TACHOMETER - (1) A small ac or dc generator, sometimes referred to as a rate generator, that converts its shaft speed into an electrical output. The tachometer is frequently used in servosystems to sense the velocity of a load . (2) An instrument that measures the rate at which a shaft is turning .

TANK CIRCUIT - A tuned circuit used to temporarily store energy. Also referred to as a parallel-resonant circuit .

TAPE CONTAMINATION - (See tape-to-head separation.)

TAPE NOISE - (See noise.)

TAPE PACK - The form taken by the tape wound on a reel.

TAPE SKEW - (1) The tape's deviation from following a linear path when transported across the heads. (2) The terms static and dynamic distinguish between the physically fixed components and the fluctuating components of total tape skew.

TAPE SPEED - (1) The speed at which the tape is transported across the read/write head during normal recording or reproduction. (2) Long-term speed is averaged over a minimum of 15 inches of tape (in inches per second). (3) Short-term speed is the instantaneous (dynamic) tape speed (in inches per second).

TAPE-TO-HEAD SEPARATION - (1) Separation. - The separation between a magnetic head and the magnetic tape caused by the (a) foil-bearing effect, (b) improper head contour, which generates standing waves in the tape, and (c) surface roughness of the tape. These conditions are interrelated and are greatly influenced by tape tension and tape compliancy. In a properly designed system, tape roughness is the limit of head-to-tape separation, usually <10 fm. (2) Changes. - (a) Head contamination is the debris attached to the head, which causes the tape to lift away from the head, forming a tent-like deformation of the tape. This tent does not move or change shape until the contamination is removed. (b) Tape contamination includes particles attached to the tape, resulting in a tent that moves across the head with the tape. (3) Effective. - (a) The actual distance from the magnetic storage material on the tape to the top of the active magnetic core material at the read or write gape. (b) The effective head-to-tape separation is usually somewhat larger than the mechanical head-to-tape separation.

TAPE TRANSPORT - (1) The mechanism that extracts magnetic tape from a storage device, moves it across magnetic heads at a controlled speed and then feeds it into another storage device. (2) Typical storage devices are tape loops, bins, reels, cassettes, and cartridges. (3) The tape transport is the part of a magnetic tape recorder/reproducer system that normally consists of magnetic heads, magnetic tape, transport, record electronics, and reproduce electronics.

TAPPED RESISTOR - A wire-wound, fixed resistor having one or more additional terminals along its length, generally for voltage-divider applications .

TARGET - In radar, a specific object of radar search or detection .

TARGET RESOLUTION - The ability of a radar to distinguish between two or more targets that are close to each other .

TEAR STRENGTH - The force required to initiate and/or propagate a tear in a specially shaped specimen of tape or base film.

TELECOMMUNICATIONS - The transmission, emission, or reception of signs, signals, writings, images, or sounds. This is done by visual, oral, wire, radio, or other means .

TELEPROCESSING - A method of data processing in which communication devices are used.

TELETYPEWRITER - A machine that can transmit and/or receive letters, numbers, or symbols. It may have a keyboard similar to a typewriter .

TEMPERATURE COEFFICIENT - The amount of change of resistance in a material per unit change in temperature .

TEMPERATURE INVERSION - The condition in which warm air is formed above a layer of cool air that is near the earth's surface .

TEMPEST - A term normally used to describe compromising emanations. These emanations are unintentionally radiated signals that could disclose classified information .

TENSILE STRENGTH - The greatest stress a substance can withstand along its length without tearing apart .

TERMINAL - A device linked to the central processor for entering or receiving data and programs.

TERMINAL BOARD - Also called a terminal strip. An insulating base or slab equipped with terminals for connecting wiring .

TERMINAL DIAGRAM - A diagram of a switch, relay, terminal board, or other component showing the connections to the equipment .

TERMINAL LUG - A device attached to a conductor to permit connection to a terminal .

TEST EQUIPMENT - A general term applied to devices used to test electrical and electronic circuits .

TEST EQUIPMENT INDEX - The Navy guide used to assist in identifying portable electrical/ electronic test equipment required for support of prime electrical/electronic, IC, weapons, and reactor instrumentation systems .

TEST POINTS - Locations in equipment that are accessible to the technician's test probes where operating voltages or signals can be monitored .

TETRODE TUBE - A four-electrode electron tube containing a plate, a cathode, a control grid, and a screen grid .

THERMAL INERTIA - The capacity of a soldering iron to generate and maintain a satisfactory soldering temperature while giving up heat to the material being soldered .

