18WuD2x

intermittent commercial and amateur service • international farad 375
periods, as in amateur (hobbyist) activity or infrequent
commercial service. ICAS ratings are
higher than continuous commercial service (CCS)
ratings. Compare CONTINUOUS COMMERCIAL
SERVICE.
intermittent condition A defect in a circuit or device
that causes erratic and unreliable operation.
The cause of such a problem is often difficult to
determine.
intermittent dc See INTERMITTENT DIRECT
CURRENT.
intermittent direct current A regularly pulsed
unidirectional current. Also called PULSATING
DIRECT CURRENT.
intermittent duty A DUTY CYCLE of less than
100 percent, but greater than zero. Generally, an
operating duty cycle of 25 to 50 percent.
intermittent-duty rating The dissipation or
power rating of a component, circuit, or system,
under conditions of intermittent use, usually a
25-percent to 50-percent DUTY CYCLE.
intermittent operation Operation characterized
by often long nonoperating intervals. Intermittent
operation is often random, whereas on-off operation
tends to be regular.
intermittent signal An interrupted signal resulting
from the intermittent operation of a circuit or
device.
intermodulation Abbreviation, IM. 1. The (usually
undesired) modulation of one signal by another,
caused by nonlinear processing of the signals. 2.
The heterodyning of components in the sidebands
produced by an amplitude-modulated (AM)
or single-sideband (SSB) transmitter.
intermodulation distortion Abbreviation, IMD. 1.
Distortion products in the output of an amplitude-modulated
(AM) or single-sideband (SSB)
transmitter, caused by heterodyning of components
in the sidebands. 2. Distortion products in
the output of an audio amplifier, caused by heterodyning
of the fundamental components. 3.
The extent to which distortion as defined in 1
occurs. See INTERMODULATION-DISTORTION
PERCENTAGE.
intermodulation-distortion meter See INTER-
MODULATION METER.
intermodulation-distortion percentage Abbreviation,
IDP. The degree to which a low-frequency
test signal modulates a higher-frequency test signal
when both are applied simultaneously (in a
prescribed amplitude ratio) to a device under test;
IDP = 100(b – a)/a, where a is the peak-to-peak
amplitude of the unmodulated high-frequency
wave and b is the peak-to-peak amplitude of the
modulated high-frequency wave.
intermodulation meter An instrument for measuring
percentage of intermodulation distortion
(IMD). The instrument combines a dual-frequency
signal generator, filter circuits, and percent-ofmodulation
meter. Also see INTERMODULATION-
DISTORTION PERCENTAGE.
intermodulation noise Electrical noise produced
in one channel by signals in another; it is caused
by INTERMODULATION.
internal absorptance The ratio of flux absorbed in
a substance to the flux leaving at the entry surface
of the substance. It does not include energy
reflected at the entry surface.
internal amplification In a radioactivity counter
tube, current enhancement resulting from cumulative
ionization initiated by an ionizing particle.
internal arithmetic In a digital computer, arithmetic
operations performed in the computer, as
opposed to those performed by peripherals.
internal impedance The impedance in a device, as
opposed to that added from the outside. Compare
INTERNAL RESISTANCE.
internal input impedance The impedance in a circuit
or device, as “seen” from the input terminals.
Compare INTERNAL OUTPUT IMPEDANCE.
internal input resistance The resistance in a circuit
or device, as “seen” from the input terminals.
Compare INTERNAL OUTPUT RESISTANCE.
internal noise Electrical noise generated within a
circuit, as opposed to that picked up from outside.
Such noise comes from transistors, diodes,
integrated circuits, resistors, and any other component
through which current flows.
internal output impedance The impedance in a
circuit or device, as “seen” from the output terminals.
Compare INTERNAL INPUT IMPEDANCE.
internal output resistance The resistance in a circuit
or device, as “seen” from the output terminals.
Compare INTERNAL INPUT RESISTANCE.
internal resistance 1. The resistance of a device,
as opposed to added resistance. See, for example,
METER RESISTANCE. 2. In a cell or battery, the
equivalent resistance, resulting from imperfect
conductivity of the electrolyte and electrodes,
which limits the maximum deliverable current.
internal thermal shutdown In an integrated circuit,
the junction temperature at which thermal
shutdown occurs. It is generally indicated in degrees
Celsius (°C).
internal transmittance The ratio of flux reaching
the exit surface of a material to the flux leaving
the entry surface. Reflection is not taken into account.
The sum of internal transmittance and IN-
TERNAL ABSORPTANCE is always equal to 1.
international broadcast station A shortwave
broadcast station transmitting programs for international
reception between 6 and 26.6 MHz.
international callsign The call letters of a station,
assigned within a country, according to the
method of arrangement (identifying letters, or letters
and numerals) prescribed by the International
Telecommunication Union.
international candle See CANDLE.
international coulomb A unit of electrical quantity,
equal to 0.99985 absolute coulomb.
international farad A unit of capacitance, equal to
0.99952 absolute farad.