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)
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