J
jack 1. A socket to which the wires of a circuit are connected at one end, and into which a plug is inserted at the other end. 2. A type of two-way, or more, concentric contact socket for carrying audio signals. 3. A receptacle into which a mating connector may be plugged. 4. The receptacle that accepts a plug, specifically a phone plug. 5. A plug-in type terminal widely used in electronic apparatus for temporary connections or those requiring frequent connections and disconnections. A connection is made to a jack simply by plugging a probe or plug attached to a flexible insulated wire or cable into the jack. 6. Receptacle for a plug connector leading to the input or output circuit of a tape recorder or other piece of equipment. A jack matches a specific plug.
jack bay Also called patch bay. A panel containing a number of signal jacks (usually standard phone jacks or mini phone jacks), commonly used in studio recording consoles and in equipment racks to provide flexibility in rerouting signals (beyond that provided by normal switches or controls). The jack bay also offers convenience when temporarily connecting certain equipment to a system, or troubleshooting and aligning equipment.
jacket 1. Pertaining to wire and cable, the outer sheath that protects against environment and may also provide additional insulation. 2. An outer, nonmetallic, protective covering applied over an insulated wire or cable.
jack panel An assembly composed of a number of jacks mounted on a board or panel.
jackscrew A screw attached to one half of a two-piece, multiple-contact connector and used to draw both halves together and to separate them.
jaff Slang for the combination of electronic and chaff jamming.
jag In facsimile, distortion caused in the received copy by a momentary lapse in synchronism between the scanner and recorder.
jaggies Irregular edges on something that should look smooth, a byproduct of the method of searching a scene and of too coarse a bit map.
jam 1. In punch-card machines, a condition in the card feed that interferes with the normal travel of the punch cards through the machine. 2. To interfere electronically with the reception of radio signals.
jam input The presetting or loading of a counter, using inputs provided for the purpose. Also, the establishment of a desired logic state or logic line by the direct application of the appropriate voltage level to the line, regardless of the outputs of other devices connected to it.
jammer An electronic device for intentionally introducing unwanted signals into radar sets to render them ineffective.
jammer band The radio-frequency band where the jammer output is concentrated. It is usually the band between the points where the intensity is 3 dB down from maximum.
jammer finder Also called burnthrough. Radar that attempts to obtain the range of the target by training a highly directional pencil beam on a jamming source.
jammers tracked by azimuth crossings Semiautomatic strobe processing and tracking that permits automatic detection and tracking on the basis of azimuth information obtained from the jamming signals emanating from an airborne vehicle.
jamming Also called active electronic countermeasures. 1. The intentional transmission of radio signals in order to interfere with the reception of signals from another station. 2. Interference with hostile radio or radar signals for the purpose of deceiving or confusing the operator. It may be accomplished by saturating a receiver with sufficient noise to prevent detection and location of a target, or by deceiving the operator with intentionally misleading signals or false echoes without his knowing that such signals are present. 3. The deliberate radiation, reradiation, or reflection of electromagnetic energy to impair the use of electronic devices, equipment, or systems by the enemy. Equipment may consist of rudimentary cw or noise transmitters, broadband transmitters, or complex systems that generate deceptive signals.
jamming effectiveness The jamming-to-signal ratio, that is, the percentage of information incorrectly received in a test message.
JAN specification Joint Army-Navy specification. The forerunner of present military specifications; generally superseded by the designation MIL.
J-antenna A half-wave antenna fed at one end by a parallel-wire, quarter-wave section having the configuration of a J.
Java A platform-independent programming language invented by Sun Microsystems that is specifically designed for writing programs that can be safely downloaded to a computer through the Internet and immediately run without fear of viruses or other harm to the computer or to files. Using small Java programs (called applets), web pages can include functions such as animations, calculators, and other fancy tricks.
J-carrier system A broadband carrier system that provides 12 telephone channels and utilizes frequencies up to about 140 kilohertz by means of four-wire transmission on a single open-wire pair.
J-display Also called J-scan. In radar, a modified A-display in which the time base is a circle and the target signal appears as a radial deflection from it.
JEDEC Acronym for Joint Electron Device Engineering Council. An industry-sponsored organization whose function is to provide a means of standardization for the industry. This encompasses numbering systems, testing methods and techniques, specifications uniformity, and similar attempts on the part of the component manufacturers to assist the users of electronic components. In addition, JEDEC attempts to establish a code of ethics for the industry and to offer a set of standards for nonmilitary parts.
