M - A unit of measurement approximately equal to one million and used to express the capacity of a computer memory. 1M is about 1,000,000 units. Memory size is usually measured in words or bytes.

MACHINE KEYING - A method of cw keying using punched tape or other mechanical means to key a transmitter .

MACHINE LANGUAGE - Machine instructions in binary bit patterns that the central processing unit can execute directly without additional interpretation or translation.

MACHINE (TAKE-UP) REEL - A reel that remains on the tape drive and on which magnetic tape is wound during the processing of a tape.

MAGIC T - See BALANCED MIXER .

MAGIC-T JUNCTION - A combination of H-type and E-type T-junctions .

MAGNET WIRE - Wire coated with an enamel insulation and used in coils, relays, transformers, motor windings, and so forth .

MAGNETIC AMPLIFIER - An elecromagnetic device that uses one or more saturable reactors to obtain a large power gain. This device is used in servosystems requiring large amounts of power to move heavy loads .

MAGNETIC FIELD - (1) The region in which the magnetic forces created by a permanent magnet or by a current-carrying conductor or coil can be detected . (2) The field that is produced when current flows through a conductor or antenna .

MAGNETIC INDUCTION - Generating a voltage in a circuit by the creation of relative motion between a magnetic field and the circuit. The relative motion can be the result of physical movement or the rise and fall of a magnetic field created by a changing current .

MAGNETIC INSTABILITY - (1) The property of a magnetic material that causes variations in the residual flux density of a tape to occur with temperature, time, and/or mechanical flexing. (2) A function of particle size, magnetizing field strength, and anisotropy.

MAGNETIC LINES OF FORCE - Imaginary lines used for convenience to designate the direction in which magnetic forces are acting as a result of magnetomotive force .

MAGNETIC MEDIA - Magnetic cards, tapes, disks, drums, cartridges, and cassettes used to record data or information.

MAGNETIC MICROPHONE - A microphone in which the sound waves vibrate a moving armature. The armature consists of a coil wound on the armature and located between the pole pieces of a permanent magnet. The armature is mechanically linked to the diaphragm .

MAGNETIC POLES - The section of a magnet where the flux lines are concentrated; also where they enter and leave the magnet .

MAGNETIC TAPE - A mass storage device in which information is stored on a plastic tape coated with a magnetic film. The tape is wound on reels that are rotated by tape drives. Information is stored and retrieved sequentially by magnetically sensitive read/write heads.

MAGNETIC TRIP ELEMENT - A circuit breaker trip element that uses the increasing magnetic attraction of a coil with increased current to open the circuit .

MAGNETISM - The property possessed by certain materials by which these materials can exert mechanical force on neighboring masses of magnetic materials and can cause currents to be induced in conducting bodies moving relative to the magnetized bodies .

MAGNETIZING FIELD STRENGTH - The instantaneous strength of the magnetic field applied to a sample of magnetic material.

MAGNETRON OSCILLATOR - An electron tube that provides a high power output. Theory of operation is based on interaction of electrons with the crossed electric and magnetic fields in a resonant cavity .

MAINFRAME COMPUTERS - This term is usually used to designate large-scale computer systems, although the precise definition of mainframe is the cpu and the control elements of any computer system.

MAIN STORAGE (MEMORY) - See storage, primary.

MAINTENANCE - Work done to correct, reduce, or counteract wear, failure, and damage to equipment .

MAJOR LOBE - The lobe in which the greatest amount of radiation occurs .

MAJORITY CARRIERS - The mobile charge carriers (hole or electron) which are predominate in a semiconductor material; for example, electrons in an N-type region .

MARCONI ANTENNA - A quarter-wave antenna that is operated with one end grounded and is positioned perpendicular to the earth .

MARK - An interval during which a signal is present. Also the presence of an rf signal in cw keying. The key-closed condition (presence of data) in communications systems .

MARKING - The state where a circuit is closed and current flows in teletypewriter operation .

MASK - A device used to deposit materials on a substrate in the desired pattern .

MASS STORAGE - Any external storage medium (magnetic tape, disk, drum, and so on) that supports and can be linked to the cpu's main memory in the computer. When the power is turned off, information in the mass storage is retained (not lost).

