needle centered with FROM flag.

Rotate OBS 5 either side and confirm half scale

deflection, 10

for full scale. Set 180 on CDI.

Confirm needle centered with TO flag.

Must be accurate within 4.


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VOR Check Point: Signs indicate a location on the aerodrome maneuvering surface

where receiver may be accurately checked against the publishedradial.

Tune VOR frequency.

Identify.

Set published radial on CDI.

Confirm needle centered.

Check needle sensitivity by changing OBS 10 each way.

Set reciprocal of radial, and check TO-FROM flag change.

Must be accurate within 4


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Compare two VOR receivers:

The accuracy of the receivers may be checked

against each other in the absence of the previous

check facilities. Tune both receivers to the same VOR frequency.

Identify on both.

Center both CDI needles.

Check needle sensitivity. Must be accurate within 4


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Airborne VOR Check: Receiver may be checked on a published

radial over a fix or landmark.

Tune VOR frequency. Identify.

Confirm position.

Center CDI needle.

Check needle sensitivity.

Must be accurate within 6


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RANGE

The VHF signals associated with VORs

are propagated through line-of-sight.

Approximate range can be calculated by

using the formula 1.23AGL.

The need for a ground based station within

line-of-sight range makes transoceanic

VOR navigation impractical.


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LIMITATIONS

Range: limited by line-of-sight.

Terrain: VORs are sensitive to the interferenceof terrain. The placement of VOR ground

stations takes this into account in most cases,but is not always possible.

Published airways are designed to avoid any

unusable quadrants, however care must be

taken when navigating off airways.


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ACCURACY

Published VOR radials are accurate within 3.

Unpublished radials are not subject to this standard. Anysite specific anomalies will be published in the CFS.

The accuracy of VOR equipment is relative to distance

from the ground station. A one dot CDI needle deflectionat 1nm indicates a course deviation of 200 feet; a onedot CDI needle deflection at 30nm indicates a coursedeviation of 1 mile. (1 in 60 rule)

If you attempt to fix your position using two VOR radialsat an appreciable distance form the station and accountfor the allowable 4 receiver error the accuracy is greatlyundermined. Adding accurate distance informationreduces this inaccuracy. (DME)

06vhf Omnidirectional Range

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