JETEC Acronym for Joint Electron Tube Engineering Council.
jewel bearing A natural or synthetic jewel, usually sapphire, used as a bearing for a pivot or other moving parts of a delicate instrument.
jezebel A system for the detection and classification of submarines.
JFET Abbreviation for junction field-effect transistor. A semiconductor device that operates by altering the conductivity of a region of the semiconductor (the channel) between two contacts (source and drain) by application of a voltage to a third terminal (gate). The current flow between source and drain is controlled by the gate voltage. In a JFET device, the gate voltage is applied to the channel across a pn junction, in contrast to its application across an insulator in a conventional MOS-EET. JFETs are of two types: p channel and n channel, depending on whether the channel is n type or p type.
JHG Abbreviation for Joule heat gradient.
jitter 1. Instability of a signal in either its amplitude or its phase, or both, due to mechanical disturbances or to changes in supply voltage, component characteristics, etc. 2. In relation to cathode-ray tube displays, error in the signal amplitude, phase, or both that results in small, rapid abberations in size or position of the image. 3. Error of synchronization between a facsimile’s transmitter and receiver characterized by a raggedness in the copy. 4. An aberration of a repetitive display, indicating instability of the signal or of the oscilloscope. May be random or periodic, and is usually associated with the time axis. 5. A loss of synchronization caused by electrical or mechanical malfunctions. 6. Type of analog-communication-line distortion caused by a signal’s variation from its reference timing position, which can cause data-transmission errors, particularly at high speeds. This variation can be in amplitude, time, frequency or phase. See flicker, 3; fortuitous telegraph distortion.
jittered pulse recurrence frequency The random variation of the pulse-repetition period. Provides a discrimination capability against repeater-type jammers.
J-K flip-flop A flip-flop with two conditioning inputs (J and K) and one clock input. If both conditioning inputs are disabled prior to a clock pulse, the flip-flop does not change condition when a clock pulse occurs. If the J input is enabled and the K input is disabled, the flip-flop will assume the 1 condition upon arrival of a clock pulse. If the K input is enabled and the J input is disabled, the flip-flop will assume the 0 condition when a clock pulse arrives. If both the J and K inputs are enabled prior to the arrival of a clock pulse, the flip-flop will complement, or assume the opposite state, when the clock pulse occurs. The J-K flip-flop is a refinement of the R-S flip-flop with the advantage that it has a determinate state when signals appear on both input terminals; it changes state when all inputs are activated. J and K have no particular meaning, but were selected to avoid conflict with other commonly used symbols.
job 1. A group of tasks specified as a unit of work for a computer. Usually by extension, a job includes all necessary programs, linkages, files, and instructions for the operating system. 2. In a computer, a collection of tasks, grouped and run together in order to perform a specific function.
job control language A special computer command language designed for use in batch systems to inform the systems software and computer operator of unique requirements for the running of a computer program.
job library A related series of user-identified, partitioned data sets that serve as the primary source of load modules for a given job.
job statement A control statement that identifies the start of a series of job control statements for a single job.
job step The carrying out of a computer program explicitly identified by a job control statement. The execution of several job steps may be specified by a job.
jogging Also called inching. Quick and repeated opening and closing of a motor starting circuit to produce slight movements of the motor.
Johnson counter Also called Mobius counter or twisted-ring counter. A counter composed of an N-stage shift register with the complement of the last stage returned to the input. It normally has 2N states through which it cycles. It has the distinguishing characteristic that only one stage changes state at each count. See ring counter, 2.
Johnson noise Also called thermal noise. 1. The noise generated by any resistor at a temperature above absolute zero. It is proportionate to the absolute temperature and the bandwidth according to the following formula:
K is Boltzmann’s constant, or 1.38047 × 10–23
T is he absolute temperature in kelvins
2. A frying or sizzling sound produced by thermal agitation voltages generated in amplifier circuits. It usually occurs in the input circuit (or front end) of an amplifier. Discovered by J. B. Johnson in the late 1920s, this thermal noise may be generated by a resistor at a temperature above absolute zero. It is random noise engendered by thermal agitation.
joined actuator A multiple breaker such that when one pole trips, all trip, but whereas the faulted pole is tripfree, the other poles may be kept maintained by a restraining actuator.
joint A connection between two or more conductors, or the connecting point of two conductors.
joint circuit A communication link in which there is participation by the elements of more than one service, through control, operations, management, etc.
joint communications The common use of communication facilities by two or more services of the same country.
