Electrical Engineering Dictionary - part 74

portional to the frequency resolution; the un-
certainty principle places a lower bound on
the time-frequency resolution product.

frequency response

consider a system

with transfer function given by

H(s) =

Y (s)

F (s)

The term frequency response is used to de-
note

H(jω), (commonly written H (ω)). The

frequency response is often used in describ-
ing the steady-state (stable) system response
to a sinusoidal input. For example, in the
case of a stable continuous-time system with
input signal

f (t) = A cos(ωt), the steady-

state output signal is given by

(t) = A|H (jω) cos(ωt +

H (jω) .

The term

|H (jω)|, −∞ < ω < ∞, is

called the magnitude response.

The term

H(jω), −∞ < ω < ∞, is called the

phase response. The magnitude and phase
responses are typically represented in the
form of a Bode plot. See also

Bode plot

transfer function

frequency reuse

a way to increase the ef-

fective bandwidth of a satellite system when
available spectrum is limited. Dual polariza-
tions and multiple beams pointing to different
earth regions may utilize the same frequen-
cies as long as, for example, the gain of one
beam or polarization in the directions of the
other beams or polarization (and vice versa)
is low enough. Isolations of 27–35 dB are
typical for reuse systems.

frequency reuse cluster

a group of

cells in a cellular communications network
wherein each frequency channel allocated to
the network is used precisely once (i.e., in one
cell of the group). The size of the frequency
reuse cluster is one of the major factors that
determines the spectral efficiency and ulti-
mately the capacity of a cellular network. For
a given channel bandwidth, the smaller the
cluster size, the higher the network capacity.

frequency selective filter

a filter that

passes signals undistorted in one or a set
of frequency bands and attenuate or totally
eliminate signals in the remaining frequency
bands.

frequency selective surface (FSS)

fil-

ter made of two-dimensional periodic arrays
of apertures or metallic patches of various
shapes. Several layers can be used to obtain
a structure with a set of desired spectral prop-
erties.

frequency shift keying (FSK)

(1) an en-

coding method where different bits of infor-
mation are represented by various frequen-
cies; used for spread-spectrum signal encod-
ing for security and reduced interchannel in-
terference.

(2) a digital modulation technique in

which each group of successive source bits
determines the frequency of a transmitted si-
nusoid.

frequency space

the transformed space

of the Fourier transform.

frequency synchronization

the process

of adjusting the frequency of one source so
that it exactly matches that of another source:
more specifically, so that

n periods of one

frequency are exactly equal to

m periods of

the other frequency, for integral

n and m. See

also

phase-locked loop

frequency synthesizer

an oscillator that

produces sinusoidal wave with arbitrary fre-
quency. In common cases, generated fre-
quencies are allocated with a frequency spac-
ing called the channel step.

frequency variation

a change in the elec-

tric supply frequency.

frequency-modulation recording

See

magnetic recording code

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fresh fuel

nuclear fuel which has never

participated in a nuclear reaction and is thus
only slightly radioactive.

Fresnel region

the region in space around

an antenna at which the fields have both trans-
verse and radial components and the antenna
pattern is dependent on the distance from the
antenna. The Fresnel, or near-field, region
is typically taken to be

r < 2D

/λ, where

r is the distance from the antenna, D is the
maximum dimension of the antenna, and

λ is

the wavelength.

Fresnel zone

an indicator of the signif-

icant volume of space occupied by a radio
wave propagating along a line-of-sight path
between the transmitter and receiver. At an
arbitrary point which is at distance

from

the transmitter and at distance

from the

receiver, along the axis joining the trans-
mitter and the receiver, a radio wave with
wavelength

λ occupies a volume, which at

that point between the transmitter and the re-
ceiver, has a radius which is given by the ra-
dius of the first Fresnel zone. The radius of
the first Fresnel zone is given by

R =

λd

+ d

From this equation one can see that the sig-
nificant volume occupied by a radio wave is
essentially ellipsoidal. In order for a trans-
mitter and receiver to communicate success-
fully, it is important for this volume to be
kept free from any obstruction, especially at
microwave frequencies.

fricative

a phoneme pronounced when

constricting the vocal tract so as the air
flow becomes turbulent and the correspond-
ing frequency spectrum looks like a broad-
band noise. The utterances with frication
can occur with or without phonation. When
phonation also occurs, the presence of for-
mants can be detected in the spectrum.

Friis transmission formula

a formula

used to compute the received signal power in

a radio communication link given the amount
of power transmitted, the effective apertures
or gains of the transmit and receive antennas,
the distance between the antennas, and the
wavelength.

fringing

the portion of the flux at the air

gap in a magnetic circuit that does not follow
the shortest path between the poles.

frit

a relatively low softening point mate-

rial of glass composition.

Fritchman model

N-state Markoff model

describing

N error states of a channel.

frog

the top of a tower.

front end

(1) an initial processing unit that

provides a user interface and/or reformats
input data for subsequent computations on
a special-purpose or high-performance back
end processor.

(2) the portion of the compiler that does

machine-independent analysis.

front of a motor

the end of a motor that

is opposite to the major coupling or driving
pulley.

front porch

video blanking level duration

of approximately 1.27 microseconds con-
tained within the horizontal blanking inter-
val of the composite NTSC signal. The front
porch duration is 2% of the total horizontal
line time, starting at the end of a horizontal
line of video signals and ending at the begin-
ning of the horizontal line sync signal.

frontside bus

the term used to describe

the main bus connecting the processor to the
main memory (cf. backside bus).

frustrated total reflection

See

attenuated

total reflection

See

fixed station

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FSA

finite state automata. See

finite state

machine

FSK

See

frequency shift keying

FSM

See

finite state machine

FSS

See

frequency selective surface

FSVQ

See

finite state vector quantizer

fuel cell

an electrochemical device in

which the chemical energy of a conventional
fuel converted directly and efficiently into
low voltage, direct current electrical energy.

fuel cycle

(1) the operating time of a nu-

clear reactor between shutdowns for refuel-
ing.

