digital circuit 1. A circuit that operates like a switch (it is either on or off) and can make logical decisions. It is used in computers or similar decision-making equipment. The more common families of digital integrated circuits (called logic forms) are RTL, DTL, HTL, ECL, and TTL. 2. A circuit that has only two stable states, operating in the manner of a switch, that is, it is either on or off, or high or low (i.e., high voltage or low voltage).

digital clock A series of synchronized pulses that determine the bit times (data rate) of a digital pattern.

digital communication 1. The transmission of intelligence by the use of encoded numbers — usually uses the binary rather than decimal number system. 2. A system of telecommunications employing a nominally discontinuous signal that changes in frequency, amplitude, or polarity.

digital communications interface equipment Line interface equipment, including modems.

digital computer 1. An electronic calculator that operates with numbers expressed directly as digits, as opposed to the directly measurable quantities (voltage, resistance, etc.) in an analog computer. In other words, the digital computer counts (as does an adding machine); the analog computer measures a quantity (as does a voltmeter). 2. A computer that processes information in numerical form. Electronic digital computers generally use binary or decimal notation and solve problems by repeated high-speed use of the fundamental arithmetic processes of addition, subtraction, multiplication, and division. 3. A computer system in which circuit operation is based on specific signal levels. In a binary digital computer, there are two such signal levels, one at or near zero and the other at a defined voltage. 4. A device that performs sequences of arithmetic and logic operations on discrete data. 5. A type of data-processing equipment that counts, utilizing numbers to express the values and quantities. General-purpose digital computers include central storage units and peripheral control units and are designed to solve a wide class of problems. A common feature of general-purpose equipment is the ability to externally modify the program of instructions. Special-purpose digital computers are not intended for a typical commercial physical environment and include rugged computers for military and space applications. An analog computer measures cost or conditions. Hybrid computers utilize both modes. 6. A computer that solves problems by operating on discrete representing variables by performing arithmetic and logic processes on this data.

digital data 1. Data represented in discrete, discontinuous form, as contrasted with analog data represented in continuous form. Digital data is usually represented by means of coded characters (e.g., numbers, signs, symbols, etc.). 2. Any data that is expressed in digits. The term usually implies the use of binary digits.

digital data-handling system The electronic equipment that receives digital data, operates on it in a suitable manner, records it in a suitable manner on a suitable medium, and presents it directly to a computer or a display.

digital delay line See active delay line.

digital delay module See active delay line.

digital delay unit See active delay line.

digital device 1. Typically, an IC that switches between two exclusive states or levels, usually represented by logical 1 or 0. 2. An electronic device that processes electrical signals that have only two states, such as on or off, high or low voltages, or positive or negative voltages. In electronics, digital normally means binary or two-state.

digital differential analyzer A special-purpose digital computer that performs integration and that can be programmed for the solution of differential equations in a manner similar to that of an analog computer.

digital disc recording An analog disc recording that has been made from a master tape recording that was digitally recorded.

digital filter 1. A linear computation or algorithm performed on a selected series in the form of an input signal that produces a new series as output. The computational device may be a specifically designed electronic system or a conventional computer. 2. Network that operates on discrete samples of a signal to achieve a desired transfer-function operation on that signal. Digital filters divide into two classes: nonrecursive filters produce an output that is a function of only the previous and present inputs; recursive filters produce an output that is a function of both the past and present inputs and outputs.

digital filtering 1. A computational process or algorithm by which a sampled signal or sequence of numbers, acting as input, is transformed into a second sequence of numbers called the output. The computational process may correspond to high-pass, low-pass, bandpass, or bandstop filtering, integration, differentiation, or something else. The second sequence can be used for further processing, as in a fast-Fourier-transform analyzer, or it can be converted to an analog signal, producing a filtered version of the original analog signal. 2. The process of smoothing, spectrally shaping, or removing noise from a signal. Digital filters are basically mathematical functions that are performed on the digital data stream; their characteristics can be altered under software control, which adds to their overall flexibility. Finite impulse response (FIR) and infinite impulse response (IIR) are examples of digital filter functions.

digital frequency monitor A special-purpose digital counter that permits a train of pulses to pass through a gate for a predetermined time interval, counts them, and indicates the number counted.

digital harmonic generation Abbreviated DHG. The use of circuit elements whose outputs are discontinuous functions of their inputs to produce signals that are an integral multiple of the (fundamental) input signal.

digital image analysis Technology to measure and standardize the output of a computer-interfaced vidicon system.

digital imaging The process by which an image that is in electronic form (e.g., a bit-mapped graphic) is altered.

digital information display The presentation of digital information in tabular form on the face of a digital information display tube.

digital integrated circuit 1. A switching-type integrated circuit. 2. An integrated circuit that processes electrical signals that have only two states, such as on or off, high or low voltages, or positive or negative voltages. In electronics, digital normally means binary or two-state. 3. A monolithic group of logic elements. May be small-scale integration (e.g., SSI gates, flip-flops, latches), medium-scale integration (e.g., MSI decoders, adders, counters), or large-scale integration (e.g., LSI memories, microprocessors). 4. A class of integrated circuits that processes digital information (expressed in binary numbers). The processing operations are arithmetic (such as addition, subtraction, multiplication, and division) or logical (in which the circuit senses certain patterns of input binary information and indicates the presence or absence of those patterns by appropriate output binary signals).

digital integrator Device for summing or totalizing areas under curves that gives numerical readout. See also integrator.

digital logic modules Circuits that perform basic logic decisions (AND, OR, NOT); used widely for arithmetic and computing functions, flip-flops, half-adders, multivibrators, etc. See also logic system.

digitally programmable oscillator A voltage-controlled oscillator designed to accept a digital tuning word instead of the usual analog signal. Internal digital-to-analog (d/a) converter circuits transform the digital input to an analog voltage. Tuning-curve linearization is usually accomplished through a digital memory. The frequency speed is primarily limited by the d/a circuits.

digital modulation A method of transmitting human voice or other analog signals using a binary code (0s and 1s). Digital transmission offers a cleaner signal than analog technology.

digital multimeter Abbreviated DMM. A test instrument used to measure voltage, current, and resistance. The readout of measured values is shown on a digital display which is typicallv a liquid crystal display (LCD).

digital optical processing The scanning of photographs or transparencies of images, either by a vidicon camera or flying-spot scanner, for the conversion of the images to digital form for storage on magnetic tape.

digital output An output signal that represents the size of a stimulus or input signal in the form of a series of discrete quantities that are coded to represent digits in a system of numerical notation. This type of output is to be distinguished from one that provides a continuous output signal.

digital panel meter Abbreviated DPM. 1. A compact electronic measuring system capable of converting an electrical variable into an unambiguous, accurate numerical reading. Consists of a solid-state analog-to-digital converter and a logic-driven numerical display that can provide readings with accuracies of 0.1 to 0.005 percent of full scale, without the need for eye-straining interpolation. 2. A meter with digital-numerical readout, capable of indicating a range of values from zero to rated maximum, in increments of one least-significant digit.

digital phase shifter A device that provides a signal phase shift by the application of a control pulse. A reversal of phase shift requires a control pulse of opposite polarity.

digital plotter An output unit that graphs data via an automatically controlled pen. Data is normally plotted as a series of incremental steps.

digital position transducer A device that converts motion or position into digital information.

digital programmable delay line See active delay line.

digital radio 1. Microwave radio in which one or more properties (amplitude, frequency, and phase) of the rf carrier are quantized by the modulating signal. 2. Radio whose instantaneous rf carrier can assume one of a discrete set of amplitude levels, frequency shifts, or phase shifts as a result of the modulating signal. 3. Radio in which the rf carrier, or even the baseband signal, is quantized by means of a modem. In such a radio the rf carrier is still quantized, but baseband or intermediate-frequency filtering can be used to provide some bandwidth control and thereby reduce rf filtering requirements. 4. Any radio that transmits a signal whose informational content is, in whole or in part, digital in format.

digital readout indicator An indicator that reads directly in numerical form, as opposed to an analog indicator needle and scale.

digital recording A technique for recording information as discrete points onto magnetic recording media.

digital rotary transducer A rotating device utilizing an optical sensor that produces a serial binary output as a result of shaft rotation.

digital set top Also referred to generically as a set-top unit (STU). Television set-top units that accept digital video as well as analog (traditional) video. Some digital set-top units enable interactivity and therefore support shopping, banking, games, etc.

digital signal 1. An electrical signal with two states — on or off, high or low, positive or negative — such as could be obtained from a telegraph key or two-position toggle switch. Digital normally means binary or two-state. 2. Representation of information by a set of discrete values in accordance with a prescribed law. These values are represented by numbers.

digital signals 1. Discrete or discontinuous signals whose various states are discrete intervals apart. 2. Signals made up of discontinuous pulses whose information is contained in their durations, periods, and/or amplitudes.

digital signature 1. A numerical representation of a set of logic states, typically used to describe the logic-state history at one device under test output pin during the complete test program. 2. A personal authentication method based on encryption and secret authorization codes used for “signing” electronic documents.

digital simulation See simulation.

digital speech communications Transmission of voice signals in digitized or binary form.

digital status contact A logical (on/off) input used mainly to sense the status of remote equipment in process control systems.

digital storage oscilloscope A special oscilloscope that adapts analog monitoring and recording systems to the capture and analysis of all types of one-shot physical phenomena.

digital switch 1. A means to interconnect two or more circuits whose information is represented in digital form, using a time-divided network consisting of nonlinear elements. 2. An automatic switching center capable of switching digital signals. It may be a circuit switch or a message switch.

digital switching Switching of messages digitally by use of integrated electronic circuits for logic and memory, rather than by electromechanical switches.

digital synthesizer A means of generating several different frequencies without using separate oscillators governed by crystals specially ground for each frequency. A digital synthesizer uses only one reference crystal, a phase-locked loop, and a digital counter to generate a large number of stable frequencies. These circuits are used to reduce dependence on individual crystals, which are relatively expensive.

digital telephone dialer An automatic telephone dialer that uses a digital code.

digital television Abbreviated DTV. 1. A television system in which reduction or elimination of picture redundancy is obtained by transmitting only the information needed to define motion in the picture, as represented by changes in areas of continuous white or black. 2. An umbrella term used to describe the digital television system adopted by the FCC in December 1996.

digital thermometer Electronic temperature-measuring device that reads and/or prints out numerically.

digital-to-analog conversion The generation of analog (usually variable-voltage) signals in response to a digital code.

digital-to-analog converter Abbreviated DAC, dac, or d/a converter. 1. A computing device that changes digital quantities into physical motion or into a voltage (i.e., a number output into turns of a potentiometer). 2. A unit or device that converts a digital signal into a voltage or current whose magnitude is proportional to the numeric value of the digital signal. For example:

3. A circuit that accepts the discrete, binary outputs of computers and changes them into continuous analog quantities. In general, DACs convert mathematical results into usable electrical quantities. Digital-to-analog converters are used to generate and modulate waveforms, stimulate devices under test, drive motors, or display information. They have applications in process and industrial control systems, cathode-ray-tube displays, and digitally programmed power supplies. Most DACs consist of three major blocks: a precision reference, a set of resistors forming a ladder network, and switches that connect or disconnect the resistor ladder and the reference. Some DACs also include an output amplifier that buffers the current from the ladder and interfaces it to the circuits at the DAC’s output. 4. An interface that converts data in a digital form to data in analog form. Used to permit analog output from a digital computer.

digital-to-disc recording A recording technique in which a digital master tape is transferred to a conventional master lacquer disc for the manufacturing of phonograph records.

digital transmission 1. A mode of transmission in which all information to be transmitted over the facility is first converted into digital form and then sent down the line as a stream of pulses. (Such transmission may imply a serial bit stream, but parallel forms are also possible.) When noise and distortion threaten to destroy the integrity of the pulse stream, the pulses are detected and regenerated. 2. The transmission of a signal in which information is represented by a code of discrete elements. Compare with analog transmission.

digital versatile disc See DVD.

digital video disc See DVD.

digital voltmeter 1. An indicator that provides a digital readout of measured voltage rather than a pointer indication. 2. An electronic instrument that converts an analog voltage of unknown magnitude into a digital display of known value.

digit compression In a computer, any of several techniques used to pack digits.

digitization 1. The conversion of black-and-white artwork and continuous-tone photographs to a series of binary numbers that can be stored and processed in a computer system. 2. The process of converting analog video, images, or audio into digital format (i.e., 1s and 0s).

digitize 1. To transform information from the analog (continuous wave-like signal) into a digital format, i.e., into a series of 1s and Os. 2. To convert an image or signal into digital code for input into a computer; to scan an image, trace a picture on a graphics tablet, or convert camera images. 3. To convert an analog measurement of a physical variable into a number expressed in digits in a scale or notation. 4. To translate a quantitative measurement into a coded numerical equivalent. 5. To convert drawing or picture information into digital form.

digitized image An image that has been converted into a series of discrete units that are represented in a computer by the binary digits 1 and 0; such an image can then be manipulated for various purposes.

digitized speech A numerical representation of speech in which the amplitude of the speech waveform has been recorded at regular intervals. Speech is typically sampled from 8000 to 12,500 times per second.

digitizer 1. A device that converts analog data into numbers expressed in digits in a system of notation. 2. A device that transforms graphical data into planar coordinate information that can be read and understood by a computer. These coordinates are usually presented as x and y coordinates based on the position of a cursor on the surface, or platen, of the digitizer. The cursor has a viewing area with a crosshair for alignment with the point of interest on the document, and is coupled either mechanically or electrically to a position-sensing device that provides the positional information to the computer. 3. A device that converts coordinate information into numeric form readable by a digital computer. 4. A computer peripheral device that converts an analog electrical signal into numeric form readable by a digital computer. 5. A device that translates input into digital form, to make it possible, for example, to enter sketches into a computer.

digitizing 1. The process of converting an analog signal to a digital signal. 2. Any method of reducing feature locations on a flat plane to digital representation of x and y coordinates. 3. The process of converting graphic representations, such as pictures and drawings, into digital data that can be processed by a computer system.

digitron display In a calculator, a type of display in which all digits appear in the same plane. Similar to mosaic lamp display.

digit selector In a computer, a device for separating a card column into individual pulses that correspond to punched row positions.

digit-transfer bus The main wire or wires used to transfer information (but not control signals) among the various registers in a digital computer.

diheptal base Also called diheptal socket A vacuum-tube base having 14 pins (such as the base of a cathode-ray tube).

diheptal socket See diheptal base.

DIIC Dielectrically isolated integrated circuits. Devices isolated from each other by a layer of dielectric insulation, usually glass, rather than by the more conventional reverse-biased pn junction. This “insulated substrate” structure is far more radiation resistant than junction-isolated units, making DIICs valuable in military and aerospace applications.

dimensional stability 1. The ability of a body to maintain precise shape and size. 2. A measure of dimensional change caused by such factors as temperature, humidity, chemical treatment, age, or stress, usually expressed as units per unit.

dimension ratio (L/D) The ratio of the length of a magnet in the direction of magnetization to its diameter. Or, the ratio of the length of the magnet to the diameter of a circle having an area equal to the cross-sectional area of the magnet. Used as figure of merit to find a magnet’s composite permeance coefficient.

diminished-radix complement See radix-minus-one complement.

dimmer 1. A device for controlling the amount of light emitted by a luminaire. Common types employ resistance, autotransformer, magnetic amplifier, silicon-controlled rectifier or semiconductor, thyratron, or iris control elements. 2. An electric or electronic device that regulates the voltage going to a light source as a means of varying the intensity of the light emitted by the source.

dimmer curve The performance characteristic of a light dimmer expressed as a graph of the light output of a dimmer-controlled lamp versus the setting of the control in terms of an arbitrary linear scale of 0 to 10.

DIN 1. The abbreviation for the association in West Germany that determines the standards for electrical and other equipment in that country, Deutsches institut für Normung (German Institute for Standards). Similar to the American National Standards Institute. 2. A set of standards and specifications promulgated by German manufacturers and covering such audio-related matters as connectors, frequency weighting, measurement techniques, and specifications.

D-indicator A radar indicator that combines types B and C indicators. The signal appears as a bright spot, with azimuth angle as the horizontal coordinate and elevation angle as the vertical coordinate. Each horizontal trace is expanded vertically by a compressed time sweep to facilitate separation of the signal from noise and to give a rough range indication.

