AMATEUR VHF by fjzhangweiyun

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									THE GROUND STATION
ASE 128 – Aerospace Engineering Projects Lab


Jahshan Bhatti
Purpose of a Ground Station
   A ground station consists of a set of hardware and
    software tools that allows tracking, receiving data
    from, and transmitting commands to satellites.
Satellite Communication
   Satellite communication occurs through the
    manipulation, transmission, and reception of
    electromagnetic radiation through free space.
Modulation Schemes
   Continuous Wave
   Amplitude Modulation
   Frequency Modulation
   Phase Modulation
   Digital AM, FM, and
    PM


       xt   A cos2ft   
Continuous Wave
   Misnomer; a continuous carrier wave cannot convey
    any information (zero bandwidth).
   However, if we key the carrier wave by turning it
    on/off based on the data signal, then the
    modulated signal will have finite bandwidth and
    can convey information.
   The bandwidth of a modulated CW signal is
    related to how fast the signal changes from the on
    and off states (rise and fall times).
Amplitude Modulation
   Generalization of CW modulation.
   Instead of using two discrete amplitude states
    (on/off) like CW, AM uses an “infinite” number of
    amplitude states.
   AM can be used in the transmission of an analog
    (audio) signal on an RF carrier.
   Part of the NOAA Automatic Picture Transmission
    scheme uses AM, where the amplitude corresponds
    to a shade of gray.
Frequency/Phase Modulation
   The data signal is used to vary the carrier signal’s
    frequency or phase.
   The amplitude of the modulated signal does not
    change.
   Like AM, FM and PM can be used in the transmission
    of an analog (audio) signal on an RF carrier.
Comparison of AM and FM
Comparison of AM and FM
   AM modulation/demodulation circuits are easier to
    build, but it is harder to receive the signal since the
    RF power can dip below the background noise.
   With the advent of integrated circuits and software
    defined radios, FM transceivers are now relatively
    cheap and common, making AM a relic of the past
    and rarely used in RF modulation.
Digital Modulation
   For AM, FM, and PM, the data signal was analog
    (continuous).
   However, most satellites are run by micro-computers
    that can only transmit and receive information in
    binary form, which is represented by two discrete
    states (0 and 1).
Digital Modulation
   Therefore, there are digital versions for AM, FM,
    and PM which modulate a carrier signal from a
    digital (discrete) data signal.
     AM => Amplitude Shift Keying (ASK)
     FM => Frequency Shift Keying (FSK)

     PM => Phase Shift Keying (PSK)

   If there are only two discrete states, then the
    scheme is referred to as Binary XSK.
Binary Frequency Shift Keying
Morse Code
   Can be considered a type of modulation scheme
    since it transforms an English message to a data
    signal that can be fed into a CW modulator.
   Designed so that the modulated signal can be
    easily understood by humans. However, computers
    have a lot of trouble demodulating it due to
    varying speeds and styles.
AX.25
   AX.25 is a standard binary packet format used by
    amateur radio operators.
   Similarly to Morse Code, AX.25 transforms an ASCII
    character stream (along with auxiliary information
    like sender, receiver, and repeaters) into a stream
    of binary data that is typically fed into a BPSK or
    BFSK modulator.
Combining Modulation Schemes
   Baseband Modulation with RF Modulation




   Examples
     Morse Code => CW => FM (PARADIGM beacon)
     AX.25 => BFSK => FM (PARADIGM 1200 bps data)

     AM => FM (NOAA Automatic Picture Transmission)
Ground Station Hardware
   Radio
   Rotor
   Directional Antennas
   Terminal Node Controller (TNC)
   Personal Computer (PC)
Radio
   Icom IC-910H
    VHF/UHF All Mode
    Transceiver
             for satellite
     Designed
     communication.
   Icom CT-17
     Allows for remote
     control by a computer.
Icom IC-910H Specifications
   Frequency Coverage
      Band       Direction       Range
                    TX       144.0-148.0 MHz
       2m
                    RX       136.0-174.0 MHz
                    TX       420.0-450.0 MHz
      70 cm
                    RX       420.0-480.0 MHz


