Enav222 prelim lecture

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This is a lecture about electronic navigation in JBLFMU for students.

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Enav222 prelim lecture

  1. 1. 1 ENAV222 PRELIM LECTURE By 3/Officer MOISES T. TEÑOSA
  2. 2. 2
  3. 3. 3 RADAR is an acronym for Radio Detection And Ranging. Radar is an electronic device that detects distant objects by bouncing radio waves off them and listening for those echoes.
  4. 4. 4 There are several types of radar in use and each type had their particular application. All radar operate on the same principles with modifications to suit a particular application. The type of radar used onboard ships is called a MARINE RADAR.
  5. 5. 5 RADAR THEORY Radar uses the basic principles of sound and echo. You shout towards a reflecting object and a returning sound or echo is heard seconds later from that particular direction.
  6. 6. 6 Radars designed for marine application is pulse modulated. It measures the distance to a target by measuring the time required for a short powerful burst of radio frequency energy to travel to the target and return to its source as a reflected echo.
  7. 7. 7 Since this radar waves makes a round trip, only half of the time determines the distance. Distance = (Speed X Time) / 2 Directional antennas are used to transmit these pulses and to receive the echoes.
  8. 8. 8 Radar waves travels at the speed of light at: 186,000 m/sec 300,000 km/sec 162,000 nm/sec Microsecond (usec) is used in radar applications usec = 1 second/1,000,000 1 nm = 6.18 usec 1 usec = 0.161829 nm
  9. 9. 9 RADAR COMPONENTS
  10. 10. 10 THE MAIN COMPONENTS OF A RADAR UNIT 1. POWER SUPPLY 2. MODULATOR 3. TRANSMITTER 4. ANTENNA OR SCANNER ASSEMBLY 5. RECEIVER 6. SCOPE / PLAN POSITION INDICATOR
  11. 11. 11 MAIN COMPONENTS OF A RADAR 1 - POWER SUPPLY The power supply gets its power from the ships main electrical supply then converts it to the required AC/DC voltage necessary to power the various components of the radar.
  12. 12. 12 2 - MODULATOR Modulator insures that all circuits connected with the radar system operate in a definite time relationship with each other and that the time interval between pulses is of proper length. The modulator simultaneously sends a synchronizing signal to trigger the transmitter and the indicator sweep.
  13. 13. 13 3 - TRANSMITTER This radar component is the source of radio frequency signal or energy. It gives off a strong short burst of energy known as pulse. To allow the transmitter to rest and to control the pulse length, pulse repetition rate (PRR) and synchronization, a switching devise called pulse modulation generator or modulator is employed.
  14. 14. 14 4 - ANTENNA system OR SCANNER ASSEMBLY – takes the radio frequency energy from the transmitter, radiates it in a highly directional beam, receives any returning echoes, and passes these echoes to the receiver.
  15. 15. 15 4 - ANTENNA OR SCANNER ASSEMBLY DRIVE MOTOR – this is found on the scanner housing and provides a 360 degrees scan motion of the scanner reflector at the rate of 12 - 30 RPM (refer to the manufacturer' operating manual for exact RPM).
  16. 16. 16 4 - ANTENNA OR SCANNER ASSEMBLY 4.2- FLASHER SWITCH – this provides the orientation of the ship's heading. It flashes at the scope whenever the antenna is facing dead ahead. 4.3- TYPES OF ANTENNA 1. parabolic (older models) 2. slotted wave guide (new models)
  17. 17. 17 4.6 - TYPES OF ANTENNA parabolic slotted wave guide parabolic slotted wave guide
  18. 18. 18 4 - ANTENNA OR SCANNER ASSEMBLY 4.7 - DUPLEXER OR TRANSMIT/RECEIVE CELL This enables the use of the scanner assembly for both transmitting and receiving by connecting the transmitter to the scanner assembly during the period of transmission while disconnecting the receiver.
  19. 19. 19 4.7 - DUPLEXER OR TRANSMIT/RECEIVE CELL Upon completion of the transmission, the scanner is automatically connected to the receiver. In some models a Transmit/Receive (TR) tube is used to block the pulses from entering the receiver. An Anti-Transmit/Receive (ATR) cell is used to block the echoes from entering the transmitter.
  20. 20. 20 5 - RECEIVER Amplifies the weak echoes but retaining its electronic shape (Radio Frequency/RF). 5.1 - MIXER AND LOCAL OSCILLATOR STAGE This is where the incoming echoes (in the same form of FREQUENCY) are mixed and aligned with the output of a local oscillator (KLYSTRON) producing an intermediate frequency (IF).