DIN jack A system of multipin jacks and plugs allowing several connections to be made at once. Named after the German Institute for Standards (DIN).

diode 1. An electron tube having two electrodes: a cathode and an anode. 2. See crystal diode. 3. A two-element electron tube or solid-state device. Solid-state diodes are usually made of either germanium or silicon and are primarily used for switching purposes, although they can also be used for rectification. Diodes are usually rated at less than one-half ampere. 4. A two-terminal electronic device that will conduct electricity much more easily in one direction than in the other. 5. A semiconductor device with two terminals and a single junction, exhibiting varying conduction properties depending on the polarity of the applied voltage. 6. A two-terminal semiconductor device exhibiting a nonlinear voltage-current characteristic; it has the asymmetrical voltage-current characteristic exemplified by a single pn junction.

diode amplifier A parametric amplifier that uses a special diode in a cavity. Used to amplify signals at frequencies as high as 6000 MHz.

diode assembly A single structure of more than one diode.

diode characteristic The composite electrode characteristic of a multielectrode tube, taken with all electrodes except the cathode connected together.

diode demodulator Also called diode detector. A demodulator in which one or more semiconductor or electron-tube diodes are used to provide a rectified output that has an average value proportional to the original modulation.

diode detector See diode demodulator.

diode gate An AND gate that uses diodes as switching elements.

diode isolation A method in which a high electrical resistance between an IC element and the substrate is obtained by surrounding the element with a reverse-biased pn junction.

diode laser Also called laser diode, injected laser, coherent electroluminescence device, semiconductor laser. A pn junction semiconductor electron device that converts direct forward-bias electrical input (pump power) directly into coherent optical output power via a process of stimulated emission in the region near the junction.

diode limiter A circuit employing a diode and used to prevent signal peaks from exceeding a predetermined value.

diode logic An electronic circuit using current-steering diodes in an arrangement such that the input and output voltages have relationships that correspond to AND or OR logic functions.

diode matrix 1. A two-dimensional array of diodes used for a variety of purposes, such as decoding and read-only memory. 2. A hardware pattern in which diode leads may be inserted to change solid-state control logic.

diode mixer A diode that mixes incoming radio-frequency and local-oscillator signals to produce an intermediate frequency.

diode modulator A modulator in which one or more diodes are employed to combine a modulating signal with a carrier signal. It is used chiefly in low-level signaling because it has inherently poor efficiency.

diode pack A combination of two or more diodes integrated into a solid block.

diode peak detector A diode used in a circuit to indicate when audio peaks exceed a predetermined value.

diode-pentode A vacuum tube having a diode and a pentode combined in the same envelope.

diode rectification The conversion of an alternating current into a unidirectional current by means of a two-element device such as a crystal, vacuum tube, etc.

diode switch A diode in which positive and negative biasing voltages (with respect to the cathode) are applied in sucession to the anode in order to pass and block, respectively, other applied waveforms within certain voltage limits. In this way, the diode acts as a switch.

diode-transistor logic Abbreviated DTL. 1. A logic circuit that uses diodes at the input to perform the electronic logic function that activates the circuit transistor output. In monolithic circuits, the DTL diodes are a positive-level logical AND function or a negative-level OR function. The output transistor acts as an inverter to result in the circuit becoming a positive NAND or a negative NOR function. 2. Any logic gate circuit that uses several diodes to perform the AND or OR function, followed by one or more transistors to add power to (and possibly invert) the output. Formerly very popular in digital systems, but now largely superseded by TTL circuits. 3. Logic employing diodes at the input with transistors used as amplifiers and resistor pull-up on the output.

diode-triode A vacuum tube having a diode and triode combined in the same envelope.

diopter 1. The unit of optical measurement that expresses the refractive power of a lens or prism. 2. A measure of lens power equal to the reciprocal of the lens focal length in meters.

dip 1. A drop in the plate current of a class C amplifier as its tuned circuits are being adjusted to resonance. 2. The angle between the direction of the earth’s magnetic field and the horizontal as measured in a vertical plane.

DIP Abbreviation for dual in-line package.

dip coating 1. A method of applying an insulating coating to a conductor by passing it through an applicator containing the insulating medium in liquid form. The insulation is then sized and passed through ovens to solidify. This medium can be used for magnet wire. 2. A process of applying a relatively thin (less than 50 mils) conformal coating to a part or assembly. The final coating thickness is determined by the viscosity of the coating material, rate of withdrawal, temperature, and the number of coats. 3. Method in which an object is coated by dipping into a plastisol or organosol.

dip encapsulation A type of conformai coating. An embedding process in which the insulating material is applied by immersion and without the use of an outer container. The coating conforms generally with the contour of the embedding part or assembly.

diplexer 1. A coupling unit that allows more than one transmitter to operate together on the same antenna. 2. A device that enables two (radio) transmitters operating at different frequencies to use the same antenna simultaneously.

diplex operation 1. The simultaneous transmission or reception of two messages from a single antenna or on a single carrier. 2. The operation of two radio transmitters on different frequencies into the same antenna simultaneously.

diplex radio transmission Simultaneous transmission of two signals by using a common carrier wave.

diplex reception The simultaneous reception of two signals having some feature in common, for example, a single receiving antenna or a single carrier frequency.

dipole 1. A molecule that has an electric moment. For a molecule to be a dipole, the effective center of the positive charges must be at a different point than the center of the negative charges. 2. A form of speaker that radiates in approximately equal amounts to the rear and the front. 3. See dipole antenna.

dipole antenna Also called dipole. A straight radiator usually fed in the center. Maximum radiation is produced in the plane normal to its axis. The length specified is the overall length.

dipole disc feed An antenna, consisting of a dipole near a disc, used to reflect energy to the disc.

dipping The process of impregnating or coating insulating materials or windings by the simple method of immersion in the liquid insulating material. A step in the process of treating insulating materials or electrical components by immersion in a liquid insulation, followed by draining and curing to provide increased electrical and mechanical protection.

dip soldering 1. The process of soldering component leads, terminals, and hardware to the conductive pattern on the bottom of a printed circuit board by dipping that side into molten solder or floating it on the surface. 2. A process of joining metals, previously cleaned and fluxed, by immersing them wholly or partially into molten solder. The filling of the joint is by capillary attraction. 3. A process whereby items to be soldered are brought in contact with the surface of a static pool of molten solder for the purpose of soldering the entire exposed conductive pattern in one operation. 4. Soldering by dipping fluxed and fixtured parts in a solder pot. 5. The simplest form of mass soldering. It involves the lowering of a prefluxed assembly onto a solder bath surface. The assembly is then submerged sufficiently for the solder to spread and form the required joints but not flow over the top surface of a printed wiring board.

dip solder terminal The terminals on a connector that are inserted into holes in the printed circuit board and then soldered in place.

direct A method of expressing an absolute address in an MPU instruction where the actual address would be specified in hexadecimal in the instruction.

direct access The process of storing data in, or getting data from, a storage device in such a manner that surrounding data need not be scanned to locate the desired data. The time required to get desired data from the storage device is independent of the location of the data.

direct-access device See random-access device.

direct-access file A file in which each record may be accessed directly, regardless of its relative position in the file.

direct-access storage Also called random-access storage. Pertaining to the process of obtaining data from or placing data into storage in which the time required for such access is independent of the location of the data most recently obtained or placed in storage.

direct-acting recording instrument An instrument in which the marking device is mechanically connected to or directly operated by the primary detector.

direct address An address that specifics the location in a computer of an instruction operand.

direct addressing The standard addressing mode in a computer. It is characterized by an ability to reach any point in main storage directly. Direct addressing is sometimes restricted to the first 256 bits in main storage.

direct broadcast satellite Abbreviated DBS. 1. A satellite that allows the use of inexpensive home reception dishes to receive its high-power signals, including software and data. 2. A term commonly used to describe Ku-band broadcasts via satellite directly to individual end users. The DBS band ranges from 11.7 to 12.75 GHz.

direct capacitance 1. The capacitance between two conductors, excluding stray capacitance that may exist between the two conductors and other conducting elements. 2. The capacitance measured directly from conductor to conductor through a single insulating layer.

direct-connect modem A modem that connects directly to a phone line via modular connectors, rather than going through a telephone headset and an acoustic coupler.

direct-coupled amplifier 1. A direct-current amplifier in which the plate of one stage is coupled to the grid of the next stage by a direct connection or a low-value resistor. 2. An amplifier in which the output of one stage is connected to the input of the next stage without the use of intervening coupling components.

direct-coupled transistor logic Abbreviated DCTL. A NOR-gate type of bipolar logic in which the output of one gate is coupled directly to the input of the succeeding gate. This form of logic evolved into resistor-transistor logic because of the difficulty in mass producing transistors within the close tolerances necessary for direct coupling.

direct coupling 1. The association of two or more circuits by means of an inductance, a resistance, a wire, or a combination of these so that both direct and alternating currents can be coupled. 2. Interstage coupling or speaker coupling with no intervening transformer or capacitor. To the speaker it ensures that the damping factor remains high at low frequencies (but increasing power supply impedance at low frequencies can influence this), while direct coupling generally minimizes low-frequency phase shift and encourages enhanced bass performance. 3. The connection of two circuits in such a way that both ac and dc currents can flow. Neither a transformer nor a capacitor can be used in series with the signal-carrying wires since these components do not pass dc.

direct current Abbreviated dc. 1. An essentially constant-value current that flows in only one direction. 2. A flow of continuous electric current in one direction as long as the circuit is closed (as opposed to alternating current). 3. A current that flows in only one direction in an electric circuit. It may be continuous or discontinuous, and may be constant or varying.

direct-current amplifier Also called dc amplifier. An amplifier capable of boosting dc voltages. Resistive coupling only is generally employed between stages, but sometimes will be combined with other forms.

direct-current erasing head A head that uses direct current in magnetic recording to produce the magnetic field required far erasure. Direct-current erasing is achieved by subjecting the medium to a unidirectional field. Such a medium is therefore in a different magnetic state from one erased by alternating current.

direct-current generator 1. A rotating machine that changes mechanical into electrical energy in the form of direct current This is accomplished by commutating bars on the armature. The bars make contact with stationary brushes, from which the direct current is taken. 2. A rotary machine having a commutator that generates direct current when its armature is rotated in a magnetic field by an engine or motor. The commutator reverses the alternating current generated in the armature winding to produce direct current at the machine’s output terminals.

direct-current resistance Abbreviated DCR. The resistance offered by any circuit to direct current.

direct-current restorer The means by which a direct-current or low-frequency component is reinserted after transmission. Used in a circuit incapable of transmitting slow variations, but capable of transmitting components of higher frequency.

direct-current transmission Of television, that form of transmission in which a fixed setting of the controls makes any instantaneous value of signal correspond to the same value of brightness at all times.

direct data entry The entry of data directly into a computer through machine-readable source documents or through the use of online terminals.

direct digital control Time-sharing, or multiplexing, of a computer among many controlled loops.

direct distance dialing Abbreviated DDD. 1. A telephone exchange service that enables the telephone user to call other subscribers outside his or her local area without operator assistance. 2. Direct distance dialing by subscribers over the nationwide intertoll telephone network. See also area code.

direct drive A drive system used to rotate a turntable, in which the platter is driven directly by the motor shaft at the exact speed required. These designs usually include electronic motor control.

direct-drive torque motor A servoactuator that can be directly attached to the load it is to drive. It converts electrical signals directly into sufficient torque to maintain the desired accuracy in a positioning or speed control system.

direct electromotive force A unidirectional electromotive force in which the changes in values are either zero or so small that they may be neglected.

direct grid bias The dc component of grid voltage; commonly called grid bias.

direct-insert subroutine See open subroutine.

direct inward dialing A service allowing outside parties to call directly to extensions on the customer’s premises.

direction The position of one point in space with respect to another.

directional Having radiative characteristics that vary with direction.

directional antenna An antenna that radiates radio waves more effectively in some directions than in others. (The term is usually applied to an antenna whose directivity is larger than that of a half-wave dipole.)

directional beam An electromagnetic wave that is concentrated in a given direction.

directional coupler 1. A junction consisting of two waveguides coupled together in such a manner that a traveling wave in either guide will induce a traveling wave in the same direction in the other guide. 2. A bilateral electrical network that may be used as a hybrid power splitter, power adder, or mixer.

directional filter Also called directional separation filter. A filter used to separate the two frequency ranges in a carrier system in which one range of frequencies is used for transmission in one direction and another range of frequencies for transmission in the opposite direction.

directional gain See directivity index.

directional homing The procedure of following a path in such a way that the target is maintained at a constant relative bearing.

directional hydrophone A hydrophone having a response that varies significantly with the direction of incidence of sound.

directional lobe See lobe.

directional microphone 1. A microphone whose response varies significantly with the direction of sound. See also bidirectional microphone; semidirectional microphone; unidirectional microphone. 2. A microphone that is more sensitive to sounds coming from certain directions than to sounds coming from other directions. Such microphones can be aimed so their most sensitive sides face the sound source, while their least sensitive sides face sources of noise or other undesired sound. See cardioid microphone; figure-8 microphone.

directional pattern Also called radiation pattern. A graphical representation of the radiation or reception of an antenna as a function of direction. Cross sections are frequently given as vertical and horizontal planes, and principal electric and magnetic polarization planes.

directional phase shifter A passive phase-shifting device in which the phase change for transmission in one direction is different from the phase change for transmission in the opposite direction.

directional power relay A device that functions on a desired value of power flow in a given direction, or upon reverse power resulting from arcback in the anode or cathode circuits of a power rectifier.

directional relay A relay that functions in conformance with the direction of power, voltage, current, pulse rotation, etc. See also polarized relay.

directional separation filter See directional filter.

direction angle The angle between the antenna base line and a line connecting the center of the base line with the target.

direction cosine The cosine of the angle between the base line and the line from the center of the base line to the target.

direction finder Abbreviated df. Also called radio compass. Apparatus for receiving radio signals and taking their bearings in order to determine their points of origin.

direction finding The principle and practice of determining a bearing by radio means, using a discriminating antenna system and a radio receiver so that the direction of an arriving wave, and ostensibly the direction or bearing of a distant transmitter, can be determined.

direction of lay 1. The lateral direction in which the strands of a conductor run over the top of the cable conductor as they recede from an observer looking along the axis of the conductor or cable. Also applies to twisted cable. 2. The direction, either right-hand (clockwise) or left-hand (counterclockwise), in which a conductor or group of conductors spiral around a cable core as they travel away from the observer.

direction of polarization For a linearly polarized wave, the direction of the electrostatic field.

direction of propagation At any point in a homogeneous, isotropic medium, the direction of the time-average energy flow. In a uniform waveguide, the direction of propagation is often taken along the axis. In a uniform lossless waveguide, the direction of propagation at every point is parallel to the axis and in the direction of time-average energy flow.

direction rectifier A rectifier that supplies a direct-current voltage, the magnitude and polarity of which are determined by the magnitude and relative polarity of an alternating-current selsyn error voltage.

directive gain In a given direction, 4π times the ratio of the radiation intensity to the total power radiated by the antenna.

directivity 1. The property that causes an antenna to radiate or receive more energy in some directions than in others. 2. The value of the directive gain of an antenna in the maximum-gain direction. 3. The ability of an antenna to pick up signals from one general direction (usually from the front) and effectively reject those from other directions (usually from the back and sides). The front-to-back ratio is one measure of an antenna’s directivity. 4. A tendency for some microphones to respond less strongly to sounds arriving from the sides and/or rear. Directional microphones are useful in discriminating on the basis of direction between wanted sounds (musical instruments) and unwanted sounds (audience noises). Directivity is typically graphed on a polar pattern, and is thus classed as nondirectional (onmidirectional), bidirectional (figure-8), or unidirectional (cardioid), supercardioid, or hyperdirectional.

directivity diagram of an antenna The graphical representation of the gain of an antenna in the different directions of space.

directivity factor 1. In acoustics, the directivity factor is equivalent to directivity, as applied to an antenna. 2. Of a transducer used for sound emission, the ratio of the intensity of the radiated sound at a remote point in a free field on the principal axis to the average intensity of the sound transmitted through a sphere passing through the remote point and concentric with the transducer. 3. Of a transducer used for sound reception, the ratio of the square of the electromotive force produced in response to sound waves arriving in a direction parallel to the principal axis of the transducer to the mean square of the electromotive force that would be produced if sound waves having the same frequency and mean square pressure were arriving at the transducer simultaneously from all directions with random phase. The frequency should be specified in both cases.

directivity index Also called directional gain. A measure of the directional properties of a transducer. It is the ratio, in decibels, of the average intensity or response over the whole sphere surrounding the projector or hydrophone to the intensity or response on the acoustic axis.

directivity of a directional coupler Ratio of the power measured at the forward-wave sampling terminals with only a forward wave present in the transmission line to the power measured at the same terminals when the forward wave reverses direction. This ratio is usually expressed in dB and would be infinite for a perfect coupler.

directivity of an antenna The ratio of the maximum field intensity to the average field intensity at a given distance, implying a maximum value.

directivity pattern A plot of the response of an electroacoustic transducer as a function of direction.

directivity signal A spurious signal present in the output of any coupler because its directivity is not infinite.

