18WuD2x

iased search • bifilar electrometer 71
P
N
Reverse
bias
biased diodes
P
N
Forward
bias
λ/4
Feed
biased search A scheme that a mobile robot can
use to find its way to a destination or target, by
deliberately searching off to the side and then
homing in as the approach progresses. It is so
called because the general nature of the initial error
(bias) is known, although its exact extent need
not be known.
bias oscillator In a magnetic recorder, an oscillator
operated at a frequency in the 40-kHz to 100-
kHz range to erase prerecorded material and bias
the system magnetically for linear recording.
bias resistor A usually fixed resistor, such as the
source resistor in a field-effect-transistor (FET) circuit
or the emitter resistor in a bipolar-transistor
circuit, across which a desired bias voltage is developed
by current flowing through the resistor.
bias set A control, such as a potentiometer or variable
autotransformer, that facilitates manual adjustment
of the dc bias of a circuit.
bias stabilization 1. The maintenance of a constant
bias voltage, despite variations in load
impedance or line voltage. It is usually accomplished
by means of automatic voltage regulation.
2. The stabilization of transistor dc bias voltage
by means of resistance networks or through the
use of barretters, diodes, or thermistors.
bias supply 1. Batteries that provide bias voltage
or current for bipolar or field-effect transistors. 2.
A line-operated unit for supplying dc bias and
consisting of a transformer, rectifier, and highgrade
filter.
bias voltage A steady voltage that presets the operating
threshold or operating point of a circuit or
device, such as a transistor. Compare BIAS CUR-
RENT.
bias windings The dc control windings of a saturable
reactor or magnetic amplifier.
biconical antenna A form of broadband antenna,
consisting of two conical sections joined at the
apexes. The cones are at least 1 ⁄4 wavelength in diagonal
height. The vertex angles of the cones can
vary, although the apex angle is usually the same
in each cone. The vertex angle affects the feedpoint
impedance. Such an antenna radiates, and
responds optimally to, signals with polarization
parallel to the axis of the cones.
biconical horn antenna A double-horn microwave
antenna that radiates along relatively sharp
front and back beams.
λ/4
biconical antenna
bidecal base The 20-pin base of a cathode-ray
tube. Also see DIHEPTAL, DUODECAL, and
MAGNAL.
bidirectional Radiating or receiving (usually
equally) from opposite directions (e.g., front-andback
radiation from an antenna or loudspeaker,
or front-and-back pickup with an antenna or microphone).
bidirectional antenna An antenna with a directional
pattern that consists of maximum lobes
180 degrees apart.
bidirectional bus In computers, a data path over
which both input and output signals are routed.
bidirectional bus driver In a microcomputer, a
signal-driving device that permits direct connection
of a buffer-to-buffer arrangement on one end
(the interface to I/O, memories, etc.) and data inputs
and outputs on the other. This device permits
bidirectional signals to pass and provides
drive capability in both directions.
bidirectional counter A counter that can count
consecutively up from a given number or down
from that number. Also called UP-DOWN
COUNTER.
bidirectional current A current that flows in both
directions. Utility alternating current (ac) is a
common example.
bidirectional loudspeaker A loudspeaker that delivers
sound waves to the front and rear.
bidirectional microphone A microphone that
picks up sound waves equally well from the front
and rear.
bidirectional transistor A symmetrical transistor
(i.e., one in which the two main current-carrying
electrodes can be interchanged without influencing
device performance). Some field-effect transistors
(FETs) are of this type; the drain and the
source can be interchanged.
bifilar electrometer An electrometer in which the
sensitive element consists of two long platinizedquartz
fibers. When an electric potential is ap-