THERMAL-MAGNETIC TRIP ELEMENT - A single circuit breaker trip element that combines the action of a thermal and a magnetic trip element .

THERMAL RUNAWAY - A conduction that exists when heat causes more electron-hole pairs to be generated, which, in turn, causes more heat and which may eventually cause diode destruction .

THERMAL TRIP ELEMENT - A circuit breaker trip element that uses the increased bending of a bimetallic strip caused by increased current to open a circuit .

THERMIONIC EMISSION - Emission of electrons from a solid body as a result of elevated temperature .

THERMISTOR - (1) A semiconductor device whose resistance varies with temperature . (2) A type of bolometer characterized by a decrease in resistance as the dissipated power increases .

THERMOCOUPLE - A junction of two dissimilar metals that produces a voltage when heated .

THERMOCOUPLE METER MOVEMENT - A meter movement that uses the current induced in a thermocouple by the heating of a resistive element to measure the current in a circuit; used to measure ac or dc .

THERMOPLASTIC - A synthetic mixture of rosins that is flexible and used as an insulting material. Generally used as an insulator for low- and medium-range voltages .

THETA - The greek letter (q) used to represent phase angle .

THICK FILM COMPONENTS - Passive circuit components (resistors and capacitors) having a thickness of 0.001 centimeter .

THIN FILM COMPONENTS - Passive circuit elements (resistors and capacitors) deposited on a substrate to a thickness of 0.0001 centimeter .

THREE-ELEMENT ARRAY - An array with two parasitic elements (reflector and director) and a driven element .

THREE-DIMENSIONAL RADAR (3D) - A radar set that measures the range, bearing and altitudes of a target .

THROW - In a switch, the number of different circuits each pole can control; for example, single throw and double throw .

THYRATRON - A gas tube used as a modulator switching device .

THYRATRON TUBE - A gas-filled triode in which a sufficiently large positive pulse applied to the control grid ionizes the gas and causes the tube to conduct, after which the control grid has no effect in conduction .

TICKLER COIL - A small coil connected in series with the collector or plate circuit of a transistor or tube and inductively coupled to the base or grid-circuit coil to establish feedback (regeneration) .

TIME CONSTANT - Time required for an exponential quantity to change by an amount equal to 63.2 percent of the total change that can occur .

TIME-DIVISION MULTIPLEXING - The process that periodically samples the full 360 degrees of each sine wave. The sample can be of a received signal or of a signal to be transmitted .

TIME LAG - The delay in a servosystem between the application of the input signal and the actual movement of the load .

TIME-DOMAIN REFLECTOMETER - A piece of test equipment used to test a transmission line for defects, such as shorts and opens. It transmits an electrical pulse into the transmission line and analyzes the resulting reflections in terms of emplidute versus distance.

TIME SHARING - A processing mode in which many users share the computer systems' resources through online terminals. Each user gets a slice of computer time.

TIMER - See SYNCHRONIZER .

TINNING - The process of applying a thin coat of solder to materials prior to their being soldered; for example, application of a light coat of solder to the filaments of a conductor to hold the filaments in place prior to soldering of the conductor .

TOLERANCE - (1) The maximum permissible error or variation from the standard in a measuring instrument. (2) A maximum electrical or mechanical variation of specifications that can be tolerated without impairing the operation of a device .

TONES - Musical sounds .

TONE-TERMINAL SET - Equipment that converts tty dc pulses into audio tones for modulation of a transmitter in audio-frequency-tone shift transmissions .

TOP-HAT - An antenna that is center-fed and capacitively loaded .

TORQUE - A measure of how much load a machine can turn. This measurement is expressed either in ounce-inches for torque synchro systems or in pound-feet for heavy machinery .

TORQUE DIFFERENTIAL RECEIVER (TDR) - A type of differential synchro that takes two electrical inputs, one to the rotor and one to the stator, and produces a mechanical output. The output is the angular position of the rotor that represents the algebraic sum or difference of the two electrical inputs .

TORQUE DIFFERENTIAL SYNCHRO SYSTEM - A synchro system containing either a TDX or a TDR. This system is used in applications where it is necessary to compare two signals, add or subtract the signals, and furnish an output proportional to the sum or difference between the two signals .

TORQUE DIFFERENTIAL TRANSMITTER (TDX) - This type of synchro is functionally the same as the CDX, except that it is used in torque systems rather than control systems .

TORQUE GRADIENT - A term used in the rating of torque synchros. It is expressed in the number of inch-ounces of torque required to pull a specific synchro 1 degree away from its normal position; for example, 0.4 inch-ounce per degree .