direct light Light from a luminous object such as the sun or an incandescent lamp, as opposed to reflected light.

direct lighting A system of lighting that delivers a majority of light in useful directions without being deflected from the ceiling or walls. Any lamp equipped with a glass or metal reflector arranged to reflect the light toward the object to be illuminated is classified as direct lighting.

directly grounded See solidly grounded.

directly heated cathode A wire, or filament, designed to emit the electrons that flow from cathode to plate. This is done by passing a current through the filament; the current heats the filament to the point at which electrons are emitted. In an indirectly heated cathode, the hot filament raises the temperature of a sleeve around the filament; the sleeve then becomes the electron emitter.

direct material A semiconductor material in which electrons move directly from the conduction band to the valence band to recombine with holes. The process of recombination conserves energy and momentum.

direct memory access Abbreviated DMA. 1. A technique that permits a peripheral device to enter or extract blocks of data from a microcomputer memory without involving the central processing unit. In some cases, a CPU can perform other functions while the transfer occurs. 2. A method of I/O data transfer that does not alter minicomputer instruction-execution flow. The peripheral “steals” memory or CPU cycles to transfer data. 3. A mechanism that allows an input/output device to take control of the CPU for one or more memory cycles in order to write into memory or read from memory. The order of executing the program steps (instructions) remains unchanged. 4. Direct access to a block of memory by more than one system. 5. The technique generally used to transfer blocks of data between a peripheral and random-access memory. It is called direct because the host does not handle the data during the transfer operation. 6. A method of transferring blocks of data directly between an external device and system memory without the need for CPU intervention. This method significantly increases the data transfer rate and hence system efficiency. See also cycle stealing.

direct metal mask A metal mask made by etching a pattern into a sheet of metal.

direct numerical control A system connecting a set of numerically controlled machines to a common memory for part program or machine program storage with provision for on-demand distribution of data to the machines. Direct numerical control systems have additional provisions for collection, display, or editing of part programs, operator instructions, or data related to the numerical control process.

director 1. A parasitic antenna element located in the general direction of the major lobe of radiation for the purpose of increasing the radiation in that direction. 2. Equipment in common-carrier telegraph message switching systems, used to make cross-office selection and connection from an input-line to an output-line equipment in accordance with addresses in the message. 3. A telephone switch that translates the digits dialed into the directing digits actually used to switch the call. 4. Electromechanical equipment that is used to track a moving target in azimuth and angular height and that, with the addition of other necessary information from an outside source such as a radar set or a range finder, continuously computes firing data and transmits them to the guns. 5. In a machine-tool or process control system, the part of the system that receives the command signals from a controller and converts and amplifies these signals to make them usable by the control devices in the machine or process. 6. In a liquid crystal system, a local symmetry axis around which the long-range order of the crystal is aligned. For the nematic phase, the molecular long axis is — on average — parallel to the director.

directory Also called a catalog. 1. A table of contents designed to allow convenient access to specific files. 2. A file containing information concerning the other files on a mass-storage device. 3. In the logical format of a disk or disc, a branch of the information tree containing other directories (subdirectories) and/or files. 4. An index of the files on a disk. A directory can contain individual files in addition to other directories.

direct outward dialing Abbreviated DOD. 1. Dialing of a call into the city system from a PAX/PABX extension without the help of an operator. Usually accomplished by first dialing the digit 9. 2. The dialing of a call from a local system into a toll network without the help of an operator.

direct pickup Transmission of television images without resorting to an intermediate magnetic or photographic recording.

direct piezoelectricity A name sometimes given to the piezoelectric effect in which an electric charge is developed on a crystal by the application of mechanical stress.

direct point repeater A telegraph repeater in which the relay controlled by the signals received over a line sends corresponding signals directly into another line or lines without the use of any other repeating or transmitting apparatus.

direct radiative transition A transition that involves photons alone. See transition, 1.

direct radiator A speaker that is not horn loaded. The term usually refers to a cone-type speaker, as opposed to a compression driver/horn assembly.

direct-radiator speaker A speaker in which the radiating element acts directly on the air instead of relying on any other element such as a horn.

direct recording 1. The production of a visible record without subsequent processing, in response to received signals. 2. Analog recording in which continuous amplitude variations are recorded linearly through the use of ac bias.

direct-recording magnetic tape A method of recording using a high frequency bias in which the electrical input signal is applied to the recording head without alteration.

direct/reflected speaker A form of speaker in which a small part of the total output is radiated directly forward, with the major part reflected from the wall behind the speaker.

direct resistance-coupled amplifier An amplifier in which the plate of one stage is connected either directly or through a resistor to the control grid of the next stage, with the plate-load resistor being common to both stages. Used to amplify small changes in direct current.

direct route In wire communications, the trunks that connect two switching centers, regardless of the geographical path the actual trunk facilities may follow.

direct scanning A scanning technique in which the object is illuminated the entire time, and in which picture elements of the object are viewed singly by the television camera.

direct sound wave A wave emitted from a source in an enclosure prior to the time the wave has undergone its first reflection from a boundary of the enclosure. Frequently a sound wave is said to be direct if it contains reflections that have occurred from surfaces within about 0.05 second after the sound was first emitted.

direct synthesizer 1. A frequency synthesizer producing an output frequency that is related to the reference frequency by the ratio of two integers. The primary advantage of this type of synthesizer lies in its ability to change output frequencies at a moderately fast rate (typically in the microsecond range) and in a random way. Principal applications include frequency-agile radars, secure communication links, and electronic countermeasures. 2. Derives an output from one or more fixed-frequency reference oscillators, using combinations of frequency division, multiplication, mixing, summing, and filtering.

direct-to-disc recording A technique in which a live performance is recorded directly onto the master lacquer disc for manufacturing of phonograph records.

direct voltage Also called dc voltage. A voltage that forces electrons to move through a circuit in the same direction and thereby produce a direct current.

direct wave 1. A wave that is propagated directly through space, as opposed to one that is reflected from the sky or ground. 2. A radio wave that travels from the transmitting antenna to the point of reception without reflection or refraction.

direct Wiedemann effect See Wiedemann effect.

direct-wire circuit A supervised protective signaling circuit usually consisting of one metallic conductor and a ground return and having signal-receiving equipment responsive to either an increase or a decrease in current.

direct writing galvanometer recorder Recorder using a pen attached directly to a galvanometer movement for direct writing of signals of frequencies up to about 300 Hz.

disable To prevent the passage of binary signals by application of the proper signal to the disable terminal of a device.

disassemblers Programs that do the opposite of compiler programs. Given a machine-code program listing, the disassembler turns it back into an assembly listing, with mnemonic representations, for troubleshooting purposes.

disassembly 1. Retranslation of machine language into mnemonics during debugging. 2. Translation of binary machine code into assembly-language statements.

disc 1. A phonograph record. 2. The blank used in a recorder. See also disk.

disc capacitor A small disc-shaped capacitor with a ceramic dielectric, generally used for bypassing or for temperature compensation in tuned circuits.

disc files A type of storage medium consisting of numbers of discs that rotate; each disc has a special coating for retaining stored information.

disc generator A capacitive-charge type of voltage generator.

discharge 1. In a storage battery, the conversion of chemical energy into electrical energy. 2. The release of energy stored in a capacitor when a circuit is connected between its terminals. 3. The conversion of dielectric stress of a capacitor into an electric current.

discharge breakdown Breakdown of a material as a result of degradation due to gas discharges.

discharge key A device for switching a capacitor suddenly from a charging circuit to a load through which it can discharge.

discharge lamp A lamp containing a low-pressure gas or vapor that ionizes and emits light when an electric discharge is passed through it. Fluorescent materials are sometimes used on the inside of the glass envelope to increase the illumination, as in an ordinary fluorescent lamp.

discharge rate The amount of current a battery will deliver over a given period of time. A slower discharge rate generally results in more efficient use of a battery.

discharge tube A tube containing a low-pressure gas that passes a current whenever sufficient voltage is applied.

discharge voltage Also called clamping voltage. The maximum peak voltage measured across suppressor device terminals when subjected to peak pulse current.

discone antenna A special form of biconical antenna in which the vertex angle of one cone is 180°.

disconnect Also called release. 1. To break an electric circuit. 2. To remove the power from an electrical device (colloquially, “to unplug the device”). 3. To disengage the apparatus used in a connection and to restore it to its ready condition when not in use. 4. A device or group of devices that removes electrical continuity from between the conductors of a circuit and the source of supply.

disconnecting means A device whereby the current-carrying conductors of a circuit can be disconnected from their source of supply.

disconnector release A device that disengages the apparatus used in a telephone connection to restore it to the condition in which it exists when not in use.

disconnect signal 1. A signal sent from one end of a trunk or subscriber line to indicate at the other end that the established connection should be released. 2. The on-hook signal in a telephone system by which the calling and called terminals notify the switching equipment that an established connection is no longer needed and should be released.

disconnect switch (motor circuit switch) A switch intended for use in a motor branch circuit. It is rated in horse power and is capable of interrupting the maximum operating overload current of a motor of the same rating at the rated voltage.

discontinuity 1. A broken connection, or the loss of a specific connection characteristic. 2. The temporary interruption or variation in current or voltage. 3. A point of abrupt change in the impedance of a circuit, where wave reflections can occur.

discontinuous amplifier An amplifier that reproduces an input waveform on some type of averaging basis.

disc pack A set of magnetic discs that can be removed from a disc storage as one unit.

disc recorder A recording device in which the sounds are mechanically impressed onto a disc; as opposed to a tape recorder, which impresses the sound magnetically on a tape.

discrete 1. An individual circuit component, complete in itself, such as a resistor, diode, capacitor, or transistor, and used as an individual and separable circuit element. 2. Pertaining to distinct elements, such as characters, or to representation by means of distinct elements. 3. A term applied to four channels when there are four electrically independent signals, as opposed to matrix. 4. A quad disc or record-playback method that keeps four signals separate, distinct, and independent from recording to playback. 5. Having an individual identity. Fabricated prior to installation and/or separately packaged, not part of an integrated circuit.

discrete circuit 1. A circuit built from separate components that are individually manufactured, tested, and assembled. 2. Electronic circuit built of separate components (transistors, resistors, etc.) connected by wiring or printed-circuit etched conductors.

discrete component 1. A component that has been fabricated prior to its installation (e.g., resistors, capacitors, diodes, and transistors). 2. A circuit component having an individual identity, such as a transistor, capacitor, or resistor.

discrete device 1. A class of electronic components, such as power MOSFETs, bipolar power transistors, MOVs, optoelectronic devices, rectifiers, power hybrid circuits, intelligent power discretes, and transistors. Typically, these devices contain one active element, such as a transistor or diode. However, hybrids, optoelectronic devices, and intelligent discretes may contain more than one active element. In contrast, integrated circuits typically contain hundreds, thousands, or even millions of active elements in a single die. 2. An individual electrical component, such as a resistor, capacitor, or transistor, as opposed to an integrated circuit, which is equivalent to several discrete components.

discrete element An electronic element, such as a resistor or transistor, fabricated in such a way that it can be measured and transported individually.

discrete part A separately packaged single circuit element supplying one fundamental property as a lumped characteristic in a given application. Examples: resistor, transistor, diode.

discrete sampling The lengthening of individual samples so that the sampling process does not deteriorate the intelligence frequency response of the channel.

discrete thin-film component An individually packaged electronic component having one or more thin films serving as resistive, conductive, and/or insulating elements. Resistors and potentiometers having thin-film metallic resistance elements are examples.

discretionary wiring The use of a selective metallization pattern in the interconnection of large numbers of basic circuits on a slice of semiconductor material to form complex arrays. The metallization pattern connects only the “good” circuits on the wafers. Discretionary wiring requires a different interconnection pattern for each wafer.

discrimination 1. The difference between losses at specified frequencies, with the system or transducer terminated in specified impedances. 2. In a frequency-modulated system, the detection or demodulation of the imposed variations in the frequency of the carriers. 3. In a tuned circuit, the degree of rejection of unwanted signals.

discrimination ratio The ratio of the width of the passband of a filter to the width of the stopband of the filter.

discriminator 1. A device in which amplitude variations are derived in response to frequency or phase variations. 2. A facsimile auxiliary device between the radio receiver and the recorder that converts an audio-frequency-shifted facsimile signal to an amplitude-modulated facsimile signal.

discriminator transformer A transformer used in FM receivers to convert frequency changes directly to audio-frequency signals.

discriminator tuning unit A device that tunes the discriminator to a particular subcarrier.

disc-seal tube Also called lighthouse tube or megatron. An electron tube with disc-shaped electrodes arranged in closely spaced parallel layers to give a low interelectrode capacitance along with a high power output in the UHF region.

dish 1. A microwave antenna, usually shaped like a parabola, that reflects the radio energy leaving or entering the system. 2. A parabolic type of radio or radar antenna, roughly the shape of a soup bowl. 3. A colloquial expression for a parabolic antenna. 4. Common term for a parabolic microwave antenna.

dish illumination The area of a dish as seen by the feedhorn.

disk 1. An electromagnetic storage medium for digital data. 2. High-capacity random-access magnetic storage medium. See also disc.

disk cartridge The flat, round, removable disk pack, containing programs and data, that is placed into a disk drive.

disk drive 1. Identified floppy, removable, and nonremovable bulk storage for most minicomputer and mainframe systems, and microcomputer systems needing several megabytes of storage. 2. A disk player that rotates the disk, writes data onto it, and reads data from it as instructed by a program.

diskette See floppy disk.

disk operating system Abbreviated DOS. 1. The software that organizes how a computer reads, writes, and reacts with its disks and talks to its various peripherals (input/output devices), such as keyboards, screens, serial and parallel ports, printers, modems, etc. The most popular operating system for PCs is MS-DOS from Microsoft. 2. An operating system (set of programs) that instructs a disk-based computing system to manage resources and operate related equipment. 3. A set of programs that controls a computer. The DOS performs a variety of tasks, including managing communications between the computer and its peripherals. See also operating system.

disk pack The vertical stacking of a series of magnetic disks in a removable self-contained unit.

disk storage 1. Random-access auxiliary memory device in which information is stored on constantly rotating magnetic disks. 2. The storage of data on the surface of magnetic disks. 3. A mass storage memory device employing a flat, rotating medium onto which data can be stored via magnetic recording techniques and retrieved by magnetic playback. 4. A method of high-speed bulk storage of programs and data. The medium is a rotating circular plate coated with a magnetic material, such as iron oxide. Data is written (stored) and read (retrieved) by fixed or movable read/write heads positioned over data tracks on the surface of the disk. Addressable portions can be selected for read or write operations.

dislocation In a crystal, a region in which the atoms are not arranged in the perfect crystal-lattice structure.

dispatcher In a digital computer, the section that transfers the words to their proper destinations.

dispenser A device that automatically distributes radar chaff from an aircraft.

disperse In data processing, to distribute grouped input items among a larger number of groups in the output.

dispersion 1. Separation of a wave into its component frequencies. 2. Scattering of a microwave beam as it strikes an obstruction. 3. The property of an optical material that causes some wavelengths of light to be transmitted through the material at different velocities, with the velocity a function of the wavelength. (This causes each wavelength of light to have a different refractive index.) 4. In a magnetostrictive delay line, the variation of delay as a function of frequency. 5. The frequency difference that can be analyzed in one sweep by a spectrum analyzer. Dispersion can be considered as that frequency width over which sampling can be performed, and is always equal to or less than the frequency range. 6. The extent to which a speaker distributes acoustical power widely and evenly into the listening area. 7. The undesirable effect of the broadening of optical pulses caused by lengthening of rise and fall times as the pulse travels along the fiber. Sometimes referred to as pulse spreading, it results from either modal or material effects in the fiber that reduce bandwidth. Expressed in nanoseconds per kilometer. 8. A fiber-optic phenomenon that causes pulse widths of transmitted data to lengthen. Dispersion is caused by the arrival of data at the far terminal at different times due to the varying lengths of optical paths in multimode fiber, and by inherent properties in the fiber. Dispersion increases with length of conductor and is caused by the difference in ray path lengths within the fiber core.

dispersive medium A medium in which the phase velocity of a wave is related to the frequency.

displacement 1. The vector quantity representing change of position of a particle. 2. A number that a computer must add to a base address to form an effective address.

displacement current A current that exists in addition to ordinary conduction current in ac circuits. It is proportional to the rate of change of the electric field. The current at right angles to the direction of propagation determined by the rate at which the field energy changes.

displacement of porches The difference in level between the front and back porch of a television signal.

displacement transducer A device that converts mechanical energy into electrical energy, usually by the movement of a rod or an armature. The amount of output voltage is determined by the amount the rod or armature is moved.

