18WuD2x

CQ • critical field 153
CQ A general call signal used in radio communication,
especially by amateur stations, to invite a
response from any station that hears it.
Cr Symbol for CHROMIUM.
cracked-carbon resistor A high-stability resistor
in which the resistance material is particulate
carbon.
cracker A hacker with malicious intent (also see
HACKER). Such a person attempts to gain access
to computer systems or databases in order to
steal something or inflict damage. Examples include
theft, erasure, or mutilation of data; fraudulent
debiting of bank accounts; alteration of
credit information; and identity theft.
cradle guard See GUARD WIRE.
cradlephone A telephone set in which the microphone
and earphone are mounted on opposite
ends of a handle. This handle, called the receiver,
rests on the crossmember of a stand connected to
a base containing the dial and ringing circuits.
Also called French phone, French telephone, and
handset.
crash 1. A condition in which a computer or network
server becomes inoperative because of a
software or memory-management problem. 2. In
a computer hard disk or diskette drive, contact of
the read/write head with the surface of a disk or
platter. Usually, it is the result of excessive physical
vibration or shock.
crate A foundation unit into which modules are
plugged to establish a circuit.
crawl 1. See CREEPING COMPONENT. 2. The
credits (names of staff and their contribution to
content) superimposed and moving on a television
picture at the end of a program.
crazing The formation of tiny cracks in materials,
particularly in such dielectrics as plastic and ceramic.
creep See COLD FLOW.
creepage Current leakage across the surface of a
dielectric.
creeping component A quantity, such as current,
voltage, or frequency, that slowly changes in
value with time.
crest factor See AMPLITUDE FACTOR.
crest value The maximum amplitude of a composite
current or voltage.
crest voltmeter A peak-reading (or sometimes
peak-responsive) voltmeter.
crippled mode The mode of operation for a computer
or other hardware in which some of the
components are inoperable. Compare GRACE-
FUL DEGRADATION.
crisscross neutralization See CROSS-CON-
NECTED NEUTRALIZATION.
crisscross rectifier circuit A conventional bridge
rectifier circuit configured in such a way that two
of the diodes are connected in crisscross fashion
between the input and output terminals.
critical angle 1. In radio communications, an angle
of departure that a transmitted electromag-
netic field subtends, with respect to the horizon
at the transmitting (TX) point, below which the
ionosphere will reliably return the signal to the
earth, and above which the ionosphere will not
reliably return the signal. This angle (shown by
the double arc marked X in the drawing) depends
on the frequency of the transmitted electromagnetic
wave, and also on ionospheric conditions. 2.
For an electromagnetic wave or ray approaching
a boundary at which the index of refraction
abruptly decreases, the minimum angle of incidence
(relative to a line perpendicular to a plane
tangent to the boundary) at which the energy is
totally reflected.
TX
X
Earth’s surface
critical angle, 1
Ionized layer
critical characteristic A parameter that has a disproportionate
effect on other variables. A small
change in this characteristic can result in a large
change in the operating conditions of a circuit or
system.
critical component A component or part that is
especially important in the operation of a circuit
or system.
critical coupling The value of coupling at which
maximum power transfer occurs. Increasing the
extent of coupling beyond the critical value decreases
power transfer.
critical damping The value of damping that yields
the fastest transient response without overshoot.
critical dimension The cross-sectional size of a
waveguide that determines its minimum usable
frequency.
critical failure A component or circuit failure that
results in shutdown of a system, or a malfunction
that results in improper operation.
critical field The smallest magnetic-field intensity
in a magnetron that keeps an electron, emitted
from the cathode, from reaching the anode.