1. Azimuth is the angle, in degrees, measured along the horizon, between true north and the point on the horizon directly beneath the satellite. Azimuth is always measured clockwise from true north, and it is always a positive number The horizon is defined as a great circle of the celestial sphere perpendicular to the vertical. It is equidistant from the zenith (point straight overhead) and the nadir (point exactly opposite the zenith).
2. Elevation is the angle between horizontal plane and the satellite and can be either +ve or -ve (below horizon hence invisible)
3. True North = Geographical north pole (constant) Magnetic North = Point where magnetic field lines of Earth are vertical and enter the Earth (It varies) NOTE: The geographical north pole (True North) is magnetic South pole.
4. receivers
   1. interface
      1. TTL
      2. RS232
   2. Baud-rate
      1. upto
         1. 115200 bps
   3. messages
      1. types
         1. GGA
            1. GPS Fix data
            2. which provides
            3. 3D Location Data
            4. Accuracy Data
         2. GSA
            1. Nature of fix
            2. no fix
            3. 2D
            4. 3D
            5. PRNs of Sats (and hence their number) used in the current solution
            6. DOP
            7. Dilution of precision
            8. smaller the better
            9. 1.0 for 3D fix
         3. GSV
            1. Satellites in view
            2. PRNs of the Sats in view
            3. Eelevation angle of each sat
            4. Azimuth angle of each sat
         4. GGL
            1. Geographical Pos. Lat/Long
         5. RMC
            1. Recommended minimum specific GNSS data
         6. VTG
            1. Course over Ground and Ground Speed, horizontal course and horizontal velocity
         7. ZDA
            1. Time & Date
      2. standardized
         1. by
            1. NMEA
            2. for
            3. GNSS
            4. GPS
            5. LORAN
            6. Omega
            7. Transit
      3. 8-bit ASCII data
         1. 1 start bit
         2. 1 stop bit
         3. No parity
      4. max characters=79
         1. excluding
            1. $
            2. <CR>
            3. <LF>
5. can
   1. determine
      1. position & time
         1. accurately
            1. position
            2. position to within 20m to approx. 1mm
            3. time(UTC)