  21. 21. 21 5 - RECEIVER 5.1 - MIXER AND LOCAL OSCILLATOR STAGE Tuning is accomplished when the local oscillator is made to produce the IF and is aligned over the incoming RF signal.
  22. 22. 22 5 - RECEIVER 5.2 - INTERMEDIATE FREQUENCY STAGE This is composed of six (6) stages, whose amplification is controlled by the following: 1. Gain Control 2. STC – slow time control (anti-sea clutter control) 3. FTC – fast time control (anti-rain/snow control)
  23. 23. 23 6 - INDICATOR The primary function of the indicator is to provide a visual display of the ranges and bearings of radar targets from which echoes are received. Or it produces a visual indication of the echo pulses in a manner that furnishes the desired information.
  24. 24. 24 A trace or sweep rotates about the screen in synchronization with the scanner. Contacts or targets appear as bright spots or blips/pips about the screen. The screen, which is coated with phosphorescent material, lights up with persistence until the next rotation of the sweep passes over again to repaint the blips/pips. A trace or sweep rotates about the screen in synchronization with the scanner. Contacts or targets appear as bright spots or blips/pips about the screen.
  25. 25. 25 This part is also commonly called as: 1. Cathode Ray Tube (CRT) 2. The Scope 3. Plan Position Indicator (PPI)
  26. 26. 26
  27. 27. 27
  28. 28. 28 MODULATOR POWER SUPPLY WAVEGUIDE SCANNER TARGET PPI TRANSMITTER DUPLEXER RECEIVER
  29. 29. 29 MODULATOR POWER SUPPLY WAVEGUIDE SCANNER TARGET PPI TRANSMITTER TR RECEIVER A-TR
  30. 30. 30 RADAR SYSTEM CONSTANTS
  31. 31. 31 PULSE LENGTH Radars can operate both at short and long pulse. Pulse length in some radars are shifted automatically when selecting the shorter or longer range scales.
  32. 32. 32 Range Resolution is a measure of the capability of a radar set to detect the separation between targets on the same bearing but having small differences in range.
  33. 33. 33 If the leading edge of the pulse strikes a slightly farther target, while the trailing edge is still striking the closer target, the reflected echoes of the targets will appear as one elongated target.
  34. 34. 34 POWER RELATION The useful power of the transmitter is that contained in the radiated pulses and is called the PEAK POWER of the system. Power is normally measured as an average value over a relatively long period of time.
  35. 35. 35 CHARACTERISTICS OF RADAR PROPAGATION
  36. 36. 36 THE RADAR WAVE The radar radio frequency energy (radar wave) is emitted in pulses. These radar energy travels at the speed of light and is subject to atmospheric refraction or bending. It has energy, frequency, amplitude, wavelength and rate of travel.
  37. 37. 37 THE RADAR WAVE Each pulse of energy transmitted during a few tenths of a microsecond or few microseconds contains hundreds of complete oscillations. A CYCLE is one complete oscillation or complete wave.
  38. 38. 38 THE RADAR WAVE FREQUENCY is the number of cycles completed per second. HERTZ (Hz) is the unit for frequency as: 1 Hertz (Hz) = 1 cycle/second 1 kilohertz (kHz) = 1,000 cycles/second 1 megahertz (MHz) = 1 million cycles/second
  39. 39. 39 THE RADAR WAVE WAVELENGTH is the distance along the direction of propagation between successive crests or troughs. When one cycle has been completed, the wave has traveled one wavelength. AMPLITUDE is the maximum displacement of the wave from its mean or zero value.
  40. 40. 40 THE RADAR WAVE Marine radars operates at a wavelengths of 3 centimeters ( X band), 10 centimeters (S band). Wavelength is the length of one cycle.
  41. 41. 41 4.1 - THE RADAR WAVE
  42. 42. 42 Short wavelength Long wavelength
  43. 43. 43 Pulse Length 2 usec 1 usec
  44. 44. 44 Short powerful burst during transmission Echoes has the same characteristics but weaker Pulse Repetition Rate 1 pulse 1 pulse1 pulse 1 usec
  45. 45. 45 REFRACTION If radar waves travel in straight lines or rays; the distance to the horizon would be dependent only on the height of the antenna. Without the effects of refraction, the distance to the radar horizon would be the same as that of the geometrical horizon for the antenna height.