display Also called readout. 1. Visual presentation of a received signal on a cathode-ray tube or video screen. 2. Row of digits across the top of a calculator, showing input or final answer. In printing-type calculators, referred to as printout. 3. The observable illustration of an image, scene, or data on a screen, such as a console or CRT screen, seen as a graph, report, or drawing. 4. The representation of data in visible form, e.g., on a cathode-ray tube, by lights or indicators on the console of a computer, or a printed report.

display console A visual display used with a computer to give access to the many elements of data as an array of points. With the display console, an operator may check information in the computer and change it if required.

display-generation time The time span between the output of data from the host computer and the moment at which the complete display can be viewed.

display generator An electronic device that interfaces computer-graphics display information with a graphics-display device. Typically, the interface is made between a digital computer and a CRT. In general, a display generator for a rasterscan display contains four subsystems: display controller, display processor, refresh memory, and video driver.

display highlighting The ability of the word processor to intensify or blink certain portions of the display screen — either the characters themselves or the screen atea behind the characters — to emphasize a text segment designated for some special activity such as deleting or moving.

display information processor A computer used in a combat operations center to generate situation displays.

display loss See visibility factor.

display modes Each display mode, such as vector, increment, character, point, vector continue, or short vector, specifies the manner in which points are to be displayed on the screen.

display panel The substrate containing the media for creating an image, including electric connections but excluding the electronic interface.

display primaries Also called receiver primaries. The red, green, and blue colors produced by a color television receiver and mixed in proper proportions to produce other colors.

display processor A component of a display generator used to add intelligence. Typically, the device is a microcomputer with stored programs that perform high-level graphics functions.

display-storage tube A special cathode-ray tube with a long and controllable image presistence and high luminescence.

display unit A device used to provide a visual representation of data.

display window The width of the portion of the frequency spectrum presented on panoramic presentation, expressed in frequency units, usually megahertz.

disruptive discharge The sudden, large current through an insulating medium when electrostatic stress ruptures the medium and thus destroys its insulating ability.

dissector In optical character recognition, a mechanical or electronic transducer that sequentially detects the level of light in different areas of a completely illuminated sample space.

dissector tube A camera tube having a continuous photocathode on which a photoelectric emission pattern is formed. Scanning is done by moving the electron optical image of the pattern over an aperture. See also image dissector, 1.

dissipation The undesired loss of electrical energy by conversion into heat.

dissipation constant A constant of proportionality between the power dissipated and the resultant temperature rise in a thermistor at a specified temperature.

dissipation factor 1. Symbolized by D. Ratio between the permittivity and conductivity of a dielectric. The reciprocal of the dissipation factor (df) is the storage factor, sometimes called the quality factor (Q). 2. A measure of the ac loss. Dissipation factor is proportional to the power loss (P_L) per cycle (f) per potential gradient squared (E²) per unit volume (V) as follows:

dissipation factor = (P_L/kE^{2 fV})

where k is a constant. Dissipation factor is approximately equal to power factor when the loss angle is small.

dissipation line A length of stainless-steel or Nichrome wire used as a noninductive impedance for termination of a rhombic transmitting antenna when power of several kilowatts must be dissipated.

dissonance The formation of maxima and minima by the superposition of two sets of interference fringes from light of two different wavelengths.

dissymmetrical network See dissymmetrical transducer.

dissymmetrical transducer Also called dissymmetrical network. A transducer with unequal input and output image impedances.

distance mark Also called range mark. A mark that indicates, on a cathode-ray screen, the distance from the radar set to a target.

distance-measuring equipment Abbreviated DME. A radio navigational aid for determining the distance from a transponder beacon by measuring the time of transmission to and from it.

distance protection The effect of a device operative within a predetermined electrical distance on the protected circuit to cause and maintain an interruption of power in a faulty circuit.

distance relay 1. A protective relay, the operation of which is a function of the distance between the relay and the point of fault. 2. A device that functions when the circuit admittance, impedance, or reactance increases or decreases beyond predetermined limits.

distance resolution The ability of a radar to differentiate targets solely by distance measurement. Generally expressed as the minimum distance the targets can be separated and still be distinguishable.

distortion 1. Undesired changes in the waveform of a signal so that a spurious element is added. All distortion is undesirable. Harmonic distortion disturbs the original relationship between a tone and other tones naturally related to it. Intermodulation distortion (IMD) introduces new tones caused by mixing of two or more original tones. Phase distortion, or nonlinear phase shift, disturbs the natural timing sequence between a tone and its related overtones. Transient distortion disturbs the precise attack and decay of a musical sound. Harmonic and IMD distortion are expressed in percentages; phase distortion in degrees; transient distortion is usually judged from oscilloscope patterns. 2. Unwanted changes in the purity of sound being reproduced or in rf signals. In audio, it generally implies intermodulation and/or harmonic distortion. These are derived from phase differences and/or amplitude distortion in which the amplitude of the output does not bear the same proportion to the input at all frequencies. 3. With a signal frequency (sine wave) signal, distortion appears as harmonics (multiples) of the input frequency. The rms (effective ac point) sum of all harmonic distortion components, plus hum and noise, is known as total harmonic distortion, or THD. When a two-tone test signal is used, distortion components appear at frequencies that are sums and differences of multiples of the input frequencies. Their magnitude is expressed as intermodulation distortion, which is more distressing to hear than THD. The lower the distortion in any form, the better. 4. Any difference in the waveshape after the signal has traversed the transmission circuit. 5. The unwanted changes in signal or signal shape that occur during transmission between two points.

distortion factor See harmonic distortion.

distortion factor of a wave The ratio of the effective value of the residue after the elimination of the fundamental to the effective value of the original wave.

distortionless line A transmission line whose propagation constant is independent of frequency. (This is approached in a practical case by adjusting the line parameters, series inductance (l), shunt capacitance (c), series resistance (r), and shunt conductance (g) so that r/g = 1/c.)

distortion meter 1. An instrument that measures the deviation of a complex wave from a pure sine wave. 2. An instrument that measures the harmonic content of a sine wave, usually calibrated to read in percent distortion.

distortion tolerance Of a telegraph receiver, the maximum signal distortion that can be tolerated without error in reception.

distress frequency A frequency reserved for distress calls, by international agreement. It is 500 kHz for ships at sea and aircraft over the sea.

distributed Spread out over an electrically significant length, area, or time.

distributed amplifier A multistage amplifier in which the high-frequency limitation, due to the input and output capacitances of the active element, is circumvented by making these capacitances the shunt elements of lumped-parameter device lines. In this way the overall gain is the sum of the gains of the individual stages rather than the product, thus allowing amplification even when the individual gains are less than unity.

distributed capacitance Also called self-capacitance. Any capacitance not concentrated within a capacitor, such as the capacitance between the turns in a coil or choke, or between adjacent conductors of a circuit.

distributed computer network A collection of computers and I/O devices that can communicate with each other. See distributed processing.

distributed constants Constants such as resistance, inductance, or capacitance that exist along the entire length or area of a circuit, instead of being concentrated within circuit components.

distributed data processing Abbreviated DDP. The functional distribution of certain data-processing activities along logical organizational lines.

distributed-emission photodiode A broadband photodiode for use in detecting modulated laser beams at millimeter wavelengths.

distributed inductance The inductance along the entire length of a conductor, as distinguished from the inductance concentrated within a coil.

distributed network 1. An electrical-electronic device that for proper operation depends on physical size in comparison to a wavelength and physical configuration. 2. A network configuration in which all node pairs are connected either directly or by redundant paths through intermediate nodes.

distributed parameter network A network in which the parameters of resistance, capacitance, and inductance cannot be taken as being concentrated at any one point in space. Rather, the network must be described in terms of its magnetic and electric fields and the quantities related to the distributed constants of the network.

distributed paramp A paramagnetic amplifier consisting essentially of a transmission line shunted by uniformly spaced, identical varactors. The varactors are excited in sequence by the applied pumping wave to give the desired traveling-wave effect.

distributed pole A motor has distributed poles when its stator or field windings are distributed in a series of slots located within the arc of the pole.

distributed processing 1. A multiprocessing computer technique in which each processor has a specific task or set of tasks to perform. These processors transfer commands and data via a standard communication interface. 2. Performing a data-processing task by performing the needed calculations in a distributed computer network. The efficiency of the data-processing task is improved through the simultaneous performance of operations in several interconnected processors of a distributed computer network. 3. Data-processing tasks performed simultaneously in several interconnected processors of a computer network.

distributing amplifier An amplifier, either radio frequency or audio frequency, having one input and two or more isolated outputs.

distributing cable See distribution cable.

distributing frame A structure for terminating permanent wires of a central office, private branch exchange, or private exchange and for permitting the easy change of connection between them by means of cross-connecting wires.

distributing terminal assembly A frame situated between each pair of selector bays to provide terminal facilities for the selector bank wiring and facilities for cross connection to trunks running to succeeding switches.

distribution Also called frequency distribution. The number of occurrences of the particular values of a variable as a function of those values.

distribution amplifier 1. A power amplifier designed to energize a speech, music, or antenna distribution system. Its output impedance is sufficiently low that changes in the load do not appreciably affect the output voltage. 2. A device that provides several isolated outputs from one looping or bridging input, and has a sufficiently high input impedance and input-to-output isolation to prevent loading of the input source.

distribution cable Also called distributing cable. 1. A cable extended from a feeder cable for the purpose of providing service to a specific area. 2. In a system, the transmission cable from the distribution amplifier to the drop cable.

distribution center In an alternating-current power system, the point at which control and rotating equipment is installed.

distribution coefficients Equal-powered tristimulus values of monochromatic radiations.

distribution switchboard A power switchboard used for the distribution of electrical energy at the voltage common for each distribution within a building.

distributive sort A sorting procedure that divides data elements into two or more distinct groups or subsets. The partition sort is an example.

distributor 1. See memory register. 2. The electronic circuitry that acts as an intermediate link between the accumulator and drum storage.

distributorless A semiconductor automotive ignition system that does not utilize breaker contacts to time or trigger the system, nor does it utilize a distributor distribution of the secondary voltage.

disturbance 1. An irregular phenomenon that interferes with the interchange of intelligence during transmission of a signal. 2. An interruption of a quiet state. 3. Any form of interference with normal communications.

disturbed-one output A “one” output of a magnetic core to which partial-read pulses have been applied since that core was last selected for writing.

disturbed-zero output A “zero” output of a magnetic core to which partial-write pulses have been applied since that core was last selected for reading.

disturbing conductor A conductor carrying energy that creates spurious signals in another conductor.

dither 1. An oscillation introduced for the purpose of overcoming the effects of friction, hysteresis, or clogging. 2. A small electrical signal deliberately injected into an electromechanical device for the purpose of overcoming static friction in the device. In a recording instrument it makes the indicator ready to jump. 3. Constant vibration about a point. 4. The technique of adding controlled amounts of noise to a signal to improve overall system loop control, or to smear quantizing error in an analog-to-digital converter application.

dithering 1. The application of intermittent or periodic acceleration forces sufficient to minimize the effect of static friction with a transducer, without introducing other errors. 2. The creation of additional colors or shades of gray to create special effects or to make hard edges softer.

divergence loss The part of transmission loss that is caused by the spreading of sound energy.

diverging lens A lens that is thinner in the center than at the edges. Such a lens causes light passing through to spread out, or diverge.

diversity 1. A form of transmission and/or reception using several modes, usually in space or in time, to compensate for fading or outages in any one of the modes. In the space diversity system, the same signal is sent simultaneously over several different transmission paths, which are separated enough so that independent propagation conditions can be expected. With time diversity, the same path may be used, but the signal is transmitted more than once, at different times. There are other forms of diversity, using different frequencies or different polarizations to provide the separate transmission pole. See diversity reception. 2. The practice of constructing a portion of the system or backup system by using a different technology, component, or design, such that the two portions of the total system are not vulnerable to a common-cause failure.

diversity factor The ratio of the sum of the individual maximum demands of the subdivisions of a system (or part of a system) to the maximum demand of the entire system (or part of the system).

diversity gain The gain in reception as a result of the use of two or more receiving antennas.

diversity reception 1. A method of minimizing the effects of fading during reception of a radio signal. This is done by combining and/or selecting two or more sources of received-signal energy that carry the same intelligence but differ in strength or signal-to-noise ratio in order to produce a usable signal. See frequency-diversity reception; space-diversity reception. 2. A technique for reducing the adverse effects of multipath fading by receiving the same signal on two or more diverse, or different, antenna-receiver combinations with a means of choosing the combination with the strongest signal. A two-channel system is known as dual diversity; a three-channel system, triple diversity. Diversity reception is widely and effectively used in commercial high-frequency installations.

diverter pole generator A compound-wound direct-current generator with the series winding of the diverter pole opposing the flux generated by the shunt-wound main pole; provides a close voltage regulation.

divide-by-N counter A group of counter stages that can be programmed to divide an input frequency by any number up to N.

divide-by-16 counter A logic device in which four flip-flops count from 0 through 15 and then recycle to 0. All 16 states of the combination of four flip-flops are used. Sometimes referred to as a hexadecimal counter.

divïde-by-10 counter See decade counter.

divide-carrier modulation The process by which two signals are added so that they can modulate two carriers of the same frequency but 90° out of phase. The resultant signal will have the same frequency as the carriers, but its amplitude and phase will vary in step with the variations in amplitude of the two modulating signals.

divide check In a computer, an indicator that shows that an invalid division has occurred or has been attempted.

divider See counter, 4.

dividing network Also called speaker dividing network and crossover network. A frequency-selective network that divides the audio-frequency spectrum into two or more parts to be fed to separate devices such as amplifiers or speakers.

D layer The lowest ionospheric layer, located between about 35 to 55 miles (56 to 88 km) above the earth. Its intensity is proportional to the height of the sun and is greatest at noon. Waves below approximately 3 MHz are absorbed by the D layer when it is present. High-angle radiation may penetrate the D layer and be reflected by the E layer.

DMA Abbreviation for direct memory access. A method in which a device in a computer other than the main processor can access main memory directly. It must first obtain control of the bus from the processor or other DMA devices. Then it can read and write to memory directly. This is a very fast method of transferring large amounts of data from a peripheral to main memory. Using the main processor to handle the data transfer requires more software overhead and reduces system throughput.

DMI Abbreviation for dual-mode ignition. An adaptation of the Duraspark (Ford Motor) electronic ignition system that allows its use on smaller four-cylinder engines like the 2.3-liter size.

DMM Abbreviation for digital multimeter.

DMOS Abbreviation for double-diffused metal-oxide FET semiconductor. A process in which n and p atoms are diffused through the same mask opening to give precisely sized narrow channels. Used on discrete field-effect transistors (not MOS ICs) for ultrahigh gains and frequency performance. A very fast MOSFET fabricated with an extra diffusion step.

DNC Abbreviation for direct numerical control.

DNL See dynamic noise limiter.

DOC files Document files. The default file extension for Microsoft Word. Most files with this extension are Microsoft Word files, but there are many that are plain text.

documentation An orderly collection of recorded hardware and software data such as tables, listings, diagrams, etc.

document reader A general term referring to OCR or OMR equipment that reads a limited amount of information (one to five lines). Generally operates from a predetermined format and is therefore more restricted in the location of information to be read. The forms involved are generally tab card size or slightly smaller or larger.

doghouse A small enclosure located near the base of a transmitting-antenna tower and used to house antenna tuning equipment.

Doherty amplifier A radio-frequency linear power amplifier divided into two sections, the inputs and outputs of which are connected by quarter-wave (90°) networks. As long as the input-signal voltage is less than half the maximum amplitude, section No. 2 is inoperative and section No. 1 delivers all the power to the load. The load presents twice the optimum impedance required for maximum output. At one-half the maximum input, section No. 1 is operating at peak efficiency but is beginning to saturate. Above this level, section No. 2 comes into operation and decreases the impedance presented to section No. 1. As a result, section No. 2 delivers more and more power to the load until, at maximum signal input, both sections are operating at peak efficiency and each section is delivering one-half the total output power.

Dolby 1. A technique that increases the signal-to-noise ratio of a recording medium by raising the volume of quiet passages prior to recording, and lowering them to their original levels during playback. The lowering process automatically reduces any noise that was introduced as a result of the recording or playback processes. 2. Noise-reduction circuit that boosts the recorded signal at the tape hiss frequencies for low levels and reduces the boost progressively as the signal becomes large enough to mask the noise. (The Dolby system has the important advantage that it is standardized and any Dolby tape can be replayed accurately on any other Dolby machine.) 3. Name of a noise-reduction system available as a special circuit on some stereo cassette tape decks. 4. A proprietary electronic device or circuit that reduces the amount of noise (principally tape hiss) introduced during the recording process by boosting — in carefully controlled amounts — the strength of weak high-frequency signals before they are recorded. During playback the signals (and the noise) are cut back by an exactly equivalent amount. The original dynamics are restored, but the noise is reduced by 10 dB.

