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level-0 security • life 405
willing to spend the money and/or time to obtain
the necessary equipment. Examples are amateur
(“ham”) radio and Citizens’ Band (CB) voice communications.
level-1 security Also called wire-equivalent security.
In communications, the implementation of
security measures such that the circuit is protected
to the extent of a typical hard-wired link.
The encryption is anticipated to be unbreakable
for at least 12 months, and preferably for
24 months or more. The technology is updated
at least every 12 months, and preferably every
6 months.
level-2 security Also called commercial-level security.
In communications, the implementation of
security measures such that the circuit is
deemed safe for ordinary commercial transactions.
The encryption is anticipated to be of such
a nature that engineers believe it would take a
hacker at least 10 years, and preferably 20 years
or more, to break the cipher. The technology
should be updated at least every 10 years, but
preferably every 3 to 5 years, and more often if
possible.
level-3 security Also called mil-spec security. In
communications, the implementation of security
involving the most sophisticated forms of encryption
and personnel restriction that a government
can muster.
level 1. The amplitude at which a device is functioning
or at which a phenomenon occurs (e.g.,
collector-current level, or received signal level).
2. The minimum amplitude at which a phenomenon
occurs; also called threshold amplitude. 3.
A functional plateau or echelon.
level clipper See CLIPPER.
level compensator 1. An automatic gain control
(AGC) that effectively reduces amplitude variations
in a received signal. 2. An automatic gain
control in telegraph receiving equipment.
level control 1. The adjustment of amplitude or
threshold. 2. A potentiometer or other variable
component for adjusting the amplitude or threshold
of a quantity.
level indicator See VOLUME INDICATOR.
level translator Any circuit or device that alters
the voltage levels of input signals. An example is
a converter that changes positive-logic signals to
negative-logic signals.
level-triggered flip-flop A flip-flop that responds
to voltage level, rather than to the frequency of an
input signal.
lever switch 1. A switch designed for rapid making
and breaking of a circuit. 2. A radiotelegraph key.
Lewis antenna A form of antenna used at ultrahigh
and microwave frequencies. It resembles a
horn antenna.
Leyden bottle See LEYDEN JAR.
Leyden jar [Leyden, Holland (also Leiden), site of
the invention in 1745 by Peiter van Musschenbroek,
1692–1761.] The first practical capacitor.
In modern form, it is a glass jar covered inside
and out with metal foil and has a rod topped by a
metal ball that touches the inner foil. It is still
used occasionally in classrooms for demonstrating
static electricity. The Leyden jar was coinvented
by van Musschenbroek and invented
independently by E. G. von Kleist of Pomerania,
among others.
Inner,
electrode
metal
plate
Leyden jar
Insulating
cover
Glass
Chain
Outer metal
plate
Leyden phial See LEYDEN JAR.
Leyden vial See LEYDEN JAR.
LF Abbreviation of LOW FREQUENCY.
L F band A section of the L BAND extending from
1.35 to 1.45 GHz.
L fitting See ELL.
LHD Abbreviation of LOAD/HAUL/DUMP.
Li Symbol for LITHIUM.
librarian program A computer program controlling
a LIBRARY.
library In digital-computer and data-processing
operations, the permanent storage of data or instructions.
Also called permanent mass storage.
libration fading In earth-moon-earth (EME) communications,
also known as moonbounce, rapid
and deep fading, accompanied by phase modulation,
that takes place because the moon does not
always show the earth exactly the same portion of
its surface. The moon “wobbles” slightly back and
forth on its axis. This causes changes in the relative
phases of signals reflected from the topographic
features (mountains, in particular) on the
lunar surface.
licrystal An acronym from liquid and crystal. See
LIQUID CRYSTAL.
lidar See LIGHT DETECTION AND RANGING.
lie detector See POLYGRAPH.
life 1. The duration of useful service (or of operation
before failure) of electronic equipment. 2. For
a non-rechargeable cell or battery, the length of
time it will last in a given application before it
must be discarded and replaced. 3. In robotics
and artificial intelligence (AI), a general term that
refers to qualitative similarities between machines
and animate creatures, including human
beings.