Joint electron device Engineering Council See JEDEC.
Joint electron tube Engineering Council See JETEC.
joint pole Pole used in common by two or more utility companies.
joint use The simultaneous use of pole, line, or plant facilities by two or more kinds of utilities.
Jones plug A type of polarized connector designed in the form of a receptacle and having several contacts.
Josephson effect 1. The phenomenon described by Brian Josephson to explain the action of currents through and voltages across hairlike gaps in superconductors. On the basis of theoretical considerations, it is predicted that if two superconductors would be brought close enough together, a current could be made to flow across the gap between them. Under certain conditions, a voltage appears across the gap, and high-frequency radiation emanates from it. This predicted radiation would have a frequency precisely equal to 2eV/h, where V is the measured voltage across the gap. 2. Characteristic of radiation detectors that produce energy that is similar to the energy of superconductive gaps when interacting with photons.
joule 1. The work done by a force of 1 newton acting through a distance of 1 meter. The joule is the unit of work and energy in the mksa system. 2. The energy required to transport 1 coulomb between two points having a potential difference of 1 volt. The joule is 107 ergs. The kilowatt-hour is 3.6 × 106 joules. 3. A unit of energy of work CV2/2 equal to 1 wattsecond. Energy stored in a capacitor is equal to CV2/2 joules or wattseconds, where C is capacitance in farads and V is voltage in volts at the capacitor’s terminals. The letter symbol for joule is J.
Joule effect In a circuit, electrical energy is converted into heat by an amount equal to I2R. Half of this heat flows to the hot junction and the other half to the cold junction.
Joule heat The thermal energy produced as a result of the Joule effect.
Joule heat gradient Abbreviated JHG. The rate at which the thermal heat produced by the Joule effect increases or decreases.
Joule’s law of electric heating The amount of heat produced in a conductor is proportional to the resistance of the conductor, the square of the current, and the time.
joystick 1. A control device consisting of a handle with freedom of motion in all directions of a plane, connected to potentiometers or other control devices through suitable linkage permitting natural human input of positioning or other information. The term is derived from the joystick of aircraft. 2. A data-entry device used to manually enter coordinate values in special X-, Y-, and Z-input registers. The device consists of a vertically mounted stick or column that can be moved and twisted. When it is moved backward or forward or sideways, coordinate values are stored in the X- and Y-input registers. The Z-input register is varied whenever the joystick is twisted clockwise and counterclockwise. These registers must be scanned by the host computer since joysticks normally do not generate interrupts when they are activated. Usually the joystick is used to move a cursor and/or tracking symbol on the face of the CRT screen. Used mainly for computer games. 3. A type of four-channel pan potentiometer that has a shaft with a handle that can be moved forward and back, left and right, or anywhere in between to direct a single input signal to any of four output channels.
J-scope Also called class J oscilloscope. A cathode-ray oscilloscope that presents a J-display.
J/S ratio A ratio, normally expressed in dB, of the total interference power to the signal-carrier power in the transmission medium at the receiver.
juice Slang for electric current.
jump 1. To cause the next instruction to be selected from a specific storage location in a computer. 2. A departure from the normal one-step incrementing of the program counter. By forcing a new value (address) into the program counter, the next instruction can be fetched from an arbitrary location (either further ahead or back). For example, a program jump can be used to go from the main program to a subroutine, from a subroutine back to the main program, or from the end of a short routine back to the beginning of the same routine to form a loop. 3. Transfer of program logic flow by bypassing a number of instructions. The jump can be forward over a positive number of bytes or backward by expressing a negative number of bytes. The jump can be conditional on the status of the accumulator or other registers.
jumper 1. A short length of wire used to complete a circuit temporarily or to bypass a circuit. 2. A direct electrical connection, which is not a portion of the conductive pattern, between two points in a printed circuit. 3. An electrical connection between two points on a printed board added after the intended conductive pattern is formed. 4. A short length of cable used to make electric connections within, between, among, and around circuits and their associated equipment. 5. A length of conductor used to establish connections (often temporary) between two points or to provide a path around a break in a circuit. A jumper can interconnect board to connector, board to board, or power supply to black box unit. 6. A direct electrical connection between two points on a film circuit. Jumpers are usually portions of bare or insulated wire mounted on the component side of the substrate. 7. A patch cable or wire used to establish a circuit, often temporarily, for testing or diagnostics.
jumper cable A short flat cable interconnecting two printed wiring boards or devices.
