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

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

Navstar GPS CHG 98/14/20 M97/1114-20

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 M97/1114-21

Pseudo Range to One Satellite

Correcting for Receiver Clock Error

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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