Dolby A The original form of the Dolby noise-reduction device, intended for professional use. It has four independently controlled noise-reduction channels, to increase signal-to-noise ratio at low, middle, high and very high frequencies.

Dolby B 1. A simplified version of the original Dolby A, intended primarily for use by nonprofessional recordists. Dolby B functions identically to Dolby A, but has only one controlled frequency band, which is effective primarily on tape hiss. 2. A noise-reduction system widely used in cassette recorders, as well as in some open-reel and cartridge machines and in FM broadcasting. The high-frequency portions of signals being recorded are compressed, with the degree of compression being greater as signal level decreases. An opposite expansion process takes place in playback, restoring the original frequency response, but with a reduction in high-frequency hiss. 3. A complementary noise-reduction system designed to reduce tape (and FM) hiss. A Dolby B circuit boosts low-level high-frequency signals during recording and reduces them, along with the tape’s added noise, in a complementary fashion during playback. Noise can be reduced up to 10 db above 5 kHz with the Dolby B system. It is now in virtually universal use in cassette decks.

Dolby B & C noise reduction (cassette deck) Two systems of noise/hiss reduction invented by Ray Dolby. They work by boosting high frequencies during recording (also called encoding) and attenuating them during playback (also called decoding). Dolby B noise reduction boosts the level of the high-frequency range during recording and tapers the high frequencies during playback, reducing tape hiss by 8 to 10 dB. Dolby C noise reduction uses the same principle as Dolby B, with the addition of a second stage in which the frequencies affected are lower by about one octave. This results in a 15 to 18 dB reduction in tape hiss over an extended frequency range.

Dolby digital The multi-channel audio encoding formed for DVD.

dolly A wheeled platform or frame on which the tripod or frame supporting a television camera or other apparatus is mounted to give it wider mobility.

domain 1. In magnetic theory, that region of a magnetic material in which the spontaneous magnetization is all in one direction. In conventional magnetic-tape coatings, this corresponds to one oxide particle. 2. A region within a ferromagnetic substance where the atomic magnets of many atoms tend to orient themselves parallel to each other; the north poles pointing one way act spontaneously. The domains may be treated as small bar magnets of microscopic dimension. 3. In the Internet and other networks, an extension in a host name that identifies the type of host. The seven domains established by the Inter-NIC are .arpa (ARPANET), .com (company/commercial), .edu (educational institutions), .gov (government), .mil (military), .net (Internet access providers), and .org (organization). Outside the United States, the domain name is a two-letter country code (for example, .fr for Prance and .ca for Canada).

domain name The unique name that identifies an Internet site. Domain names always have two or more parts, separated by dots. The part on the left is the most specific, and the part on the right is the most general. A given machine may have more than one domain name, but a given domain name points to only one machine. Usually, all of the machines on a given network will have the same thing as the right-hand portion of their domain names.

domains See particles.

domestic induction heater A home cooking utensil that is heated by induced currents within it. The unit contains a primary inductor, with the utensil itself acting as the secondary.

dominant mode Also called fundamental mode or principal mode. In waveguide transmission, the mode with the lowest cutoff frequency. Designations for this mode are TE_0,1 and TE_1,1 for rectangular and circular waveguides, respectively.

dominant wave The guided wave that has the lowest cutoff frequency. It is the only wave that will carry energy when the excitation frequency is between the lowest and the next higher cutoff.

dominant wavelength 1. Of a color sample, the wavelength of light that matches it in chromaticity when mixed with white light. 2. The wavelength that is a quantitative measure of the apparent color of light as perceived by the human eye.

dominant wavelength of a color The predominant wavelength of light in a color.

donor Also called donor impurity. 1. An impurity atom that tends to give up an electron and thereby affects the electrical conductivity of a crystal. Used to produce n-type semiconductors. 2. A chemical that adds electrons to crystal lattices. 3. An impurity from column V of the periodic table, which adds a mobile electron to the conduction band of silicon, thereby making it more n-type. Commonly used donors are arsenic and phosphorous (compare with acceptor).

donor impurity An element or compound whose atoms or molecules have more valence electrons than those of the intrinsic semiconductor material into which they are introduced in small quantities as an impurity or dopant. Because the donor impurity possesses more valence electrons, the material doped with a donor impurity is an n-type semiconductor. See donor.

donor-type semiconductor An n-type semiconductor.

donut See land, 2.

door cord A short, insulated cable with an attaching block and terminals at each end used to conduct current to a device, such as foil, mounted on the movable portion of a door or window.

doorknob tube A vacuum tube so called because of its shape designed for UHF transmitter circuits. It has a low electron-transit time and low interelectrode capacitance because of the close spacing and small size, respectively, of its electrodes.

door trip switch A mechanical switch mounted so that movement of a door will operate the switch.

dopant 1. An impurity added to a semiconductor to improve its electrical conductivity; any material added to a substance to produce desired properties in the substance. 2. Selected impurity introduced into semiconductor substrates in controlled amounts, the atoms of which form negative (n-type) and positive (p-type) conductive regions. Phosphorus, arsenic, and antimony are n-type dopants for silicon; boron, aluminum, gallium, and indium are p-type dopants for silicon.

dope To add impurities (called dopants) to a substance, usually a solid, in a controlled manner to cause the substance to have certain desired properties. For example, the number of electrical carriers in silicon can be increased by doping it with small amounts of other semimetallic elements. Ruby is aluminum oxide doped with chromium oxide.

doped junction A semiconductor junction produced by the addition of an impurity to the melt during crystal growth.

doped region A layer of an integrated circuit in which impurities have been introduced.

doped solder Solder to which an element not normally found in solder has been intentionally added.

doping The addition of controlled amounts of impurities to a semiconductor to achieve a desired characteristic, such as to produce an n-type or p-type material, accomplished through thermal diffusion or ion implantation. Common doping agents for germanium and silicon include aluminum, antimony, arsenic, gallium, and indium.

doping agent An impurity element added to semiconductor materials used in crystal diodes and transistors. Common doping agents for germanium and silicon include aluminum, antimony, arsenic, gallium, and indium.

doping compensation The addition of donor impurities to a p-type semiconductor or of acceptor impurities to an n-type semiconductor.

Doppler cabinet A speaker cabinet in which either the speaker or a baffle board is rotated or moved to change the length of the sound path cyclically and thereby produce a vibrato effect mechanically.

Doppler effect 1. The observed change of frequency of a wave caused by a time rate of change of the effective distance traveled by the wave between the source and the point of observation. As the distance between a source of constant vibration and an observer diminishes or increases, the received frequencies are greater or less. 2. The apparent change in the frequency of radio wave reaching an observer, due either to motion of the source toward or away from the observer, to motion of the observer, or both. 3. The apparent change in frequency of sound or radio waves when reflected from or originating from a moving object. Utilized in some types of motion sensors. 4. The radiation emitted from a source that moves away from an observer appears to be of lower frequency than the radiation emitted from a stationary source. The radiation emitted from a source moving toward the observer appears to be of a higher frequency than that from a stationary source.

Doppler principle The theory established by Doppler in 1842 that states that the rate of change in distance between a perceiver and a radiation source determines the change in frequencies.

Doppler radar A radar unit that measures the velocity of a moving object by the shift in carrier frequency of the returned signal. The shift is proportionate to the velocity of the object as it approaches or recedes.

Doppler ranging Abbreviated as doran. A cw trajectory-measuring system that utilizes the Doppler shift to measure the distance between a transmitter, missile, transponder, and several receiving stations. From these measurements, trajectory data is computed. In contrast to a similar system, doran circumvents the necessity of continuously recording the Doppler signal by performing the distance measurements with four different frequencies simultaneously.

Doppler shift 1. The change in frequency of a wave reaching an observer or a system, caused by a change in distance or range between the source and the observer or the system during the interval of reception. It is due to the Doppler effect. 2. The change in frequency with which energy reaches a receiver when the source of radiation or a reflector of the radiation and the receiver are in motion relative to each other. The Doppler shift is used in many tracking systems. 3. The magnitude, expressed in cycles per second, of the alteration in the wave frequency observed as a result of the Doppler effect.

Doppler signal The signal, traveling from transmitter to receiver, that has an altered frequency due to the Doppler effect.

Doppler velocity and position 1. Having to do with a beacon tracking system in which pulses are sent from a tracking station to a receiver in the object to be tracked, and returned to the station on a different frequency. 2. Having to do with a Doppler trajectory-measuring system for determining target position relative to transmitting and receiving stations on the ground.

doran See Doppler ranging.

DOS Abbreviation for disk operating system.

dosage meter See dosimeter; intensitometer.

dose A measure of energy actually absorbed in tissue as a result of ionizing radiation.

dosimeter Also called intensitometer or dosage meter. 1. An instrument that measures the amount of exposure to nuclear or X-ray radiation utilizing the ability of such radiation to produce ionization of a gas. 2. Quartz fiber electrometer that is charged by a battery and discharges when exposed to radiation. Can be direct reading or indirect reading. Measures the total radiation dose received, in rem, and is carried by a person who works with radiation.

DOS prompt The letter informing DOS system users what drive they’re in, followed by the greater-than symbol (C>), which indicates that the system is ready to receive a command.

dot 1. See button, 2. 2. Also called bubble. A symbol placed at the input of a logic symbol to indicate that the active signal input is negative. The absence of a dot indicates a positive active signal.

dot AND See wired AND.

dot-bar generator An instrument that generates a specified output pattern of dots and bars. Used for measuring scan linearity and geometric distortion of TV cameras, video monitors, and TV receivers. Also used for converging cathode-ray tubes as recommended by color monitor and receiver manufacturers.

dot cycle One cycle of a periodic alternation between two signaling conditions, each condition having unit duration. Thus, two-condition signaling consists of a dot, or marking element, followed by a spacing element. In teletypewriter applications, one dot cycle consists of a mark and a space. The speed of telegraph transmission sometimes is stated in terms of dot cycles per second, or dot speed (half the speed of transmission expressed in bauds).

dot encapsulation A packaging process in which cylindrical components are inserted into a perforated wafer to form a solid block with interconnecting conductors on both surfaces joining the components.

dot generator An instrument used in servicing color television receivers. It produces a pattern of white dots so that convergence adjustments can be made on the picture tube.

dot matrix 1. A pattern of dots in a fixed area used for formulation of characters. A method of display character generation in which each character is formed by a grid or matrix pattern of 5 × 7 to 7 × 9 dots, combinations of which form characters on a video or hardcopy medium. For very high quality, 11 × 13 patterns or greater are required. 2. The printing of characters by a matrix pattern of ink dots. 3. A technique for representing characters by composing them out of selected dots from within a rectangular matrix of dots.

dot-matrix character 1. A printed character formed of dots so close together that it gives the impression of having been printed by uninterrupted strokes. The dots are formed by wire ends, jets of ink, electrical charge, or laser beams. 2. A character composed from a rectangular matrix of dots.

dot-matrix display 1. A display format consisting of small light-emitting elements arranged as a matrix. Various elements are energized to depict a character. A typical matrix is 5 × 7. 2. A display composed of dots in close, rectangular array, capable of being individually illuminated to produce alphanumeric characters and graphic displays.

dot-matrix printer A printer that forms letters by striking the paper with small pins or other means of making a mark (such as a small jet of ink), forming each letter with a pattern of dots. More marks per letter result in a denser image. Some dot-matrix printers squeeze the dots so closely together that they look almost like letter-quality print, which is made by machines that form letters with a single impact, as do traditional typewriters. When dot-matrix printers produce letters that are close to the quality of traditional electric typewriters, the result is often called correspondence-quality or letter-quality print. 2. See also wireprinter.

dot pattern Small dots of light produced on the screen of a color picture tube by the signal from a dot generator. If overall beam convergence has been obtained, the three color-dot patterns will merge into one white-dot pattern.

dot pitch 1. A measure of picture quality or resolution in RGB color monitors. 2. The shortest distance between two phosphor dots of the same color on the screen. The smaller the dot pitch, the better the resolution of the monitor. High-resolution monitors usually have a dot pitch of 0.28 mm. 3. For printers, the number of dots per linear inch; for example, a desktop laser printer prints at least 300 dpi. The larger the number, the higher the resolution. 4. A measure of picture quality or resolution in RGB color monitors, which is more commonly known as pixel resolution. Dot pitch is the distance between screen dots (pixels) measured in millimeters. The shorter the distance, the better the resolution. It is specified in pixels/mm.

dot sequential Pertaining to the association of the primary colors in sequence with successive picture elements of a color television system. Examples: dot-sequential pickup, dot-sequential display, dot-sequential system, dot-sequential transmission.

double-amplitude-modulation multiplier A multiplier in which a carrier is amplitude modulated by one variable, and the modulated signal is again amplitude modulated by a second variable. The product of the two variables is obtained by applying the resulting double-modulated signal to a balanced demodulator.

double armature An armature having two windings and commutators but only one core.

double-base diode See unijunction transistor.

double-base junction transistor Also called tetrode junction transistor. Essentially a junction triode transistor with two base connections on opposite sides of the central region of the transistor.

double-beam cathode-ray tube A cathode-ray tube having two electron beams capable of producing on the screen two independent traces that may overlap. The beams may be produced by splitting the beam of one gun or by using two guns.

double-bounce calibration A method of calibration used to determine the zero set error by using round-trip echoes. The correct range is the difference between the first and second echoes.

double-break contacts A set of contacts in which one contact is normally closed and makes simultaneous connection with two other contacts.

double-break switch A switch that opens the connected circuit at two points.

double bridge See Kelvin bridge.

double-button carbon microphone Also called differential microphone. A microphone with two carbon resistance elements or buttons, one on each side of a central diaphragm. They are connected in parallel to the current source in order to give twice the resistance change obtainable with a single button.

double-channel duplex A method for simultaneous communication between two stations over two rf channels, one in each direction.

double-channel simplex A method for nonsimultaneous communication between two stations over two rf channels, one in each direction.

double-checkerboard pattern See worst-case noise pattern.

double-clocking Incorrect setting of a flip-flop due to bounce in input signal.

double-conversion receiver A receiver using a superheterodyne circuit in which the incoming signal frequency is converted twice, first to a high IF and then to a lower one.

double-current generator A machine that supplies both direct and alternating current from the same armature winding.

double density A type of diskette that allows twice as much data to be stored as single density.

double-diffused epitaxial mesa transistor See epitaxial-growth mesa transistor.

double-diffused metal-oxide FET semiconductor See DMOS.

double-diffused transistor Also called double-emitter-and-base transistor. A transistor in which two pn junctions are formed in the semiconductor wafer by gaseous diffusion of both p-type and n-type impurities. An intrinsic region can also be formed.

double diode Also called duodiode. A vacuum tube or semiconductor having two diodes in the same envelope.

double-diode limiter A type of limiter used to remove all the positive signals from a combination of positive and negative pulses or to remove all the negative signals from such a combination of positive and negative pulses.

double-doped transistor A transistor formed by growing a crystal and successively adding p- and n-type impurities to the melt while the crystal is being grown.

double-doublet antenna An antenna composed of two half-wave doublet antennas criss-crossed at their centers; one is made shorter than the other to give broader frequency coverage.

double drop An alarm-signaling method often used in central-station alarm systems, in which the line is first opened to produce a break alarm and then shorted to produce a cross alarm.

double-emitter follower See Darlington amplifier.

double frequency-shift keying A multiplex system in which two telegraph signals are combined and transmitted simultaneously by frequency shifting among four radio frequencies.

double-grip terminal A solderless terminal with an extended flared barrel that permits a crimp to be made over the insulation of a wire as well as over the stripped portion.

double image A television picture consisting of two overlapping images due to reception of the signal over two paths that differ in length so signals arrive at slightly different times.

double insulation The insulation system resulting from a combination of functional and supplementary insulation.

double-junction photosensitive semiconductor A semiconductor in which the current flow is controlled by light energy. It consists of three layers of a semiconductor material, with electrodes connected to the ends of each.

double-length number Also called double-precision number. An electronic computer number having twice the normal number of digits.

double local oscillator An oscillator mixing system that generates two rf signals accurately spaced a few hundred hertz apart and mixes these signals to give the difference frequency that is used as the reference. This equipment is used in an interferometer system to obtain a detectable signal containing the phase information of an antenna pair, and the reference signal to allow removal of the phase data for use.

double-make contacts A set of contacts in which one contact is normally open and makes simultaneous connection with two other independent contacts when closed.

double moding Changing from one frequency to another abruptly and at irregular intervals.

double modulation 1. The process of modulation in which a carrier wave of one frequency is first modulated by a signal wave, and the resultant wave is then made to modulate a second carrier wave of another frequency. 2. A two-step modulation scheme in which an intelligence wave modulates a subcarrier, and then the modulated subcarrier is used to modulate a higher-frequency carrier.

