18WuD2x

direct scanning • discrete capacitor 199
direct scanning In television, the sequential viewing
of parts of a scene by the camera—even
though the entire scene is continuously illuminated.
direct serial file organization A technique of organizing
files stored in a direct access device, in
which a record can be chosen by number and
amended where it is without altering other members
of the file.
direct sound wave A sound wave arriving directly
from its source—especially a wave within an enclosure
that is not affected by reflection.
direct substitution 1. An exact component replacement.
2. Installing an exact component replacement.
direct synthesizer A device for producing random,
rapidly changing frequencies for security purposes.
A reference oscillator provides a comparison
frequency; the output frequency is a
rational-number multiple of this reference frequency.
direct voltage See DC VOLTAGE.
direct wave A wave that travels from a transmitter
to a receiver without being reflected by the ionosphere
or the ground. Compare SKYWAVE.
direct Wiedemann effect Twisting force (torque)
in a wire carrying current in a longitudinal magnetic
field. Occurs because of interaction between
the longitudinal field and the circular magnetic
field around the wire.
direct-wire circuit A communications or control
line of wires connecting a transmitter (or control
point) and a receiver (or controlled point) without
an intermediary, such as a switchboard.
direct-writing recorder See GRAPHIC RE-
CORDER.
direct-writing telegraph 1. See PRINTING TELE-
GRAPH. 2. See TELAUTOGRAPH.
dis- A prefix meaning “deprived of.” For the formation
of electronic terms, the prefix must be distinguished
from un-, meaning “not.” For example, a
discharged body is one that was charged, but has
been emptied of its charge. An uncharged body is
one that ordinarily or presently is not charged.
disable 1. To deliberately render a circuit, device,
or system inoperative. 2. In digital computer
operations, to defeat a software or hardware
function.
disc See DISK.
disc engraving 1. Recording sound by cutting a
groove in a record disc. 2. The groove resulting
from such a process.
discharge The emptying or draining of electricity
from a source, such as a battery or capacitor. The
term also denotes a sudden, heavy flow of current,
as in DISRUPTIVE DISCHARGE. Compare
CHARGE.
discharge current 1. Current flowing out of a capacitor.
2. Current flowing out of a cell—especially
a storage cell. Compare CHARGING
CURRENT.
discharge key See DISCHARGE SWITCH.
discharge lamp A gas-filled tube or globe in which
light is produced by ionization of the gas between
electrodes. Familiar examples are the neon bulb
and fluorescent tube.
discharge phenomena The effects associated with
electrical discharges in gases, such as luminous
glow.
discharge potential See IONIZATION POTENTIAL.
discharger 1. A short-circuiting tool for discharging
capacitors. 2. A spark gap or other device for
automatically discharging an overcharged capacitor.
discharge rate 1. The current that can be supplied
by an electrochemical cell or battery reliably during
its discharging cycle. Usually expressed in
milliamperes or amperes. 2. An expression of the
speed with which a battery is being discharged at
a specific point in time. It is usually specified in
amperes or milliamperes.
discharge switch A switch for connecting a
charged capacitor to a resistor or other load,
through which the capacitor discharges. In some
circuits, when the switch is in its resting position,
it connects the capacitor to the charging source.
discharge voltage See IONIZATION POTENTIAL.
discharging 1. The conversion of chemical energy
to electrical energy by an electrochemical cell or
battery. 2. The release of stored electrical energy
from a capacitor, or from a network containing
capacitors.
discharging tongs See DISCHARGER, 1.
discone antenna An antenna consisting of a horizontal
metal or wire-mesh disk above a metal or
wire-mesh cone. The antenna has an omnidirectional
radiation pattern in the horizontal plane,
and provides a good match to a coaxial transmission
line over a frequency range of several octaves.
Commonly used at very-high frequencies
(VHF) and ultra-high frequencies (UHF).
disconnect 1. To separate leads or connections,
thereby interrupting a circuit. 2. A type of connector
whose halves can be pulled apart to open
a cable or other circuit quickly. 3. To open a
switch or relay.
disconnector See DISCONNECT, 2 and DISCON-
NECT SWITCH.
disconnect signal A signal sent over a telephone
line, ending the connection.
disconnect switch A switch whose main function
is to open a circuit quickly (either manually or
automatically) in the event of an overload.
discontinuity 1. A break in a conductor. 2. A
point at which the impedance in a transmission
line abruptly changes.
discontinuous wave trains See DAMPED WAVES.
discrete 1. Complete and self-contained, as opposed
to a part of something else. 2. Composed of
individual, separate members.
discrete capacitor Capacitance that is entirely
self-contained, rather than being electrically dis-