Monday, October 05, 2015

Fixing High Upstream Power on a Cable Modem

One cause of random cable modem disconnects is upstream power that is too high. The power levels on most cable modems can be checked by going to and finding the page with the signal levels on it. Signals should be in the following ranges:

Downstream Power (-15dbmV to +15dbmV)
0 is the "optimal" level

Upstream Power (37dbmV to 55dbmV)
Recommended: +35 to +52

Signal/Noise Ratio (SNR , >30dB)
Recommended: =<40 p="">
I was experiencing disconnects and noticed that my upstream power was at 59dbmV. The meant the cable modem was working too hard to communicate upstream. However, the downstream power and SNR were within recommended ranges.

On the end of the cable connecting to my cable modem was an amplifier. Since my downstream and SNR levels were very good, I removed it. This solved the upstream power issue, and upstream power levels moved into the 40s.

When we first had the cable modem, the line outside was not connected properly. The cable tech who came over put on an amplifier. It worked problem free, more or less, for almost three years until an outage. After they fixed that outage the random disconnects began. Evidently whoever fixed the latest outage bumped the signal levels making my amplifier a hindrance rather than a help. It is curious to me; if a cable tech thinks that an amplifier is needed it would be a better choice to fix the line.

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