18WuD2x

226 echo area • eddy-current loss
echo area The area of a target that will return a
radar signal as an echo.
echo attenuation In a bidirectional wirecommunication
circuit equipped with repeaters
or multiplexers, the attenuation of echo currents
set up by conventional operation.
echo box A resonant-cavity device used to test a
radar set. Part of the transmitted energy enters
the box, which retransmits it to the receiver. The
signal reaching the receiver is a slowly decaying
transient whose intensity eventually falls below
the level that can be displayed on the screen; the
time required to reach this level indicates radar
performance.
echo chamber A reverberation chamber, electronic
recording device, or room for acoustic tests or for
simulating sonic delays.
echo check In data communication, a means of
checking the accuracy of received data by sending
it back to the transmitting station for comparison
with the original data.
echo depth sounder See ACOUSTIC DEPTH
SOUNDER.
echo eliminator 1. A device that quiets a navigational
instrument after receipt of a pulse, to prevent
reception of a subsequent, delayed pulse. 2.
In a two-way telephone circuit, a voice-operated
device that suppresses echo currents caused by
conversation currents going in the opposite direction.
echoencephalograph An ultrasonic medical instrument
that allows viewing of internal organs.
Used for diagnostic purposes in certain situations,
instead of the X-ray machine.
echogram In acoustics, a graph of the sound
decrement in an enclosure. Time is plotted on
the horizontal axis; signal amplitude is plotted
on the vertical axis. An intense pulse is transmitted
from a speaker; a microphone picks up the
echoes and sends them to a pen recorder or microprocessor.
echo intensifier A device used at a radar target to
boost the intensity of reflected energy.
echo interference Radio interference resulting
from a reflected signal arriving slightly later than
the direct signal.
echo matching In an echo-splitting radar system,
the trial-and-error orientation of the antenna to
find the direction from which the pulse indications
are identical.
echo ranging An ultrasonic method of determining
the bearing and distance of an underwater object.
echo send In an audio mixer, an output for delivering
signals to external systems, such as an
echo box (see ECHO, 5). It can also provide an
auxiliary output for a second set of speakers, a
tape recorder, etc.
echo sounder See ACOUSTIC DEPTH SOUNDER.
echo splitting Separating a radar echo into two
parts so that a double indication appears on the
radar screen.
echo suppression In a telephone circuit, a device
that chokes off reflected waves, thereby minimizing
audible echo.
echo suppressor See ECHO ELIMINATOR.
echo talk Echo in a telephone system that results
in distracting interference.
echo wave A reflected wave, such as a radio wave
reflected alternately between earth’s surface and
the ionosphere.
ECL Abbreviation of EMITTER-COUPLED LOGIC.
eclipse effect A decrease in the critical frequency
of the E and F1 layers of the ionosphere during a
solar eclipse.
ecliptic orbit Any orbit that lies in the same plane
as the orbit of the earth around the sun (the ecliptic
plane). The ecliptic plane is slanted about
23.5° from the plane of the earth’s equator.
ECM Abbreviation of ELECTRONIC COUNTER-
MEASURES.
ECO Abbreviation of ELECTRON-COUPLED OS-
CILLATOR.
econometer An instrument for continuously monitoring
the amount of carbon dioxide in (factory)
flue gases.
E core A transformer or transducer core having the
shape of an E. Coils can be wound on one, two, or
all three of the crosspieces.
E core
ECPD Abbreviation of Engineer’s Council for Professional
Development.
ECTL Abbreviation of emitter-coupled transistor logic.
EDD Abbreviation of ENVELOPE-DELAY DISTOR-
TION.
eddy current A circulating current induced in a
conducting material by a varying magnetic field,
often parasitic in nature. Such a current can, for
example, flow in the iron core of a transformer.
eddy-current device A brake, coupling, clutch,
drag cup, drive unit, or similar device whose operation
is based on the generation of torque, pull,
or opposition by the action of eddy currents.
eddy-current heating Heating caused by eddycurrent
loss in a material.
eddy-current loss Power loss resulting from eddy
currents induced in nearby structures by an