PACKAGED SOFTWARE - Programs already written (and tested) to solve specific types of
problems; usually designed by a central design agency (CDA) or purchased from a software
firm or computer manufacturer.
PACKAGING LEVELS - A system developed to assist maintenance personnel in determining
the repairability of components, printed circuit boards, modules, and so forth .
PACKED DECIMAL - In ASCII and EBCDIC, the representation of two digits stored in one
eight-bit byte.
PACKING DENSITY - The amount of digital information recorded along the length of a
tape, measured in bits per inch.
PAGE PRINTER - A high-speed printer that prints teletypewriter characters one at a time
in a full-page format .
PAPER TAPE - See punched tape.
PARABOLIC REFLECTOR - An antenna reflector in the shape of a parabola. It converts
spherical wavefronts from the radiating element into plane wavefronts .
PARALLAX ERROR - The error in meter readings that results when you look at a meter from
some position other than directly in line with the pointer and meter face. A mirror
mounted on the meter face aids in eliminating parallax error .
PARALLEL CIRCUIT - Two or more electrical devices connected to the same pair of
terminals so separate currents flow through each; electrons have more than one path to
travel from the negative to the positive terminal .
PARALLEL-CONNECTED DUPLEXER - Configuration in which the tr spark gap is connected
across the two legs of the transmission line one-quarter wavelength from the T-junction .
PARALLEL LIMITER - A resistor and diode, connected in series with the input signal, in
which the output is taken across (parallel to) the diode .
PARALLEL-NEGATIVE LIMITER - A resistor and diode, connected in series with the input
signal, in which the output is taken across the diode and the negative alternation is
eliminated
PARALLEL-POSITIVE LIMITER - A resistor and diode connected in series with the input
signal, in which the output is taken across the diode and the positive alternation is
eliminated .
PARALLEL-RESONANT CIRCUIT - A resonant circuit in which the source voltage is connected
across a parallel circuit (formed by a capacitor and an inductor) to furnish a high
impedance to the frequency at which the circuit is resonant. Often referred to as a tank
circuit .
PARALLEL TRANSMISSION - A method of data transmission in which all bits of a particular
character are transmitted simultaneously.
PARALLEL-WIRE - A type of transmission line consisting of two parallel wires .
PARASITIC - In electronics, an undesirable frequency in an electronic circuit. Usually
associated with vacuum-tube amplifiers and oscillators.
PARASITIC ARRAY - An antenna array containing one or more elements not connected to the
transmission line .
PARASITIC ELEMENT - The passive element of an antenna array that is connected to
neither the transmission line nor the driven element .
PARITY BIT - A check bit; an extra bit added to a group of bits for use in detecting
errors during data transfer.
PARITY CHECK - An internal error checking method in which the binary digits in a
character or word are added and the sum is checked against a single previously computed
parity digit. The check tests whether the number of one bits in a character or word are
odd or even, depending on the parity of the computer.
PART - A part is one component or two or more components joined together. It is not
normally subject to disassembly without destruction .
PARTICLE ORIENTATION - The rotation of needle-like particles so that their longest
dimensions tend to lie parallel to one another.
PARTICLE SHAPE - The needle-like particles of gamma-ferric oxide used in conventional
magnetic tape, with a dimensional ratio of about 6 to 1.
PARTICLE SIZE - The physical dimensions of magnetic particles used in a magnetic tape.
PASSIVE SATELLITE - A satellite that reflects radio signals back to earth .
PASSWORD - A protected word or string of characters that identifies or authenticates a
user for access to a specific resource, such as a file or record.
PATCH PANEL - A panel used to tie a receiver or transmitter to its associated equipment
.
PEAK AMPLITUDE - The maximum value above or below the reference line .
PEAK CURRENT - The maximum current that flows during a complete cycle .
PEAK DETECTION - Detection that uses the amplitude of pam or the duration of pdm to
charge a holding capacitor and restore the original waveform .
PEAKING COIL - An inductor used in an amplifier to provide high-frequency compensation,
which extends the high-frequency response of the amplifier .
PEAK POWER - The maximum value of the transmitted pulse .
PEAK-REVERSE VOLTAGE - The peak ac voltage that a rectifier tube will withstand in the
reverse direction .
PEAK-TO-PEAK - The measure of absolute magnitude of an ac waveform, measured from the
greatest positive alternation to the greatest negative alternation .
PEAK VALUE - The maximum instantaneous value of a varying current, voltage, or power.
It is equal to 1.414 times the effective value of a sine wave .
PEAK VOLTAGE - The maximum value present in a varying or alternating voltage. This
value may be positive or negative .
PENTAVALENT IMPURITY - A type of impurity that contains five valence electrons and
donates one electron to the doped material. Also called DONOR IMPURITY .
PENTODE TUBE - A five-electrode electron tube containing a plate, a cathode, a control
grid, and two grids .
PERCENT OF MODULATION - The degree of modulation defined in terms of the maximum
permissible amount of modulation .
PERFORATOR - A device that stores a teletypewriter message on a paper tape .
PERIGEE - The point in the orbit of a satellite closest to the earth .
PERIOD TIME - The time required to complete one cycle of a waveform .
PERIODIC WAVE - A waveform that undergoes a pattern of changes, returns to its original
pattern, and then repeats the same pattern of changes. Examples are square waves,
rectangular waves, and sawtooth waves .
PERIPHERAL EQUIPMENT - Equipment used for data entry, storage, or retrieval, but which
is not a part of the central processing unit. Peripherals include crt displays, terminals,
printers, and mass storage (tape, disk, and drum) devices.