MASTER OSCILLATOR - In a transmitter, the oscillator that establishes the carrier frequency of the output .

MASTER OSCILLATOR POWER AMPLIFIER (MOPA) - A transmitter in which the oscillator is isolated from the antenna by a power amplifier .

MATRIX - In computers, a logic network in the form of an array of input leads and output leads with logic elements connected at some of their intersections .

MATTER - Any physical entity that possesses mass .

MAXIMUM USABLE FREQUENCY - Maximum frequency that can be used for communications between two locations for a given time of day and a given angle of incidence .

MEASURE (METROLOGY AUTOMATED SYSTEM FOR UNIFORM RECALL AND REPORTING) - The Navy data processing system designed to provide a standardized system for the recall, scheduling, and documenting of test equipment into calibration facilities .

MECHANICAL-ROTATION FREQUENCY - The speed in revolutions per minute of armatures in electric motors and engine-driven generators; blade speed in turbines .

MECHANICAL SCANNING - The reflector, its feed source, or the entire antenna is moved in a desired pattern .

MECHANIZATION - Using electric or electro-mechanical switches to represent logic circuits (AND, OR, NOT, NOR, NAND) .

MEDIUM - The vehicle through which a wave travels from one point to the next. Air, water, and wood are examples .

MEDIUM ALTITUDE ORBIT - An orbit from 2,000 to 12,000 miles above the earth. The rotation rate of the earth and satellite are quite different, and the satellite moves quickly across the sky .

MEDIUM FREQUENCY - The band of frequencies from 300 kilohertz to 3 megahertz .

MEGA - A prefix meaning one million; also MEG .

MEGGER - Common name for a megohmmeter .

MEGOHMMETER - A meter that measures very large values of resistance; usually used to check for insulation breakdown in wires .

MEMORY - A device or section of the computer in which computer instructions and data can be stored for retrieval (synonymous with primary or internal storage).

METALLIC ARMOR - A protective covering for wires or cables. Made as a woven wire braid, metal tape, or interlocking metal cover. Made from steel, copper, bronze, or aluminum .

METALLIC, INSULATOR - A shorted quarter-wave section of transmission line .

METALLIC RECTIFIER - Also known as a DRY-DISC RECTIFIER. A metal-to-semiconductor, large-area, contact device in which a semiconductor is sandwiched between two metal plates. This asymmetrical construction permits current to flow more readily in one direction than the other .

METAL-OXIDE SEMICONDUCTOR FIELD-EFFECT TRANSISTOR - See MOSFET .

METER - A device used to measure a specific quantity, such as current, voltage, or frequency .

METER MOVEMENT - The part of the meter that moves to indicate some value .

METER SHUNT - A resistor placed in parallel with the meter terminals; used to provide increased range capability .

METROLOGY CALIBRATION (METCAL) PROGRAM - A Navy calibration program designed to ensure the accuracy of test equipment through comparisons with calibration laboratory standards of known accuracy.

MFM - (See modified frequency modulation.)

MHO - Unit of conductance; the reciprocal of the ohm .

MICRO - A prefix meaning one-millionth .

MICROCIRCUIT - A small circuit having high equivalent-circuit-element density, which is considered as a single part composed of interconnected elements on or within a single substrate to perform an electronic-circuit function .

MICROCIRCUIT MODULE - An assembly of microcircuits or a combination of microcircuits and discrete components that perform one or more distinct functions .

MICROCOMPUTERS - The smallest category of computers, usually with the entire central processing unit on a single chip. Unlike large-scale and minicomputer systems, they are designed to be used by one person at a time (hence the term, personal computer [PC]).

MICROELECTRONICS - The solid-state concept of electronics in which compact semiconductor materials are designed to function as an entire circuit or subassembly rather than as circuit components .

MICROPHONE - An energy converter that changes sound energy into electrical energy .

MICROPHONICS - Electrical noise caused by the mechanical motion of the internal parts of a device. The term is usually associated with vacuum tubes.

MICROPROCESSOR - The semiconductor central processing unit (cpu) of a microcomputer that fits on a small silicon chip. The microprocessor is the central chip containing the control units of the computer.

MICROSECOND - One millionth of a second.

MICROWAVE REGION - The portion of the electromagnetic spectrum from 1,000 megahertz to 100,000 megahertz .

