VOR Navigation System Advantages

• Non-Directional Beacon (NDB) navigation is not necessarily easy
• Flying an instrument approach is tricky and requires practice
• Aircraft altitude and adherence to course is crucial to avoid obstacles

Addressing NDB Navigation Limitations

• In 1945, VHF Omni-Range (VOR) navigation became available
• VHF Omni-Range (VOR) navigation stations are more sophisticated than ADF navigation
• VOR is a radio beacon that transmits precise azimuth information
• If equipped, aircraft can use ADF in airports without VOR facilities

Overview of VOR System Advantages

• VOR has been the standard radio navigation system for cross-country flying for years
• VOR operation offers infinite number of radials or course indications
• VOR reduces indication errors from atmospheric conditions
• VOR accurately provides directional information

VOR Operational Details

• VOR reception is strictly line-of-sight in the VHF range 108 to 118 MHz
• Line of sight signal limits reception at low altitudes or over mountainous terrain
• VOR is for short and medium-range flight distances, used along airways and in airport terminal control areas
• VOR stations emit position lines similar to a lighthouse, but refers to magnetic north

VOR Operation

• When a VOR frequency is entered, the VOR indicator connected to that radio helps aircraft positioning relative to the VOR station
• RMI or HSI pointer indicates bearing to or from the VOR ground station regardless of aircraft heading
• VOR systems enable flight crews to navigate accurately along a planned route using VOR transmitters as waypoints and helps follow a desired path

Introduction to VOR

• The VHF Omni-directional Radio Range, has abbreviations 'VOR' and 'Omni'
• It enables the pilot to determine direction to or from a beacon and track on a selected bearing
• VOR is a Very High Frequency (VHF) navigation aid
• VOR range is limited to 'line of sight' VHF transmission
• VOR range depends on the VOR beacon's location and the aircraft's flying height

VOR Navigation Advantages

• VOR is static-free, with information visually displayed on cockpit instruments
• Infinite number of bearings can be obtained, visualized as spokes from a wheel's hub
• The number of bearings are practically limited to 360, called radials

Operational Use of VOR

VOR enables pilots to select, identify, and locate a line of position from a particular VOR beacon:

• Magnetic bearing of the aircraft from the VOR beacon
• Magnetic bearing from the aircraft to the VOR beacon
• Aircraft position relative to a selected radial i.e. port or starboard (left or right)
• Aircraft is closing or flying along a selected radial of the beacon
• Aircraft passes over the VOR beacon

Automatic VOR

• Phase angle is shifted automatically by the 30 Hz reference signal to measure the angle between the variable signal denoted as (V) and reference signal (R)
• Switch on and tune the receiver to an in-range station to obtain a continuous reading on the RMI

Manual VOR Operation

• Pilot tunes the receiver and selects a radial to position the aircraft
• The deviation indicator provides left or right, and TO/FROM indications if the course is not aligned to the VOR bearing set by the OBS

Cone of Confusion

• The cone of confusion sits above the VOR transmitter
• Signals from the VOR station can be spurious in the area of the cone
• Signals are unreliable or unusable in that area
• The TO/FROM indicator and needle on the deviation indicator fluctuate erratically in the cone
• Distorted signals are ignored until the signals settle again
• The disturbance depends on aircraft altitude and angle above the station, typically around 40°
• An aircraft at 1200 ft traverses 800 ft in the cone, and at 12,000 ft, 8,000 ft

Key Terminology

• Heading: Direction nose is pointing, using true north, magnetic north, or compass
• Track: Actual path over ground, usually refers to magnetic track
• Selected Course: Intended path over ground, may be true, magnetic, or compass course
• Radial: Omni-bearing line with magnetic direction FROM the station to an aircraft

Radial Orientation

• At the VOR station the aircraft would be either at A, B, C, D, or E, depending on position
• A is on the 270° with respect to the VOR radials
• B is on 045°
• C is on 360° while approaching directly from north
• D is on 180° after passing over it
• E is 180° after reversing direction back toward station

Homing Directly to a VOR Station

The process works this way:

• First, identify the VOR station position, frequency. and ID from an appropriate publication
• Second, tune in and listen to the identifier which is either Morse Code, voice or both
• Third, note the magnetic bearing as displayed on the RMI of the VOR station
• Fourth, set the bearing on the course indicator via its knob so it appears in the window
• Fifth, turn the aircraft to face the magnetic heading selected to show TO through the indicator
• Sixth, keep the localiser needle centered to fly direct to the station