(2) the life cycle of nuclear fuel, e.g., raw

materials, to fresh fuel, to irradiated fuel, to
spent fuel, to recycling, and finally to residual
waste.

fuel pool

a large vat of water used to store

both fresh and spent nuclear fuel at the reactor
site.

fuel rod

long, thin canister, typically made

of zirconium or other metal, which contains
the radioactive fuel in a nuclear reactor core.

fulgurite

a vitrified tube of fused sand cre-

ated by power fault arcs or lightning strikes
to sandy soil.

full adder

a combinational logic circuit

that produces a two-bit sum of three one-bit
binary numbers.

full bridge amplifier

a class-D amplifier

based on a full-bridge inverter configuration.

full load amperage (FLA)

a value, found

on the nameplate of an induction motor, in-
dicating the expected current drawn by the
motor when operating at rated voltage and
load.

full permutation symmetry

See

nonlinear

susceptibility

full rank Jacobian

a Jacobian matrix

where dim

(R(J )) = r, dim(N(J )) = n − r.

At a singular configuration of the Jacobian,
one has dim

(R(J )) + dim(N(J )) = n in-

dependently of the rank of the matrix

J .

See

null space of the Jacobian

and

range of

Jacobian

full-load amperage

the current measured

at the input of an electrical apparatus which
has a rated variable at the output. The full-
load amperage is also defined as a value that
permits the system to operate in a safe con-
dition if it is equal to the rated value. The
full-load amperage is equal to the rated value
if and only if the voltage is at its rated value.
The full load is defined with the electrical
power in the case of transformers, genera-
tors, or power electronics converters and it is
defined with the mechanical power for elec-
trical motors.

full-load speed

the speed of a motor that

produces rated power when operating at rated
voltage and, for AC motors, frequency.

full-load torque

the torque of a motor that

is producing rated power at rated speed.

full-wave analysis

the rigorous compu-

tation of electromagnetic fields without ap-
proximations (apart for numerical discretiza-
tion) is often referred to as full-wave analysis.

full-wave control

both the positive and

negative half cycle of the waveforms are con-
trolled.

full-wave rectifier

a device that passes

positive polarity portions of a signal and re-
verses negative polarity portions of an AC
signal. Ideally, for a sinusoidal input

(t) =

cos

(ωt), the output of an ideal full-wave

rectifier is

(t) = |V

cos

(ωt)|.

2000 by CRC Press LLC

full width at half max (FWHM)

the

width of a distribution function (i.e., the hor-
izontal distance between two points having
the same vertical coordinate) defined at a
vertical position halfway between the max-
imum and minimum. This value exists for
certain functions that are of interest as pos-
sible point spread functions (e.g., Gaussian,
Moffat function) and gives a rough idea of
the amount of blur to be expected.

fully associative cache

a cache block

mapping technique where a main memory
block can reside in any cache block position.
A number of bits from the address received
from the CPU is compared in parallel with
the cache tags to see if the block is present
in the cache. Although costly to implement,
and impractical for large cache sizes, it is
the most flexible mapping method. See also

cache

direct mapped cache

and associativ-

ity

function

a programming construct that

creates its own frame on a stack, accepting ar-
guments, performing some computation, and
returning a result.

function sensitivity

in a circuit described

by the function

F (s, x) where s is a complex

variable, and

x is a passive or active element

in the circuit realization of the function, the
equation

F (s,x)

∂F (s, x)

∂x

F (s, x)

Under conditions of sinusoidal steady state,
when

s = jω, the function F (jω, x) is de-

scribed by the sensitivity

F (jω,x)

Im S

F (jω,x)

|F (jω,x)|

∂argF (jω, x)

∂x/x

Thus, the real part of the function sensitivity
gives the relative change in the magnitude
response, and the imaginary part gives the
change in the phase response, both with re-
spect to a normalized element change.

function test

a check for correct device

operation generally by truth table verifica-
tion.

function-oriented design

a design method-

ology based on a functional viewpoint of a
system starting with a high-level view and
progressively refining it into a more detailed
design.

functional block

ASICs designed using

this methodology are more compact than ei-
ther gate arrays or standard cells because
the blocks can perform much more complex
functions than do simple logic gates.

functional decomposition

the division of

processes into modules.

functional redundancy checking

an er-

ror detection technique based on checking
bus activity generated by a processor (mas-
ter) with the use of another slave processor
which monitors this activity.

functional unit

a module, typically within

a processor, that performs a specific limited
set of functions. The adder is a functional
unit.

fundamental component

the first order

component of a Fourier series of a periodic
waveform.

fundamental frequency

for a continuous

time periodic signal,

f (t) with fundamental

period

T (seconds), ω

= 2π/T (rad/sec).

See also

periodic signal

fundamental mode

(1) operating mode of

a circuit that allows only one input to change
at a time.

(2) lowest order mode of a laser cavity;

usually refers to a Gaussian transverse field
distribution without regard to the longitudi-
nal mode order.

fuse

an overcurrent device that employs

one or more fusible elements in series. The

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