radio navaids

Grunt Productions 2007

Radio Radio NavaidsNavaids

A brief by Lance A brief by Lance GrindleyGrindley

Radio Fixing AidsRadio Fixing Aids

SYSTEM BASIS/BAND RANGE ACCURACY(95% Probability) REMARKS

DECCA

LORAN C

NAVSTAR GPS

HYPERFIX

MF/DF

Phase comparison LF (70-130kHz)

300 nm (day)75-240 (night)

50 metres up to 100 nm from master station,

day.6 nm at 200+ nm,

winter, night

Accuracy depends on time of day, month,

distance from station.

Time comparisonLF (100kHz)

800-1200 nm(ground wave)1800-2400 nm

(sky wave-night)

50 metres (ground wave)

(200 metres near baseline)

10-20 nm (sky wave)

Not commonly used in European waters.

No ambiguity

Signal time conversionUHF (1575.42 & 1227.6

MHz)Worldwide 21 metres (PPS)

100 metres (SPS)

Provides time reference. P(Y) code

encryption.

Phase comparisonMF/HF (1·6 - 3.4 MHz)

380 nm (day)135 nm (night)

10 metres (day)50 metres (night)

Fixed and random errors. Modern version

of Hifix.

Non-directional shore based

radio beacons LF/MF

500 nm (day)75 nm (night)

± 3 degrees(ideal conditions)

Only provides bearing. Many sources of error.

Limited range.

References: Admiralty Manual of Navigation Vol. 3., Admiralty List of Radio Signals Vol.2.


Navstar GPS


Navstar GPS - 24 Satellites plus 4 Spares, 6 Orbital Planes


The Navstar System

SPACE SEGMENT28 Satellites6 Orbits

UPLINK DATASatellite EphemerisClock DriftPropagation Delay

USER SEGMENTShipsHelicoptersetc

CONTROL SEGMENT5 Monitor Stations3 Antennae1 Master Control Station

DOWNLINK DATANavigationMessageData


Pseudo Range to One Satellite


Correcting for Receiver Clock Error


GPS Navigation Signals

L1 = 1575.42 MHz

C/A Codeat

1.023 MHz

L2 = 1227.6 MHz

P-Codeat

10.23 MHz

P-Codeat

10.23 MHz


Geometry of the Satellites

a. Good (Low) Dilution of Precision b. Poor (High) Dilution of Precision


GPS Accuracyfor the Fully Operational System

Absolute global time transfer to a fraction of a microsecond available continuously

Horizontalwithin 8 metres

Horizontalwithin 8 metres

Verticalwithin 10

metres

Velocity within0.1 knots


4 Satellites provide 3 Dimensional Fix

Expected Accuracy (67%) Position 30ftVelocity 0.1ktsTime 10 Nano Secs


Differential GPS System Elements

SatcomLink

DGPSUser

DifferentialCorrectionBroadcast

DataCommsLink

Control Centre

DifferentialReferenceStation andBroadcastTransmitter

Radio Fixing Radio Fixing AidsAidsFREQUENCY SPECTRUM

Category Frequency Wavelength SystemVLF 0-30kHz Very Long OmegaLF 30-300kHz Long Decca LoranMF 300-3000kHz Medium MFDF ConsolHF 3-30MHz Short

VHF 30-300MHz MetricUHF 300-3000MHz Decimetric Navstar TransitSHF 3000-30000MHz Centimetric

E/F-BandI-Band

EHF 30000-300000MHz Millimetric

PROPAGATIONGround WavesThe lower the frequency, the greater the range of the ground wave signal. Ground wave signal decreases as frequency increases due to:

A. Increased attenuationB. A decrease in the bending of waves around the earth’s surface.

Sky WavesThese occur at frequencies between VLF and HF. Attenuation of sky waves decreases as frequency increases, therefore increased frequency gives improved reception.


Ground-Wave and Sky-Wave PathsGround-Wave and Sky-Wave PathsUNREFLECTED

WAVE

150

27

Tx D REGIONREFLECTION

GROUNDWAVE

Rx

F LAYER

E LAYER

D REGION

50

90

190


UNREFLECTEDWAVE

150

27


GROUNDWAVE

Rx

F LAYER

E LAYER

D REGION

50

90

Ground-Wave and Sky-Wave PathsGround-Wave and Sky-Wave Paths

TWO HOP

190


Ground-Wave and Sky-Wave PathsGround-Wave and Sky-Wave Paths

ONE HOP

UNREFLECTEDWAVE

150

27


GROUNDWAVE

Rx

F LAYER

E LAYER

D REGION

50

90

190


Theory of Phase ComparisonTheory of Phase Comparison1. STATION A radiates CW signals on a known frequency, and thus at a known

wavelength.



wavelength.

