18WuD2x

584 reactance chart • readthrough
reactance chart A nomograph for capacitance, inductance,
and frequency.
reactance factor The ratio of the alternatingcurrent
resistance of a conductor to the directcurrent
resistance. The reactance factor generally
increases as the frequency increases because of
skin effect and because the length of the conductor
might be a sizable part of the wavelength of
the transmitted energy.
reactance modulator A frequency modulator using
a variable reactance, usually a varactor diode
in the oscillator.
AF
in
− +
Varactor
bias
reactance modulator
To
osc.
Circuit
reactance transistor A transistor used as a REAC-
TANCE MODULATOR.
reaction-time meter See NEOMATACHOGRAPH
and NEOMATACHOMETER.
reactive absorber In acoustics, a device that dissipates
impinging sound waves by means of reflection,
resonance, and other effects, besides
dissipation in the form of heat.
reactive attenuator An attenuator that functions
by means of reactance, rather than by means of
resistance.
reactive current The component of alternating
current that is not in phase with the voltage.
Compare RESISTIVE CURRENT.
reactive kilovolt-ampere Abbreviation, kVAR. A
unit of high apparent power; it is the product of
kilovolts and amperes in a reactive component of
a circuit. Also see APPARENT POWER, KILO-
VOLT-AMPERE, REACTIVE VOLT-AMPERE, and
VOLT-AMPERE.
reactive load 1. A load device that is capacitive or
inductive, rather than resistive. 2. A load device
that contains reactance as well as resistance.
reactive power See REACTIVE KILOVOLTAM-
PERE and REACTIVE VOLT-AMPERE.
reactive volt-ampere Abbreviation, VAR. A unit of
apparent power; it is the product of volts and amperes
in a reactive component of a circuit. Also see
APPARENT POWER, KILOVOLT-AMPERE, REAC-
TIVE KILOVOLT-AMPERE, and VOLT-AMPERE.
reactor 1. An inductor, especially one having very
low internal resistance, used principally for its inductive
reactance. 2. A chamber in which the nuclei
of atoms are split to provide atomic energy.
Also see NUCLEAR REACTOR. 3. In industrial
chemistry, a vat in which reactions take place.
read 1. In computer operations, to extract data
from memory or a storage medium and (usually)
transfer it to another area of memory or other
medium. Compare WRITE. 2. In digital communications,
to transcribe data into printed form. 3. In
radiotelegraphy, to listen to Morse-code signals
and comprehend the text without necessarily
writing it down. 4. To observe and note the indication
of an instrument, such as a meter.
readability In electronic communications, the degree
to which a desired signal can be recognized
and interpreted in a given context.
readback In a multiplexer, a feature that facilitates
inspection of the contents of the control latch.
reader A device that transcribes digital signals or
markings into meaningful data. Examples:
Morse-code reader and bar-code reader.
read head In a magnetic memory or in a tape
recorder or wire recorder used for data recording,
the head that picks up the magnetic pulses from
the drum, tape, disk, or wire. Compare WRITE
HEAD.
reading rate The number of input characters per
second that a computer or other data-processing
device handles.
read-only memory Abbreviation, ROM. In a computer
or calculator, a memory unit in which instructions
or data are permanently stored for use
by the machine or for reference by the user. The
stored information is read out nondestructively.
readout lamp An electron tube containing several
cathodes, filled with a gas (such as neon), and
used as a numeric or alphanumeric display device.
Each cathode is connected to a separate pin
on the base. A single anode is common to all
cathodes. The cathode(s) to which a voltage is applied
glow(s), showing the shape of a numeral, letter
of the alphabet, or other symbol. In recent
years, this type of display has been replaced by
light-emitting diodes (LEDs) and liquid-crystal
displays (LCDs).
readout pulse In a random-access memory (RAM),
a pulse applied to the word line, facilitating readout
of the information in a certain storage slot.
read pulse In computer operations, a pulse that
activates the read function (see READ). Compare
WRITE PULSE.
read rate The number of data units an input read
device can transcribe per unit of time [e.g., bits
per second (bps) and words per minute (wpm)].
readthrough 1. The reception of signals between
transmitted pulses at the same frequency.
2. The continuous monitoring of a signal being
jammed. Any change in the frequency, modulation,
or other characteristics of the signal can