Flying the Vertical Needle

• It is possible to fly towards the station on an Omni station
• If the needle moves right of center, then turn the aircraft to the right
• If the needle moves left of center, then turn the aircraft to the left

Interception of an Inbound Track

• Tune in and ID the VOR and orient the aircraft to find the magnetic bearing to the VOR beacon
• The track is set via the 'window' of the track that the aircraft is required to fly to the station
• For example - via ATC, given clearance to fly on the 120° radial i,e, set display to 300° magnetic
• Displaying the TO indicator confirms that the aircraft selected the correct track
• Alternatively, if FROM appears, reset track or cross to other side of the beacon
• It becomes clear where the needle points is where to fly so it defends to the right on inbound

Interception of an Outbound Track

• It's easier than the inbound track because on this route, for example the 260° radial would simply proceed on a track of 260°
• The reciprocal of the radial is no longer needed
• FROM would be shown by the TO/FROM indicator instead of TO

Correction of Needle Centering

• Rotate the OBS knob; the needle needs to center with the FROM in the window at a known position
• Select 260° FROM if proceeding outbound from the 260° radial
• It is evident that deflections to the RIGHT indicate the aircraft must be turned on to an appropriate heading

Sine Wave Comparison

• Sine waves illustrate VOR audio signals and compare phase differences of the two audio signals (30 Hz)
• The phases of the audio signals are compared as follows:
  • In direction, the signal V passes the reference line in a positive direction 90° before signal R, called leading R by 90°
• Signal R has R leading signal V by 90°
• If point C of signal R compared with point B of signal V, R lags by 270°
• One signal leads the other by a number of degrees or lags by those degrees plus 180° as determined from points
• Signals R and V that are 180°out of phase can either lag or lead the other by 180°

VOR Principle of Operation

• Bearing to a lighthouse uses the time it takes the light to revolve
• Some lighthouses have a red light that flashes north
• If hits when light flashes you are directly north of the light house
• Divide full rotations and timing by vector range to calculate the angular displacement of the light house
• VOR works the same with the reference signal replacing the red light
• The signal tells aircraft its calculations and angular displacement through the transmitter

VOR Transmissions

• VOR has two signals in its transmission
• One runs at all times, and the other varies
• At magnetic North both signals are in phase, but at magnetic south the variable lags the fixed signal by 180°
• The receivers reads the difference to determine direction as the radials

VOR Signal specifics

• Omni name leads one to believe it can travel range so it provides range info
• A VOR transmitter provides only bearing info and not range so “range” is a misnomer

VOR Beacon Frequencies

• VOR stations use channels at 50 kHz from 108.00 MHz to 117.95 MHz except odd tenths of MHz from 108.1 to 111.9 MHz
• The frequency of 108.00 MHz is for testing

VOR Signal Specifics

• Reference phase signals include a RF carrier and a 9960 Hz subcarrier
• The subcarrier modulates between 10,440 Hz and 9480 Hz at 30 Hz
• The signal radiates constantly across the azimuth
• Station ID transmits the FM subcarrier, in Morse code, repeating a 2 or 3 letter word three times over 30 seconds, modulate between1020 HZ (+ or - 50 Hz) limits voice modulation
• Variable phase is a RF carrier signal that diagonal antennas radiate with strength that rotates through 360° azimuth at 1800 rev/min i.e. at 30hz

VOR signal modulation and azimuth

• The variable phase signal has direct signal azimuth and is called space modulation VOR Beacon Antenna
• VOR radiates its signal with a 5-element antenna array

VOR Signal Combination

• Reference and variable signals align when figure eight aligns with north
• As the positive lobe rotates 360°, it increases the phase angle between reference and variable
• When it aligns other than north, positive voltage maxima occurs later, with phase displacement designates
• Phase differences are measured in the aircraft to indicate course and that it is related to that radial

Field strength

• Eight signal reinforces omnidirectional field strength on the in-phase and weakens the out-of-phase side
• Cardioid revolving 30 rev/sec
• An additional 30 Hz signal is apparent at the receiver input with FM signal and an AM component
• There phase in circuits allows 30 Hz signal compare for relational proportionality

Phase Adjustment

• The phasing of reference and variable signals is adjusted during magnetic north
• The 9960 Hz subcarrier is modulated in frequency between 9480 Hz/10,440 Hz at 30 Hz
• It synchronises with rotation of the dipole antenna
• At 10,440 Hz, the antenna faces magnetic north
• It decreases as the antenna turns clockwise to 180° , to 9480 Hz and is 9960Hz during 90 and 270°

