18WuD2x

340 high order • hiss
the one holding the higher place value is the highorder
digit (e.g., 2 is the high-order digit in 25).
high-pass filter A combination of capacitance, inductance,
and/or resistance, intended to produce
large amounts of attenuation below a certain frequency
and little or no attenuation above that frequency.
The frequency at which the transition
occurs is called cutoff. At cutoff, the power attenuation
is 3 dB with respect to the minimum attenuation.
At frequencies above cutoff, the power
attenuation is less than 3 dB. At frequencies below
cutoff, the power attenuation is more than
3 dB. The simplest circuit consists of a parallel
inductor or a series capacitor. The inductancecapacitance
(LC) circuit has a combination of parallel
inductors and series capacitors. In the
resistance-capacitance (RC) circuit, resistors are
substituted for the inductors. Compare BAND-
PASS FILTER, BAND-REJECTION FILTER, LOW-
PASS FILTER.
In
C
L L L
C
high-pass filter
Out
high-pass-filter method A method of measuring
the total harmonic distortion (THD) percentage
using a high-pass filter to separate the harmonics
from the fundamental. The output voltage V o of
the filter is compared with the input voltage V i ;
then THD = 100V o /V i .
high-performance Pertaining to apparatus designed
for continuous operation with maximum reliability.
high-performance navigation system Acronym
HIPERNAS. An electromechanical guidance system
that is purely inertial and self-compensating.
high-potential test A high-voltage test of insulation,
in which the applied voltage is continuously
increased until the breakdown point of the dielectric
is reached.
high-power rectifier A rectifier designed for highvoltage,
high-current operation.
high Q For a component or circuit, a high value for
the ratio X/R (reactance to resistance). This is a
relative term because a particular numerical
value of Q, considered high in one situation,
might be regarded as low under other circumstances.
Also see FIGURE OF MERIT.
high-resistance joint In the wiring of electronic
equipment, a joint or connection between conductors
that is poorly made, thereby introducing
a high resistance between the parts.
high-resistance voltmeter A voltmeter having an
input resistance of at least several megohms.
high-speed carry In computer operation, a carry
into a column causing a carry out, circumventing
the usual intermediate adding circuit.
high-speed diode See COMPUTER DIODE.
high-speed flip-flop A flip-flop having short
switch-on and switch-off time.
high-speed oscilloscope An oscilloscope with excellent
high-frequency and unit-function response. It
can reproduce high-speed pulses faithfully.
high-speed relay A relay with a short make or
short break interval.
high-speed transistor See SWITCHING TRANSIS-
TOR.
high tension Pertaining to utility power-transmission
lines on which there are very high voltages,
typically 100 kilovolts (100 kV) or more.
high-tension line A power-transmission line carrying
a very high voltage. It is generally used for
the transfer of electric power over long distances.
high-threshold logic See HIGH-NOISE-IMMUNITY
LOGIC.
high voltage 1. A voltage considerably higher than
those ordinarily encountered in a particular application.
The term is comparative; a few hundred
volts might be considered high in one situation,
but low in another. 2. In a cathode-ray tube, the
voltage that accelerates the beam electrons. 3. In
a television receiver, the picture-tube anode voltage.
4. In a vacuum-tube power amplifier, the
plate supply voltage.
high-voltage probe A very-high-resistance probe
for measuring high voltages with a low-range
voltmeter.
highway A path over which multiple signals are
propagated using time-division multiplexing.
HILAC Acronym for heavy-ion linear accelerator.
hill-and-dale recording See VERTICAL RECORD-
ING.
hinged-iron instrument An alternating-current
meter whose input transformer core is hinged in
two parts. By means of a thumb trigger, the core
can be opened, then closed around the currentcarrying
conductor that induces magnetism in the
core; a secondary coil delivers current to the meter.
Also called clamp ammeter or clamp voltmeter.
HIPERNAS Acronym for HIGH-PERFORMANCE
NAVIGATION SYSTEM.
hipernick A high-permeability alloy of iron and
nickel.
hipot Contraction of high potential. See HIGH-
POTENTIAL TEST.
hiss 1. A high-pitched sound rich in sibilants (s,
sh, and z sounds) produced by random highfrequency
fluctuations in current. 2. The characteristic,
high-pitched background noise (as in 1)
accompanying super-regeneration. 3. Internally
generated noise in a communications receiver,
amplified by the audio-frequency stages and appearing
at the speaker or headphones.