double operand An instruction type containing two address fields: source operand address field and destination operand address field.

double orthomode coupler A dish-mounted device that allows reception of both vertically and horizontally polarized signals.

double photoresist A technique for eliminating pinholes in the photoresist coating during fabrication of microelectronic integrated circuits. The method may consist of two separate applications and exposures of photoresist emulsions of the same or different types.

double-play tape Tape having half the thickness, and hence double the running time (for a given reel size) of standard 1.5-mil tape.

double pole A term applied to a contact arrangement to denote that it includes two separate contact forms (i.e., two single-pole contact assemblies).

double-pole, double-throw switch Abbreviated dpdt. A switch that has six terminals and is used to connect one pair of terminals to either of the other two pairs.

double-pole, single-throw switch Abbreviated dpst. A switch that has four terminals and is used to connect or disconnect two pairs of terminals simultaneously.

double-pole switch A switch that operates simultaneously in two separate electric circuits or in both lines of a single circuit.

double precision 1. Having to do with the use of two computer words to represent one number. 2. The technique of allocating twice the data storage space for representing numeric information in order to achieve twice the accuracy.

double-precision arithmetic The use of two computer words to represent a single number. This is done where it is necessary to obtain a greater accuracy than a single word of computer storage will provide. It effectively doubles the data word size.

double-precision number See double-length number.

double-pulsing station A loran station that receives two pairs of pulses and emits pulses at two pulse rates.

double pumping A technique of pumping a laser for a relatively long time to store energy in subthreshold-level excited states, followed immediately by a very brief second pumping in which the threshold condition is exceeded in some region. This triggers laser oscillation throughout the entire active region and produces peak output powers several times larger than normally seen.

double rail See dual rail.

double-rail logic Pertaining to self-timing asynchronous circuits in which each logic variable is represented by two electrical lines that in combination can assume three meaningful states: zero, one, and undecided.

double screen A three-layer screen consisting of a two-layer screen with the additional second long-persistence coating having a different color and different persistence from the first.

double-shield enclosure A shielded enclosure or room whose inner wall is partially isolated electrically from the outer wall.

double sideband Amplitude-modulated intelligence that is transmitted at frequencies both above and below the carrier frequency by the audio-frequency value of the intelligence.

double-sideband transmitter A transmitter that transmits not only the carrier frequency, but also the two sidebands resulting from modulation of the carrier.

double-sided board A printed board with a conductive pattern on both sides.

double-spot tuning Superheterodyne reception of a given station at two different local-oscillator frequencies. The local oscillator is adjusted either above or below the incoming signal frequency by the intermediate-frequency value.

double-Stream amplifier A microwave traveling-wave amplifier in which amplification occurs through interaction of two electron beams having different average velocities.

double-stub tuner An impedance-matching device consisting of two stubs, usually fixed three-eighths of a wavelength apart, in parallel with the main transmission lines.

double superheterodyne reception Also called triple detection. The method of reception in which two frequency converters are employed before final detection.

double-surface transistor A point-contact transistor, the emitter and collector whiskers of which are in contact with opposite sides of the base.

doublet The output voltage waveform of a delay line under linear operating conditions when the input to the line is a current step function.

doublet antenna An antenna consisting of two elevated conductors substantially in the same straight line and of substantially equal length, with the power delivered at the center.

double tape mark A delimiter, consisting of two consecutive tape marks, that is used to indicate the end of a volume or of a file set.

double throw A term applied to a contact arrangement to denote that each contact form included is a break-make.

double-throw circuit breaker A circuit breaker by means of which a change in the circuit connections can be obtained by closing either of two sets of contacts.

double-throw switch A switch that alternately completes a circuit at either of its two extreme positions. It is both normally open and normally closed.

double-track recorder See dual-track recorder.

double trigger A trigger signal consisting of two pulses spaced by a fixed amount for coding.

double triode See duotriode.

double-tuned amplifier An amplifier in which each stage utilizes coupled circuits having two frequencies of resonance for the purpose of obtaining wider bands than are possible with single tuning.

double-tuned circuit A circuit in which two circuit elements are available for tuning.

double-tuned detector A type of FM discriminator in which the limiter output transformer has two secondary windings, one tuned a certain amount above the center frequency and the other tuned an equal amount below the center frequency.

double-V antenna Also called fan antenna. A modified single dipole that has a higher input impedance and broader bandwidth than an ordinary dipole.

double-winding synchronous generator A synchronous generator that has two similar windings in phase with one another, mounted on the same magnetic structure but not connected electrically, designed to supply power to two independent external circuits.

doubling The generation of large amounts of second-harmonic distortion by nonlinear motion of a loudspeaker cone.

doubly balanced modulator A modulator circuit in which two class A amplifiers are supplied with modulating and carrier signals of equal amplitudes and opposite polarities. Carrier suppression takes place because the two amplifiers share a common plate circuit and only the sidebands appear at the output.

downconversion The process of converting microwave signals down into a frequency range in which signal processing components are less expensive. Typically, this is a VHF frequency of 70 MHz.

downconverter 1. A type of converter whose input is a radio frequency and whose output is an intermediate frequency. 2. A microwave system (consisting of local oscillators, mixers, and bandpass filters) that accomplishes downconversion. 3. The front end of the satellite TV receiver. 3. The part of a satellite receiving system that converts the downlink signals to a 70-MHz intermediate frequency that is used by the receiver. Although it is sometimes part of the receiver, it is more often externally mounted directly at the LNA so that inexpensive coaxial cable can bring the signal to the receiver.

down lead Also called a lead-in wire. The wire that connects an antenna to a transmitter, receiver, or downconverter.

downlink 1. A satellite-to-earth microwave channel and related components, such as the earth station receiving equipment. The satellite contains a downlink transmitter; downlink components in the earth station are involved with the reception and processing of satellite-transmitted signals. 2. The communication path from a TV satellite to its ground (earth) stations.

download 1. The process of sending communications instructions, operating software or data from a central computer to individual terminals, including personal computers. To electronically copy a file from one computer to another computer. 2. To receive a file from a remote computer. 3. To transfer information stored in a remote computer system to the user’s system. The reverse process is an upload.

downloading 1. The electronic transfer of information from one computer to another, generally from a larger computer to a smaller one, such as a microcomputer. 2. Transferring information from a host computer to another computer. 3. To transfer data stored in one computer to a storage device in another computer. 4. The process of sending configuration parameters, operating software, or related data from a central source to remote stations. 4. Direct transfer of code from a host system (MDS) into a target system or a PROM programmer.

downstream Outlet side of an instrument.

downtime 1. Any period of time during which a system or device cannot be used as a result of a failure or routine maintenance, but not because of a lack of work or the absence of an operator. 2. The period during which computer or network resources are unavailable to users because of a system or component failure.

downward compatibility Software that can run on older and/or less powerful versions of a computer it was designed to run on.

downward modulation Modulation in which the instantaneous amplitude of the modulated wave is never greater than that of the unmodulated carrier.

dpdt Abbreviation for double-pole, double-throw.

dpi (dots per inch) A measurement of resolution, usually used with printers and scanners.

DPM See digital panel meter.

dpst Abbreviation for double-pole, single-throw.

draft mode A low-quality printing mode available on some printers.

drag Selecting and moving an on-screen icon via a mouse.

drag angle A stylus cutting angle of less than 90° to the surface of the record. So called because the stylus drags over the surface instead of digging in. It is the opposite of dig-in angle.

drag cup A nonmagnetic metal rotated in a magnetic field to generate a torque or voltage proportional to its speed.

drag-cup motor A small, high-speed, two-phase, alternating-current electric motor having a two-pole, two-phase stator. The rotating element consists only of an extremely light metal cup attached to a shaft rotating on ball bearings. Reversal is accomplished by reversing the connections to one phase. Used in applications requiring quick starting, stopping, and reversal characteristics.

dragging An interactive technique for repositioning an image on a display screen.

drag magnet See retarding magnet.

drag soldering A form of mass soldering in which a printed circuit board is mounted on a conveyor and contacts the surface of a static pool of molten solder at a slight angle when entering and exiting the solder bath. The board remains in contact with solder for a defined length (the dragging length) of time, travelling horizontally across the solder surface.

drain 1. The current taken from a voltage source. 2. The working-current terminal (at one end of the channel in a FET) that is the drain for holes or free electrons from the channel. Corresponds to a collector of a bipolar transistor. 3. Terminal that receives carriers from the MOS channel. 4. One of the three regions that form a field-effect transistor. Majority carries that originate at the source and traverse the channel are collected at the drain to complete the current path. The flow between source and drain is controlled by the voltage applied to the gate.

drainage equipment Equipment used to protect connected circuits from transients produced by the operation of protection equipment.

drain conductor A conductor in continuous contact with a shield for ground termination.

drain cutoff current The current into the drain terminal of a depletion-type transistor with a specified reverse gate-to-source voltage applied to bias the device to the off state.

drain terminal The terminai electrically connected to the region into which majority carriers flow from the channel.

drain wire 1. An uninsulated solid or stranded tinned copper wire that is placed directly under a shield. It touches the shield throughout the cable, and therefore may be used in terminating the shield to ground. It is completely necessary on spiral shielded cables because it eliminates the possibility of induction in a spiral shield. 2. An uninsulated wire, usually placed directly beneath and in electrical contact with a shield. It is used for making shield connections through terminal strips and to ground.

DRAM Abbreviation for dynamic random-access memory (pronounced “dee-ram”). 1. The least expensive and most popular type of semiconductor read/write memory chip, in which the presence or absence of a capacitive charge represents the state of a binary storage element (0 or 1). The charge must be periodically refreshed. 2. Memory that requires periodic refreshing because of charge leaking from capacitors in the cell circuit. 3. Main memory system of large computers, minicomputers, and even some large microcomputers.

drawing In the manufacture of wire, pulling the metal through a die or series of dies for reduction of diameter to a specified size.

D-region The region of the ionosphere up to about 90 kilometers above the earth’s surface. It is below the E-region.

dress 1. The exact placement of leads and components in a circuit to minimize or eliminate undesirable feedback and other troubles. 2. To arrange wire connections, cable ends, or cables so that they present a neat and orderly appearance.

dressed contact A contact that has a locking spring member permanently attached.

drift 1. Movement of carriers in a semiconductor as voltage is applied. 2. A change in either absolute level or slope of an input-output characteristic. 3. See flutter, 1. 4. See degradation, 1. 5. An undesired change in one of the output parameters of a power supply (voltage, current, frequency, etc.) over a period of time. The change is unrelated to all other variables, such as load, line, and environment. Drift is measured over a period of time by keeping all variables (such as line, load, and environment) constant. Specifications usually apply only after a warm-up period. 6. The angular displacement of an aircraft by the wind, generally expressed in degrees. 7. In a dc amplifier, the change in output with constant input, usually measured in terms of the dc input signal required to restore normal output; may be called out as microvolts or millivolts per hour. 8. A change in output attributable to any cause. 9. A change in the properties of an electrical circuit, as a result of aging or temperature changes.

drift current 1. The flow of carriers in a semiconductor due to an electric field. In the same electric field, holes and electrons will flow in opposite directions due to their opposite charge. 2. The relatively small directional bias that becomes superimposed on the random motion of carriers in an excited crystal lattice under the influence of an applied electric field (drift field).

drifting An instability in a preset voltage, frequency, or other electronic circuit parameter.

drift mobility The average drift velocity of carriers in a semiconductor per unit electric field. In general, the mobilities of electrons and holes are not the same.

drift space 1. In an electron tube, a region substantially free of alternating fields from external sources, in which relative repositioning of the electrons depends on their velocity distributions and the space-charge forces. 2. The distance between the buncher and catcher in a velocity-modulated vacuum tube.

drift speed Average speed at which electrons or ions progress through a medium.

drift transistor A type of transistor manufactured with a variable-conductivity base region. Such a base sets up an electric field that speeds up the carriers, thus reducing the transit time and improving high-frequency operation. See also diffused-alloy transistor.

drift velocity Net velocity of charged particles in the direction of the applied field.

drip loop A loop formed in a transmission line at a point where it enters a building. Condensation of moisture and water that may form on the line will drip off at the loop and thus will not enter the building.

drip-proof motor A motor in which the ventilating openings are such that foreign matter falling on the motor at any angle not exceeding 15° from the vertical cannot enter the motor either directly or indirectly.

driptight enclosure An enclosure that is intended to prevent accidental contact with the enclosed apparatus and, in addition, is so constructed as to exclude falling moisture or dirt.

drive 1. A unit used in mass storage applications to hold and operate the medium (e.g., disk or tape) being used to store data or programs. 2. Also called excitation. The signal applied to the input of a power amplifier. See excitation, 2.

drive belt A belt used to transmit power from a motor to a driven device.

drive circuit A circuit, usually a printed circuit card or an encapsulated module, that converts an input pulse to the appropriate winding excitation sequence to produce one step of the motor shaft.

drive control See horizontal drive control.

driven element 1. An antenna element connected directly to the transmission line. 2. An element of an antenna, such as of a Yagi antenna, that is energized directly from the antenna feed line.

driven sweep A sweep signal triggered by an incoming signal only.

drive pattern In a facsimile system, an undesired pattern of density variations that result from periodic errors in the position of the recording spot.

drive pin In disc recording, a pin similar to the center pin but located at one side of it and used to prevent a disc record from slipping on the turntable.

drive pulse A pulsed magnetomotive force applied to a magnetic cell from one or more sources.

driver 1. An electronic circuit that supplies input to another electric circuit. 2. A stage of amplification that precedes the power output stage. 3. In a radar transmitter, a circuit that produces a pulse to be delivered to the control grid of the modulator tube. 4. An element coupled to the output stage of a circuit to increase the power- or current-handling capability or fanout of the stage; for example, a clock driver is used to supply the current necessary for a clock line. 5. A device in a logic family controlled with normal logic levels whose output has the capability of sinking or sourcing high current. The output may control a lamp, relay, or a very large fanout of other logic devices. Also a device driving a higher-output device or transistor by supplying power, voltage, or current to it. 6. Any individual speaker within an audio system, such as the woofer, tweeter, etc. 7. A transistor output circuit that has an emitter-follower configuration. 8. A dc driver output module that contains driver output circuits. Each load must be connected between the output and ground as specified in the module data sheet. 9. Amplifier circuit used to reshape signals on a bus when more than one TTL load is present. 10. The low-power oscillator-modulator-amplifier unit that supplies the excitation to a power amplifier. See also exciter. 11. A program or routine that controls either external devices or other programs. 12. Typically, an electronic function used to provide amplification to drive high current loads. Term often used to denote bus drivers that rapidly charge and discharge capacitance. Also used to denote the ability to control power, such as when driving a solenoid or other high-current device.

driver element An antenna array element that receives power directly from the transmitter.

driver gate An analog switch, usually including two parts: the switch gate and a driver that controls the switch.

driver stage The amplifier stage preceding the power-output stage.

driving-point admittance The complex ratio of the alternating voltage for an electron tube, network, or other transducer.

driving-point impedance 1. At any pair of terminals in a network, the driving-point impedance is the ratio of an applied potential difference to the resultant current at these terminals, all terminals being terminated in any specified manner. 2. The input impedance of a transmission line or of an antenna.

driving power The power supplied to the grid circuit of a tube where the grid swings positive and draws current for part of each cycle of the input signal.

driving-range potential The voltage difference between the potential of the electrochemically more active anode and the less active protected metal or cathode. One example of driving potential is the electromotive force in a cathodic protection system that causes current between the protected structure (cathode) and the anode. The driving potential decreases as the electrodes become polarized.

driving signal Television signals that time the scanning at the pickup point. Two kinds of driving signals are usually available from a central sync generator, one composed of pulses at the line frequency and the other of pulses at the field frequency.

driving spring The spring driving the wipers of a stepping relay.