            4. time to within 60ns to approx. 5ns
      2. speed & direction
      3. speed
         1. from
            1. Doppler shift measurement
6. types
   1. GPS
      1. uses
         1. military
            1. Precise Positioning Services (PPS)
            2. authorized
         2. civilian
            1. Standard Positioning System(SPS)
            2. free
      2. constellation
         1. orbits
            1. inclined
            2. @55 degress
            3. equator
            4. 6 planes
            5. period
            6. Approx. 12 hrs
            7. altitude
            8. 20180 km or 12539 miles
            9. derived
            10. by
            11. various organisations
            12. using
            13. carrier phase
            14. post processing
         2. Satellites
            1. Up to 32 satellites 4 to 5 satellites/orbital plane
            2. plus spares satellites
            3. at least 4 visible anytime anywhere
            4. Atomic Clocks
            5. 4/satellite
            6. Csx2
            7. Rbx2
            8. Stability = 10^-12 to 10^-15 1s in 30,000 to 1,000,000 yrs
            9. precision
            10. better than
            11. 10ns or 3 meters
            12. transmit
            13. position
            14. time
            15. signal
            16. frequency
            17. L1
            18. 1575.42MHz
            19. wavelength ~ 19cm
            20. L2
            21. 1227.60MHz
            22. wavelength ~ 24.4cm
            23. L5
            24. 1176.45MHz
            25. strength
            26. minimum
            27. -158 to -160 dBW
            28. maximum
            29. -153dBW
            30. L1 carrier transmission power @ sat.
            31. 21.9 W = 13.4dB
            32. information
            33. rate
            34. 50bps
            35. total time for transmission
            36. 1 frame or page = 1500 bits <> 30s 25 frames = 30s* 25 = 12.5 minutes
            37. 1 frame = 5 sub-frames 1 sub-frame = 300bits = 10 words 1 word = 30bits
            38. contents
            39. Sat. time and correction for signal transit delay
            40. sat. health and positional accuracy
            41. Precise orbital data (ephemeris)
            42. Approx. orbital data for all sats.(almanac)
            43. UTC offset
            44. data on ionosphere
            45. L1
            46. SPS
            47. C/A-signal
            48. modulation
            49. BPSK(1)
            50. chip rate
            51. 1.023MHz
            52. PRN
            53. 1023 bits
            54. 1ms
            55. unique/satellite
            56. L1C
            57. modulation
            58. TMBOC(6,1,1/11)
            59. PRN
            60. 10230 bits
            61. 10ms
            62. chip rate
            63. 1.023MHz
            64. PPS
            65. P(Y)-signal
            66. modulation
            67. BPSK(10)
            68. chip rate
            69. 10.23MHz
            70. unencrypted
            71. P code
            72. PRN
            73. 6.18x10^12 bits
            74. 1 week long
            75. encrypted
            76. Y code
            77. multiplication
            78. Precise (P code)
            79. Encryption (W code)
            80. M+ signals
            81. modulation
            82. BOC(10,5)
            83. code frequency (chip rate)
            84. 5.115M
            85. sub-carrier freq
            86. 10.23MHz
            87. L2
            88. PPS
            89. P(y)-signal
            90. M+ signals, BOC(10,5)
            91. SPS
            92. L2C
            93. L5
            94. SPS
            95. more robust
            96. In future
            97. Righthand circular polarised (RHCP)
         3. link: note: rotating earth
      3. employs
         1. phase difference
            1. to
            2. determine
            3. Sat. range
      4. observables
         1. pseudorange
            1. offset
            2. between
            3. PRN coded signal from Sat.
            4. Replica code generated in the receiver
            5. speed of light
         2. accumulated delta range (ADR)
            1. measure
            2. of
            3. carrier phase
      5. Segments
         1. Space Segment
         2. Control segment
            1. maintains
            2. constellation
            3. comprises
            4. Master Control Station
            5. in
            6. Colorado US
            7. 5 monitor stations around the world
            8. determine
            9. orbit and clock parameters
            10. equipped with
            11. atomic clocks
            12. 3 ground control stations
            13. transmit to
            14. sats.
            15. compute
            16. ephemeris
            17. synchronise
            18. Onboard sat. time
            19. relay
            20. ephemeris
            21. almanac
            22. sat. health, clock error etc.
         3. User Segment
   2. GALILEO
      1. sats.
         1. 30
      2. orbits
         1. 3
         2. circular
         3. altitude
            1. 23,616km
         4. inclination
            1. 56 degree
7. Definitions/ Facts
   1. Pseudorange
      1. The clock at the receiver is not perfectly synchronised with the atomic clock on satellite. Therefore the calculated distance referenced to the local clock (s=vt) has a discrepancy and is called pseudorange.
   2. No. transmitters required for position
      1. When an unsynchronised local clock is used to determine position the number of time signal transmitters should exceed the number of unknown dimensions by one.
   3. Signal travel time
      1. 67.3ms to reach earth surface 1 nanosecond/30cm 3.3 microsecond/Km 1 microsecond/300m 1 millisecond/300Km c = 299,792,458 (3x10^8) m/s or 300 million m/s or 3 hundred thousand km/s
8. HW interfaces
   1. antennas
      1. no adjustment necessary
      2. passive
      3. active
         1. contains
            1. LNA preamplifier
         2. powered by
            1. GNSS receiver
            2. over
            3. RF signal line
      4. types
         1. patch
            1. often combined
            2. patch passive
            3. active patch(with LNA)
            4. suitable for flat assembly applications
         2. helix
            1. active helix
            2. passive helix
            3. better directivity than patch
         3. chip
            1. target mass market
            2. can be built into the board
   2. time pulse
      1. 1pps
      2. sync to UTC
      3. usually
         1. TTL
9. Standards
   1. international
      1. data exchange
         1. GPS
            1. NMEA
         2. DGPS
            1. RTCM
   2. proprietry
      1. ublox
10. used
    1. for
       1. positioning
       2. locating
       3. navigating
       4. timing
    2. by
       1. plane
          1. finding
             1. land
       2. ship
          1. seeking
             1. assistance
       3. hiker
          1. disorientated
             1. by weather
       4. motorist
          1. find
             1. an address
       5. bussinesses
          1. track
             1. mobile
             2. assets