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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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