18WuD2x

Hall generator • handoff 329
Hall generator A semiconductor device exhibiting
the HALL EFFECT. It is a thin wafer or film of indium
antimonide or indium arsenide with leads
on opposite edges.
M
Hall current
Magnetic field
perpendicular
to ohmic
contact
Ohmic
contact
Control current
Hall generator
Hall-effect
element
Control
electrode
Hall mobility For a conductor or semiconductor,
the product of conductivity and the HALL CON-
STANT.
Hall network A resistance-capacitance null circuit
whose general configuration is two cascaded
high-pass tee-sections bridged by a high resistance.
The circuit can be tuned with one potentiometer.
Input
R1
C1 C2 C3
R2
R3
Hall network
Output
Hallwacks effect The phenomenon (observed by
Hallwacks in 1888) in which ultraviolet light
falling on a polished zinc plate causes a negatively
charged electroscope to which it is connected
to discharge.
hallucination In complex computers and artificially
intelligent systems, the generation or appearance
of data for no apparent reason.
halo See AFTERGLOW and PERSISTENCE.
halo antenna A horizontally polarized antenna,
consisting of a circular half-wave dipole whose
ends are capacitance loaded. Commonly used at
very high frequencies (VHF).
halogen Abbreviation, hal. A group of five very active
nonmetallic elements whose similar chemical
properties put them in group VIIA of the periodic
table; they are astatine, bromine, chlorine, fluorine,
and iodine.
Halowax A chlorinated naphthalene wax used as
an impregnant for paper capacitors. Dielectric
constant, 3.4 to 5.5. Resistivity, 10 13 to 10 14 ohmcm.
halt A stop during the execution of a computer
program run, often resulting from a HALT IN-
STRUCTION.
halt instruction An instruction in a computer program
that causes a break in the program’s execution,
as by BASIC’s STOP command, for example.
ham Colloquialism for AMATEUR RADIO operator.
ham radio See AMATEUR RADIO.
Hamilton’s principle Also called the principle of
least action. Motion tends to occur in such a
way that the integral of the product of kinetic energy
and elapsed time is minimal.
hammer 1. The striking member in a WHEEL
PRINTER. 2. The clapper in an electric bell or
gong.
hammer-and-wheel See WHEEL PRINTER.
Hamming code An error-correction code used in
some digital communications circuits.
hand capacitance Also called body capacitance.
Capacitive coupling effects between a circuit and
the human body (e.g., as evidenced between an
operator’s hand and a device having extremely
high impedance and poor grounding and/or
shielding).
hand generator An electric generator operated by
turning a hand crank.
handheld computer Also called personal digital
assistant (PDA) or palmtop computer. The names
PalmPilot and Palm are proprietary (Palm Computing,
Inc.) and refer to specific families of handheld
computers, although they might someday
become generic and refer to handheld computers
in general. A battery-powered portable computer,
smaller than a notebook computer, and used
for simple tasks such as note-taking and
record keeping. Some units incorporate wireless
modems for connection to the Internet. Others include
paging, wireless fax, videoconferencing capability,
remote-control capability, and other
features. Many units can recognize a specialized
form of handwriting so users can enter data with
a penlike device called a stylus.
Handie-Talkie Abbreviation, HT. Tradename for a
portable transceiver small enough to be held in
the hand during operation.
hand key Also called brass pounder. An oldfashioned,
hand-operated telegraph key, operated
by manual downward pressure.
handoff In cellular communications networks, the
changeover of reception from, and transmission