Page 74 - The Illustrated Dictionary of Electronics

5059F-pB_56-92 4/9/01 4:45 PM Page 59

Bakelite • balanced low-pass filter 59

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