DRO memory Destructive readout memory. A memory in which the contents of a storage location are destroyed in being read. Information must be rewritten after reading, if it is to be returned. An example of a DRO memory is the common computer core memory.

drone cone An undriven speaker cone mounted in a bass-reflex enclosure.

droop The decrease in mean pulse amplitude, expressed as a percentage of the 100-percent amplitude, at a specified time following the initial attainment of 100-percent amplitude.

drop 1. To develop a specified difference of potential between a pair of terminals as the result of a flow of current. 2. See voltage drop.

drop bar A protective device used to ground a high-voltage capacitor when opening a door.

drop bracket transposition Reversal of the relative positions of two parallel wire conductors while depressing one, so that the crossover is in a vertical plane.

drop cable In a cable TV system, the transmission cable from the distribution cable to a dwelling.

drop channel A type of operation in which one or more channels of a multichannel system are terminated (dropped) at some intermediate point between the end terminals of the system.

drop-down menu A type of computer menu that drops from the menu bar when requested and remains open without further action until the user closes it or chooses an item from the menu. Same as pull-down menu.

drop-in The reading of a spurious signal of amplitude greater than a predetermined percentage of the nominal signal amplitude.

drop indicator An indicator for signaling, consisting of a hinged flap normally held up by a catch. The catch is released by an electromagnet, allowing the flap to drop when a signal is received.

drop-in mike A surreptitious listening device that transmits phone conversations only, by rf, to a radio receiver. So called because it is “dropped in,” replacing the standard carbon microphone in the ordinary telephone handset.

dropout 1. A momentary loss of volume or treble response due to a brief separation of the tape from the surface of the record or play head. A very slight separation causes a treble dropout; more severe loss of head-to-tape contact causes the whole signal to drop out. Dropouts can be caused by buckled or crinkled tape, lumps or pits in the magnetic coating, or detached clumps of oxide passing across the head surface. 2. Short pause in tape replay due to bad tape coating. 3. Momentary loss of signal in a transmission channel. 4. Momentary signal losses due to imperfections in the surface of recording tape or phonograph record.

dropout compensator Circuitry that senses a signal loss produced by dropout and substitutes missing information with signal from the preceding line; if one line drops out of a picture, it is filled in with the preceding line, resulting in no dropout on the screen.

dropout error An error, such as loss of a recorded bit, that occurs in recorded magnetic tape because of foreign particles on or in the magnetic coating or because of defects in the backing.

dropouts Also called keys. Special images inserted at certain points in the array on a photomask used in the production of monolithic circuits.

dropout value The maximum value of current, voltage, or power that will deenergize a previously energized relay. See also hold current; pickup value (voltage, current, or power).

dropout voltage The input-output voltage differential at which a regulator circuit ceases to regulate against further reductions in input voltage.

dropping resistor 1. A resistor used to decrease a given voltage by an amount equal to the potential drop across the resistor. 2. A resistor placed in series between a voltage source and a load to reduce the voltage supplied to the load.

drop rate The rate of discharge or decay rate of the sample-and-hold capacitor of a sample-and-hold device. The rate is a function of switch leakage current and the current required by other circuit elements connected to the capacitor. It is expressed as millivolts per second.

drop relay A relay activated by incoming ringing current to call the attention of an operator to the subscriber’s line.

drop repeater A microwave repeater station equipped for local termination of one or more circuits.

dropsonde A parachute-carried radiosonde dropped from a high-flying aircraft to measure weather conditions and report them to the aircraft. It is used over water or other areas where ground stations cannot be maintained.

drop wire A wire suitable for extending an open wire or cable pair from a pole or cable terminal to a building.

dross Oxide and other contaminants that form on the surface of molten solder.

drum 1. A random-access auxiliary memory device in which information is stored on a revolving drum that is coated with a magnetic material. 2. Rotating magnetic memory that uses the surface of a cylinder.

drum controller 1. A device in which electrical contacts are made on the surface of a rotating cylinder or sector. 2. A device in which contacts are made by the operation of a rotating cam.

drum memory A rotating cylinder or disk coated with magnetic material so that information can be stored in the form of magnetic spots.

drum parity A parity error that occurs during the transfer of information to or from drums.

drum plotter Plotter that draws an image on paper or film mounted on a drum.

drum printer A type of printer that employs a rotating cylinder. A complete set of characters is embossed on the circumference of the drum for each print position. A set of hammers is used to strike the drum (through the paper and ribbon) and print the proper character each time the drum rotates. (No longer used.)

drum programmer An electromechanical device that provides stored program logic for control of a sequential operation such as batch processing or machine cycling. It ranks between relay and solid-state systems in the cost/complexity scale.

drum recorder A facsimile recorder in which the record sheet is mounted on a rotating cylinder. (No longer used.)

drum sequencer Mechanical programming device that can be used to operate switches or valves.

drum speed The number of revolutions per minute made by the transmitting or receiving drum of a facsimile transmitter or recorder.

drum storage A storage device in which information is recorded magnetically on a rotating cylinder; a type of addressable storage associated with some computers.

drum switch A switch in which the electrical contacts are made on pins, segments, or surfaces on the periphery of a rotating cylinder.

drum transmitter A facsimile transmitter in which the copy is mounted on a rotating cylinder. (No longer used.)

drum-type controller 1. A multicircuit timing device, with or without a motor, using a cylindrical carriage into which pins are inserted to program events. 2. A multicircuit timing device intended to be driven from an external rotary power source.

drunkometer A device measuring the degree of alcoholic intoxication by analyzing the subject’s breath.

dry 1. A condition in which the electrolyte in a cell is immobilized. The electrolyte may be either in the form of a gel or paste or absorbed in the separator material. 2. Said of circuits or contacts that do not carry direct current.

dry battery Two or more dry cells arranged in series, parallel, or series-parallel within a single housing to provide desired voltage and current values.

dry cell 1. A voltage-generating cell having an immobilized electrolyte. The commonest form has a positive electrode of carbon and a negative electrode of zinc in an electrolyte of sal ammoniac paste. 2. A source of energy produced by the reaction of an acid or alkaline paste on dissimilar metals or on a metal and a carbon electrode. Normal open-circuit voltage is 1.5 volts. The paste is sealed in a container in normal use, and the cell cannot be recharged.

dry-charged battery A battery with the plates charged but lacking electrolyte. When ready to be placed in service, the electrolyte is added.

dry circuit 1. A circuit in which current and voltage are so low that there is no arcing to roughen the contacts. As a result, an insulating film can develop that prevents an electrical closing of the circuit when contacts are brought together, if the proper means are not employed to prevent the initial formation of the film. 2. A circuit in which the open-circuit voltage is 0.03 V or less and the current 200 mA or less. (The voltage is most important because at such a low level it is not able to break through most oxides, sulfides, or other films that can build up on contacting surfaces.) 3. A telephone circuit over which voice signals are transmitted and which carries no direct circuit.

dry-circuit contact A contact that carries current but neither makes nor breaks while its load circuit is energized. Sometimes erroneously used if referring to low level.

dry contacts Contacts through which there is no direct current.

dry-disc rectifier A rectifier consisting of discs of metal and other materials in contact under pressure. Examples are the copper-oxide and the selenium rectifier.

dry dross Nonmetallic components normally found on still solder pots and drag machines. A dry dross may be mixed in with lux, oil, or any other organic material. The term dry refers basically to the absence of any metallic solder.

dry-electrolytic capacitor An electrolytic capacitor with a paste rather than liquid electrolyte. By eliminating the danger of leakage, the paste electrolyte permits the capacitor to be used in any position.

dry flashover voltage The voltage at which the air surrounding a clean, dry insulator or shell completely breaks down between electrodes.

dry-reed contact An encapsulated switch containing two metal wires that serve as the contact points for a relay.

dry-reed relay A relay that consists of one or more capsules containing contact mechanisms that are generally surrounded by an electromagnetic coil for actuation. The capsule consists of a glass tube with a flattened ferromagnetic reed sealed in each end. These reeds, which are separated by an air gap, extend into the tube so as to overlap. When placed in a magnetic field, they are brought together and close a circuit.

dry shelf life The length of time that a cell can stand without electrolyte before it deteriorates to a point at which a specified output cannot be obtained.

dry-type forced-air-cooled transformer (class AFA) A transformer that is not immersed in oil and that derives its cooling by the forced circulation of air.

dry-type self-cooled/forced-air-cooled transformer (class AA/FA) A transformer that is not immersed in oil and that has a self-cooled rating with cooling obtained by the forced circulation of air.

dry-type self-cooled transformer (class AA) A transformer that is cooled by the natural circulation of air and that is not immersed in oil.

dry-type transformer A transformer that is cooled by the circulation of air and that is not immersed in oil.

dsc Abbreviation for double silk-covered.

D-scope A radar display similar to a C-scope except that the blips extend vertically to give a rough estimate of the distance.

“D” service FAA service pertaining to radio broadcast of meteorological information, advisory messages, and notices to airmen.

DSP Abbreviation for digital signal processor. A specialized chip and/or system that is dedicated to processing real-time signals. Typically used for modems, audio, imaging, and video applications.

DSU See data service unit.

DT-cut crystal A crystal cut to vibrate below 500 kHz.

DTE See data termination equipment.

DTL Abbreviation for diode-transistor logic.

DTMF Abbreviation for dual-tone multifrequency (signaling).

DTP Abbreviation for desktop publishing.

DTV Abbreviation for digital television.

D-type flip-flop A flip-flop that, on the occurrence of the leading edge of a clock pulse, propagates to the 1 output whatever information is at its D (data) conditioning input prior to the clock pulse.

dual Either of a pair of systems, circuits, etc., that are described by equations of the same form in which the same functional relationships hold provided that the dependent and independent dynamic variables are interchanged between these equations.

dual-beam oscilloscope An oscilloscope in which the cathode-ray tube produces two separate electron beams that may be individually or jointly controlled.

dual capacitor Two capacitors within a single housing.

dual capstan See closed loop drive.

dual-channel amplifier An amplifier that has two channels independent of each other, but similar in design, construction, and output.

dual coaxial cable Two individually insulated conductors laid parallel or twisted and placed within an overall shield and sheath.

dual cone Speaker unit containing a main cone for bass and middle frequencies and a smaller, stiffer inner cone for treble frequencies, sometimes called a full-range speaker unit.

dual-diversity receiver 1. A radio receiver that receives signals from two different receiving antennas and uses whichever signal is the stronger at each instant to offset fading. In one arrangement, two identical radio-frequency systems, each with its own antenna, feed a common audio-frequency channel. In another arrangement, a single receiver is changed over from one antenna to the other by electronic switching at a rate fast enough to prevent loss of intelligibility. 2. The operation of combining two identical signals received over diverse paths to obtain an improvement of up to 3 dB in signal-to-noise ratio.

dual-emitter transistor A passivated pnp silicon planar epitaxial transistor with two emitters; used as a low-level chopper.

dual feedhorn A feedhorn that can simultaneously receive both horizontally and vertically polarized signals.

dual-frequency induction heater A type of induction heater in which work coils operating at two different frequencies induce energy, either simultaneously or successively, to material within the heater.

dual-groove record See Cook system.

dual in-line package Abbreviated DIP. 1. A type of housing for integrated circuits. The standard form is a molded plastic container about ¾ inch long and 1/3 inch wide (1.9 × 0.8 cm), with two rows of pins spaced 0.1 inch (2.5 cm) between centers. This package is more popular than the flat pack or TO-type can for industrial use because it is relatively inexpensive and is easily dip-soldered into printed circuit boards. 2. Carrier in which a semiconductor integrated circuit or other components, such as transistor, diodes, capacitors, inductors, resistors, or film hybrid circuits, are assembled and sealed. Package consists of a plastic or ceramic body with two rows of seven or more vertical leads that are inserted into a circuit board and secured by soldering. 3. The most common type of integrated-circuit package, which can be either plastic (DIP-plastic) or ceramic (CERDIP). Circuit leads or pins extend symmetrically outward and downward from opposite sides of the rectangular package body. “DIP, side-brazed” is a dual in-line package with leads brazed externally, on the sides of the package.

dual meter A meter constructed so that two aspects of a circuit may be read simultaneously.

dual-mode ignition See DMI.

dual-mode phone A phone that operates on both analog and digital networks.

dual modulation The use of two different types of modulation, each conveying separate intelligence, to modulate a common carrier or subcarrier wave.

dual operation A logic operation whose result is the negation of the result of an original operation when applied to the negation of its operands; for example, the OR operation is the dual of the AND operation. A dual operation is represented by writing 0 for 1 and 1 for 0 in the tabulated values of P, Q, and R for the original operation.

dual pickup See turnover pickup.

dual rail Also called double rail. Pertaining to a method of transferring data in which the data and the complement of the data are available on different input or output lines or wires.

dual slope converter An integrating analog-to-digital converter in which the unknown signal is converted to a proportional time interval that is then measured digitally.

dual-tone multifrequency Abbreviated DTMF. 1. A signaling method in which are employed set pairs of specific frequencies used by subscribers and PBX attendants, if their switchboard positions are so equipped, to indicate telephone address digits, precedence ranks, and end of signaling. 2. A portion of the touch-tone telephone dialing system developed by AT&T that combines two of a set of standard frequencies. The result of the combination is a third or beat frequency (signal) that is the desired or useable signal. DTMF signaling transports precisely defined and matched tone pair signals over sharply tuned amplitude-guarded channels to achieve highly error-immune operation.

dual-tone multifrequency signaling Abbreviated DTMF signaling. Sending numerical address information from a telephone by sending, simultaneously, a combination of two tones out of a group of eight. The eight frequencies are 697, 770, 852, 941, 1209, 1336, 1477, and 1633 Hz.

dual trace A mode of operation in which a single beam in a cathode-ray tube is shared by two signal channels. See also alternate mode; chopped mode.

dual-track recorder Normally a monophonic recorder in which the recording head covers slightly less than half the width of a standard quarter-inch tape, making it possible to record one track on the tape in one direction and, after turning the reels over, a second track in the opposite direction. Known also as half-track or two-track recorder.

dual-use line A communications link that normally is used for more than one mode of transmission (e.g., for voice and data).

dub Also called rerecording. 1. A copy of a recording. 2. To make a copy of a recording by recording on one machine what another machine is playing.

dubbing 1. In radio broadcasting, the addition of sound to a prerecorded tape or disc. 2. Copying of already recorded material. In tape recording, playing a tape or disc on one machine while recording it on another. The copy is called a dub.

duct 1. An overhead or underground protective tube or pipe used for carrying electrical conductors. 2. In microwave transmission, atmospheric conditions may cause radio waves to follow a narrower path than usual. The narrower path is called a duct. The presence of ducting sometimes causes unusual transmission because the transmission waves do not follow the intended path.

ducting The trapping of an electromagnetic wave, in a waveguide action, between two layers of the earth’s atmosphere, or between a layer of the atmosphere and the earth’s surface.

DUF Abbreviation for diffusion under the epitaxial film. A method for providing a low-resistance path between the active region of an IC transistor and the contact electrode at the surface. A region of high conductance is formed by selective diffusion in the required location prior to deposition of the epitaxial layer.

dumb terminal 1. Conversational slave to a host computer in a communication network. 2. An inexpensive means of interactive computer control that is good for online fixed-program applications. All software is in the host computer mainframe. A dumb terminal contains no user programming or memory for data manipulation. 3. The minimum equipment necessary to communicate with a computer. It consists of a monitor and a keyboard and will do little more than send and receive data. 4. A display terminal with no processing capabilities other than that associated with screen formatting. For processing, the terminal is entirely dependent on the main computer with which it communicates.

dummy 1. A device that can be substituted for another, but which has no operating features. 2. A telegraphy network used to simulate a customer’s loop for adjustment of a telegraph repeater. The dummy side of the repeater is the side toward the customer. 3. In a computer, an artificial address, instruction, or other unit of information inserted solely for the purpose of fulfilling such prescribed conditions as word length or block length without affecting operations. 4. A simulating circuit that has no features.

dummy antenna See artificial antenna.

dummying The process of removing metallic impurities from plating solution with a large-area dummy cathode.

dummy instruction An artificial instruction or address inserted in a list of instructions to a computer solely to fulfill prescribed conditions (such as word length or block length) without affecting the operation.

dummy load See artificial load.

dummy variable In a computer program, a symbol inserted at definition time, which will later be replaced by the actual variable.

dump Also called power dump. 1. To withdraw all power from a computer, either accidentally or intentionally. 2. To transfer all or part of the contents of one section of a digital-computer memory into another section. 3. To transfer information from a register word to a memory position. 4. To transfer all of the information contained in a record into another storage medium. For example, a disc record could be dumped onto tape. 5. Copying contents of memory from one place to another. Same as memory dump.

dump check Checking a computer by adding all digits as they are dumped (transferred) to verify the sum to make sure no errors exist as the digits are retransferred.

dump circuit One form of transient suppression circuit, a self-biased snubber. The dump circuit is virtually inactive until the voltage across it exceeds the recent (slow) average value.

dumping resistor A resistor whose function is to discharge a capacitor or network for safety purposes.