MIL - The diameter of a conductor equal to 1/1000 (.001) inch .

MIL FOOT - A unit of measurement for conductors (diameter of 1 mil, 1 foot in length.) .

MILITARY SPECIFICATIONS (MIL-SPEC) - Technical requirements and standards adopted by the Department of Defense that must be met by vendors selling materials to DOD .

MILITARY STANDARDS (MILSTD) - Standards of performance for components or equipment that must be met to be acceptable for military systems .

MILLI - A prefix meaning one-thousandth .

MILLISECOND - One thousandth of a second.

MINIATURE ELECTRONICS - Modules, packages, pcbs, and so forth, composed exclusively of discrete components .

MINICOMPUTERS - Midsize computers that are smaller than large-scale systems but with the same components. They are less expensive and have less strict environmental requirements.

MINIMUM DISCERNIBLE SIGNAL (MDS) - The weakest input signal that produces a usable signal at the output of a receiver. The weaker the input signal, the more sensitive the receiver .

MINORITY CARRIERS - Either electrons or holes, whichever is the less dominant carrier in a semiconductor device. In P-type semiconductors, electrons are the minority carriers; in N-type semiconductors, the holes are the minority carriers .

MINORITY CURRENT - A very small current that passes through the base-to-collector junction when this junction is reverse biased .

MINOR LOBE - The lobe in which the radiation intensity is less than that of a major lobe .

MIXER - In radar, a circuit that combines the received rf signal with a local-oscillator signal to effectively convert the received signal to a lower IF frequency signal .

MODE SHIFTING - In a magnetron, the inadvertent shifting from one mode to another during a pulse .

MODE SKIPPING - Operation in which the magnetron fires randomly, rather than firing on each successive pulse as desired .

MODEM - Acronym for MOdulator-DEModulator. A device that converts data from digital-to-analog format for transmission on analog transmission lines and converts data in analog format to digital format for computer processing.

MODIFIED FREQUENCY MODULATION (MFM) - (1) A code that has a "1" and a "O" corresponding to the respective presence or absence of a transition in the center of the corresponding bit cell. (2) Additional transitions at the cell boundaries occur only between bit cells that contain consecutive "0" values. (3) Also called delay modulation.

MODIFIED TRANSISTOR OUTLINE (TO) - An IC package resembling a transistor .

MODULAR CIRCUITRY - A technique where printed circuit boards are stacked and connected together to form a module .

MODULAR PACKAGING - Circuit assemblies or subassemblies packaged to be easily removed for maintenance or repair .

MODULATED WAVE - A complex wave consisting of a carrier and a modulating wave that is transmitted through space .

MODULATING WAVE - An information wave representing intelligence .

MODULATION - The process of impressing intelligence upon a transmission medium, such as radio waves .

MODULATION FACTOR (M) - An indication of relative magnitudes of the rf carrier and the modulating signal .

MODULATION INDEX - The ratio of frequency deviation to the frequency of the modulating signal .

MODULATION NOISE - (See noise.)

MODULATOR - (1) A device that produces modulation; that is, a device that varies the amplitude, frequency, or phase of an ac signal . (2) A circuit used in servosystems to convert a dc signal to an ac signal. The output ac signal is a sine wave at the frequency of the ac reference voltage. The amplitude of the output is directly related to the amplitude of the dc input. The circuit's function is opposite to that of a DEMODULATOR . (3) In radar, it produces a high-voltage pulse that turns the transmitter on and off .

MODULATOR SWITCHING DEVICE - Controls the on (discharge) and off (charge) time of the modulator .

MODULE - A circuit or portion of a circuit packaged as a removable unit. A separable unit 3n a packaging scheme displaying regularity of dimensions .

MOISTURE LAPSE - Abnormal variation of moisture content at different altitudes because of high moisture located just above large bodies of water .

MONOLITHIC CIRCUIT - A circuit where all elements (resistors, transistors, and so forth) associated with the circuit are fabricated inseparably within a continuous piece of material (called the substrate), usually silicon .

MONOLITHIC IC - ICs that are formed completely within a semiconductor substrate. Silicon chips .

