18WuD2x

404 least upper bound • level-0 security
least upper bound The smallest value of a parameter
that can be obtained without changing some
characteristic of a circuit, program or system.
Lecher frame A sturdy assemblage of LECHER
WIRES.
Input
coupling
link
from
RF
source
Standoff
insulator
Short-circuiting
slider
Pointer
Lecher frame
Diode
dc
Milliammeter
Pickup
ink
Base
Scale
Lecher lines See LECHER WIRES.
Lecher oscillator A self-excited radio-frequency
oscillator using Lecher wires in place of an inductance-capacitance
(LC) tank circuit. Also see
LINE-TYPE OSCILLATOR.
Lecher wires A circuit segment consisting of two
parallel wires or rods joined by a coupling loop on
one end, the other end being open. A shortcircuiting
bar is moved along the wires to vary the
effective length of the circuit. Radio-frequency energy
is inductively coupled into the system
through the loop, and the bar is slid along to various
response points, as indicated by a meter or
lamp coupled to the wires. The frequency can be
determined by measuring the distance between
adjacent response points. It is used at very-high
frequencies (VHF), ultra-high frequencies (UHF),
and microwave frequencies. Also called Lecher
frame and Lecher lines.
Leclanche cell See DRY CELL, 1.
LED See LIGHT-EMITTING DIODE.
LED phototransistor isolator An optoelectronic
isolator in which the light source is a lightemitting
diode and the light-sensitive component
is a phototransistor.
LEDE Abbreviation for LIVE END/DEAD END.
LEF See LIGHT-EMITTING FILM.
left-hand lay See DIRECTION OF LAY.
left-hand motor rule See FLEMING’S LEFT-HAND
RULE.
left-hand polarized wave See COUNTERCLOCK-
WISE-POLARIZED WAVE.
left-hand taper Potentiometer or rheostat taper in
which most of the resistance is in the counterclockwise
half of rotation as viewed from the
front. Compare RIGHT-HAND TAPER.
left justified An item of data that occupies consecutive
locations in storage, starting at the lefthand
end of its area; empty locations might
appear consecutively at the right-hand end if the
item needs fewer positions than have been provided.
left shift A shift operation in which the digits of a
word are displaced to the left; the effect is multiplication
in an arithmetic shift.
leg 1. Any one of the distinct branches of a circuit
or network; also called ARM or BRANCH. 2. In a
computer program, a path in a routine or subroutine.
L electron In certain atoms, an electron whose orbit
is outside of, and nearest to, the orbit of the K
electrons.
Lenard rays See CATHODE RAYS.
length 1. The number of bits or characters in a
record, word, or other data unit. 2. The endto-end
dimension of a device, circuit, line, etc.
3. The start-to-finish duration of a time interval.
length to fault In cable or line measurements from
the home station, the distance (i.e., the cable or
line length) to the point at which a fault, such as
a short circuit or ground, is located.
lens 1. A usually circular piece of transparent material
with one or both surfaces curved in cross
section, used (through its refractive properties) to
focus or spread rays that pass through it. Lenses
for visible light must be transparent, but those
for other radiation, such as radio waves, need not
transmit light. Also see ANTENNA LENS. 2. In a
cathode-ray tube, one or more high-voltage electrodes
for focusing an electron beam to a fine
point on the screen.
lens antenna See ANTENNA LENS.
lens disk A NIPKOW DISK having a lens in each
hole.
lens speed The light-transmitting ability of a lens,
given as an f-stop number: the lens’ focal length
divided by its diameter.
lens turret A multiple-lens mount on a camera
that can be rotated for quick lens interchange.
LEO Acronym for LOW EARTH ORBIT.
LEO satellite system A set of several dozen low
earth orbit (LEO) satellites in polar orbits spaced
strategically around the globe such that, for any
point on the earth, there is always at least one
satellite in range. The satellites can relay messages
throughout the fleet. Any two points on the
surface are always able to make contact through
the satellites.
Lepel discharger See QUENCHED SPARK GAP.
letter-identification word See PHONETIC ALPHA-
BET CODE WORD.
letters patent See PATENT.
letters shift In a text communications terminal, a
control character that causes all of the following
characters to occur in the lower case. This can be
an automatic or a manual control character.
let-through current The current conducted by a
circuit breaker during a short-circuit.
level-0 security In communications, the complete
lack of security measures. Anyone can listen in
on a conversation at any time, provided they are