Dunmore cell See lithium chloride sensor.

duodecal socket A vacuum-tube socket having 12 pins. Used for cathode-ray tubes.

duodecimal 1. Pertaining to a characteristic or property involving a selection, choice, or condition in which there are 12 possibilities. 2. Pertaining to the numbering system with a radix of 12.

duodiode Also called dual diode. A vacuum tube or semiconductor having two diodes within the same envelope.

duodiode-pentode An electron tube containing two diodes and a pentode in the same envelope.

duodiode-triode An electron tabe containing two diodes and a triode in the same envelope.

duolateral coil See honeycomb coil.

duopole An all-pass action with two poles and two zeros.

duotriode Also called double triode. An electron tube containg two triodes in the same envelope.

duplex 1. The method of operation of a communication circuit in which each end can simultaneously transmit and receive. (Ordinary telephones are duplex. When used on a radio circuit, duplex operation requires two frequencies.) 2. Two-in-one, as two conductors with a common overall insulation or two telegraph transmission channels over one wire. 3. Two conductors twisted together, usually with no outer covering. This term has a double meaning; it is possible to have parallel wires and jacketed parallel wires, and still refer to them as duplex. 4. Two-way data transmission. Full duplex describes two data paths that allow simultaneous data transmission in both directions. Half duplex describes one data path that allows data transmission in either of two directions, but only one direction at a time.

duplex artificial line A balancing network simulating the impedance of the real line and distant terminal apparatus; it is employed in a duplex circuit for the purpose of making the receiving device unresponsive to outgoing signal currents.

duplex cable A cable composed of two insulated stranded conductors twisted together. They may or may not have a common insulating covering.

duplex channel A communication channel providing simultaneous transmission in both directions.

duplexer 1. A radar device that, by using the transmitted pulse, automatically switches the antenna from receive to transmit at the proper time. 2. Highly selectable, tunable filters that allow a transmitter and receiver to use one common antenna.

duplexing assembly (radar) See transmit-receive switch.

duplex operation Simultaneous operation of transmitting and receiving apparatus at two locations.

duplex system A system with two distinct and separate sets of facilities, each of which is capable of assuming the system function while the other assumes a standby status. Usually both sets are identical in nature.

duplex tube A combination of two vacuum tubes on one envelope.

duplicate To copy in such a way that the result has the same physical form as the source. For example, to make a new punched card that has the same pattern of holes as an original punched card.

duplication check A computer check in which the same operation or program is checked twice to make sure the same result is obtained both times.

Duraspark Conventional (Ford Motor) electronic ignition for use with high-voltage, high-energy spark timing control.

duration control A control for adjusting the time duration of reduced gain in a sensitivity time control circuit.

duress alarm device A device that produces either a silent alarm or local alarm under a condition of personnel stress such as holdup, fire, illness, or other panic or emergency. The device is normally manually operated and may be fixed or portable.

duress alarm system An alarm system that employs a duress alarm device.

during cycle The interval while a timer is operating for its preset time period.

dust core A pulverized iron core consisting of extremely fine iron particles mixed with a binding material for use in radio-frequency coils.

dust cover A device specifically designed to cover the mating end of a connector so as to provide mechanical and/or environmental protection.

DUT Abbreviation for device under test.

duty cycle 1. Ratio of working time to total time for intermittently operated devices. 2. The ratio of on-time to off-time in a periodic on-off cycle. 3. The ratio of operating time to total elapsed time of a device that operates intermittently, expressed as a percentage. 4. In percent, 100(t_o/T), where T is the period between pulses and t_o is the pulse width.

duty cyclometer A test meter that gives a direct reading of duty cycle.

duty factor 1. In a carrier composed of regularly recurring pulses, the product of their duration and repetition frequency. 2. Ratio of average to peak power. 3. Same as duty cycle except it is expressed as a decimal rather than a percentage. Usually calculated by multiplying pulses per second times pulse width.

duty ratio In a pulsed system, such as radar, the ratio of average to peak power.

DVD Abbreviation for the digital versatile disc and digital video disk. A high capacity optical storage medium with improved capacity and bandwidth over the CD for prerecorded multimedia program material with applications in video playback and PC areas.

dv/dt The rate of change of voltage with respect to time. Proportional to current in a capacitor.

Dvorak keyboard A keyboard arrangement designed by August Dvorak for increased speed and comfort. It reduces the rate of errors by placing the most frequently used letters in the center of the keyboard for use by the strongest fingers.

DX 1. Abbreviation for distance. 2. Reception of distant stations. 3. Distant and/or difficult to hear radio stations.

DXer One who listens to distant or hard-to-hear stations as a hobby.

DX hound An amateur who specializes in making distant contacts.

DXing The hobby of listening to distant or otherwise hard-to-hear stations.

dyadic Boolean operator A Boolean operator that has two operands. The dyadic Boolean operators are AND, exclusive OR, NAND, NOR, and OR.

dyadic operation An operation on two operands.

dye laser A laser using a dye solution as its active medium. Its output is a short pulse of broad spectral content, and its achievable gain is high. Dye lasers function at room temperature. Synchronous pumping can be used to produce a continuous train of tunable picosecond pulses for sustained periods.

dynamic 1. Of, concerning, or dependent on conditions or parameters that change, particularly as functions of time. 2. A speaker drive principle using the interaction between the magnetic field surrounding a voice coil carrying a signal current and a fixed magnetic field to move the coil and the cone to which it is attached. 3. A headphone driver using a voice coil in a magnetic field driving a paper or plastic diaphragm, as in a speaker.

dynamic acceleration Acceleration in a constantly changing magnitude and direction, either simple or complex motion, usually called vibration. Also measured in gravity units.

dynamically balanced arm A type of tonearm whose masses are balanced about its pivot, with tracking force applied by a spring. This type of arm does not require that the turntable be level for proper tracking.

dynamic analogies The similarities in form between the differential equations that describe electrical, acoustical, and mechanical systems that allow acoustical and mechanical systems to be reduced to equivalent electrical networks, which are conceptually simpler than the original systems.

dynamic analysis Execution of an instrumented program to collect information on its behavior and correctness.

dynamic behavior The way a system or individual unit functions with respect to time.

dynamic braking 1. A system of braking of an electric drive in which the motor is used as a generator, and the kinetic energy of the motor and driven machinery is employed as the actuating means of exerting a retarding force. 2. A type of motor braking caused by current being applied to the windings after the power is shut off. This is accomplished either by self-excitation (dc motors) or by separate excitation (ac motors).

dynamic burn-in High-temperature test with devices subject to actual or simulated operating conditions.

dynamic cell A memory cell that stores data as charge (or absence of charge) on a capacitor. A typical cell isolates the capacitor from the data line (bit line) with a transistor switch. Thus, when no read or write operation is desired, there is essentially no power required to maintain data. However, normal leakage requires that the charge be periodically restored by a process called refresh. Characteristics of a dynamic cell are very low data retention power, fewer transistors per bit (a one-transistor cell is common), and, usually, less area and lower cost per bit than for static cells.

dynamic characteristics Relationship between the instantaneous plate voltage and plate current of a vacuum tube as the voltage applied to the grid is varied.

dynamic check A check used to ascertain the correct performance of some or all components of equipment or a system under dynamic or operating conditions.

dynamic contact resistance 1. In a relay, a change in contact electrical resistance due to a variation in contact pressure on mechanically closed contacts. For example, during wiping motion of sliding contacts during make or prior to break. Also when contact members no longer actually open, as in contact bounce, but members are still vibrating and varying the contact pressure and hence its resistance. 2. A varying contact resistance on contacts mechanically closed.

dynamic convergence 1. The condition in which the three beams of a color picture tube come together at the aperture mask as they are deflected both vertically and horizontally. 2. A composite horizontal and vertical voltage used to ensure correct convergence of the three beams of a tricolor picture tube over the entire surface of the phosphor-dot faceplate. See also horizontal dynamic convergence; vertical dynamic convergence.

dynamic crosstalk A condition (in an amplifier utilizing a single power supply) in which the demands made on one channel will effectively modulate the output of the other channel because the power supply feeding both is pumping up and down. To completely eliminate dynamic crosstalk may require separate and well-shielded power supplies for each channel.

dynamic decay In a storage tube, decay caused by an action such as that of ion charging.

dynamic demonstrator A three-dimensional schematic diagram in which the components of the radio, television receiver, etc., are mounted directly on the diagram.

dynamic deviation The difference between the ideal output value and the actual output value of a device or circuit when the reference input is changing at a specified constant rate and all other transients have expired.

dynamic dump A dump performed while a program is being executed.

dynamic electrode potential The electrode potential measured when current is passing between the electrode and the electrolyte.

dynamic equilibrium of an electromagnetic system 1. The tendency of any electromagnetic system to change its configuration so that the flux of magnetic induction will be maximum. 2. The tendency of any two current-carrying circuits to maintain the flux of magnetic induction linking the two at maximum.

dynamic error An error in a time-varying signal resulting from inadequate dynamic response of a transducer.

dynamic focus The application of an ac voltage to the focus electrode of a color picture tube to compensate for the defocusing caused by the flatness of the screen.

dynamic headroom The ability of an amplifier to produce more than its rated power for very short periods of time. An amplifier rated at 100 watts per channel with 3 dB of dynamic headroom can briefly produce 200 watts per channel.

dynamic magnetic field A field whose intensity is changing and whose lines of force are expanding or contracting. Such change can be periodic or random. Unlike the static field, the dynamic field can transfer energy from one point to another without relative motion between the points.

dynamic memory 1. A type of semiconductor memory in which the presence or absence of an electrical or capacitive charge represents the two states of a binary storage element. Without refresh, the data represented by the electrical charge would be lost. 2. An MOS RAM memory using dynamic circuits. Each bit is stored as a charge on a single MOS transistor. This results in very high-density storage (only one transistor per bit). The charge leaks; therefore, a typical dynamic memory must be refreshed every 2 ms by rewriting its entire contents. In practice, this does not slow down the system, but requires additional memory refresh logic. (Dynamic chips are inexpensive and generally preferred to static ones for sizes over 16 K.)

dynamic memory allocation Allocation of a limited main memory to successive programs in function of an allocation strategy based on priority, availability, or size.

dynamic microphone See moving-coil microphone.

dynamic MOS array A circuit made up of MOS devices that requires a clock signal. The circuit must be tested at its rated (operating) speed. Known as clock-rate testing.

dynamic mutual-conductance tube tester See transconductance tube tester.

dynamic noise limiter Abbreviated DNL. A compatible circuit designed primarily for use with tape recorders. It improves the effective signal-to-noise ratio during replay by selective filtering at low signal levels.

dynamic noise suppressor An audio filter whose bandpass is adjusted automatically to the signal level. At low signal levels, filtering is highest; at high signal levels, all filter action is removed.

dynamic output impedance See output impedance, 2.

dynamic pickup A phonograph pickup whose electrical output is the result of the motion of a conductor in a magnetic field.

dynamic plate impedance The internal resistance to the flow of alternating current between the cathode and plate of a tube.

dynamic plate resistance See ac plate resistance.

dynamic power See music power.

dynamic printout In a computer, a printout of data that occurs as one sequential operation during the machine run.

dynamic problem check A dynamic check used to ascertain that the solution determined by an analog computer satisfies the given system of equations.

dynamic programming 1. A procedure used in operations research for optimization of a multistage problem solution in which a number of decisions are available at each stage of the process. 2. A method of sequential decision making in which the result of the decision in each stage affords the best possible answer to exploit the expected range of likely (yet unpredictable) outcomes in the following decision-making stages.

dynamic RAM See DRAM.

dynamic range 1. The difference, in decibels, between the overload level and the minimum acceptable signal level in a system or transducer. 2. The span of volume between the loudest and softest sounds, either in an original signal (original dynamic range) or within the span of a recorder’s capability (recorded dynamic range). Dynamic range is expressed in decibels. See signal-to-noise ratio. 3. The range of signal amplitudes, from the loudest to the quietest, that can be reproduced effectively by an equipment. Limited by the intrinsic noise of the amplifier and the ambient background noise level of the listening environment and by the power capacity of the amplifier and speaker system. 4. The ratio between the maximum recorded level (usually that which results in 3-percent playback distortion) and the playback noises from a tape recorded with no signal input. Expressed in decibels. 5. The difference between the maximum acceptable signal level and the minimum acceptable signal level. 6. The ratio of the largest to the smallest values of range, often expressed in decibels. 7. The ratio of the maximum output signal to the smallest output signal that can be processed in a system, usually expressed logarithmically in dB. (Dynamic range can be specified in terms of harmonic distortion, signal-to-noise ratio, spurious-free dynamic range, or other ac input-based performance criteria.)

dynamic register A memory in which the storage takes the form of capacitively charged circuit elements and therefore must be continually refreshed, or recharged, at regular intervals.

dynamic regulator A transmission regulator in which the adjusting mechanism is in self-equilibrium at only one or a few settings and requires control power to maintain it at any other setting.

dynamic relocation The ability to move computer programs or data from auxiliary memory to any convenient location in the memory. Normally the addresses of programs and data are fixed when the program is compiled.

dynamic reproducer See moving-coil pickup.

dynamic resistance Incremental resistance measured over a relatively small portion of the operating characteristic of a device.

dynamic router A router that automatically broadcasts routing information throughout the Internet at regular intervals. Other dynamic routers use this information to update their routing tables in case any changes have been made to the network.

dynamic run Also called dynamic test. 1. The test performed on an instrument to obtain the overall behavior and to establish or corroborate specifications such as frequency response, natural frequency of the device, etc. 2. Test based on a time-interval measurement as, for example, the rise time or fall time of a pulse. 3. A test of one or more of the signal properties or characteristics of equipment that is energized or in a nonquiescent state.

dynamic sequential control A method of operation in which a digital computer can alter instructions or their sequence as the computation proceeds.

dynamic shift register A shift register in which information is stored by means of temporary charge storage techniques. The major disadvantage of this method is that loss of the information occurs if the clock repetition rate is reduced below a minimum value.

dynamic skew Short-term misalignment of the read head of a tape player as referenced to a master skew tape. It results from variations in tape-path geometry and tape-path alignment and slitting and “snaking” tolerances of magnetic tape.

dynamic speaker See moving-coil speaker.

dynamic storage 1. A data-storage device in which the data is permitted to move or vary with time in such a way that the specified data is not always immediately available for recovery. Magnetic drums and disks are permanent dynamic storage; acoustic delay line is a volatile dynamic storage. 2. Information storage using temporary charge storage techniques. It requires a clock repetition rate high enough to prevent loss of information.

dynamic storage allocation A storage-allocation technique in which program and data locations are determined by criteria applied at the moment of need.

dynamic subroutine In digital-computer programming, a subroutine that involves parameters (such as decimal point position) from which a properly coded subroutine is derived. The computer itself adjusts or generates the subroutine according to the parametric values chosen.

dynamic test See dynamic run.

dynamic transfer-characteristic curve A curve showing the variation in output current as the input current changes.

dynamo 1. Normally called a generator. A machine that converts mechanical energy into electrical energy by electromagnetic induction. 2. In precise terminology, a generator of direct current — as opposed to an alternator, which generates alternating current.

dynamoelectric Pertaining to the relationship between mechanical force and electrical energy or vice versa.

dynamometer 1. An instrument in which the force between a fixed and a moving coil provides a measure of current, voltage, or power. 2. Equipment designed to measure the power output of a rotating machine by determining the friction absorbed by a hand brake opposing the rotation.

dynamotor Also called a rotary converter or synchronous inverter. 1. A rotating device for changing a dc voltage to another value. It is a combination electric motor and dc generator with two or more armature windings and a common set of field poles. One armature winding receives the direct current and rotates (thus operating as a motor), while the others generate the required voltage (and thus operate as a dynamo or generator). 2 A rotary electrical machine used to convert direct current to alternating current. The machine has a single field structure and a single rotating armature having two windings, one equipped with a dc commutator and the other with ac slip rings.

dynaquad A germanium pnpn semiconductor switching device that is base controlled and has three terminals. Its operation is similar to that of a flip-flop circuit or latching relay.

dynatron Also called negatron. A type of vacuum tube in which secondary emission of electrons from the plate causes the plate current to decrease as the plate voltage increases, with the result that the device exhibits a negative-resistance characteristic. Used in oscillator circuits. See tetrode.

dynatron oscillator A negative-resistance oscillator with negative resistance derived between the plate and cathode of a screen-grid tube operating such that secondary electrons produced at the plate are attracted to the higher-potential screen grid.

dyne The fundamental unit of force in the cgs system that, if applied to a mass of 1 gram, would give it an acceleration of 1 cm/s².

dyne per square centimeter Also called microbar. The unit of sound pressure. One dyne per square centimeter was originally called a bar in acoustics, but the full expression is used in this field now because the bar is defined differently in other applications.

dynistor A nonlinear semiconductor having the characteristics of a small current flow as voltage is applied. As the applied voltage is increased, a point is reached at which the current flow suddenly increases radically and will continue at this rate even though the applied voltage is reduced.

dynode 1. An electrode having the primary function of supplying secondary electron emission in an electron tube. 2. The auxiliary electrode that, when functioning within a photomultiplier tube and when bombarded by photoelectrons, gives rise to secondary emission and amplification.