2. STATION B also radiates CW signals on same frequency, and thus at same wavelength.



wavelength.


3. If both signals start in phase and are an exact number of wavelengths apart, then a receiver at P will show zero phase difference, since they will have travelled the same distance, i.e. AP - BP = O.



wavelength.


3. If both signals start in phase and are an exact number of wavelengths apart, then a receiver at P will show zero phase difference, since they will have travelled the same distance, i.e. AP - BP = O.

4. Now consider points Q and R, situated away from P. At both these points phase of

each signal = 180°, i.e. signal again has zero phase difference.

5. It can therefore be seen that lines of zero phase difference occur at intervals of ._2

_2


B

Hyperbolic Fixing Systems (2)Hyperbolic Fixing Systems (2)

BASE LINE

EXTENSION

BASE LINE

EXTENSIONA



BASE LINE

EXTENSION

BASE LINE

EXTENSIONA B



BASE LINE

EXTENSION

BASE LINE

EXTENSIONBA


Hyperbolic Patterns, Simultaneous TransmissionsHyperbolic Patterns, Simultaneous Transmissions

0

AB

1800

BASE LINEEXTENSION

1800

BASE LINEEXTENSION


250´

280´

350´

150´25

0´

Q

Q


0

AB

1800

BASE LINEEXTENSION

1800

BASE LINEEXTENSION

300600

900

1200

1500

150´

Q

Q


250´

280´

350´

150´25

0´

Q

Q


0

AB

1800

BASE LINEEXTENSION

1800

BASE LINEEXTENSION

300600

900

1200

1500

300 600

900

1200

1500

150´

Q

Q


Hyperbolic Position LinesHyperbolic Position Lines

Diagram shows development of a lattice pattern

Station 3Slave

Station 1Master

Station 2Slave


LORAN CLORAN CBASIC FREQUENCY = 100kHz

RANGE = Groundwave 1200MSkywave Up to 3000M

ACCURACY = Groundwave 200M < 300 FT500M 200 - 700 FT750M 300 - 1100 FT

1000M 500 - 1700 FTSkywave Up to 11M (95% Probability)

COVERAGE = Limited see ALRS Vol 2

CHARTS =Found in 300 series folios (Not used)

PRINCIPLE OF OPERATION = Time Difference.The time difference between master

and two slaves are measured.


Theory of Loran Time DifferenceTheory of Loran Time Difference


Hyperbolic Fixing StationsHyperbolic Fixing Stations



1. Simultaneous transmissions - ambiguity exists.

2. Master triggers Slave - Slave delays 500s ambiguity resolved.



1. Simultaneous transmissions - ambiguity exists.


Layout of a StationLayout of a Station

The master station transmits first and then secondaries follow in sequence after “secondary coding delay”.

Notes: Coding delay ensures:1. Slaves cannot be received out of alphabetical sequence.

2. Correct identification of slave by time difference “slot”.


Loran C Signal FormatLoran C Signal Format

All stations transmit 8 pulses 1000 secs apart.

The master transmits a 9th pulse 2000 secs after the eighth pulse for identification.

This ninth pulse can “blink” to warn of a defect in the chain. The blink can be coded to identify the defect.

The first two pulses of a defective secondary can also be made to “blink”.



LORAN C

BASIC FREQUENCY = 100kHz

RANGE = Groundwave 1200MSkywave Up to 3000M

ACCURACY = Groundwave 200M < 300 FT500M 200 - 700 FT750M 300 - 1100 FT1000M 500 - 1700 FT

Skywave Up to 11M (95% Probability)

COVERAGE = Limited see ALRS Vol 2

CHARTS = Found in 300 series folios

PRINCIPLE OF OPERATION = Time Difference.The time difference between master and two slaves are measured.

radio navaids

Technology

grunt productions

skywave pathsgroundwave

nm ground wave

metres ground wave

nm sky wavenight

known frequency

cw signals

hop unreflected wave