What should my signal levels be?

Downstream (Rx) Receive Power Level:
This is the amount of signal received by the modem from the transmitter in the cable company head-end.

For all modems:
-10 dBmV to +10 dBmV "Recommended".
-11 dBmV to -14 dBmv / +11 dBmV to +14 dBmV "Acceptable".
-15 dBmV & +15 dBmV "Maximum".

SNR (signal to noise ratio) levels:
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).

QPSK: 12 dB minimum. 15 dB or higher recommended. (often used in upstream channels)
16 QAM: 18 dB minimum. 21 dB or higher recommended. (often used in upstream channels)
64 QAM: 24 dB minimum. 27 dB or higher recommended. (often used in downstream channels)
256 QAM: 30 dB minimum. 33 dB or higher recommended. (often used in downstream channels)

*There is no upper SNR limit; however, 40 dB is the highest most people see. Going above 40 dB is possible though.

Downstream SNR levels are read at the modem on the downstream data channel and can be viewed using the modem diagnostic screens.

Upstream (Tx) Transmit Power (a.k.a. Return Signal) level:
This is the amount of signal transmitted by the modem to reach the receiver in the cable company head-end.

+8 dBmV to +58 dBmV maximum for QPSK. (DOCSIS 1.0, 1.1)
+8 dBmV to +55 dBmV maximum for 8 QAM and 16 QAM. (DOCSIS 1.0, 1.1)
+8 dBmV to +54 dBmV maximum for 32 QAM and 64 QAM. (A-TDMA DOCSIS 2.0)
+8 dBmV to +53 dBmV maximum for S-CDMA DOCSIS 2.0 (All Modulations)

*Recommended upstream signal levels are +35 dBmV to +52 dBmV.

A cable modem running a higher upstream modulation rate may downgrade itself to a lower modulation rate (i.e. 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. This downgrade can cause slow speed, packet loss, and connection loss issues depending on the condition of the upstream channel.

A 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.

Important notes concerning signal levels:
1. 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.

2. 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. If the modem's signal levels are at the maximum or minimum limits, they may be out of spec. if the temperature changes significantly. Signal levels that vary more then 3 dB in a 24-hour period usually indicate a problem that should be looked into.

3. Excess splits, bad connectors, and/or poor quality cabling will certainly effect cable signal levels and will cause problems.