1. Fixing systems using radio frequencies (NavStar GPS and LORAN C)
Radio Navigation Aids
Fixing systems using radio frequencies
(NavStar GPS and LORAN C)

2. NavStar GPS System built by USA Defence Department.
Worldwide coverage.
UHF transmissions from satellites.
Very accurate (in the region of 50 metres)

3. Navstar GPS
CHG 98/14/20
M97/

4. The Navstar System SPACE SEGMENT 28 Satellites 6 Orbits UPLINK DATA
Satellite Ephemeris
Clock Drift
Propagation Delay
DOWNLINK DATA
Navigation
Message
Data
CONTROL SEGMENT
5 Monitor Stations
3 Antennae
1 Master Control Station
USER SEGMENT
Ships
Helicopters
etc
CHG 98/14/21
M97/

5. Pseudo Range to One Satellite

6. Correcting for Receiver Clock Error

7. Geometry of the Satellites
a. Good (Low) Dilution of Precision
b. Poor (High) Dilution of Precision

8. for the Fully Operational System
GPS Accuracy
for the Fully Operational System
Vertical
within 10
metres
Horizontal
within 8
metres
Velocity within
0.1 knots
Horizontal
within 8
metres
Absolute global time transfer to a fraction of a microsecond available continuously

9. 4 Satellites provide 3 Dimensional Fix
Expected Accuracy (67%)
Position 30ft
Velocity 0.1kts
Time 10 Nano Secs

10. Differential GPS System Elements
Satcom
Link
Differential
Reference
Station and
Broadcast
Transmitter
DGPS
User
Differential
Correction
Broadcast
Data
Comms
Link
Control Centre

11. LORAN C BASIC FREQUENCY = 100kHz RANGE = Groundwave 1200M
Skywave Up to 3000M
ACCURACY = Groundwave 200M < 300 FT
500M FT
750M FT
1000M FT
Skywave Up to 11M (95% Probability)
COVERAGE = Limited see ALRS Vol 2
PRINCIPLE OF OPERATION = Time Difference.
The time difference between master and two slaves are measured.

12. Ground-Wave and Sky-Wave Paths
UNREFLECTED
WAVE
TWO HOP
190
F LAYER
150 90
E LAYER 50
D REGION 27
GROUND
WAVE Tx Rx
D REGION
REFLECTION
CHG 98/13/3b
M97/1097/3b

13. Ground-Wave and Sky-Wave Paths
UNREFLECTED
WAVE
ONE HOP
190
F LAYER
150 90
E LAYER 50
D REGION 27
GROUND
WAVE Tx Rx
D REGION
REFLECTION
CHG 98/13/3c
M97/1097/3c

14. Theory of Loran Time Difference
CHG 98/13/20a
M97/1097/20a

15. Theory of Loran Time Difference
CHG 98/13/20b
M97/1097/20b

16. Theory of Loran Time Difference
CHG 98/13/20c
M97/1097/20c

17. Theory of Loran Time Difference
CHG 98/13/20d
M97/1097/20d

18. Hyperbolic Fixing Systems (2)
BASE LINE
EXTENSION
BASE LINE
EXTENSION A B
CHG 98/13/5a
M97/1097/5a

19. Hyperbolic Fixing Systems (2)
BASE LINE
EXTENSION
BASE LINE
EXTENSION A B
CHG 98/13/5b
M97/1097/5b

20. Hyperbolic Fixing Systems (2)
BASE LINE
EXTENSION
BASE LINE
EXTENSION A B
CHG 98/13/5c
M97/1097/5c

21. Hyperbolic Fixing Systems (2)
BASE LINE
EXTENSION
BASE LINE
EXTENSION A B
CHG 98/13/5d
M97/1097/5d

22. Layout 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”.
CHG 98/13/24
M97/1097/24

23. Loran 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”.
CHG 98/13/23
M97/1097/23