2. 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 comparison
LF (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 conversion
UHF (1575.42 & 1227.6
MHz)
Worldwide
21 metres (PPS)
100 metres (SPS)
Provides time
reference. P(Y) code
encryption.
Phase comparison
MF/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.
5. Grunt Productions 2007
The Navstar System
SPACE SEGMENT
28 Satellites
6 Orbits
UPLINK DATA
Satellite Ephemeris
Clock Drift
Propagation Delay
USER SEGMENT
Ships
Helicopters
etc
CONTROL SEGMENT
5 Monitor Stations
3 Antennae
1 Master Control Station
DOWNLINK DATA
Navigation
Message
Data
10. Grunt Productions 2007
GPS Accuracy
for the Fully Operational System
Absolute global time transfer to a fraction of a microsecond available continuously
Horizontal
within 8
metres
Horizontal
within 8
metres
Vertical
within 10
metres
Velocity within
0.1 knots
11. Grunt Productions 2007
4 Satellites provide 3 Dimensional Fix
Expected Accuracy (67%) Position 30ft
Velocity 0.1kts
Time 10 Nano Secs
12. Grunt Productions 2007
Differential GPS System Elements
Satcom
Link
DGPS
User
Differential
Correction
Broadcast
Data
Comms
Link
Control Centre
Differential
Reference
Station and
Broadcast
Transmitter
13. Radio FixingRadio Fixing
AidsAidsFREQUENCY SPECTRUM
Category Frequency Wavelength System
VLF 0-30kHz Very Long Omega
LF 30-300kHz Long Decca Loran
MF 300-3000kHz Medium MFDF Consol
HF 3-30MHz Short
VHF 30-300MHz Metric
UHF 300-3000MHz Decimetric Navstar Transit
SHF 3000-30000MHz Centimetric
E/F-Band
I-Band
EHF 30000-300000MHz Millimetric
PROPAGATION
Ground Waves
The lower the frequency, the greater the range of the ground wave signal. Ground wave
signal decreases as frequency increases due to:
A. Increased attenuation
B. A decrease in the bending of waves around the earth’s surface.
Sky Waves
These occur at frequencies between VLF and HF. Attenuation of sky waves decreases as
frequency increases, therefore increased frequency gives improved reception.
Grunt Productions 2007
14. Ground-Wave and Sky-Wave PathsGround-Wave and Sky-Wave Paths
UNREFLECTED
WAVE
150
27
Tx D REGION
REFLECTION
GROUND
WAVE
Rx
F LAYER
E LAYER
D REGION
50
90
190
Grunt Productions 2007
16. Ground-Wave and Sky-Wave PathsGround-Wave and Sky-Wave Paths
ONE HOP
UNREFLECTED
WAVE
150
27
Tx D REGION
REFLECTION
GROUND
WAVE
Rx
F LAYER
E LAYER
D REGION
50
90
190
Grunt Productions 2007
17. Theory of Phase ComparisonTheory of Phase Comparison
1. STATION A radiates CW signals on a known frequency, and thus at a known
wavelength.
Grunt Productions 2007
18. Theory of Phase ComparisonTheory of Phase Comparison
1. STATION A radiates CW signals on a known frequency, and thus at a known
wavelength.
2. STATION B also radiates CW signals on same frequency, and thus at same
wavelength.
Grunt Productions 2007
19. Theory of Phase ComparisonTheory of Phase Comparison
1. STATION A radiates CW signals on a known frequency, and thus at a known
wavelength.
2. STATION B also radiates CW signals on same frequency, and thus at same
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.
Grunt Productions 2007
20. Theory of Phase ComparisonTheory of Phase Comparison
1. STATION A radiates CW signals on a known frequency, and thus at a known
wavelength.
2. STATION B also radiates CW signals on same frequency, and thus at same
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 λ 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 λ._
2
_
2
Grunt Productions 2007
21. B
Hyperbolic Fixing Systems (2)Hyperbolic Fixing Systems (2)
BASE LINE
EXTENSION
BASE LINE
EXTENSION
A
Grunt Productions 2007
22. Hyperbolic Fixing Systems (2)Hyperbolic Fixing Systems (2)
BASE LINE
EXTENSION
BASE LINE
EXTENSION
A B
Grunt Productions 2007
23. Hyperbolic Fixing Systems (2)Hyperbolic Fixing Systems (2)
BASE LINE
EXTENSION
BASE LINE
EXTENSION
BA
Grunt Productions 2007
24. Hyperbolic Fixing Systems (2)Hyperbolic Fixing Systems (2)
BASE LINE
EXTENSION
BASE LINE
EXTENSION
BA
Grunt Productions 2007
25. Hyperbolic Patterns, Simultaneous TransmissionsHyperbolic Patterns, Simultaneous Transmissions
0
A
B
1800
BASE LINE
EXTENSION
1800
BASE LINE
EXTENSION
Grunt Productions 2007
27. 250´
280´
350´
150´
250´
Q
Q
Hyperbolic Patterns, Simultaneous TransmissionsHyperbolic Patterns, Simultaneous Transmissions
0
A
B
1800
BASE LINE
EXTENSION
1800
BASE LINE
EXTENSION
300600
900
1200
1500
300 600
900
1200
1500
150´
Q
Q
Grunt Productions 2007
28. Hyperbolic Position LinesHyperbolic Position Lines
Diagram shows development of a lattice pattern
Station 3
Slave
Station 1
Master
Station 2
Slave
Grunt Productions 2007
29. LORAN CLORAN C
BASIC FREQUENCY = 100kHz
RANGE = Groundwave 1200M
Skywave Up to 3000M
ACCURACY = Groundwave 200M < 300 FT
500M 200 - 700 FT
750M 300 - 1100 FT
1000M 500 - 1700 FT
Skywave 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.
Grunt Productions 2007
30. Theory of Loran Time DifferenceTheory of Loran Time Difference
Grunt Productions 2007
31. Theory of Loran Time DifferenceTheory of Loran Time Difference
Grunt Productions 2007
32. Theory of Loran Time DifferenceTheory of Loran Time Difference
Grunt Productions 2007
33. Theory of Loran Time DifferenceTheory of Loran Time Difference
Grunt Productions 2007
37. 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”.
Grunt Productions 2007
38. Loran C Signal FormatLoran C Signal Format
All stations transmit 8 pulses 1000µ secs apart.
The master transmits a 9th pulse 2000µ 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”.
Grunt Productions 2007
39. Grunt Productions 2007
LORAN C
BASIC FREQUENCY = 100kHz
RANGE = Groundwave 1200M
Skywave Up to 3000M
ACCURACY = Groundwave 200M < 300 FT
500M 200 - 700 FT
750M 300 - 1100 FT
1000M 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.
