Troubleshooting guide

BSR Troubleshooting Guide
4-62
This section also describes how to configure the upstream input power level when
problems occur. The upstream input power level is configured in either an
absolute or relative mode. If the upstream input power level is set in relative
mode, the input power level changes when the upstream channel width is changed.
If the upstream input power level is set to the absolute mode, the input power level
does not change when the upstream channel width is changed. Defining the input
power level in absolute mode could possibly cause upstream return lasers to clip
on a completely populated upstream channel. Caution must be used when the input
power level is increased in absolute mode because the CMs on the HFC network
increase their transmit power level by 3 dB for every incremental upstream
channel bandwidth change causing an increase in the total power on the upstream
channel and possibly violating the upstream return laser design parameters.
Table 4-6 describes how the upstream channel bandwidth setting corresponds to
the input power-level range and default power-level range for a specific upstream
channel.
Follow these steps to troubleshoot upstream power-level problems:
1. Check all upstream passive equipment, such as combiners, couplers, and
attenuators and cabling for flaws. The upstream signal may be weak because
of low input power levels on a portion or portions of the upstream spectrum (5
to 42 MHz). This is known as a frequency response problem in the HFC
network. The cause of a frequency response problem may be defective passive
equipment, or damaged cable on the upstream path.
2. Verify that the path between the optical receiver and CMTS matches the
design specification.
Table 4-6 Upstream Input Power Level Range Parameters
Channel Bandwidth Default Range
200 KHz -1 dBmV -16 to +14
dBmV
400 KHz +2 dBmV -13 to +17
dBmV
800 KHz +5 dBmV -10 to +20
dBmV
1.6 MHz +8 dBmV -7 to +23 dBmV
3.2 MHz +11 dBmV -4 to +26 dBmV