18WuD2x

half-bridge • half-wavelength 327
X
Input
Y
ac
Input
half-adder
Carry output
half-bridge
Sum output
half-bridge A bridge rectifier that has diodes in two
arms and resistors in the other two.
half-cell A voltaic cell consisting of a single electrode
immersed in an electrolyte and having a
definite difference of potential; it is, in effect, half
of a primary cell. Also see HELMHOLTZ DOUBLE
LAYER.
half-cycle Half of a complete alternation (i.e., 180
degrees of phase).
half-cycle magnetizer A magnetizer using halfcycles
of rectified alternating current as the magnetic-field
source.
half-duplex channel A communications channel
in a HALF-DUPLEX SYSTEM.
half-duplex system In data communications, a
system that transmits data in both directions,
but not simultaneously. Compare FULL-DUPLEX
SYSTEM.
half-lattice crystal filter A band-pass crystalfilter
circuit using two piezoelectric crystals
in a four-arm bridge. Also see CRYSTAL RES-
ONATOR.
half-nut In a facsimile receiver, a device that
guides the lead screw.
half-power point In a response curve or directional
pattern, such as for a selective filter or a
unidirectional antenna, the points on each side of
maximum at which the power is 3 dB below the
peak value.
+
dc
Output
−
half-power width In a directional antenna system,
an expression of beamwidth. It is usually listed as
the horizontal-plane angle, in degrees, between
the half-power points in the main lobe of the directive
pattern.
half-step 1. In audio engineering, the frequency
interval between two sounds, whose ratio is
1.06:1. 2. The difference in pitch between the
notes produced by two adjacent keys on a
piano.
half tap A bridging circuit or device that can shunt
another circuit with the least electrical disturbance.
half-track recorder A magnetic tape recorder that
applies signals to both halves of a tape with a
head that covers only half the tape’s width in
each of two directions. Also called dual-track
recorder.
half-track tape Magnetic tape recorded by a
HALF-TRACK RECORDER.
half-wave Half of a complete wave (i.e., a complete
rise and fall in one direction). Its graphic representation
is similar in appearance to that for a
half-cycle.
half-wave antenna An antenna whose radiator
measures an electrical half wavelength from end
to end. Such a radiator is about 5 percent less
than a free-space half-wavelength long, because
of capacitive effects and the velocity factor of the
conductor.
half-wave chopper A chopper that closes a circuit
during only half the switching signal cycle.
half-wave dipole A center-fed antenna whose radiator
measures 0.5 electrical wavelength from end
to end. Also see DIPOLE ANTENNA.
half-wave doubler See HALF-WAVE VOLTAGE
DOUBLER.
half-wave feeder See HALF-WAVE TRANSMIS-
SION LINE.
half-wavelength Symbol λ/2. The distance that
corresponds to 180 degrees of phase as an electromagnetic
(EM) field is propagated in free
space, it is related to the frequency by a simple
equation:
L ft = 492/f
where L ft represents λ/2 in feet, and f represents
the frequency in megahertz. If λ/2 is expressed in
meters, then the formula is:
L m = 150/f
where L m represents the displacement in meters.
In general, if ν is the velocity factor (expressed as
a ratio) in a given medium, then:
L ft = 492ν/f
and
L m = 150ν/f
Compare FULL WAVELENGTH, QUARTER
WAVELENGTH.