Page 197 - Electrical Engineering Dictionary

includes switches, a low pass filter (to at- verse transfer function characteristic of the
tenuate the switching frequency ripple), and pre-emphasis network situated at the trans-
a load. The size of magnetic components mitter. See the figure for a de-emphasis net-
and capacitors can be reduced and bandwidth work. See pre-emphasis.
can be increased when operating at high fre-
quency. Most DC–DC converters are pulse- de-regulation the removal of some gov-
width modulated (PWM), while resonant or ernmentcontrolsonpublicutilities, generally
quasi-resonant types are found in some appli- including the unbundling of certain services,
cations. Commonly used topologies include the dismantling of vertically-integrated util-
the buck converter, boost converter, buck- ities, and the introduction of competition
´
boost converter, and Cuk converter. Isola- among various utility companies for cus-
tion can be achieved by insertion of a high tomer services.
frequency transformer.
dead band (1) the portion of the operating
DC-free code See balanced code. range of a control device or transducer over
which there is no change in output.
DCA See dynamic channel assignment. (2) referring to an automatic controller be-
havior, a range of values of the controlled
DCE Seedatacommunicationsequipment variable in which no corrective action occurs.
or distributed computing environment. This type of controller behavior is responsi-
ble for the time lag, called dead zone lag,
DCS-1800 digitalcommunicationsystem– which can cause instability of the controlled
1800 MHz. A micro-cell version of GSM system if other conditions are present.
that operates at a lower transmitter power, Also known as dead zone.
higher frequency band, and has a larger spec-
trum allocation than GSM, but in most other dead end an installation in which an elec-
respects is identical to GSM. The DCS-1800 tric power line terminates at a pole or tower,
spectrum allocation is 1710–1785 MHz for typically for purposes of structural stabilty.
the up-link and 1805–1880 MHz for the
down-link (i.e., 2 × 75 MHz). The peak dead man (1) a stand on which to rest a
transmit power for portable DCS-1800 ter- utility pole when setting the pole by hand.
minals is 1 W. (2) a buried log used as a guy anchor.

DCT See discrete cosine transform. dead-end shoe a fixture for securing a
wire or strain insulator to a utility pole.
de Haas–Shubnikov oscillation See
Shubnikov–de Haas oscillation. dead tank breaker a power circuit
breaker where the tank holding the interrupt-
de-assert to return an enabling signal to ing chamber is at ground potential. Oil cir-
its inactive state. cuit breakers, for example, are typically dead
tank breakers.
de-emphasis refers to the receiving pro-
cess of correcting the amplitude of cer- dead zone See dead band.
tain signal components that have been “pre-
emphasized” prior to transmission in order to deadbeat 2-D observer a system de-
improve signal-to-noise (S/N) ratio. In com- scribed by the equations
mercialFMbroadcastreceivers, de-emphasis
is accomplished with a simple resistor ca- z i+1,j+1 = F 1 z i+1,j + F 2 z i,j+1 + G 1 u i+1,j
pacitor lowpass filter that represents the in- + G 2 u i,j+1 + H 1 y i+1,j + H 2 y i,j+1

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2000 by CRC Press LLC