VHF Omnirange Radio

VHF OMNIRANGE RADIO(VOR)

WHAT IS VOR?

• VOR or VHF Omnirange Radio– a navigational aid equipment designed to provide

bearing information to aircraft.

Types of VOR

• Conventional VOR (CVOR)Ref Signal = FMVariable Signal = AMFrequency = 108MHz-118MHz

• Doppler VOR (DVOR)Ref Signal = AMVariable Signal = FM

Frequency = 108MHz-118MHz

WHAT IS BEARING?

• Bearing refers to the direction from a certain place towards another. In VOR application, this refers to the bearing from an airplane to a VOR station.

ALL DIRECTIONS ASSOCIATED WITH A VOR STATION ARE RELATED TO MAGNETIC NORTH.

VOR240°

VOR

90°

N

N N

These are shown in the figures below:

Bearing Information

Bearing Information

• How is the bearing information produced by the VOR ?– This is done by radiating two signals from two

sets of antenna, the central or reference antenna and the variable or sideband antennas surrounding the central antenna.

The phase of the signal received from the reference or central antenna is the same regardless of aircraft position.

0° 30° 60° 90° 120° 150° 180° 210° 240° 270° 300° 330° 360°

0° 30° 60° 90° 120° 150° 180° 210° 240° 270° 300° 330° 360°

N

Bearing Information

0° 30° 60° 90° 120° 150° 180° 210° 240° 270° 300° 330° 360°

However, the signal received from the sideband or variable antennas depend on the aircraft’s position.

0° 30° 60° 90° 120° 150° 180° 210° 240° 270° 300° 330° 360°

N

Bearing Information

The aircraft’s VOR receiver then processes these two signals to obtain its angular position with respect to magnetic north.

0° 30° 60° 90° 120° 150° 180° 210° 240° 270° 300° 330° 360°

0° 30° 60° 90° 120° 150° 180° 210° 240° 270° 300° 330° 360°

N

Bearing Information

90 degrees

0° 30° 60° 90° 120° 150° 180° 210° 240° 270° 300° 330° 360°

Supposed the aircraft is in the east (or 90°) radial.The phase difference between the two signals would then be:

90°

N

Bearing Information

Bearing Information

• In practice the aircraft’s VOR receiver has three dials:• one of which can be set

manually to any desired course,

• the second of which tells whether the plane is to the left or right of the course, and

• the third of which resolves 180° ambiguity by indicating either “from” or “to” .

• VOR magnetic bearing sine & cosine signals are combined with selected course information. The difference between these two parameters is the VOR deviation.

• For a difference of 5˚ left the receiver output is standardized at 75μA that causes a VOR deviation bar deflection of one dot.

• For a difference of 20˚, the receiver output is 300μA produces a four dot deflection.

VOR Indicator

• A : Rotating Course Card is calibrated from 0 to 360 degrees, which indicates the VOR bearing chosen as the reference to fly by pilot.

• B : Omni Bearing Selector or OBS knob , used to manually rotate the course card to where the point to fly to.

• C : TO-FROM indicator . The triangle arrow will point UP when flying to the VOR station. The arrow will point DOWN when flying away from the VOR station. A red flag replaces this TO-FROM arrow when the VOR is beyond reception range or the station is out.

Engr. Divino Fiel A. de Bien, ECE Navigational Aid 12

• D : Course Deviation Indicator (CDI). This needle moves left or right indicating the direction to turn the aircraft to return to course.

• DOT : The horizontal dots at center represents the aircraft away from the course . Each dot represent 2 degrees deviation from desired course.

N 36

E33

S

W24

12

1521

30

0 1 5

COURSE

Indicates desired course

Tells whether the airplane is to the LEFT or RIGHT of desired course

“TO or “FROM” ARROW

0 1 5

Bearing Information

(Selected Course 90)

VOR

REGARDLESS of AIRPLANE HEADING

RADIO DEVIATION calls for LEFT TURN anywhere in here

RADIO DEVIATION calls for RIGHT TURN anywhere in here

Selected Course - 090

N

VOR Deviation - “Left” Or “Right” Sense

Signal

anywhere

in

here

is

a

“FROM”

Signal

(Selected Course 90)REGARDLESS of AIRPLANE HEADING

VOR Selected Course - 090

Signal

anywhere

in

here

is

a

“TO”

Signal

N

VOR “TO” or “FROM” Sense

magnetic North

40°

to

on th

e ri

ght

on th

e le

ft

0

18

27

09

selected bearing

Ground station

from

040

0

09

18

27

from

040

18

30

09

27

0

to

040

from

ONBOARD VOR INFORMATIONS

24

Terminal VOR

En-route VOR

VOR APPLICATION

TERMINAL VOR FREQUENCY BAND ( 40 channels, 50 khz spacing)

108 111,85108,05 111,80108,20 108,25

EN ROUTE VOR FREQUENCY BAND ( 120 channels 50 khz spacing)

