18WuD2x

272 external feedback • extreme
external feedback Negative or positive feedback
through a separate path outside of and around
the main circuit. Example: negative feedback
through a resistance-capacitance (RC) path between
the output terminals and the input terminals
of an amplifier.
External
feedback
external feedback
external impedance Load impedance (i.e., an
impedance connected to the output terminals of a
generator or amplifier).
external load See EXTERNAL IMPEDANCE.
external loudspeaker See EXTERNAL SPEAKER.
externally caused chatter In a relay, contact
chatter caused by mechanical vibration outside
of the relay.
externally caused failure Failure of a circuit or
component resulting from unfavorable environmental
factors.
external memory In computer operations, a memory
unit outside of the computer mainframe.
external power supply A power supply unit situated
apart from the powered equipment. Such
separation is helpful in eliminating the disturbing
effects of heat, hum, and vibration associated
with internal power units.
external Q For a microwave tube, the quantity
1/(1/Q 1 + 1/Q 2 ), where Q 1 is the loaded Q and Q 2
is the unloaded Q.
external S-meter A signal-strength meter connected
to a receiver, but not installed in its panel.
external speaker A loudspeaker that doesn’t share
an enclosure with an amplifier, receiver, or other
device that drives it. Such isolation is helpful in
eliminating the undesirable effects of vibration
and acoustic feedback.
external storage In computer operations, storage
media (such as magnetic diskettes or tapes) that
are outside of the computer.
extinction potential See DEIONIZATION POTEN-
TIAL.
extinction voltage See DEIONIZATION POTEN-
TIAL.
Extra-class license An amateur-radio license that
conveys all available amateur operating privileges
in the United States. The highest class of amateur
license.
extract 1. To remove a signal or quantity from
some product containing it, or from its source.
Examples: extracting a fifth harmonic from a
complex signal, extracting the direct-current (dc)
component from a signal containing both alternating
current (ac) and dc. 2. To derive a factor
(e.g., to extract a root). 3. To separate certain
classes of information from an aggregate of information.
extract instruction In computer operations, the
instruction to generate a new word by the serial
arrangement of designated segments of specified
words.
extractor 1. A circuit or device for removing a signal
(or a signal component) from another circuit
or device. A demodulator probe, for example, extracts
the modulation from a modulated signal.
2. A device for removing used active devices from
a circuit board. Such extractors can also employ
heat to desolder, as well as remove the devices.
extraneous component A usually undesired inherent
effect that results from the physical
nature of a component or device. Examples:
distributed capacitance of a coil, internal inductance
of a capacitor.
extraneous emission Undesired emission from a
transmitter (e.g., excessive harmonics).
extraneous response The unintended response of
a circuit or device (e.g., image response in a superheterodyne
communications receiver).
extraneous root In the solution of an equation derived
from another equation, one or more roots
that satisfy the derived equation but not the original
one.
extraneous signal A superfluous and potentially
interference-causing signal.
extranuclear Outside the nucleus of an atom.
extraordinary ray Of the two rays resulting from
the double refraction of electromagnetic waves,
the one that does not follow the usual laws of refraction.
Also see X WAVE.
extraordinary wave See X WAVE.
extrapolar 1. Outside of electrical or magnetic
poles. 2. Not between electrical or magnetic poles.
extrapolation Estimation of values beyond the
range of available data. An example is the extension
of a curve beyond its final plotted point to determine
a value for a variable. There is always
some margin for error, which increases as the
process is extended further and further beyond
the range of actual data values. Commonly done
by computers (e.g., prediction of the probable
path of a hurricane 12, 24, 36, and 48 hours in
advance).
extrared See INFRARED.
extraviolet See ULTRAVIOLET.
extreme 1. The lowest or highest value of a