hard magnetic material a ferromagnetic
material that retains its magnetization when
the magnetizing field is removed; a magnetic
material with significant coercivity.
hardreal-time Seehardreal-timesystem.
hardreal-timesystem a real-time system
in which missing even one deadline results in
system failure. Compare with soft real-time,
firm real-time.
hard X-ray having sufficient photon en-
ergy to penetrate “hard” material; usually
more than about 15 keV.
hard-decision decoding decoding of en-
coded information given symbol decisions
of the individually coded message symbols.
Compare with soft-decision decoding.
hardware computer constructs that have
a physical manifestation.
hardware accelerator a piece of hard-
ware dedicated to performing a particu-
lar function (such as image convolution or
matrix-vector products) which would other-
wise be performed in software. Although
much less flexible, dedicated hardware im-
plementations can give significant speed im-
provements over software, and are especially
useful for real-time applications.
hardware interrupt an interrupt gener-
ated by a hardware device, for example, key-
board, the DMA, PIC, the serial adapter, the
printer adapter, etc. Other hardware inter-
rupts can be generated by the control unit or
by the ALU, for example, for the presence of
a division per zero, for attempting to execute
an unknown instruction. This last class of
hardware interrupts is called internal excep-
tion.
hardware noise radio frequency emis-
sions due to arcing of utility lines at defective
connectors.
harmonic (1) the name associated with a
number used to denote the frequency com-
ponents that exist in a certain fourier series
representation for a certain function of time
f(t). The Fourier series representation is
given
f(t)=∞
n=−∞
Fn∗[cos(nωot)+jsin (nωot)]
where n=0,1,2,3,...,ωo=2π/T ,j=
√−1, Tis the period of the function f(t),
Fnis the coefficient of the Fourier series for
a certain value of n:
1st harmonic has Fn=F1and
[cos(1ω0t)+jsin (1ω0t)]
2nd harmonic has Fn=F2and
[cos(2ω0t)+jsin (2ω0t)]
3rd harmonic has Fn=F3and
[cos(3ω0t)+jsin (3ω0t)]
etc.
(2) sinusoidal component of a periodic
waveform that has a frequency equal to an
integer multiple of the basic frequency (or
fundamental frequency). Thus the third har-
monic of a power system voltage in the U.S.
hasafrequencyof3×60,or180Hz. Forelec-
tric systems powered by sinusoidal sources,
harmonics are introduced by nonlinear de-
vices such as saturated iron cores and power
electronic devices.
harmonic amplifier a type of amplifier
that utilizes various forms of harmonic and
mixing actions. These amplifiers may pump
up the fundamental by increasing the switch-
ing efficiency of the active device. Others
mayactuallybeusedasfrequencymultipliers
or frequency converters (mixers). All class
F, G, and H amplifiers fit into this general
c
2000 by CRC Press LLC
www.FreeEn
g
ineerin
g
booksPd
f
.com
group. Parameters such as device character-
istics, quiescent bias point, RF load line, sig-
nificantharmonicand/or mixing frequencies,
and amplitude and waveform of the applied
signal(s) should be included with the class
definition, thus defining the major contribu-
tors to the physical actions taking place in
one of these amplifiers.
harmonic analysis the branch of math-
ematics dealing with the decomposition of
signal functions as a linear combination of
basis functions which represent “waves” of
various frequencies. When the basis func-
tions are sines and cosines each with a fre-
quency that is an integer multiple of the
signal’s frequency, we have trigonometric
harmonic analysis, in other words classical
Fourier analysis, which provides the ampli-
tudesand phasesof the constituentsinusoids.
(See Fourier transform. ) With other basis
functions, for example wavelets, we have
non-trigonometric harmonic analysis (See
wavelet,wavelet transform). Abstract har-
monic analysis studies the generalization of
Fourier analysis to abstract spaces.
harmonic balance technique one of sev-
eral techniques for analyzing nonlinear cir-
cuits. The nonlinear circuit is divided into
two portions of linear and nonlinear ele-
ments, and aportion of linearelements iscal-
culated in a frequency domain and a portion
of nonlinear elements is calculated in a time
domain, respectively. The calculated volt-
ages or currents at connecting nodes of these
portions are balanced by using Fourier trans-
forming or inverse Fourier transforming.
harmonic component a Fourier compo-
nent of order greater than one of a periodic
waveform.
harmonic content the internally gener-
ated, harmonically related spectral output
from a device or circuit. Harmonic energy
is that energy that is at exact multiples of
the fundamental frequency, generated by the
nonlinearitieswithinthedeviceorcircuitact-
ing on the fundamental frequency.
