Troubleshooting guide

BSR Troubleshooting Guide
4-66
1. Check all downstream passive equipment (such as combiners, couplers, and
attenuators) and cabling for flaws. The downstream signal may be weak
because of a low power level on a portion of the downstream spectrum
(88-860 MHz). This is known as a frequency response problem on the HFC
network. The cause of a frequency response problem may be defective passive
equipment, or damaged cable on the downstream path.
2. If the downstream physical cabling and passive equipment is in good
condition and the problem persists, check the downstream input power-level
configuration.
To set the downstream power level to a value from 45 to 65 decibels per
millivolt (dBmV), use the cable downstream power-level command, as
shown below:
RDN(config-if)#cable downstream <n> power-level {450-650}
where:
n is the number of the downstream cable port.
450-650 is the downstream power level
To return to the 55 dBmV default power-level setting, use the no cable
downstream power-level command in Interface Configuration mode, as
shown below:
RDN(config-if)#no cable downstream <n> power-level {450-650}
where n is the number of the downstream cable port.
3. Check for laser clipping on fiber-optic transmitters on the downstream path
from the cable headend to the CMs. If the downstream power level is set too
high for the downstream path, laser clipping can occur. Laser clipping
prevents the transmission of light, which can cause high bit error rates on the
downstream path.
Note: The downstream power level must be expressed in increments of
ten.