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HiSeasNet Modems. Spectrum analyzers. aka “SpecAn” Measure energy in a given frequency bands Axes are frequency (x-axis) and RF energy (y-axis) Controls are Frequency (where the center of the plot is) Span (how wide the plot is) Amplitude (how tall the carriers are)

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hiseasnet modems

HiSeasNet Modems

SIO Aug \'09

spectrum analyzers
Spectrum analyzers
  • aka “SpecAn”
  • Measure energy in a given frequency bands
    • Axes are frequency (x-axis) and RF energy (y-axis)
  • Controls are
    • Frequency (where the center of the plot is)
    • Span (how wide the plot is)
    • Amplitude (how tall the carriers are)
  • Shows what is happening in space. Sensitive to antenna size and footprint position!

SIO Aug \'09

spectrum analyzer use
Spectrum analyzer use
  • Troubleshooting and system monitoring
  • They tell you:
    • How good a signal is
      • On/off the air
      • Quality/Level (shoulders? short? relative to other ships)
    • What your antenna is seeing
      • What kind of carriers
      • Which carriers
      • What satellite
  • All ships should have one to help see what is going on with your antenna

SIO Aug \'09

modem concepts
Modem concepts
  • MODulation and DEModulation
    • Translate data packets of 0s and 1s into RF waveform wiggles
    • And back again on the other end (need pairs of modems to be useful)
  • 2 carriers involved…uplink and downlink
  • Parameters are:
    • Frequency (Tx and Rx)
    • Data rate (Tx and Rx)
    • Forward Error Correction (FEC, Tx and Rx)
    • Power level and Tx mode (On/Off/RTI)
    • Spectral Inversion
    • Test Modes (Loopback, CW, etc.)

SIO Aug \'09

modem monitoring
Modem monitoring
  • EbNo: Energy per bit over noise…”signal quality”
  • Rx parameters (Bit Error Rate)
  • Panel lights (Fault, Rx lock, Tx on/off, Online, Stored Events)
  • Error log and stored events
  • Serial port interface (EIA-530 is RS-422 in DB-25 package)
  • Web/SNMP in newer modems

SIO Aug \'09

l band additions
L-band additions
  • Block Uplink Converter
    • Power DC
    • 10 MHz reference oscillator
    • FSK comms
    • Address
  • Low Noise Block downcoverter
    • Power
    • 10 MHz reference oscillator or PLL (Phase Lock Loop)
    • Local Oscillator frequency

SIO Aug \'09

features we don t use
Features we don’t use
  • Automatic Uplink Power Control (AUPC)
    • Auto power level adjust based on the quality of the signal we receive
    • Used to compensate for rain fade
    • We cannot use it since we move around…power level change based on location is part of our bandwidth contract.
  • Alarm masks
    • Opens and closes pins on the 15-pin alram interface on the back panel.
    • Really…would you monitor your alarm port?

SIO Aug \'09

spectrum
Spectrum
  • Power Equivalent Bandwidth (PEB)
    • Its how we pay for space segment bandwidth
    • Power allotted in dBw per MHz
    • So its like this:
      • Each satellite has so much power in its amplifier to use to repeat signals (~20 W)
      • Each satellite has so many transponders that operate on a fixed chunk of spectrum (generally 36 MHz)
      • Divide each MHz on satellite by total power, and you get how much power it can use per MHz.
      • We buy 1-2 MHz, therefore have a limit to the power we can use.
      • If we need more power for smaller dish, we buy more bandwidth that we will not occupy

SIO Aug \'09

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