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Bakelite • balanced low-pass filter 59
Bakelite The trade name for a specialized plastic
dielectric material. Its chemical composition is
phenol-formaldehyde resin.
baker An obsolete phonetic alphabet code word for
letter B. BRAVO is commonly used instead.
baking-out In the process of evacuating a system,
the procedure of heating the system to a high
temperature to drive out gases occluded in the
glass and metal parts.
balance
1. See BRIDGE. 2. To null a bridge or similar
circuit. 3. To equalize loads, voltages, or signals
between two circuits or components. 4. In a
high-fidelity stereo sound system, a control or set
of controls that adjusts the relative loudness of
the left and right channels. 5. Alignment of a balanced
modulator for minimum carrier output amplitude.
6. A condition in which two branches of a
circuit have identical impedances, relative to
ground.
balance coil 1. A type of autotransformer that enables
a three-wire ac circuit to be supplied from a
two-wire line. A series of taps around the center of
the winding enables the circuit to be compensated
for unequal loads. 2. See BALANCING COIL.
balance control A variable component, such as a
potentiometer or variable capacitor, that is used
to balance bridges, null circuits, or loudspeakers.
balanced Having identical impedances, with respect
to ground.
balanced amplifier Any amplifier with two
branches that have identical impedances, with
respect to ground. Usually, the two branches are
in phase opposition (180 degrees out of phase).
balanced antenna An antenna system where two
halves are exact replicas of each other, geometrically
and electrically. Such an antenna normally
must either be fed with a balanced transmission
line or with a coaxial cable and balun.
balanced antenna system A balanced antenna, fed
with a balanced transmission line, that has currents
of equal magnitude in each side. An example
90°
Xmtr
Center-fed
horizontal
radiator
balanced antenna system
Two-wire
feed line
is a half-wave dipole at uniform height above electrical
ground, fed at the center with parallel-wire
line. It is important that the transmission line
runs away from the antenna at a right angle for at
least 1 ⁄4 wavelength, preferably 1 ⁄2 wavelength or
more, to prevent line imbalance caused by currents
induced from the radiated field.
balanced bridge Any four-leg bridge circuit in
which all legs are identical in all electrical respects.
balanced circuit 1. A circuit that has its electrical
midpoint grounded, as opposed to the singleended
circuit, which has one side grounded. 2. A
bridge circuit in the condition of null.
balanced converter See BALUN.
balanced currents Currents with the same value.
In the two conductors of a balanced transmission
line, these currents are equal in amplitude
and opposite in phase at every point along the
line.
balanced delta A set of coils or generators in a
three-phase system, connected so that the currents
in any two coils differ in phase by 120 degrees.
balanced detector A symmetrical demodulator,
such as a full-wave diode detector or a discriminator.
balanced electronic voltmeter An electronic voltmeter
circuit in which two matched transistors
are connected in a four-arm bridge arrangement.
The drift in one half of the circuit opposes that in
the other half; the resulting drift of the zero point
is virtually eliminated.
balanced filter A filter consisting of two identical
sections, one in each branch of a balanced system,
such as a parallel-wire transmission line.
balanced input An input circuit whose electrical
midpoint is grounded. Compare SINGLE-ENDED
INPUT.
balanced input transformer An input transformer
in which the center tap of the primary winding is
grounded.
balanced line A pair of parallel wires that possesses
a uniform characteristic impedance. The
two conductors are of the same material and have
identical diameters. The distance between them
is constant. In a balanced two-wire line, the currents
in the two conductors are of equal amplitude
and opposite phase.
balanced lines In high-fidelity audio systems, a
cable that consists of two parallel conductors
surrounded by a single braid. The parallel wires
carry the audio-frequency (AF) signals, and the
braid is grounded for shielding.
balanced loop antenna A loop antenna with a
grounded electrical midpoint, determined by the
junction of two identical series-connected capacitors
shunting the loop.
balanced low-pass filter A low-pass filter used in
a balanced system or balanced transmission
line.