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Radio navaids
LORAN-C is a hyperbolic radio navigation system that uses time difference measurements between signals transmitted by master and slave stations to determine a user's position. It operates at a basic frequency of 100kHz and can achieve accuracies of less than 300 feet within 1200km of groundwave coverage or up to 11 meters within 3000km of skywave coverage. Charts for LORAN-C can be found in folios of the 300 chart series, and it functions by measuring the time difference between signals from a master station and two slave stations.
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Radio navaids
- 1. Grunt Productions 2007 RadioNavaidsRadio Navaids A brief by LanceA brief by Lance GrindleyGrindley
- 2. Radio Fixing AidsRadioFixing 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.
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- 4. Grunt Productions 2007 NavstarGPS - 24 Satellites plus 4 Spares, 6 Orbital Planes
- 5. Grunt Productions 2007 TheNavstar 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
- 6. Grunt Productions 2007 PseudoRange to One Satellite
- 7. Grunt Productions 2007 Correctingfor Receiver Clock Error
- 8. Grunt Productions 2007 GPSNavigation Signals L1 = 1575.42 MHz C/A Code at 1.023 MHz L2 = 1227.6 MHz P-Code at 10.23 MHz P-Code at 10.23 MHz
- 9. Grunt Productions 2007 Geometryof the Satellites a. Good (Low) Dilution of Precision b. Poor (High) Dilution of Precision
- 10. Grunt Productions 2007 GPSAccuracy 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 4Satellites provide 3 Dimensional Fix Expected Accuracy (67%) Position 30ft Velocity 0.1kts Time 10 Nano Secs
- 12. Grunt Productions 2007 DifferentialGPS System Elements Satcom Link DGPS User Differential Correction Broadcast Data Comms Link Control Centre Differential Reference Station and Broadcast Transmitter
- 13. Radio FixingRadio Fixing AidsAidsFREQUENCYSPECTRUM 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-WavePathsGround-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
- 15. UNREFLECTED WAVE 150 27 Tx D REGION REFLECTION GROUND WAVE Rx FLAYER E LAYER D REGION 50 90 Ground-Wave and Sky-Wave PathsGround-Wave and Sky-Wave Paths TWO HOP 190 Grunt Productions 2007
- 16. Ground-Wave and Sky-WavePathsGround-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 PhaseComparisonTheory 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 PhaseComparisonTheory 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 PhaseComparisonTheory 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 PhaseComparisonTheory 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, SimultaneousTransmissionsHyperbolic Patterns, Simultaneous Transmissions 0 A B 1800 BASE LINE EXTENSION 1800 BASE LINE EXTENSION Grunt Productions 2007
- 26. 250´ 280´ 350´ 150´ 250´ Q Q Hyperbolic Patterns, SimultaneousTransmissionsHyperbolic Patterns, Simultaneous Transmissions 0 A B 1800 BASE LINE EXTENSION 1800 BASE LINE EXTENSION 300600 900 1200 1500 150´ Q Q Grunt Productions 2007
- 27. 250´ 280´ 350´ 150´ 250´ Q Q Hyperbolic Patterns, SimultaneousTransmissionsHyperbolic 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 LinesHyperbolicPosition Lines Diagram shows development of a lattice pattern Station 3 Slave Station 1 Master Station 2 Slave Grunt Productions 2007
- 29. LORAN CLORAN C BASICFREQUENCY = 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 LoranTime DifferenceTheory of Loran Time Difference Grunt Productions 2007
- 31. Theory of LoranTime DifferenceTheory of Loran Time Difference Grunt Productions 2007
- 32. Theory of LoranTime DifferenceTheory of Loran Time Difference Grunt Productions 2007
- 33. Theory of LoranTime DifferenceTheory of Loran Time Difference Grunt Productions 2007
- 34. Hyperbolic Fixing StationsHyperbolicFixing Stations Grunt Productions 2007
- 35. Hyperbolic Fixing StationsHyperbolicFixing Stations 1. Simultaneous transmissions - ambiguity exists. 2. Master triggers Slave - Slave delays 500µs ambiguity resolved. Grunt Productions 2007
- 36. Hyperbolic Fixing StationsHyperbolicFixing Stations 1. Simultaneous transmissions - ambiguity exists. Grunt Productions 2007
- 37. Layout of aStationLayout 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 SignalFormatLoran 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 LORANC 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.