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?

When 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. This significant drop in the signal level suggests that there are issues in the transmission line, possibly caused by impedance mismatches, connectors, or other physical anomalies resulting in signal reflections. High micro-reflections can create disturbances in signal integrity, potentially leading to data errors and affecting overall modem performance.

In contrast, low signal strength in the cable typically presents as a more consistent attenuation across the bars rather than a sharp drop between specific measurements. Normal operation of the modem would not typically exhibit such a disparity between consecutive tap responses, and if the signal were being heavily amplified, we would expect to see a more uniform strength rather than abrupt drops. Therefore, the noted decrease in signal strength specifically points to issues related to micro-reflections rather than general signal strength or normal functionality.