What does it indicate if the ninth bar in a cable modem's PreEqualization Tap response is less than 10 dB below the eighth bar?

If the ninth bar in a cable modem's PreEqualization Tap response is less than 10 dB below the eighth bar, it indicates the presence of high micro-reflections near the modem. In the context of cable modems, the PreEqualization Tap response measures the variation in signal levels at different frequencies to help diagnose issues such as reflections and noise in the cable plant.

Micro-reflections can be caused by various issues, such as poor connections, splitters, or impedance mismatches. When the response shows a minimal drop (less than 10 dB) between these bars, it suggests that the signal integrity is compromised due to reflections occurring close to the modem. This can lead to performance issues, such as reduced data rates and increased errors. Understanding this helps technicians target specific locations for troubleshooting and repairs in the network.