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Preparing for Installation 2-7
Wiring and Cabling
If wires exceed recommended distances, or if wires pass between buildings, give special
consideration to the effect of a lightning strike in your vicinity. The electromagnetic pulse
caused by lightning or other high-energy phenomena can easily couple enough energy into
unshielded conductors to destroy electronic devices. If you have had problems of this sort
in the past, you might want to consult experts in electrical surge suppression and shielding.
Coaxial Cable Quality
CATV coaxial cable quality can vary dramatically at each installation site. Poor insulation,
improperly installed additional outlets, the condition and length of the cable’s center
conductor, and the quality of the cable can negatively affect the connectivity and
performance of the Cisco uBR904 cable modem for digital data transmission. Coaxial cable
tolerances for the transmission of two-way digital data are much lower than the tolerances
for the transmission of downstream-only video. Coaxial cable used to carry two-way digital
data must be of very high quality.
Note A 5 dB reduction in signal quality for analog downstream video might cause a slight
degradation of picture clarity, which might or might not be noticeable to a subscriber.
A small reduction in signal quality for digital data might completely disrupt service to a
Cisco uBR904 cable modem user.
Check the cables for general quality level, tears or cuts in the insulation, insulation that is
at least 80% braid with foil, a broken or bent center conductor at the conductor ends, the
length of the center conductor, and splitters or amplifiers that have been added to extend
video connectivity at the installation site.
Note The center conductor should extend 1/8 in. (3.2 mm) beyond the end of the
conductor.