Consumers - SB8200: Cable Signal Levels

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SB8200: Cable Signal Levels

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What are the acceptable cable signal levels for the SB8200?
Cable signal levels for all DOCSIS cable modems require to be within the acceptable level for the modem operate properly.  The three signal levels that need to be within the acceptable level are Downstream Power, SNR (Signal to Noise Ratio), and Upstream Power.  Downstream Power refers to the line signal sent from the cable provider to cable modem.  Downstream SNR (Signal to Noise Ratio) refers to the signal being sent in relation to the noise on the line.  Upstream Power refers to the line signal from the cable modem to transmit data back to the cable provider.  This document describes how to check the three signal levels to be within the acceptable level for the modem operate properly. 

Checking Signal Level​

: If the SB8200 is connected to a router, it is recommended to disconnect the router and connect the SB8200 directly to a computer with an Ethernet cable.
  1. Launch a web browser, such as Internet Explorer, Firefox, or Safari.  Enter into the address box and press the Enter key.  The Login page will appear.

    NOTE 1: 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 2: The admin login is not available on firmware version prior to and the Connection page will appear. 
  2. On the Login page, enter admin in the Username field.
  3. Enter password or the last 8 digit of the serial number located on the bottom white sticker in the Password field.

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  4. Click the Login button.  The Connection page will appear. 

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  5. In the Downstream Bonded Channels section, verify Power levels are within the acceptable range of - 15 dBmV to + 15 dBmV for each downstream channel. 

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  6. In the Downstream Bonded Channels section, identify the Modulation and Power to find verify SNR levels are within the acceptable range for each downstream channel. 

    Acceptable SNR Levels (dB)
    If QAM64SNR should be 23.5 dB or greater. 
    If QAM256 and DPL( -6 dBmV to +15 dBmV) SNR should be 30 dB or greater. 
    If QAM256 and DPL(-15 dBmV to -6 dBmV) SNR should be 33 dB or greater.   

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  7. In the Upstream Bonded Channels section, identify the number of Channels and Type to find verify Upstream Power levels are within the acceptable range for each upstream channel. 

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    Acceptable Upstream Power Levels (dBmV)

    Upstream Transmit Power Level
    ChannelUS Channel TypeAcceptable Upstream Power Levels
    SingleSC-QAM45 dBmV to 61 dBmV
    TwoSC-QAM45 dBmV to 54 dBmV
    Three or moreSC-QAM45 dBmV to 51 dBmV
  8. Refresh the page at least twice to identify variations in SNR, Downstream Power, and Upstream Power.   

    NOTE: If the either of the signal levels are outside of the acceptable range, power cycle or factory reset the modem. 

  9. 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
64 QAMn/a23.5 dB or greater
256 QAM-6 dBmV to +15 dBmV30 dB or greater
-15 dBmV to -6 dBmV33 dB or greater
Upstream Transmit Power Level
ChannelUS Channel TypeAcceptable Upstream Power Levels
Single (1)SC-QAM45 dBmV to 61 dBmV
Two (2)SC-QAM45 dBmV to 54 dBmV
Three or more (>=3)SC-QAM45 dBmV to 51 dBmV



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