18WuD2x

interactive photovoltaic system • interference stub 373
companies. Energy is sold to the companies during
times of daylight and minimum usage, and is
bought back from the companies at night or during
times of heavy usage. The principal advantage
of this system is that the user can keep using
electricity (by buying it all from the utilities) if the
solar-energy system breaks down. But such a
system does not provide the independence from
utility companies that some users desire. Compare
STAND-ALONE PHOTOVOLTAIC SYSTEM.
interactive program A computer program in
which the machine and its operator engage in
two-way communication. Most personal computing
software is of this type, in contrast to programs
that carry out all their functions without
operator intervention (other than initialization).
interactive television Television provided to consumers,
in which viewers can transmit data, as
well as receive it. For example, a survey might be
conducted in which viewers are polled and send
in their responses. Another example: products
might be ordered while viewing an advertisement.
interactive mode See CONVERSATIONAL MODE.
interbase resistance The internal resistance between
the bases of a unijunction transistor.
interblock A part of a computer program or a
hardware device that will prevent interference between
parts of a computer system.
interblock space 1. On a magnetic tape, the space
between recordings, caused by starting and stopping
the tape. 2. On magnetic tape used as a
computer storage medium, the interval between
recorded blocks.
intercarrier receiver A television (TV) receiver circuit
in which video, sound, and sync components
of the composite TV signal are amplified
together in the radio-frequency (RF), intermediate-frequency
(IF), and video IF stages; then they
are separated in the video detector and video amplifier
stages. Compare SPLIT-SOUND RE-
CEIVER.
intercept receiver In military service, a search receiver
tuned over a wide band of frequencies to locate
and evaluate enemy signals.
interchangeability The ability of one component
to substitute directly for another component of
the same kind. Example: capacitor interchangeability,
transistor interchangeability. Also see RE-
PLACEMENT.
intercharacter space The three-unit interval between
letter symbols in telegraphy. Compare IN-
TERWORD SPACE.
intercom A comparatively simple two-way telephone
or low-power radio system for use on the
premises of a home or business.
intercommunicator See INTERCOM.
interconnection 1. A mutual connection of separate
circuits. 2. The interconnection of two or
more separate power-generating systems.
interdigital contacts A pair of contacts with “fingers”
that are plated, printed, or deposited on the
surface of a resistor material or semiconductor
substrate. The fingers of each contact are interconnected
at one end, the fingers of one contact
being interleaved with those of the other.
interdigital tube A magnetron having a cathode
surrounded by anode segments that are alternately
interconnected at opposite ends in the
manner of INTERDIGITAL CONTACTS.
interelectrode capacitance Capacitance between
or among electrodes—especially between the
plate and control grid of a vacuum tube.
interelement capacitance Internal pn-junction
capacitance in a semiconductor device, such as a
diode or transistor.
interface 1. The circuitry that interconnects and
provides compatibility between a central processor
and peripherals in a computer system. 2. Collectively,
the hardware and software that allows a
computer to interact with its operator. 3. To provide
an efficient pathway for data between two devices
or systems. 4. The meeting of surfaces or
regions in a material. 5. The surface of a body
that mates with another body similar or identical
to it.
interface resistance See CATHODE INTERFACE.
interface routine A computer program routine
that links one system to another.
interfacial connection A connection that runs
through a printed-circuit board and joins circuit
joints on opposite faces of the board.
interference 1. In communications, degradation
of reception caused by noise or undesired signals.
2. The interaction of acoustic or electromagnetic
waves from more than one source, especially
when they are of the same frequency, producing a
characteristic INTERFERENCE PATTERN of highamplitude
and low-amplitude regions.
interference attenuator A device or mode of operation
that reduces the amplitude of interference.
interference eliminator A filter, wavetrap, or similar
device that removes interfering signals or
noise. Also see INTERFERENCE.
interference filter See INTERFERENCE ELIMINA-
TOR.
interference pattern A regular pattern of highamplitude
and low-amplitude regions, lobes, or
bands, produced when waves of identical frequency
from two or more sources combine in
varying phase. Such patterns can be observed
with sound, radio waves, infrared, visible light,
ultraviolet, X rays, and gamma rays. The phenomenon
is of interest in acoustic engineering,
the design of radio antenna systems, and in
physics (particularly optics).
interference stub A length of twin-lead feeder cut
to appropriate length, connected to the antennainput
terminals of a television receiver, and
short-circuited at the opposite end. A stub of the
correct length resonates at the frequency of an interfering
signal and, acting as a wavetrap, keeps
it out of the receiver. Also see STUB.