  46. 46. 46 REFRACTION Radar waves are subject to bending or refraction in the atmosphere resulting from travel through regions of different density. Under standard atmosphere, distance to radar horizon is found by the formula: d = 1.22√ h h=antenna height in feet d=distance to radar horizon in nautical miles
  47. 47. 47 REFRACTION Radar waves are bent or refracted slightly downwards following the curvature of the earth. The distance to the radar horizon does not limit the distance from which echoes maybe received. Echoes maybe received from targets beyond the radar horizon if their reflecting surface extends above it.
  48. 48. 48 REFRACTION The Standard Atmosphere is a hypothetical vertical distribution of atmospheric temperature, pressure and density. Types of refraction: 1. Super-refraction 2. Sub-refraction 3. Ducting
  49. 49. 49 REFRACTION Super-refraction This occurs when there is an upper layer of warm, dry air over a surface of cold, moist air. The effect is to increase the downward bending of the radar waves and thus increase the ranges at which targets maybe detected.
  50. 50. 50 REFRACTION Sub-refraction - This occurs when there is an upper layer of cold, moist air over a surface of warm, dry air. The effect is to bend the radar waves upward and thus decrease the maximum ranges at which targets maybe detected. It also affects the minimum ranges and may result in failure to detect low lying targets at shorter range.
  51. 51. 51 Ducting This phenomena occur during extreme cases of super-refraction. Energy radiated at angles of 10 or less maybe trapped in a layer of the atmosphere called the Surface Radio Duct. Radar waves are refracted downward to the sea surface, reflected upward, downward again within the duct and so on.
  52. 52. 52 Ducting Energy trapped by the duct suffers little loss, thus targets have been detected in excess of 1,400 nm. When the antenna is above the duct, targets lying below the duct may not be detected.
  53. 53. 53 Types of Refraction
  54. 54. 54 Types of Refraction
  55. 55. 55 Sub-Refraction
  56. 56. 56 Ducting
  57. 57. 57 ATTENUATION It is the absorption and scattering of the energy in the radar beam as it passes through the atmosphere and causes a decrease in echo strength. It is greater at higher frequencies or shorter wave lengths.
  58. 58. 58 FACTORS AFFECTING DETECTION, DISPLAY AND MEASUREMENT OF RADAR TARGETS
  59. 59. 59 FACTORS AFFECTING MINIMUM RANGE 1 – Pulse length The minimum range capability of a radar is determined primarily by the pulse length. 2 – Sea Return Sea return or echoes received from waves may clutter the indicator within and beyond the minimum range established by the pulse length and recovery time.
  60. 60. 60 FACTORS AFFECTING RANGE RESOLUTION Range resolution is a measure of the capability of a radar to display as separate pips the echoes of two targets on the same bearing and are close together. A high degree of range resolution requires short pulse, low receiver gain and short range scale.
  61. 61. 61 FACTORS AFFECTING RANGE RESOLUTION 1 – Pulse Length Two targets on the same bearing and are close together cannot be seen as two distinct pips on the PPI unless they are separated by a distance greater than one the pulse length. As a result, the echoes from two targets will blend into a single pip, and range can be measured only to the nearest target.
  62. 62. 62 Targets are separated by less than the pulse length Targets are separated by more than the pulse length
  63. 63. 63 FACTORS AFFECTING RANGE RESOLUTION 2 – Receiver Gain Range resolution can be improved by proper adjustment of the receiver gain control. The echoes from two separate targets on the same bearing may appear as a single pip if the receiver is too high.
  64. 64. 64 5.3 – FACTORS AFFECTING RANGE RESOLUTION 3 – CRT Spot Size The range separation required for resolution is increased because the spot size formed by the electron beam on the screen can not be focused into a point of light. The increase in echo image length and width varies with the CRT size and range scale used.
  65. 65. 65 5.3 – FACTORS AFFECTING RANGE RESOLUTION 4 – Range Scale The pips of two targets separated by a few hundred meters may merge on the PPI when longer range scale is used. The shortest range possible should be used and proper adjustment of the receiver gain may enable their detection as separate targets.
  66. 66. 66 5.4 – FACTORS AFFECTING BEARING ACCURACY Bearing measurements can be made more accurately with narrower horizontal beam widths. Narrow beam widths will have better definition of the target. The effective beam width can be reduced by lowering the receiver gain setting; it will reduce the sensitivity, maximum detection range but better bearing accuracy.
