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HiSeasNet Modems

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

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  1. HiSeasNet Modems SIO Aug '09

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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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