   Modes
     SSB,    CW, FM, FM-N
Rotor
   Yaesu G5500
     Az/El Rotor
     Controller Box

   Yaesu GS-232B
     Allows  computer
      control of the rotors.
Tracking
   Need to know azimuth, elevation, and Doppler shift
    of a satellite at any given time to be able to
    receive satellite signals.
   Azimuth and elevation are used to point the Yagi
    antennas at the satellite.
   Doppler shift affects the apparent carrier
    frequency when received on Earth, requiring
    continuous adjustment of the radio tuner.
Two Line Elements (TLE)
   Need state vector (position and velocity) of a satellite to compute its
    azimuth, elevation, and doppler shift at a certain Earth location.
   Two Line Elements (TLE) capture the state of a satellite at a given
    epoch and are regularly generated by North American Aerospace
    Defense Command (NORAD) for thousands of space objects.
   Use the Simplified General Perturbations Satellite Orbit Model 4
    (SGP4) to propagate TLEs given at a certain epoch to a different
    time.
   For a spacecraft in a typical Low Earth orbit the accuracy that can
    be obtained with the SGP4 orbit model is in the order of 1 km.
   TLEs older than a few days will likely be less accurate.


       TLE, Time                SGP4                   State
                                                       Vector
Azimuth and Elevation

Definition of Az/El Angles   Polar Plot of GPS Satellite Passes
Doppler Shift
   Satellites travel very fast in space (7 km/s for LEO).
   Earth stations are also moving due to the Earth’s rotation.
   The relative velocity of the satellite to the receiver (range
    rate) is needed to compute the observed frequency.
   When tuning radios, the uplink Doppler shift correction is
    opposite of the downlink Doppler shift.


                       vs , r           
                  f  1 
                                         f0
                                         
                          c             
Antennas
   Directional
     Dish

     Yagi

   Omnidirectional
     Eggbeater

     Monopole    (whip) / Dipole
UHF Antenna Specifications
VHF Antenna Specifications
Terminal Node Controller (TNC)
   Kantronics KPC-9612+
     Serialinterface
     Implements AX.25

     Ports
       Low-Speed  (1200
        baud) with AFSK
       High-Speed (9600
        baud) with FSK
Personal Computer (PC)
   4 Computers
     Marconi,   Lambert
       Mac  OS X 10.4
       Runs MacDoppler software.

     Tesla,   Kepler
       OpenSUSE    11.0
       Runs Antenna or OneStop software.
       Currently connected to Radio, Rotator, and TNC hardware.
Tracking Software
   Mercury
   Global Educational Network for Satellite
    Operations (GENSO)
   OneStop: Network Enhanced Satellite Tracking &
    Optimization Program
   MacDoppler
   Antenna (needs a name!)
Antenna Block Diagram
Server/Client
   Server provides an application programming
    interface (API) over TCP/IP to control the radio,
    rotator, and TNC hardware attached to the
    computer it is running on.
   Server uses VLC to run an MP3 audio server.
   Client is a GUI that uses the Rig and TNC API to
    connect to a Server.
Client
TrackServer
   Uses satellite TLEs to compute the azimuth,
    elevation, and Doppler shift correction needed to
    track a satellite during a pass.
   Connects to Server over TCP/IP for actual tracking.
   Creates an HTML pass schedule for webserver.
   Records live audio stream from Server during pass.
   Provides a TCP/IP interface for satellite database
    management (TrackClient).
TrackClient
TrackDisplay
Ground Station Website
   http://tesla.ae.utexas.edu/
   Features
     LiveAudio Stream
     Pass Schedule

     Recordings Archive

     Automatically Converted NOAA Photos
NOAA 15, 2009-05-02T23:13:27
NOAA 15, 2009-05-03T11:34:56
NOAA 17, 2009-05-04T16:09:15
NOAA 17, 2009-05-05T15:46:08
NOAA 18, 2009-05-03T08:01:53

								
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