  67. 67. 67 5.4 – FACTORS AFFECTING BEARING ACCURACY 1 – Target Size Bearing measurements of small targets is more accurate than large targets because the center of smaller pips can be identified more accurately. 2 – Target Rate of Movement The bearings of stationary or slow moving targets can be measured more accurately than fast moving targets.
  68. 68. 68 5.4 – FACTORS AFFECTING BEARING ACCURACY 3 – Stabilization of Display Stabilized PPI display provides higher bearing accuracy than unstabilized displays because they are affected by yawing of the ship.
  69. 69. 69 5.4 – FACTORS AFFECTING BEARING ACCURACY 4 – Sweep Centering Error If the origin of the sweep is not accurately centered on the PPI, bearing measurements will be in error; more error is when the pip is near the center of the PPI. A more accurate result is by changing the range scale to shift the pip away from the center of the PPI.
  70. 70. 70 5.4 – FACTORS AFFECTING BEARING ACCURACY 5 – Parallax Error Improper use of mechanical bearing cursor will introduce bearing errors, the cursor should be viewed from a position directly in front of it. Electronic bearing cursor are not affected by parallax and centering errors, hence, provide accurate bearing measurements.
  71. 71. 71 5.4 – FACTORS AFFECTING BEARING ACCURACY 6 – Heading Flash Alignment The alignment of the heading flash with the PPI display must be such that the radar bearing must be almost the same as that by visual observation.
  72. 72. 72 5.5 – FACTORS AFFECTING BEARING RESOLUTION Bearing resolution is a measure of the capability of a radar to display as separate pips the echoes received from two targets which are at the same range and are close together. The principal factors that affect the bearing resolution are the horizontal beam width, target range and the CRT spot size.
  73. 73. 73 5.5 – FACTORS AFFECTING BEARING RESOLUTION 2 – Target Range Two targets at the same range must be separated by more than one beam width to appear as separate pips on the PPI. In as much as bearing resolution is determined primarily by horizontal beam width, a narrow horizontal beam width will provide a better bearing resolution.
  74. 74. 74 5.5 – FACTORS AFFECTING BEARING RESOLUTION 3 – CRT Spot Size The range separation required for resolution is increased because the spot size formed by the electron beam on the screen can not be focused into a point of light. The increase in echo image length and width varies with the CRT size and range scale used.
  75. 75. 75 RADAR OPERATION
  76. 76. 76 RADAR OPERATION Marine radars are classified as either Relative Motion or True Motion radars. True Motion radars can be operated with a relative motion display. Relative Motion radars are fitted with special adapters enabling operation with a true motion display.
  77. 77. 77 RADAR OPERATION There are two basic types used to portray the target’s position and motion on the PPI. The Relative Motion display shows the motion of a target relative to the motion of the observing (own) ship. The True Motion display shows the actual or true motions of the target and the observing (own) ship.
  78. 78. 78 RELATIVE MOTION RADAR In a relative motion radar, own ship is positioned at the center of the PPI, regardless whether she is stopped or in motion (underway). When own ship is stopped, successive pips of the target indicate its true direction of movement and speed.
  79. 79. 79 RELATIVE MOTION RADAR When own ship is underway, the successive pips of the target indicate its relative direction of movement and speed. A graphical solution (radar plot) is required in order to determine its true direction of movement and speed.
  80. 80. 80 Radar Transfer Plotting sheet
  81. 81. 81 RELATIVE MOTION RADAR If own ship is underway, pips of fixed targets such as landmasses, buoys, fixed platforms, ships at anchor, move on the PPI at a rate equal to the speed of own ship but in opposite direction.
  82. 82. 82 TRUE MOTION RADAR True motion radars displays own ship and moving targets in their true motion. Own ship and other moving objects move on the PPI in accordance with their true courses and speeds. Fixed objects such as landmasses are stationary on the PPI, such as that the radar operator observes own ship and other ships moving with respect to landmasses.
  83. 83. 83 True motion display Own ship Target Target Targets and own ship moves across the screen
  84. 84. 84 ORIENTATIONS OF RELATIVE MOTION DISPLAY There are two basic orientations used for the display of relative motion on the PPI. 1.Head-up (unstabilized) display. In this display, the heading flasher is aligned with the ship’s fore and aft line (0000 )regardless of the heading. The pips are at their measured distances but in a direction relative to own ship.