112 117,95112,05 117,9

Mhz108-112-118 30 Mhz 300Mhz

190/550

VHF

112,1 117,85

VOR FREQUENCY BAND

VOR CHART : LOWER SPACE

TAN 111.8

TBO 113.9

SAU 116.8

320

140

120

227

AGN 114.8

MEN 115.3

TOU 117.7

GAI 115.8

126306

300

106

346

059

178006

179

• modulations

30 hz reference tone

30 hz variable tone

voice signal : 300/3000 hz

tone identification signal : 1020 hz (Morse code)

• power radiated

VORC : 50 W

VORD : 100W

H polarisation

• DME paired frequency (from ICAO table)

VHF NAV 112.10

DME channel 58X interrogation frequency 1082 Mhz (12 µs)

reply frequency 1019 Mhz (12 µs)

bearing signals

example

VOR Specification

108 118

9960 Df ± 480

fo =115.8 f1 = 115.85

1020

30 var 30 ref

identvoice

300-3000

carrier modulation index

- 30 ref : 0.3

- 30 var : 0.3

- ident : 0.1 ( 0.05 )

- voice : 0.3

50 Khz16.5 db

Conventional Channel

108 118

9960 Df ± 480

117.7117.75

30 ref 30 varcarrier modulation index

- 30 ref : 0.3

- 30 var : 0.3

- ident : 0.1 ( 0.05 )

- voice : 0.3

50 Khz16.5 db

1020

identvoice

300-3000

DOPPLER CHANNEL

R

hD

actual radio coverage

DNM= 1.2 hft

Dkm = 4.1 hm

VOR 1

D ~ k h

VOR 2

RADIO COVERAGE

25 50 75 100 125 150 175 200 225

VOR range for long, medium and short-range beacons

10000

20000

30000

40000

50000

11 dbW 17 dbW

h : height ( in ft)

60000

Nm

23 dbW

range for receiver signal stength 90 µV/m

RADIO COVERAGE

VOR typical coverage pattern for an actual site

15000 ft

10000 ft

5000 ft

VOR100 Nm50 Nm

RADIO COVERAGE

40° min

ground station

Vertical plane radiation pattern

cone of confusion

RADIO COVERAGE

30 ref

30 var

30 ref30 var

a

30 ref

30 var

30 ref30 var

30 ref

30 vara

VOR Basics

modulation

30 ref 30 ref

carrier

sub-carrier frequency modulation

esc =Esb cos [ wsc.t + n sin W t]

with parameters : Esc , wsc = 2.p.9960, n = 16, W = 2.p.30

carrier amplitude modulation

emref = Ec { 1 + ( Esc / Ec) cos [ wsc.t + n sin W.t]} cos wc.t

m = 0.3

reference signal

30 var

Conventional VOR Basics

30 ref 30 ref

carrier

emref = f ( a ) . ec { 1 + m cos [ wsc.t + n sin W.t] }

with ec = Ec / r . cos [ wc t - 2 p r / ] . l f ( a )

and f ( a ) = 1

then

emref = ec { 1 + m cos [ wsc.t + n sin W.t]}

reference signal

radiated signal at distance r

30 var


30 ref 30 var 30 ref

carrier amplitude modulation

emvar = Emref { 1 + m cos [ W.t - a ]} cos wc.t

with parameters : Emref , wc , m = 0.3, W = 2.p.30

variable signal for azimuth a

modulationcarrier



carrier

emvar = emref { 1 + m. cos [ W.t - a ] }

emvar = emref + emref m. cos [ W.t - a ] = emref + esbo

emvar = emref + emref m. cos W.t . cos a + emref m. sin W.t . sin a


variable signal for azimuth a

SBO



carrier

em = emref + emref m. cos W.t . cos a + emref m. sin W.t . sin a


total signal for azimuth a


emref = ec { 1 + m cos [ wsc.t + n sin W t ] }

antennas radiation pattern

e1mvar = emref m cos W t . cos a

e2mvar = emref m sin W.t . sin a

1

m

a

+

+

-

-

Thomson type 512C and 540C


emref = ec + ec . m cos [ wsct + n sin W t]}

emvar = ec + ec . m cos W t . cos a + ec. m sin W t . sin a

total signal radiated at distance r

var antennas

upper ref

antenna

lower ref

antenna

Thomson type 512C and 540C

1.7l

0.85l1.05l

1.37l


emref

l3 + 3l/4

l3

l + Dl

l - Dl

emvar emvar

l/4 l/4l/4l/4

l2l2l2l2

TRANSMITTER ARCHITECTURE

1020 clock

morse code

mixer

transmitter

voice

sideband generator

FM modulator

m cos W.t . cos wc .t

m sin W.t . cos wc .t

ref signal

var signal

TRANSMITTER ARCHITECTURE

VOR (dual)front end

30 hz filter

9960 hz filter

FM demod

DF

RMIHSI

P/2

DF

DF

to/from

60

heading

30 var

30 ref

manual chain

automatic chain

OBS

to

from

heading

……….

300/3000 filter

1020 filter ident

voiceOBS selector knob

heading selector knob

RECEIVER ARCHITECTURE

Thank You

Question & Answers

Engr. Divino Fiel A. de Bien, ECE Navigational Aid 38

VHF Omnirange Radio

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