INTELLIGENT BRANDS // Cabling
Screened and
Shielded Cabling
- Noise Immunity,
Grounding, and
the Antenna Myth
Taken from a recent
white paper, Siemon
discusses screened
and shielded
cabling and more
specifically, balanced
transmission.
T
he benefit of specifying
balanced twisted-pair cabling
for data transmission is clearly
demonstrated by examining the types
of signals that are present in building
environments. Electrical signals can
propagate in either common mode
or differential (i.e. “balanced”) mode.
Common mode describes a signal
scheme between two conductors where
the voltage propagates in phase and is
referenced to ground.
Examples of common mode transmission
include dc circuits, building power, cable
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INTELLIGENTCIO
TV, HVAC circuits, and security devices.
Electromagnetic noise induced from
disturbers such as motors, transformers,
fluorescent lights, and RF sources, also
propagates in common mode. Virtually
every signal and disturber type in the
building environment propagates
in common mode, with one notable
exception - twisted-pair cabling is
optimised for balanced or differential
mode transmission.
Differential mode transmission
refers to two signals that have equal
magnitudes, but are 180º out of
phase, and that propagate over
two conductors of a twisted-pair. In
a balanced circuit, two signals are