DUMMY ANTENNASee DUMMY LOAD .
DUMMY LOADA dissipative but nonradiating device that has the impedance characteristics of an
antenna or transmission line. Also called ARTIFICIAL LOAD   .
DUPLEXERA radar device that switches the antenna from the transmitter to the receiver and vice versa
DUTY CYCLEIn a transmitter, ratio of time on to time off  .
DYNAMIC MICROPHONEA 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 .
ECHO(1) The reflection of the original sound wave as it bounces off a distant surface . (2) The RF
signal reflected back from a radar target .
ECHO BOXA 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
ECLIPSEA 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 .
EDDY CURRENTInduced circulating currents in a conducting material that are caused by a varying
magnetic field  .
EDDY CURRENT LOSSLosses caused by random current flowing in the core of a transformer. Power
is lost in the form of heat .
EDISON EFFECTAlso 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 .
EFFECTIVE VALUESame as ROOT-MEAN-SQUARE .
EFFICIENCYThe ratio of output-signal power compared to the total input power, generally expressed as
a percentage  .
E-FIELDElectric field that exists when a difference in electrical potential causes a stress in the dielectric
between two points .
ELASTICITYThe ability of a substance to return to its original state .
ELECTRIC CURRENTThe flow of electrons .
ELECTRIC (E) FIELDThe field of force that is produced as a result of a voltage charge on a conductor
or antenna  .
ELECTRICAL CHARGESymbol 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 .
ELECTRICAL CHEMICALThe action of converting chemical energy into electrical energy .
ELECTRICAL-LOCKA 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 .