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Q:What is meant by the term "Electrically Balanced"?
A:A simple open wire circuit consisting of two wires is considered to
be a uniform, balanced transmission line. A uniform transmission line
is one which has substantially identical electrical properties throughout
its length, while a balanced transmission line is one whose two conductors
are electrically alike and symmetrical with respect to ground and other
nearby conductors.* "Electrically balanced" relates to the physical
geometry and the dielectric properties of a twisted pair of conductors.
If two insulated conductors are physically identical to one another in
diameter, concentricity, dielectric material and are uniformly twisted
with equal length of conductor, then the pair is electrically balanced
with respect to its surroundings. The degree of electrical balance depends
on the design and manufacturing process. Category 6 cable requires a greater
degree of precision in the manufacturing process. Likewise, a category
6 connector requires a more balanced circuit design. For balanced transmission,
an equal voltage of opposite polarity is applied on each conductor of
a pair. The electromagnetic fields created by one conductor cancel out
the electromagnetic fields created by its "balanced" companion
conductor, leading to very little radiation from the balanced twisted
pair transmission line. The same concept applies to external noise that
is induced on each conductor of a twisted pair. A noise signal from an
external source, such as radiation from a radio transmitter antenna generates
an equal voltage of the same polarity, or "common mode voltage,"
on each conductor of a pair. The difference in voltage between conductors
of a pair from this radiated signal, the "differential voltage"
is effectively zero. Since the desired signal on the pair is the differential
signal, the interference does not affect balanced transmission. The degree
of electrical balance is determined by measuring the "differential
voltage" and comparing it to the "common mode voltage"
expressed in decibels (dB). This measurement is called Longitudinal Conversion
Loss "LCL" in the Category 6 standard. * The ABC's of the telephone
Vol.7
Category 6 Cable Questions
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