Output from at FM detector depends on the frequency:

• Frequency is positive is 10,440 Hz
• Frequency is negative is 9480 Hz
• Equal to the subcarrier rate if varying set to 30 Hz

VOR Course Error

• Left-right needle should be centered and the OBS should match the course set in the test set
• Otherwise, error is observed
• Omni accuracy must be checked as errors are completely different even if checking the cardinal points

Accuracy Tests

• Shop test is accurate to ½ to of one degree
• Aircraft omni varies and typically the error is ~±2°
• Errors increase after service

Reciprocal Error

• Left-right needle centers with two courses on the OBS - situation used with course errors
• Either the TO/FROM indicator is ‘TO’ or ‘FROM’ and reads the reciprocal (180º difference)
• If the OBS and test are set the same and left-right needle is centred with ‘TO’, then change the test and operate like flying over the station
• The right needle should stay the same
• If the receiver has difficulty as in reciprocal-centered or errors it may need service
• Typical aviation VOR is +/-2 in reciprocal or worse, and great equipment will have less

Site Effects Error

• Ground station error are superimposed by site location
• Topography modifies ground errors
• Combining effect these errors is found through commissioning
• The combined effect is less than ±3°

Terrain Distortions

• Errors are often caused by terrain
• Terrain may reflect the radial
• Quick oscillations bends and oscillates deviation indicator - oscillate or scallop on rate
• It may bend (slow) oscillate, or scallop (quicker)
• Bends do not exceed 2 from the track and a scallop is plus or minor so it gives a total error

VOR System Components

The airborne portion consists of:

• A receiver
• A control unit
• An antenna
• An indicator

Whereas the ground facility is made up of:

• A transmitter
• An antenna array

Transmission Specifics

• They can be used by all aircraft with range
• Morse and voice with emergency situations and two coded signals
• It reference around the transmitter and the signal various with relation to the directional signal

Antenna

• VHF operate within in a the radiation pattern from 118 Mhz to 108 for many systems
• They’re also able to accept receivers as both and locate in the range
• It runs along the stabiliser of aircraft
• Circuits for information of aircraft must receive decode and provide data output
• Many contains monitoring that show data and sent it to indication
• The aircraft runs to over-ILS receives

Is mainly in the aircraft equipment itself Selection is for operation of VOR and localiser with DME

• Turn power on of off for different setting stations

Indicators

• View is shown on Radio indication and there 2 switches
• The details as such depend on the instruments

Displays information:

• Horizontal, RMI with 2 pointer switched on the VOR

NAV/COMM Controller Details

• The controller is simple for frequency
• Select on rotation and code to the controls
• Transmissions can occur Volume antenna
• Horizontally polarised, multidirectional with 108 MHz frequency

VOR Specifics

• VOR is horizontal shape that forms 'V' to shape
• Shaped to be the pattern shape
• BALUN balanced from is for the shape

VOR antenna

• the VOR shape from is the antenna shape
• Emergency to connect as aircraft is reduced the unit communications
• Communication with horizontal is required

Balanced Loop

• Bar with the performance
• To solve radio issues
• To get clear signals

This antenna is made of:

• Loop radiation
• Coupled hybrid to that of the to receivers

Receiver Specifics

• Operates to about 50
• Information for memory records etc
• 12 for data bus inputs
• Power at 115 for data bus inputs
• TEST or statuses switches for the status

HSI

• VOR is horizontal to indication
• It shows display magnetic bearings and compass card
• Has the course and the HSI pointer is connected to compass card

System Tracking

• The TO/FROM indicates how the pilot flies the plane for signals received
• Track the plane and the signal back or forth as needed as direction
• Set HSI as needed to get a hold signals back with the planes

Distances

• About full scale is 10* to indicate the scale to show as intended
• Aircraft for the VOR is appropriate at half a mile
• Inaccurate, it 60 miles 1 * off can lead to 3 total off course
• It displays no RMI and does not give a bearing with signals received

Specifics

VOR is a for information:

• Radial, indicator etc

Operations

• Cone loses information
• Prevent the info of the display from working fast as data comes in
• And composite the signals to ensure operation

Signal Types

• The signal is a must for that is needed to
• To that to perform needs it
• Accuracy runs at 4
• Polarization of needed