SB6120: Cable Signal Levels

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. 
 

To verify these signal levels:

1. Launch a web browser, such as Internet Explorer, Firefox, or Safari.  Enter http://192.168.100.1 into the address box.  The Cable Modem Status page appears.
   
    
   
    
2. Click the Signal link on top of the page.  The Signal page appears.
3. On the Signal page:
   a.  For the Downstream bonded channels:
        i. Verify the amount of Channels in use.    
       ii. Verify the Signal to Noise Ratio for each channel.
       iii. Verify the Downstream Modulation for each channel.
       iv. Verify the Power Level for each channel.
     
   b.  For the Upstream bonded channels, verify the Power Level.
   
   NOTE: In the example below:
   • 3 channels are in use.
   • Signal to Noise Ratio is 37 dB for each channel.
   • Downstream Modulation is QAM256 for each channel.
   • Downstream Power Level (DPL) is 4 dBmv for the 1st and 3rd channel, and 3dBmv for the 2nd channel. 
   • Upstream Power Level (UPL) is 48 dBmv.
     
     
     
      
       

These levels apply to all Motorola cable modems and cable modem/gateways.  These values are absolutes.  If the cable modem is experiencing levels that approach the minimum or maximum acceptable levels, then it is a warning sign that there is a possible cable plant issue.  If the cable connection at the modem is OK, then it is advised to contact the cable operator to address the issue.

Acceptable Signal Levels (per channel)

Downstream Power Level (DPL):	+15 to -15dBmV
Downstream Signal to Noise Ratio (SNR):	23.5 dB or greater (if 64 QAM)
	30 dB or greater (if 256 QAM and DPL = -5 to +15 dB)
	33 dB or greater (if 256 QAM and DPL = -6 to -15 dB)
Upstream Transmit Power Level:	57dBmV or less (1 downstream channel)
	54dBmV or less (2 downstream channels)
	51dBmV or less (3 or more downstream channels)