18WuD2x

374 interference trap • intermittent commercial and amateur service
interference trap A wavetrap that suppresses interfering
signals at the rejection frequency of the
trap.
interferometer 1. A radio telescope having two antennas
spaced at a distance of many wavelengths,
providing much greater resolution than a
single antenna. Pioneered by M. Ryle of England
and J.L. Pawsey of Australia. 2. Any device that
displays an INTERFERENCE PATTERN for testing
or experimental purposes.
interfix A method used in information-retrieval
systems that eliminates ambiguity in the responses
to inquiries by describing the relationship
between keywords in a record.
Interframe A method of digital IMAGE COMPRES-
SION developed by MPEG (Moving Picture Experts
Group). It operates by eliminating redundant
data from between image frames. Compare IN-
TRAFRAME.
interharmonic beats Beat notes produced by various
combinations of the harmonics of a signal.
interim storage See TEMPORARY STORAGE.
interior label On a magnetic tape used as a computer-storage
medium, a label recorded at the beginning
of the tape. Compare EXTERIOR LABEL.
interior protection 1. In electronic security applications,
a set of sensors contained entirely within
the region to be protected. 2. The installation and
operation of a security system whose sensors are
all within the region to be protected.
interlace A form of data storage in which portions
of the data are stored in alternate locations in the
tape or disk.
interlaced field A video image field produced by
INTERLACED SCANNING.
interlaced scanning In the display of a video image,
the alternate presentation of the even- and
odd-line fields. This process increases the obtainable
image resolution for a given refresh rate, but
can result in “jerkiness” of the image when rapid
motion is portrayed.
interlace factor A number expressing the extent
to which two fields are interlaced. Also see IN-
TERLACED SCANNING.
interleaving In multiprogramming, the inclusion
in a program of segments of another program so
that both can be effectively executed simultaneously.
interlock switch See ELECTRICAL INTERLOCK.
intermediate amplifier See BUFFER.
intermediate frequency Abbreviation, IF. In a superheterodyne
circuit, the frequency of the signal
that results from beating the incoming signal
with the signal produced by the local oscillator.
intermediate-frequency amplifier In a superheterodyne
circuit, the fixed-frequency amplifier
that boosts the intermediate-frequency signal.
Also see INTERMEDIATE FREQUENCY.
intermediate-frequency channel Usually, the intermediate-frequency
amplifier in a superheterodyne
circuit, but sometimes including the second
Input
Tuned
to IF
+
Tuned
to IF
intermediate-frequency amplifier
detector, automatic gain control (AGC), and oscillator
stages.
intermediate-frequency converter See IF CON-
VERTER.
intermediate-frequency interference Interference
from signals at the intermediate frequency
of a receiver or instrument.
intermediate-frequency selectivity The selectivity
of an intermediate-frequency (IF) channel
alone, usually determined by the characteristics
of the bandpass filter(s) in the IF channel.
intermediate-frequency transformer A coupling
transformer designed for use in an intermediatefrequency
amplifier.
intermediate-puck drive In a tape recorder, a
speed-reducing drive system in which an intermediate
wheel conveys motion from the motor
shaft to the rim of the flywheel.
intermediate puck wheel See IDLER WHEEL.
intermediate repeater In wire telephony, a repeater
inserted into a line or trunk at some point
other than the end.
intermediate result Obtained during a program
run or the execution of a subroutine, a result that
is used again as an operand in deriving the final
result.
intermediate section Any of the internal sections
of a multisection filter. Thus, the middle section
of a three-section filter.
intermediate storage In a computer system, a
storage medium for temporarily holding totals or
working figures. Also called WORK AREA.
intermediate subcarrier A modulated or unmodulated
subcarrier that modulates either a carrier or
another intermediate subcarrier.
intermittent 1. Pertaining to a circuit fault, such
as an open or short circuit, that occurs some of
the time, but not all the time. 2. See INTER-
MITTENT CONDITION. 3. Pertaining to a phenomenon
that is observed some of the time, but
not all the time; sporadic. 4. Pertaining to a DUTY
CYCLE greater than zero, but less than 100 percent;
usually between 25 and 50 percent.
intermittent commercial and amateur service
Abbreviation, ICAS. Operation of equipment,
such as radio transmitters, for short, irregular
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Output