Positioning methods of Loran-C Hyperbola mode:
Measure the distance difference between a master station and two slave stations, and get the two Hyperbolas. We can get the vessel‘s position from the intersection of the two Hyperbolas.
The popular ways include impulse method, phase method and impulse with phase method.
Range finding mode: Actually, Loran-C is a range finding system. Because of the unavoidable measuring error, the range is a fake. It‘s familiar with GPS. We can integrate Loran-C in this mode with GPS to get a high-powered system. Principle chart:
SlMa
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Principle of Hyperbola mode Signal of Master Station A:
Ua(t)?E(t)cos?tSignal of Slave Station B:
Ub(t)?E(t?td??t)cos[?(t?td??t)]where
??2?f?2?/Tea(t)?tE(?t?ta/)*cos[?(t?ta)]dceb(t)?E(t?tb?td??t)*cos[?(t?tb?td??t)]Received Signals of A, B in the position of vehicle M:
dta?Ra/c;tb?Rb/c;??tn??(tb?ta?td??t)?n??a??bwhereTime difference of Signals of A, B:
Phase difference of Signals of A, B:
tn?tb?ta?td??t Or
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?tn??n/??T?n/2?(Ra?Rb)?(tn?td??t)C
LORAN Accuracy: 0.1 to 0.25 Nautical Miles (183 to 458 meters)LORAN Accuracy is affected by Crossing Angle (near 90o) Gradient (low) (ratio of TD spacing to TD difference)LORAN Accuracy is degraded within 10 nm of Shore. Close to Bridges, Power Lines and Large StructuresLORAN Repeatability is within 60 feet.Receiver Features:?LaAtitude & Longitude ?Speed Over the Ground ?Course Over the Ground ?Cross Track Error (XTE)
?Steer Right or Left?Waypoints (Destinations, enroute & final) ?Course to Steer (Bearing) to Waypoint ?Distance to Go to Waypoint
?Time to Go to Waypoint?Man Overboard Location ?Bearing & Distance to Man Overboard ?Alarms for Arrival, Anchor Watch
? Cross Track Error?LORAN Signal Alarms 2.5 Radar navigation
Objectives: 1. Be able to draw the basic diagram of the components of a radar set.
2. Outline the principles and characteristics of radar.
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3. Discuss the limitations of radar.
4. Describe the use of radar in navigation.
5. Gain an understanding of the functional positions on a typical shipboard piloting team and RadNav team. 2.5.1. Radar Components
1. Transmitter
Consists of an oscillator that produces radio-frequency (RF)
waves.2. Modulator Essentially a timing device that regulates the transmitter so that it sends out relatively short pulses of energy separated by relatively long periods of rest.
3. Antenna - Controlled by the modulator to perform two functions: forms outgoing pulses into beams and collects the returning pulses. 4. Receiver - Comprised of the circuitry that amplifies the weak returning echoes from a contact and converts them into a form, which may be presented on a display.
5. Radar Repeater - A Cathode Ray Tube (CRT) displays the radar information.
For surface navigation, the Plan Position Indicator (PPI) is used.Controls: Variable Range Ring (strobe) Variable Bearing Marker Range Rings
Range Scales can be altered
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2.5.2 Limitations and Advantages of RADAR
Limitations
1. Bearing Resolution
The minimum difference in bearing between two objects at the same range.Related to Beam Width 2. Range Resolution
The minimum difference in range between two objects on the same bearing that can be separated by a radar. Related to Pulse Width 3. Frequency & Wavelength
Determining characteristics of a RADAR.a. Propagation Affected by the prevailing meteorological conditions.
b. Antenna Size - Higher frequencies require smaller antennae.Operator Controls
Enables operator to improve the picture being displayed.a. Sensitivity Time Control
Removes sea clutter at close in ranges so that nearby contacts can be seen.
b. Fast Time Constant
Reduces the effects of rain and other unwanted echoes. c. Pulse Length
Shorter the pulse length, the better the resolution in range. 5. Range
a. Minimum Range - RADAR cannot receive a returning echo until the trailing edge of the pulse has cleared the antenna and the transmit/receive switch has switched to receive.
b. Maximum Range - Determined by the height of the antenna, power output and frequency.
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