junction 1. A connection between two or more conductors or two or more sections of a transmission line. 2. A contact between two dissimilar metals or materials (e.g., in a rectifier or thermocouple). 3. A region of transition between p- and n-type semiconductor material. The controllable resultant asymmetrical properties are exploited in semiconductor devices. There are diffused, alloy, grown, and electrochemical junctions. 4. A joining of two different semiconductors or of semiconductor and metal. 5. Optical interface.
junction barrier The opposition to the diffusion of majority carriers across a pn junction due to the charge of the fixed donor and acceptor ions.
junction battery A nuclear type of battery in which radioactive strontium 90 irradiates a silicon pn junction.
junction box 1. A box for joining different runs of raceway or cable, plus space for connecting and branching the enclosed conductors. 2. An enclosed distribution panel for connecting or branching one or more corresponding electric circuits without the use of permanent splices.
junction capacitance The total small-signal capacitance between the contacts of an uninstalled semiconductor die.
junction capacitor A capacitor in which the capacitance is that of a reverse-biased pn junction.
junction diode 1. A two-terminal device containing a single crystal of semiconducting material that ranges from p type at one terminal to n type at the other. It conducts current more easily in one direction than in the other and is a basic element of the junction transistor. Such a diode is the basic part of an injection laser; the region near the junction acts as a source of emitted light. When fabricated in a suitable geometrical form, the junction diode can be used as a solar cell. 2. A pn junction characterized by slower switching speed and higher operating voltage and temperature than the Schottky diode. The fast recovery version of the junction diode turns off faster than the conventional pn junction diode, usually in hundredths of a nanosecond. 3. A semiconductor diode having the property of conducting current more easily in one direction than the other. This device may be made by diffusion of an impurity into a semiconductor crystal to form a junction. Such diodes are the basic elements of an injection laser. Light is emitted from the area near the junction.
junction FET A field-effect transistor having one or more gates that form pn junctions with the channel. See also junction field-effect transistor.
junction field-effect transistor Abbreviated JFET. 1. A transistor made up of a gate region diffused into a channel region. The gate element is a region of semiconductor material (ordinarily, the substrate) insulated by a pn junction from the channel, which is material of opposite polarity. When a control voltage is applied to the gate, the channel is depleted or enhanced, and the current between source and drain is thereby controlled. There is no current when the channel is pinched off. 2. A field-controlled majority carrier device where the conductance in the channel between the source and the drain is modulated by a transverse electric field. The field is controlled by a combination of gate-source bias voltage, VGS, and the net drain-source voltage, VDS.
junction filter A combination of a high-pass and a low-pass filter that is used to separate frequency bands for transmission over separate paths. For example, junction filters are used to separate voice and carrier frequencies at the junction between open-wire and cable so that the carrier frequencies and voice frequencies can be sent over nonloaded and VF-loaded cable pairs, respectively.
junction-gate field-effect transistor A field-effect transistor having one or more gate regions that form pn junction(s) with the channel.
junction loss 1. In telephone circuits, that part of the repetition equivalent that can be assigned to interactive effects originating at trunk terminals. 2. The transmission loss due to the mismatch of impedance between two types of transmission facilities. See repetition equivalent.
junction pole Pole at the end of a transposition section of an open-wire line or the pole common to two adjacent transposition sections.
junction station A microwave relay station that joins a microwave radio leg or legs to the main, or through, route.
junction transistor A transistor having three alternate sections of p-type or n-type semiconductor material. See also npn transistor; pnp transistor.
junction transposition Transposition located at the junction pole between transposition sections of an open-wire line.
junctor In crossbar systems, a circuit extending between frames of a switching unit and terminated in a switching device on each frame.
Justification 1. The act of adjusting, arranging, or shifting digits to the left or right so that they conform to a prescribed pattern. 2. The automatic inserting of blank spaces within text to make the right margin even on a page.
justify To align data about a particular reference or to produce a text with flush left and right margins (a more printlike appearance).
just-operate value Also called dropout value. The measured functioning value at which a particular relay operates. Contrast just-release value.
just-release value The measured functioning value at which a particular relay releases.
just scale A musical scale formed by three consecutive triads (those in which the highest note of one is the lowest note of the other), each having the ratio 4:5:6 or 10:12:15.
jute Cordage fiber (such as hemp) saturated with tar and used as a protective layer over cable.
jute-protected cable A cable having its sheath covered by a wrapping of tarred jute or other fiber.