Page 195 - Electrical Engineering Dictionary

lope (carrier). The noise figure of receiver to source voltage (V DS ) for a fixed gate to
is a measure of the amount of noise that will source voltage (V GS ), expressed in siemens.
be added to the signal (carrier and TV signal)
by the receiver. If the receiver adds too much g d = ∂I DS

noise, the result will be a snowy picture on ∂V DS V GS = constant
the TV screen.
DC generator commutator exciter a
dBW ratio of the signal power in watts
source of energy for the field winding of a
(p watts )toa1W reference power, expressed
synchronous machine derived from a direct
in decibels referenced to 1 W (dBW). Thus
current generator. The direct current gen-
1 watt signal power is equal to 0 dBW, and
erator may be driven by an external motor,
−30 dBW is equal to 0 dBm.
a prime mover, or by the shaft of the syn-
chronous machine.
p watts
P dBW = 10 log
10
1 · Watt
DC input power the total DC or bias
power dissipated in a circuit, which is usually
DC direct current. See DC current, DC dependent on signal amplitudes, expressed
voltage. in watts. This may include input bias, bias
filtering, regulators, control circuits, switch-
DC block A circuit simulation component ing power supplies and any other circuitry
that behaves like a capacitor of infinite value. required by the actual circuit. These con-
siderations should be explicitly specified, as
DC chopper a DC to DC converter that
they will affect how efficiency calculations
reduces the voltage level by delivering pulses
are performed.
of constant voltage to the load. The average
output is equal to the input times the duty DC link the coupling between the rectifier
cycle of the switching element. and inverter in a variable speed AC drive.
DC circuit electrical networks in which DC link capacitor a device used on the
the voltage polarity and directions of current output of a rectifier to create an approxi-
flow remain fixed. Thus such networks con- mately constant DC voltage for the input to
tain direct currents as opposed to alternating the inverter of a variable speed AC drive.
currents, thereby giving rise to the term.
DC link inductor an inductor used on the
DC current constant current with no vari- output of a controlled rectifier in AC current
ation over time. This can be considered in source drives to provide filtering of the input
general terms as an alternating current (AC) current to the current source inverter. If used
with a frequency of variation of zero, or a in conjunction with a capacitor, then it is used
zero frequency signal. For microwave sys- as a filter in voltage source drives.
tems, DC currents are provided by batteries
or AC/DC converters required to “bias” tran- DC load flow a fast method of estimating
sistors to a region of operation where they power flows in an electric power system in
will either amplify, mix or frequency trans- which the problem is reduced to a DC circuit,
late, or generate (oscillators) microwave en- with line impedances modeled as resistances
ergy. and all generator bus voltages presumed to
remain at their nominal values.
DC drain conductance for an FET device
under DC bias, the slope of the output drain DC machine an electromechanical (rotat-
to source current (I DS ) versus output drain ing) machine in which the field winding is on

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2000 by CRC Press LLC