18WuD2x

718 vapor lamp • variable inductor
vapor lamp A discharge lamp consisting essentially
of a glass tube filled with a small amount of
gas under low pressure and some element, such
as mercury or sodium. A high voltage is applied
between electrodes sealed into each end of the
tube. The voltage causes the element to vaporize.
This, in turn, ionizes the gas, causing it to glow.
vapor pressure In a confined medium, the pressure
of a gas, measured in atmospheres, pounds
per square inch, or millimeters of mercury.
VAR Abbreviation of VOLT-AMPERES REACTIVE.
var Abbreviation of VARIABLE.
varactor A semiconductor-type voltage-variable
capacitor. Sometimes called a varactor diode.
varactor amplifier A dielectric amplifier using a
varactor as the voltage-variable capacitor.
varactor flip-flop A bistable multivibrator based
on the nonlinear performance of one or two varactors.
varactor frequency multiplier A frequency multiplier
(doubler, tripler, etc.) in which multiples of a
fundamental frequency result from the nonlinear
action of a varactor.
C1
C1 and L1 tuned to f
C2 and L2 tuned to F xn
L1
RF input (f ) RF output (F xn )
L2
C2
varactor frequency multiplier
varactor tuning A method of tuning a circuit or
adjusting the frequency of an oscillator, using an
inductor and a varactor to obtain the desired frequency.
The varactor acts as a variable capacitor.
VAR-hour Abbreviation, VARh. Short for voltampere-reactive-hour,
a unit of reactive energy;
1 VARh can be represented by 1 VAR for 1 hour,
2 VAR for 0.5 hour, 0.5 VAR for 2 hours, etc.
VAR-hour meter An instrument that measures reactive
energy.
variable Abbreviation, var. A quantity whose value
changes at some stated or calculable rate, and is
given names in expressions or equations, such as
x, y, or z. Compare CONSTANT. Also see DEPEN-
DENT VARIABLE and INDEPENDENT VARIABLE.
variable-area sound track See VARIABLE-WIDTH
SOUND RECORD.
variable block In computer operations, a unit of
data, such as a group of records, whose size is dependent
on data requirements (i.e., it is not fixed).
variable-capacitance diode See VARACTOR.
variable-capacitance transducer See CAPACI-
TIVE TRANSDUCER.
variable capacitor A capacitor that can be adjusted
from a low value (practically zero) to some
maximum value. A step-type unit contains a
number of fixed capacitors that can be switched
in parallel with each other until, at the last step,
all are in parallel. A continuously variable unit
has a provision for moving one plate or set of
plates, relative to another plate or set of plates; or
one plate might be moved, with respect to another,
so that the distance between them is
changed. In a voltage-variable capacitor (such as
a varactor), capacitance varies in accordance
with an applied direct-current voltage.
variable-carrier modulation See QUIESCENT-
CARRIER OPERATION.
variable connector In a flowchart, a path leading
from a box in which a decision is made, to a number
of other points on the diagram.
variable coupling Coupling that is adjustable. In
an inductively coupled circuit, the distance or angle
between the coils is usually the adjustable
factor. In a capacitively coupled circuit, a variable
capacitor is generally used.
variable-density sound record In photographic
sound-on-film recording, a sound track made by
varying, in sympathy with the sound frequency,
the amount of light reaching the film. Compare
VARIABLE-WIDTH SOUND RECORD.
variable-depth sonar A sonar device that can be
placed far below the surface, for the purpose of
detecting objects or terrain at greater depths than
would be possible with a surface-located sonar
device.
variable-efficiency modulation See EFFICIENCY
MODULATION.
variable-erase recording In magnetic-tape operations,
recording a signal by selectively erasing a
previously recorded signal.
variable field 1. Any field with an intensity that
changes with time. An electromagnetic field is a
common example. 2. In a computer record, a field
that is a variable block with a terminal symbol at
the end.
variable-frequency oscillator Abbreviation, VFO.
An oscillator (usually self-excited) whose frequency
is continuously variable.
variable-inductance pickup A phonograph pickup
in which vibration of the stylus causes the inductance
of a small coil to vary in sympathy with
the sound frequency.
variable-inductance transducer A transducer in
which a monitored quantity causes the inductance
of a coil to vary proportionately. The coil
thereby offers a varying impedance to an
alternating-current supply voltage.
variable inductor An inductor whose value can be
adjusted from zero to a certain maximum. The
variability might be in steps, provided by taps on
the inductor, or a sliding contact can be used.