Interference Considerations; Coaxial Cable Quality - Cisco uBR905 Installation Manual

Site Requirements

Interference Considerations

When wires are run for any significant distance in an electromagnetic field, interference can occur
between the field and the signals on the wires. This fact has two implications for the construction of
plant wiring:
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Category 5 data wiring and telco wiring is much more susceptible to EMI than high-grade
Note
well-shielded CATV coaxial cable.
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 unsaddled 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 cable access router 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.
A 5 dB reduction in signal quality for analog downstream video might cause a slight
Note
degradation of picture clarity, which might or might not be noticeable to a subscriber.
A 1 dB reduction in signal quality for digital data might completely disrupt service to a
Cisco uBR905 router user.
Check the cables for general quality level, tears or cuts in the insulation, insulation that is at least
80 percent 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.
The center conductor should extend 1/8 inch (3.2 mm) beyond the end of the conductor.
Note
Cisco recommends that you replace any cable that is in question and begin the installation
Tips
with clean, two-way digital data transmission media. If the cable is of high-quality and
was recently installed, replacing the connectors with high-quality connectors can also
improve performance and eliminate future service calls.
Cisco uBR905 Router Hardware Installation Guide
2-6
Bad wiring practice can result in radio interference emanating from the plant wiring.
Strong EMI, especially when it is caused by lightning or radio transmitters, can destroy the signal
drivers and receivers in the Cisco uBR905 router, and can even create an electrical hazard by
conducting power surges through lines and into equipment. (Review the safety warnings in the
"Electrical" section on page 2-2.)
Chapter 2 Preparing for Installation
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