18WuD2x

eductionism • reflected power 589
be reduced to digital logic, and thus can be duplicated
by a sufficiently powerful computer. It is of
interest to researchers in artificial intelligence.
reductionist A person who subscribes to the theory
of REDUCTIONISM.
redundancy 1. The repetition of components in a
circuit (e.g., series or parallel connection of them)
so that one will be available for circuit operation
if the other fails. 2. Having available more than
one method for performing a function. 3. Having
on hand several copies of data as a safeguard
against data loss.
redundancy check A check for the integrity of digitized
data to which extra bits have been added
for the purpose (e.g., parity check).
redundant 1. Pertaining to any two units of data
that resemble each other in such a manner that if
either unit is removed, no information is lost from
the system. 2. A unit of data that contains information
already present in the system.
redundant array of independent disks Acronym,
RAID. A set of data storage media used to store
video programs.
red video voltage In a three-gun color-television
circuit, the red-signal voltage that actuates the
red gun.
reed A usually thin metal blade, leaf, or strip used
in vibrators, reed-type relays, reed-type oscillators,
and similar devices.
reed oscillator See REED-TYPE OSCILLATOR.
reed relay See DRY-REED SWITCH and
MERCURY-WETTED REED RELAY.
reed-relay logic Logic circuits using reed relays.
Also see RELAY LOGIC.
reed switch 1. A frequency-sensitive switch in
which the movable contact is mounted on the tip
of a thin, metal strip (reed). The reed is actuated
by an alternating-current (ac) coil. The reed
closes the contacts when the ac excitation is at its
natural frequency. 2. See DRY-REED SWITCH.
reed-type oscillator An electromechanical audiofrequency
oscillator whose frequency is controlled
by a vibrating metal strip (reed) instead of
a tuning fork. Also see HUMMER.
reed-type switch See REED SWITCH.
reel 1. The spool around which a magnetic tape or
video film is wound. 2. A spool containing magnetic
tape or video film.
reentrant cavity A resonant cavity in which one or
more sections are directed inward to confine the
electric field to a small volume.
reentrant winding A winding of wire that returns
to its starting point—especially in a motor armature.
ref Abbreviation of REFERENCE.
reference address As a point of reference, an address
for instructions having relative addresses.
reference amplifier A voltage-regulation device
consisting of a transistor and Zener diode in the
same envelope.
reference angle In radar, the angle of incidence of
the beam against a target surface, measured with
respect to the normal (perpendicular) line at the
surface.
reference antenna A standard antenna, such as
an isotropic radiator or a half-wave dipole, used
to establish a reference for determining the relative
gain of another antenna.
reference bias current In a reference amplifier,
the input current that subtracts from the reference
current. It is generally measured in microamperes.
reference current range In a digital-to-analog converter,
the difference between the maximum and
minimum reference current for which the device
is within specifications for resolution.
reference diode A Zener diode whose constant
voltage drop is used as a direct-current reference
potential in calibrator circuits and voltage regulators.
reference dipole See REFERENCE ANTENNA.
reference electrode For use with a pH meter, an
electrode that provides a reference potential.
reference input slew rate In a digital-to-analog
converter, the average rate of change in output
for a given change in the reference input. It is expressed
in milliamperes or microamperes per microsecond.
reference level A specific value of a quantity (e.g.,
current, frequency, power, or voltage) to which
other values of the same quantity are referred.
reference time The point at which a trigger pulse
attains 10 percent of its maximum amplitude.
reference tone A standard audible tone of known
frequency [e.g., 440 Hz (representing A below
middle C)]. Sometimes the intensity as well, as
the frequency, is specified.
reference white level The television picture signal
value representing the uppermost limit for peak
white signals.
R eff Symbol for EFFECTIVE RESISTANCE.
reflectance 1. See MISMATCH FACTOR. 2. The reflected
part of the radiant flux striking a surface.
It is expressed as a fraction of the total incident
radiation.
reflected binary code See CYCLIC CODE.
reflected electromagnetic field In a transmission
line, the electromagnetic energy not absorbed by
the load when an impedance mismatch exists between
the load and the line. See INCIDENT
POWER and REFLECTED POWER.
reflected impedance In a coupled circuit, the
impedance in the secondary that appears in the
primary circuit, or vice-versa, as if it were reflected
through the coupling transformer.
reflected power In a transmission line not perfectly
matched to a load at the feed point, an expression
of the amount of electromagnetic field
reflected from the feed point, rather than absorbed
by the load. In general, this can be expressed
in watts or as a percentage of the
incident power. It is not a true indicator of the