harmonic converter found in a mi-
crowave receiver, this component uses the
technique of harmonic mixing to convert the
RF signal to a lower IF frequency for fur-
ther processing. Harmonic converters can be
used as part of a vector network analyzer.
harmonic distortion caused by the non-
linear transfer characteristics of a device or
circuit. When a sinusoidal signal of a single
frequency(the fundamental frequency)is ap-
plied at the input of a nonlinear circuit, the
output contains frequency components that
are integer multiples of the fundamental fre-
quency(harmonics). Theresulting distortion
is called harmonic distortion.
harmonic frequency integral multiples
of fundamental frequency. For example, for
a 60-Hzsupply, the harmonicfrequencies are
120, 180, 240, 300, ....
harmonic generation in nonlinear op-
tics, the process in which a laser beam in-
teracts with a material system to produce
new frequency components at integer multi-
ples of the frequency of the incident beam.
Under carefully controlled circumstances,
the lower-order harmonics (e.g., second and
third)canbegeneratedwithhigh(>50%)ef-
ficiency. Under different circumstances, har-
monics as high as the 30th can be generated.
harmonic load-pull measurement a
measurement method where transfer char-
acteristics of a device at the fundamental
frequency can be measured by electrically
changing the load impedance at harmonic
frequencies.
harmonic orthogonal set the set of func-
tions ejωt. It is called harmonic because
each basis function is a harmonic of a cer-
tain frequency and because the inner product
between any two functions is zero:
+∞
−∞ ejω1tejω2tdt =0,ω
1= ω2
c
2000 by CRC Press LLC
www.FreeEn
g
ineerin
g
booksPd
f
.com
+∞
−∞ ejωt1ejωt2dω =0,t
1= t2.
harmonictuning the processof tuningan
amplifier circuit to a frequency that is an in-
tegral multiple of the fundamental frequency
at which the circuit would normally operate.
harmonically pumped mixer mixer
where the intermediate frequency (IF) sig-
nal is at a frequency which is the sum or
difference of the RF and an integer multi-
ple (usually two) of the LO (local oscillator)
frequency.
Hartleyoscillator aparticularcaseofLC-
oscillators when X1+X2+2Xmis realized
as a single tapped coil, and X3is a capacitor.
Well suited for variable-frequency operation
by varying a single capacitor.
Hartley oscillators are usually not used at
VHFs of higher frequencies. Similarly, the
circuit is avoided at very low audio frequen-
cies. Itisimportant to distinguishtheHartley
oscillator from the Armstrong topology. In
the Armstrong oscillator, no ohmic connec-
tion exists between the two inductors. In-
stead, coupling is entirely magnetic.
Harvard architecture a computer design
feature where there are two separate mem-
ory units: one for instructions and the other
for data only. The name originates from an
early computer development project at Har-
vard University in the late 1940s. Compare
with Princeton architecture.
hashtable atable storingamappingfunc-
tionwhosedomainissparselyusedandthatis
accessed by indices that are computed from
the search field (“key”) using a many–one
mapping (called a hash function). Hash ta-
bles are used for many memory and name
mapping functions, such as symbol tables in
assemblers and compilers.
hashed page table a page table where
the translation of each virtual page number
is stored in a position determined by a hash
function applied to the virtual page number.
This technique is used to reduce the size of
page tables.
hashing the act of translating a search key
intoatableindexusingamany–onemapping.
See also hash table.
Hausdorffdistance animportantdistance
measure, used in fractal geometry, among
other places. Given a distance function d
defined on a Euclidean space E, one derives
fromittheHausdorffdistance Hdon the fam-
ily of all compact (i.e., bounded and topo-
logically closed) subsets of E; for any two
compact subsets K, L of E,Hd(K, L) is the
least r≥0 such that each one of K, L is con-
tained in the other’s dilation by a closed ball
of radius r,thatis:
K⊆
p∈L
Br(p) and L⊆
p∈K
Br(p),
where
Br(p) ={q∈E|d(p,q) ≤r}.
Hayes-compatible modem refers to a
modem when it is capable of responding at
the commands of modems made by Hayes
Microcomputer Products. The Hayes set of
commands represents a sort of standard for
modems.
haystack response bandpass frequency
response characterized by flat midband re-
sponse with sloping sides.
hazard a momentary output error that oc-
curs in a logic circuit because of input signal
propagationalongdifferentdelaypathsinthe
circuit.
hazardous location a classification sys-
temusedtodefine locations that are suscep-
tible to fire and explosion hazards associated
with normal electrical arcing. A class I haz-
ardous location contains a flammable con-
centration of flammable vapors. A class II
hazardous location contains a combustible
c
2000 by CRC Press LLC
1
/
3
100%
