Consumers - SBG8300: Cable Signal Levels

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SBG8300: Cable Signal Levels

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What are the acceptable cable signal levels for the SBG8300 Gateway?
Cable signal levels for all DOCSIS cable modems need to be at acceptable levels for the modem operate properly.  The three signal levels that need to be within the acceptable level are Downstream Power Level, SNR (Signal to Noise Ratio), and Upstream Power Level
  • Downstream Power Level: cable signal sent from the cable provider to cable modem.  
  • Downstream SNR (Signal to Noise Ratio): cable signal being sent in relation to the noise on the line.  
  • Upstream Power Level: cable signal from the cable modem to transmit data back to the cable provider.
This document describes how to check the three signal levels to determine if they are within the acceptable level for the modem operate properly. 

Checking Signal Levels

  1. Launch a web browser, such as Internet Explorer, Firefox, or Safari.  Enter into the address box, and press the Enter key.  The https:// Redirect page will appear.   
  2. The SURFboard Web Manager is begin redirected to a more secure connection, click the Proceed button to continue.  The Gateway > Login page will appear.

    User-added image
  3. A security or private risk alert may appear on the web browser advising users to proceed with caution when accessing the Web Manager.  There is no risk in proceeding to the Web Manager.  For instructions to by-pass the alert screen, refer to article # 18181 - Alert Message for Web Manager Access.

    NOTE: The Home Network Wizard will appear if this is the first time accessing the Web Manager.  For assistance with the wizard, refer to article # 17969 - SBG8300: Web Manager First Time Login.
  4. Enter admin in the Username field and enter the custom password in the Password field.

    NOTE: If the Login page prompts for email address and password.  Log into the Web Manager with the email and password used when setting up the SURFboard Manager app with the SBG8300.
  5. Click the Login button.  The Gateway > Summary page will appear.

    User-added image

  6. On the left hand-menu, click the Connection link then click the WAN link on the sub-menu.  The Gateway > Connection > WAN page will appear.

    User-added image

  7. In the Downstream QAM section, verify Power Levels are within the acceptable range of - 15 dBmV to + 15 dBmV for each downstream channel.  Scroll to the right to capture all the downstream channels. 

    User-added image

  8. In the Downstream QAM section, identify the Modulation and Power Level to verify SNR levels are within the acceptable range for each downstream channel.  Scroll to the right to capture all the downstream channels. 
    Downstream Signal To Noise Ratio (SNR)
    ModulationDownstream PowerAcceptable Downstream SNR 
    QAM64-15 dBmV to +15 dBmV+23.5 dB or greater
    QAM256-6 dBmV to +15 dBmV +30 dB or greater
    -15 dBmV to -6 dBmV +33 dB or greater

    User-added image
  9. In the Upstream QAM section, identify the number of Index and Symbolic Rate to verify the Power levels are within the acceptable range for each upstream channel.  Scroll to the right to capture all the Upstream channels. 
    Upstream Transmit Power Level
    IndexSymbol Rate Acceptable Upstream Power Levels
    1280 Ksym/sec45 dBmV to 61 dBmV
    2560 Ksym/sec45 dBmV to 58 dBmV 
    5120 Ksym/sec45 dBmV to 57 dBmV 
    Two1280 Ksym/sec45 dBmV to 58 dBmV
    2560 Ksym/sec45 dBmV to 55 dBmV 
    5120 Ksym/sec45 dBmV to 54 dBmV
    Three or more1280 Ksym/sec45 dBmV to 55 dBmV
    2560 Ksym/sec45 dBmV to 52 dBmV
    5120 Ksym/sec45 dBmV to 51 dBmV 
    Right click on the image to save it to your computer.
  10. Refresh the page at least twice to identify variations in SNR, Downstream Power Level, and Upstream Power Level.   

    NOTE: If either of the signal levels are outside of the acceptable range, power cycle or factory reset the modem.  Factory resetting the modem will erase any customized settings.

  11. Contact the cable provider to adjust the signal level to the acceptable level range.

    Acceptable Signal Levels

    Acceptable Downstream Power Level
    -15 dBmV to + 15 dBmV
    Downstream Signal to Noise Ratio (SNR)
    ModulationDownstream PowerAcceptable Downstream SNR
    QAM64n/a+23.5 dB or greater
    QAM256-6 dBmV to +15 dBmV+30 dB or greater
    -15 dBmV to -6 dBmV+33 dB or greater
    Upstream Transmit Power Level
    IndexSymbol RateAcceptable Upstream Power Levels 
    Single (1)1280 Kysm/sec45 dBmV to 61 dBmV
    2560 Kysm/sec45 dBmV to 58 dBmV
    5120 Kysm/sec45 dBmV to 57 dBmV
    Two (2)1280 Kysm/sec45 dBmV to 58 dBmV
    2560 Kysm/sec45 dBmV to 55 dBmV
    5120 Kysm/sec45 dBmV to 54 dBmV
    Three or more (>=3)1280 Kysm/sec45 dBmV to 55 dBmV
    2560 Kysm/sec45 dBmV to 52 dBmV
    5120Kysm/sec45 dBmV to 51 dBmV



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