User's Manual

6 Fault Localization
Any fault in the system has to go through some logical filtering to try to localize the
problem. This section assumes the installation used to work OK, and that someone
has already gone through this filtering and now suspects the wireless portion of the
system. Thus, for example if it is a user complaint, the user has already restarted
their modem, checked IP addresses, verified authorization database, etc.
6.1 Only one user impacted
If the modem indicates it has poor or no RF input:
1. Check the power inserter.
2. Check the power at the outdoor unit end. Broken cables are common.
3. Visually inspect the cable. Kinks, staples pinching the cable, slashed
insulation, abrasions (from tree branches), etc. can ruin the ability of
coaxial cable to carry the signal.
4. Inspect outdoor connectors and grounding at the building entrance. Water
ingress is common.
5. Visually check the antenna alignment. Wind, tree branches and other
things may have miss-aligned it.
6. Tree growth and seasonal leafing can obstruct the RF signal.
7. Interview the customer about recent activity.
If none of the above fix the problem, and if the modem indicates that the RF signal is
OK, but no service, then the upstream path may have a fault, causing the CMTS at
the head end to not send data. The outdoor unit’s transmitter may have failed.
Connect a spare outdoor unit temporarily and see if the problem clears. The modem
is already authenticated and authorized, so subscriber service should start
automatically. If the fault clears, mount the new unit permanently and send the old
one for repair.
If the link is intermittent, and none of the above items seem to be causing the
problem, then there may be interference coming into the outdoor unit. If a 5 GHz
802.11a WLAN is suspected, it can be detected with either an 802.11a client card on
a PC, or with a spectrum analyzer. To use a spectrum analyzer, place a tap
between the coaxial cable and the cable modem, between the cable modem and the
power inserter. Connect the spectrum analyzer to the tap and observe the 5 GHz
band when the modem is showing problems.
If interference is detected or suspected, rotate the outdoor antenna/transceiver unit 5
and 10 degrees in one direction and then the other. Often one of these positions will
place the interferer in an antenna null while still keeping the main antenna lobe
pointed at the Access Point
ARCXtend manual, August 2003 6-1