MONOPULSE (SIMULTANEOUS) LOBING - A radar receiving method using two or more (usually four) partially overlapping lobes. Sum and difference locate the target with aspect to the axis of the antenna .

MONOPULSE RADAR - A radar that gets the range, bearing, and elevation position data of a target from a single pulse .

MONOPULSE RECEIVER - See MONOPULSE RADAR .

MONOSTABLE MULTIVIBRATOR - A multivibrator that has one steady state. A signal (trigger) must be applied to cause change of states .

MOSFET - A semiconductor device that contains diffused source and drain regions on either side of a P- or N-channel area. Also contains a gate insulated from the channel area by silicon-oxide. Operates in either the depletion or the enhancement mode .

MOST SIGNIFICANT DIGIT (MSD) - The MSD is the digit whose position within a given number expression has the greatest weighting power .

MOTOR - A machine that converts electrical energy to mechanical energy. It is activated by ac or dc voltage, depending on the design .

MOTOR LOAD - Any device driven by a motor. Typical loads are drills, saws, water pumps, rotating antennas, generators, and so forth. The speed and power capabilities of a motor must be matched to the speed and power capabilities of the motor load .

MOTOR REACTION - The force created by generator armature current that tends to oppose the normal rotation of the armature .

MOTOR STARTERS - Large resistive devices placed in series with dc motor armatures to prevent the armature from drawing excessive current until armature speed develops counter emf. The resistance is gradually removed from the circuit either automatically or manually as motor speed increases .

MOVING-IRON METER MOVEMENT - Same as MOVING-VANE METER MOVEMENT .

MOVING TARGET INDICATOR - A device that limits the display of radar information to moving targets .

MOVING-VANE METER MOVEMENT - A meter movement that uses the magnetic repulsion of the like poles created in two iron vanes by current through a coil of wire; most commonly used movement for ac meters .

MSD - See MOST SIGNIFICANT DIGIT .

MTDS - An abbreviation for the marine tactical data system .

MU - Symbol for amplification factor .

MULTICONDUCTOR - More than one conductor, as in a cable .

MULTICOUPLERS - Couplers that patch receivers or transmitters to antennas. They also filter out harmonics and spurious responses and impedance-match the equipment .

MULTIELECTRODE TUBE - An electron tube normally classified according to its number of electrodes (the multielectrode tube contains more than three electrodes) .

MULTIELEMENT ARRAY - An array that consists of one or more arrays and is classified as to directivity .

MULTIELEMENT PARASITIC ARRAY - An array that contains two or more parasitic elements and a driven element .

MULTILOOP SERVOSYSTEM - A servosystem that contains more than one servo loop; each loop is designed to perform its own function .

MULTIMETER - A single meter combining the functions of an ammeter, a voltmeter, and an ohmmeter .

MULTIPATH - The multiple paths a radio wave may follow between transmitter and receiver .

MULTIPHASE - See POLYPHASE .

MULTIPLICATION FACTOR - The number of times an input frequency is multiplied .

MULTIPLEXING - A method for simultaneous transmission of two or more signals over a common carrier wave .

MULTIPROCESSING - A computer processing mode that provides for simultaneous processing of two or more programs or routines by use of multiple cpu's.

MULTIPROGRAMMING - A computer processing mode that provides for overlapping or interleaving the execution of two or more programs at the same time by a single processor.

MULTISPEED SYNCHRO SYSTEMS - Systems that transmit data at different transmission speeds; for example, dual-speed and tri-speed synchro systems .

MULTIUNIT TUBE - An electron tube containing two or more units within the same envelope. The multiunit tube is capable of operating as a single-unit tube, or each unit can operate as a separate tube .

MULTIVIBRATOR - A form of relaxation oscillator which comprises two stages that are coupled so that the input of one is derived from the output of the other .

MULTIVIBRATOR MODULATOR - An astable multivibrator used to provide frequency modulation. The modulating af voltage is inserted in series with the base return of the multivibrator transistors to produce the frequency modulation .

MUTUAL FLUX - The total flux in the core of a transformer that is common to both the primary and secondary windings. The flux links both windings .

MUTUAL INDUCTANCE - A circuit property existing when the relative position of two inductors causes the magnetic lines of force from one to link with the turns of the other. The symbol for mutual inductance is M .