TORQUE RECEIVER (TR) - A type of synchro that converts the electrical input supplied to its stator back to a mechanical angular output through the movement of its rotor .

TORQUE SYNCHRO SYSTEM - A synchro system that uses torque synchros to move light loads such as dials, pointers, and other similar devices .

TORQUE TRANSMITTER (TX) - This type of synchro is functionally the same as the CX, except that it is used in torque synchro systems .

TORQUE VECTOR - In a gyro, a vector representing the rotary motion applied to change the direction of the rotor axis. The torque vector represents the axis about which the applied force is felt .

TOTAL RESISTANCE - (RT) The equivalent resistance of an entire circuit. For a series circuit: RT = R1 + R2 + R3 ...Rn. For parallel circuits:

TOTAL THICKNESS - The sum of the thicknesses of the base film and the magnetic coating, as well as back coating, when applied. The total thickness governs the length of tape that can be wound on a given reel.

TOXIC VAPORS - Vapors emitted by a substance that can do bodily harm .

TR RECOVERY TIME - Time required for a fired tr or atr tube to deionize to a normal level of conductance .

TRACK - (1) One of seven or nine, horizontal rows stretching the entire length of a magnetic tape and on which data can be recorded. (2) One of a series of concentric circles on the surface of a disk. (3) One of a series of circular bands on a drum. .

TRACK RADAR - Radar that provides continuous range, bearing, and elevation data by keeping the rf beam on the target .

TRACK WIDTH - The width of the track corresponding to a given record gap.

TRAIC - A three-terminal device that is similar to two SCRs back-to-back with a common gate and common terminals. Although similar in construction and operation to the SCR, the Triac controls and conducts current flow during both alternations of an ac cycle.

TRANSCONDUCTANCE - Transconductance is a ratio of the change in plate current to a change in grid voltage with the plate voltage held constant. Transconductance (gm) is usually expressed in micromhos or millimhos. Mathematically,

TRANSFORMER - A device composed of two or more coils, linked by magnetic lines of force, used to transfer energy from one circuit to another .

TRANSFORMER EFFICIENCY - The ratio of output power to input power, generally expressed as a percentage.

TRANSFORMER, STEP-DOWN - A transformer so constructed that the number of turns in the secondary winding is less than the number of turns in the primary winding. This construction will provide less voltage in the secondary circuit than in the primary circuit .

TRANSFORMER, STEP-UP - A transformer so constructed that the number of turns in the secondary winding is more than the number of turns in the primary winding. This construction will provide more voltage in the secondary circuit than in the primary circuit .

TRANSISTOR - A semiconductor device with three or more elements .

TRANSITION - The time it takes to shift from a mark to a space condition or from a space to a mark condition .

TRANSIT TIME - The time an electron takes to cross the distance between the cathode and the plate .

TRANSLATION - In a gyro, a force acting through the center of gravity of the gyro that causes no torque on the gyro rotor. Translation forces do not change the angle of the plane of rotation but move the gyroscope as a unit .

TRANSLUCENT - Those substances, such as frosted glass, through which some light rays can pass but through which objects cannot be seen clearly .

TRANSMISSION LINE - A device designed to guide electrical or electromagnetic energy from one point to another .

TRANSMISSION MEDIUM - A means of transferring intelligence from point to point; includes light, smoke, sound, wire lines, and radio-frequency waves .

TRANSMIT-RECEIVE TUBE (TR) - A gas-filled rf switch that is used as a duplexer .

TRANSMITTER - Equipment that generates and amplifies an rf carrier, modulates the rf carrier with intelligence, and radiates the signal into space .

TRANSMITTER DISTRIBUTOR - A device that reads Baudot code from paper tape and allows a message to be printed on a page printer .

TRANSMITTER END - See INPUT END .

TRANSMITTER FREQUENCY (CARRIER FREQUENCY) - The frequency of the unmodulated output of a transmitter .

TRANSMITTER TRANSFER SWITCHBOARD - Equipment that selectively transfers remote station functions and signals to transmitters .

TRANSMITTING ANTENNA - The device used to send the transmitted signal energy into space .

TRANSPARENT - Those substances, such as glass, that pass almost all of the light waves falling upon them .

TRANSVERSE ELECTRIC MODE - A waveguide mode in which the entire electric field is perpendicular to the wide dimension and the magnetic field is parallel to the length. Also called the TE mode .

