1-21
DUMMY ANTENNA—See DUMMY LOAD [16].
DUMMY LOAD—A dissipative but nonradiating device that has the impedance characteristics of an
antenna or transmission line. Also called ARTIFICIAL LOAD [11] [16] [17].
DUPLEXER—A radar device that switches the antenna from the transmitter to the receiver and vice versa
[18].
DUTY CYCLE—In a transmitter, ratio of time on to time off [12] [18].
DYNAMIC MICROPHONE—A device in which sound waves move a coil of fine wire that is mounted on
the back of a diaphragm and located in the magnetic field of a permanent magnet [12].
ECHO—(1) The reflection of the original sound wave as it bounces off a distant surface [10]. (2) The RF
signal reflected back from a radar target [18].
ECHO BOX—A resonant cavity device that is used to check the overall performance of a radar system. It
receives a portion of the transmitted pulse and retransmits it back to the receiver as a slowly decaying
transient [18].
ECLIPSE—A condition in which the satellite is not in view or in direct line of sight with the sun. This
happens when the earth is between them [17].
EDDY CURRENT—Induced circulating currents in a conducting material that are caused by a varying
magnetic field [2] [5].
EDDY CURRENT LOSS—Losses caused by random current flowing in the core of a transformer. Power
is lost in the form of heat [2].
EDISON EFFECT—Also called RICHARDSON EFFECT. The phenomenon wherein electrons emitted
from a heated element within a vacuum tube will flow to a second element that is connected to a
positive potential [6].
EFFECTIVE VALUE—Same as ROOT-MEAN-SQUARE [2].
EFFICIENCY—The ratio of output-signal power compared to the total input power, generally expressed as
a percentage [1] [7].
E-FIELD—Electric field that exists when a difference in electrical potential causes a stress in the dielectric
between two points [11].
ELASTICITY—The ability of a substance to return to its original state [10].
ELECTRIC CURRENT—The flow of electrons [1].
ELECTRIC (E) FIELD—The field of force that is produced as a result of a voltage charge on a conductor
or antenna [10] [11].
ELECTRICAL CHARGE—Symbol Q, q. Electric energy stored on or in an object. The negative charge is
caused by an excess of electrons; the positive charge is caused by a deficiency of electrons [1].
ELECTRICAL CHEMICAL—The action of converting chemical energy into electrical energy [1].
ELECTRICAL-LOCK—A synchro zeroing method. This method is used only when the rotors of the
synchros to be zeroed are free to turn and their leads are accessible [15].