  85. 85. 85 ORIENTATIONS OF RELATIVE MOTION DISPLAY This type of display is only suitable for open sea watchkeeping as the targets appear on the PPI in exact position as they are visually observed. It is the targets that move every time the ship yaws and there is difficulty of converting relative bearings to true.
  86. 86. 86 ORIENTATIONS OF RELATIVE MOTION DISPLAY 2. North-up (stabilized) display. In this display, the heading flasher is aligned with the ship’s fore and aft line (0000 )regardless of the heading. A gyro repeater attached to the unit indicates the ship’s heading. The pips are at their measured distances but in a true direction from own ship.
  87. 87. 87 ORIENTATIONS OF RELATIVE MOTION DISPLAY This display is also suitable for open sea watch keeping as the targets appear on the PPI in exact position as they are visually observed, however, there is difficulty when taking bearings every time the ship yaws as the gyro repeater keeps on moving.
  88. 88. 88 ORIENTATIONS OF TRUE MOTION DISPLAY 3. True Motion radars are usually, stabilized North- up although it can also be on Head-up display. The display is similar to a navigational chart and it is the ship’s heading flasher that changes direction. It is best for coastal navigation and watchkeeping. When on stabilized mode, the Cathode Ray Tube (CRT) of True and Relative motion radars are automatically rotated to compensate for the setting.
  89. 89. 89 000 45 180 90 125 270 225 315 90 000 0 45 180 90125 270 225 315 45 180 125 270 225 315 Unstabilized Head-up Stabilized North-up
  90. 90. 90 Fig. 1: Own ship and targets underway Stabilized; North-up
  91. 91. 91 Fig. 2: Own ship altered course Fig. 3: Movement of targets after course alteration Stabilized; North-up
  92. 92. 92 Fig. 4: Own ship and targets underway Unstabilized; Head-up
  93. 93. 93 Fig. 5: Own ship altered course Fig. 6: Movement of targets after course alteration Unstabilized; Head-up
  94. 94. 94 RADAR CONTROLS
  95. 95. 95 7 – RADAR CONTORLS Advanced electronic technology has made modern radars more accurate, reliable and compact than the older models and these includes their operating controls. Due to communication, language and designs, the radar operating controls were internationally standardized by the use of symbols. Modern design and technology has eliminated some of these operating controls.
  96. 96. 96 ONINSKI
  97. 97. 97 Head - up North - up Heading Marker Alignment
  98. 98. 98 Transmitted Power Monitor Display Brilliance Scale Illumination
  99. 99. 99 Gain Tuning Range Rings Brilliance Short Pulse Long Pulse Selector
  100. 100. 100 11.07 12 Bearing Marker Variable Range Marker Transmit/Receive Monitor Range Selector Range Indicator Variable Range Indicator
  101. 101. 101 Anti-Clutter Rain Minimum Anti-Clutter Rain Maximum Anti-Clutter Sea Maximum Anti-Clutter Sea Minimum
  102. 102. 102
  103. 103. 103 SETTING – UP PROCEDURE
  104. 104. 104 SETTING – UP PROCEDURE The proper set up switch off procedure must be observed before a radar is operated. Observing the proper procedure will prolong the life of the various delicate parts and components of a radar.
  105. 105. 105 Steps for setting up a radar. 1.Make sure that the scanner is free of all obstruction. 2.Switch the power to “ON”; wait for 2-3 or until the ready light is light. 3.Switch to “OPERATE”.
  106. 106. 106 4. Adjust the “BRILLIANCE” control; just enough to see a little speckled background. 5. Set the “RANGE SCALE” medium range. 6.Set either to “SHORT or LONG PULSE”. 7.Adjust the “GAIN, and TUNING”.
  107. 107. 107 8. Adjust the brightness of the “FIX RANGE RINGS, VRM, PANEL. 9. Adjust the “RAIN and SEA anti-clutter” as appropriate. A radar should not be continuously switch “ON” and “OFF”, instead it should be “STANDY” mode.
  108. 108. 108 Too little gain Normal gain Excessive gain
  109. 109. 109 Too little brilliance Normal brilliance Excessive brilliance
  110. 110. 110 Performance monitor working properly Performance monitor improperly working
  111. 111. 111 Clutter caused by rain (no anti-rain clutter) Break up of rain clutter by means of anti-rain clutter control
  112. 112. 112 FTC not in use FTC in use
  113. 113. 113 STC setting too low Correct STC setting STC setting too high
  114. 114. 114 Thank you.. 3/OFFICER MOISES T. TEÑOSA

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