Consumers - TM822G/CT & TM822R: Cable Signal Levels
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TM822G/CT & TM822R: Cable Signal Levels

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Question
What are the acceptable cable signal levels for the TM822G/CT & TM822R Modem?
Answer
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 Levels

NOTE: If the TM822 is connected to a router, it is recommended to disconnect the router and connect the T822 directly to a computer with an Ethernet cable.

  1. Launch a web browser, such as Internet Explorer, Firefox, or Safari.  Enter http://192.168.100.1 into the address box, and press the Enter key.  The Status page will appear.
     
  2. In the Downstream section, verify Power levels are within the acceptable range of - 15 dBmV to + 15 dBmV for each downstream channel. 

    User-added image

     
  3. In the Downstream section, identify the Modulation and Power to 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.   

    User-added image

     
  4. In the Upstream section, identify the number of Upstream ChannelsChannel Type, and Symbolic Rate to verify thePower levels are within the acceptable range for each upstream channel. 

    Acceptable Upstream Power Levels (dBmV):

    Right click on the image to save it to your computer.

     
    Upstream Transmit Power Level
    ChannelUS Channel TypeSymbol RateAcceptable US Power Levels
    Single
     
     
    TDMA1280 Ksym/sec45 dBmV to 61 dBmV
    ATDMA2560 Ksym/sec45 dBmV to 58 dBmV
    5120 Ksym/sec45 dBmV to 57 dBmV
    TwoTDMA1280 Ksym/sec45 dBmV to 58 dBmV 
    ATDMA2560 Ksym/sec45 dBmV to 55 dBmV
    5120 Ksym/sec45 dBmV to 54 dBmV 
    Three or moreTDMA1280 Ksym/sec45 dBmV to 55 dBmV
    ATDMA2560 Ksym/sec45 dBmV to 52 dBmV
    5120 Ksym/sec45 dBmV to 51 dBmV
  5. 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.  Factory resetting the modem will eliminate any customized settings.

     
  6. 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 BmV30 dB or greater
-6 dBmV to -15 dBmV33 dB or greater
Upstream Transmit Power Level
ChannelUS Channel TypeSymbol RateAcceptable Upstream Power Levels
Single (1)TDMA1280 Ksym/sec45 dBmV to 61 dBmV
ATDMA2560 Ksym/sec45 dBmV to 58 dBmV
5120 Ksym/sec45 dBmV to 57 dBmV
Two (2)TDMA1280 Ksym/sec45 dBmV to 58 dBmV
ATDMA2560 Ksym/sec45 dBmV to 55 dBmV
5120 Ksym/sec45 dBmV to 54 dBmV
Three or more (>=3)TDMA1280 Ksym/sec45 dBmV to 55 dBmV
ATDMA2560 Ksym/sec45 dBmV to 52 dBmV
5120 Ksym/sec45 dBmV to 51 dBmV

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