TRANSVERSE MAGNETIC MODE - A waveguide mode in which the entire magnetic field is perpendicular to the wide dimension and some portion of the electric field is parallel to the length. Also called the TM mode .

TRANSVERSE WAVE MOTION - The up and down motion of a wave as the wave moves outward .

TRAVERSE (BEARING) SIGNAL - In a monopulse radar system, the combination of individual lobe signals that represents target-offset direction and amplitude from the antenna axis .

TREMENDOUSLY HIGH FREQUENCY - The band of frequencies from 300 gigahertz to 3,000 gigahertz.

TRIAC - A three-terminal device that is similar to two SCRs back to back with a common gate and common terminals. Although similar in construction and operation to the SCR, the triac controls and conducts current flow during both alternations of an ac cycle .

TRIATIC - A special type of monopole antenna array .

TRIGGER - A short pulse, either positive or negative, that can be used to cause an electronic function to take place .

TRIGGER GENERATOR - See SYNCHRONIZER .

TRIGGER PULSES - In radar, pulses that are used to initiate specific events .

TRIODE TUBE - A three-electrode electron tube containing a plate, a cathode, and a control grid .

TRIP-ELEMENT - The part of a circuit breaker that senses any overload condition and causes the circuit breaker to open the circuit .

TRIP-FREE CIRCUIT BREAKER - A circuit breaker that will open a circuit even if the operating mechanism is held in the ON position .

TRIVALENT IMPURITY - Acceptor impurities containing only three valence electrons .

TROPOSPHERE - The portion of the atmosphere, closest to the earth's surface, where all weather phenomena take place .

TROPOSPHERIC SCATTER - The propagation of radio waves in the troposphere by means of scatter .

TROUBLE INDICATORS - Signal lights used to aid maintenance personnel in locating troubles quickly .

TROUBLESHOOTING - The process of locating and diagnosing faults in equipment by means of systematic checking or analysis .

TROUBLE TABLES - Tables of trouble symptoms and probable causes, furnished by many manufacturers to help technicians isolate problems .

TROUGH (BOTTOM) - The peak of the negative alternation (maximum value below the line) of a sine wave .

TRUE BEARING - Angle between a target and true north measured clockwise in the horizontal plane .

TRUE NORTH - Geographic north .

TRUE POWER - The power dissipated in the resistance of the circuit, or the power actually used in the circuit .

TRUNCATED PARABOLOID - A paraboloid reflector that has been cut away at the top and bottom to increase beam width in the vertical plane .

TRUTH TABLE - A table that describes a logic function by listing all possible combinations of input values and indicating, for each combination, the true output values .

TUBE DYNAMIC CONDITION - Refers to the testing condition in which a vacuum tube is actually performing its function .

TUBE STATIC CONDITION - Refers to the testing condition in which a tube has certain voltages applied but is not in its normal operating condition .

TUNED CIRCUIT - (1) A circuit consisting of inductance and capacitance that can be adjusted for resonance at a desired frequency . (2) A circuit that is used as a filter which passes or rejects specific frequecies . (3) An LC circuit used as a frequency-determining device .

TUNED LINE - Another name for the resonant line. This line uses tuning devices to eliminate the reactance and transfer maximum power from the source to the line .

TUNING FORK - A two-pronged mechanical device that is designed to vibrate only at its natural frequency. In electronics, it is used primarily to determine the correct speed of a motor.

TUNNEL DIODE - A heavily doped semiconductor device that has high gain and fast switching capabilities . See NEGATIVE-RESISTANCE ELEMENT .

TUNNELING - The piercing of a potential barrier in a semiconductor by a particle (current carrier) that does not have sufficient energy to go over the barrier .

TURN - One complete loop of a conductor about a core .

TURNS RATIO - The ratio of the number of turns in the primary winding to the number of turns in the secondary winding of a transformer .

TURNSTILE ANTENNA - A type of antenna used in vhf communications that is omnidirectional and consists of two horizontal half-wave antennas mounted at right angles to each other in the horizontal plane .

TWISTED PAIR - A line consisting of two insulated wires twisted together to form a flexible line without the use of spacers .

TWO-DIMENSIONAL RADAR (2D) - Measures the range and bearing to a target .

TWO-M (2M) - Miniature/microminiature repair program .

TWO-WIRE OPEN LINE - A parallel line consisting of two wires that are generally spaced from 2 to 6 inches apart by insulating spacers .

TWO-WIRE RIBBON (TWIN LEAD) - A parallel two-wire line in which uniform spacing is assured by two wires imbedded in a low-loss dielectric .