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Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

B coefficient
See loss coefficient
B-ISDN
broadband integrated services digital network.

back EMF
See counter-EMF
backfeed
in power distribution work, power which flows from the secondary lines into the primary lines through the distribution transformer, e.g.,from an emergency generator connected to customer load.
backflash
an arc which forms along a tower during a lightning strike due to high tower or footing impedance.

background noise
the noise that typically affects a system but is produced independent of the system. This noise is typically due to thermal effects in materials, interpreted as the random motion of electrons, and the intensity depends on the temperature of the material. In radio channels, background noise is typically due to radiation that is inherent to the
universe and due mainly to radiation from astronomical bodies. There is a fundamental lower bound on the intensity of such noise which is solely dependent on the universe and independent of antenna and receiver design.

See thermal noise
balanced line
symmetric multiconductor transmission line in which the voltage on each conductor along the transmission line
has the same magnitude, but the phases are such that the voltage would sum to zero. In a two conductor transmission line, the voltages would be equal and 180 degrees out of phase. This is the equivalent of a virtual ground plane or zero E-field plane at the geometric center plane of the transmission line cross section, or balanced with respect to virtual ground. Balanced wiring configurations are often used to prevent noise problems such as ground loops. Contrast with unbalanced line.
balanced load
a load on a multi-phase power line in which each line conductor sees the same impedance.

ballast
a starting and control mechanism for fluorescent and other types of gas-discharge lamps. Initially a ballast supplies the necessary starting (or striking) voltage in order to ionize the gas to establish an arc between the two filaments in the lamp. Once the gas is ionized, the ballast controls the input power and thus the light output to maximize the efficiency and life of the lamp.

balun
a network for the transformation from an unbalanced transmission line, system or device to a balanced line, system or
device. Baluns are also used for impedance transformation. Derived from "balanced to unbalanced".
In antenna systems, baluns are used to connect dipole-type antennas to coaxial cable, to balance the current on dipole armatures, and to prevent currents from exciting the external surface of the coaxial shield.
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