![]() Signal levels that vary more then 3 dB in a 24-hour period usually indicate a problem that should be looked into.ģ. if the temperature changes significantly. If the modem's signal levels are at the maximum or minimum limits, they may be out of spec. It's recommended to have the modem's signal levels at least 3dB away from the maximum/minimum levels listed above due to normal temperature related signal variation. Signal levels not within the specifications listed above can cause slow speeds, connection problems, and connection loss due to packet errors, packet loss, and/or constant packet retransmission.Ģ. Important notes concerning signal levels:ġ. ![]() This downgrade can cause slow speed, packet loss, and connection loss issues depending on the condition of the upstream channel.Ī house or drop amplifier will NOT fix an upstream signal problem because most house amplifiers don't amplify the upstream signals they only pass the upstream signal through with some loss. 64 QAM to 16 QAM or 16 QAM to QPSK) if the upstream transmit level is higher than the maximum signal level allowed for the higher modulation rate and the CMTS is configured to allow such a change. *Recommended upstream signal levels are +35 dBmV to +49 dBmV.Ī cable modem running a higher upstream modulation rate may downgrade itself to a lower modulation rate (i.e. +8 dBmV to +52 dBmV maximum for A-TDMA & TDMA (DOCSIS 3.0) +8 dBmV to +53 dBmV maximum for S-CDMA DOCSIS 2.0 (All Modulations) ![]() +8 dBmV to +54 dBmV maximum for 32 QAM and 64 QAM. +8 dBmV to +55 dBmV maximum for 8 QAM and 16 QAM. This is the amount of signal transmitted by the modem to reach the receiver in the cable company head-end. Also, the upstream SNR level provided by most CMTSs is not specific to any single modem, but is an averaged, aggregate level from all modems on that upstream channel on the upstream port. Only the provider can read the upstream SNR level, directly from the CMTS. The end-user cannot get the upstream SNR directly. Upstream SNR levels are read at the CMTS on the upstream data channel, not the modem or the modem diagnostic screens. Going above 40 dB is possible though.ĭownstream SNR levels are read at the modem on the downstream data channel and can be viewed using the modem diagnostic screens. *There is no upper SNR limit however, 40 dB is the highest most people see. (often used in downstream channels)Ģ56 QAM: 30 dB minimum. (often used in upstream channels)Ħ4 QAM: 24 dB minimum. (often used in upstream channels)ġ6 QAM: 18 dB minimum. Not all QAM demodulator chipsets accurately calculate SNR levels that approximate actual MER levels, so these levels may vary depending on which chipset and/or firmware is used in the equipment. The SNR levels listed here are based on commonly recommended MER levels for digital cable signals. This is how clear the signal is at either the modem receiver (downstream SNR) or the receiver in the cable company head-end (upstream SNR).ĭOCSIS specifications list minimum CNR (carrier to noise ratio) levels not SNR levels. Lower than -15 dBmV & Higher than +15 dBmV - "Out Of Spec." 11 dBmV to -15 dBmV / +11 dBmV to +15 dBmV - "Maximum" 8 dBmV to -10 dBmV / +8 dBmV to +10 dBmV - "Acceptable" This is the amount of signal received by the modem from the transmitter in the cable company head-end.
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