PERMANENT ELONGATION - The percentage of elongation remaining on a tape or a length of
base film after a given load applied for a given time has been removed.
PERMANENT MAGNET SPEAKER - A speaker with a permanent magnet mounted on soft iron pole
pieces .
PERMEABILITY - The measure of the ability of a material to act as a path for magnetic
lines of force .
PERSISTENCE - The length of time a phosphor dot glows on a crt before disappearing .
PERSONAL COMPUTER (PC) - A computer, usually a microcomputer, that is more affordable
than minicomputers or mainframes and is used by one person at a time.
PHANTASTRON - A variable-length sawtooth generator often used to produce a sweep on an
A-scope .
PHASE - The angular relationship between two alternating currents or voltages when the
voltage or current is plotted as a function of time. When the two are in phase, the angle
is zero; both reach their peak simultaneously. When out of phase, one will lead or lag the
other; that is, at the instant when one is at its peak, the other will not be at peak
value and (depending on the phase angle) may differ in polarity as well as magnitude .
PHASE ANGLE - The number of electrical degrees of lead or lag between the voltage and
current waveforms in an ac circuit .
PHASE MODULATION (pm) - Angle modulation in which the phase of the carrier is
controlled by the modulating waveform. The amplitude of the modulating wave determines the
amount of phase shift, and the frequency of the modulation determines how often the phase
shifts .
PHASE-SHIFT DISCRIMINATOR - See FOSTER-SEELEY DISCRIMINATOR .
PHASE SHIFTER - A device used to change the phase relationship between two ac signals .
PHASE-SHIFT KEYING - Similar to ON-OFF cw keying in AM systems and frequency-shift
keying in fm systems. Each time a mark is received, the phase is reversed. No phase
reversal takes place when a space is received .
PHASE SPLITTER - A device that provides two output signals from a single input signal.
The two output signals differ from each other in phase (usually by 180 degrees) .
PHOSPHOR - The material used to convert the energy of electrons into visible light .
PHOTOCELL - A light-controlled variable resistor which has a light-to-dark resistance
ratio of 1:1000. Used in various types of control and timing circuits .
PHOTODIODE - A light-controlled PN junction. Current flow increases when the PN
junction is exposed to an external light source .
PHOTOELECTRIC VOLTAGE - A voltage produced by light .
PHOTOETCHING - Chemical process of removing unwanted material in producing printed
circuit boards .
PHOTOTRANSISTOR - An optoelectronic device that conducts current when exposed to light.
Produces more current and is much more sensitive to light than the photodiode .
PHOTOVOLTAIC CELL (SOLAR CELL) - A device that acts much like a battery when exposed to
light and converts light energy into electrical energy .
PICO - A prefix adopted by the National Bureau of Standards meaning 10-12 .
PICTORIAL DIAGRAM - A diagram showing actual pictorial sketches of the various parts of
an equipment and the electrical connections between the parts .
PICTURE ELEMENT - Synonym for pixel. See pixel.
PIEZOELECTRIC EFFECT - The effect of producing a voltage by placing a stress, either by
compression, expansion, or twisting, on a crystal and, conversely, producing a stress in a
crystal by applying a voltage to it .
PIP (BLIP) - On a crt display, a spot of light or a baseline irregularity representing
the radar echo .
PITCH - A term used to describe the frequency of a sound heard by the human ear .
PIXEL - In computer graphics, the smallest element of a display surface that can be
independently assigned color or intensity.
PLANAR TUBE - An electron tube, constructed with parallel electrodes and a ceramic
envelope, that is used at uhf frequencies. It is commonly referred to as a lighthouse tube
.
PLANE OF POLARIZATION - The plane (vertical or horizontal), with respect to the earth,
in which the E field propagates .
PLANE WAVEFRONTS - Waves of energy that are flat, parallel planes and are perpendicular
to the direction of propagation .
PLANNED-POSITION INDICATOR - A radar display in which range is indicated by the
distance of a bright spot or pip from the center of the screen and the bearing is
indicated by the radial angle of the spot .
PLATE - (1) One of the electrodes in a storage battery . (2) One of the electrodes in a
capacitor . (3) The principal electrode to which the electron stream is attracted in an
electron tube .
PLATE DISSIPATION - The amount of power lost as heat in the plate of a vacuum tube .
PLATE KEYING - A keying system in which the plate supply is interrupted .
PLATE MODULATOR - An electron-tube modulator in which the modulating voltage is applied
to the plate circuit of the tube .
PLATE RESISTANCE - The plate voltage change divided by the resultant plate current
change in a vacuum tube, all other conditions being fixed .
PLASTICIZER - (See additive.)
POINT BENDER - A tool used to adjust the contact spacing on a relay .
POINT-CONTACT DIODE - A diode in which the end of a fine wire is pressed against a
semiconductor. Used as a detector or mixer over the microwave region .
POINT OF ZERO DISPLACEMENT - See REFERENCE LINE .
POINT-TO-POINT WIRING - Individual wires run from terminal to terminal to complete a
circuit .
POLAR - The teletypewriter operation in which current flow of one polarity represents a
mark, and current of the opposite polarity represents a space .
POLAR-COORDINATE GRAPH - A graph with a pair of axes. One consists of a series of
circles with a common center, and the other consists of a rotating radius extending from
the center of the concentric circles .
POLARITY - (1) The condition in an electrical circuit by which the direction of the
flow of current can be determined. Usually applied to batteries and other direct voltage
sources. (2) Two opposite charges, one positive and one negative. (3) A quality of having
two opposite magnetic poles, one north and the other south .
POLARIZATION - (1) The effect of hydrogen surrounding the anode of a cell, which
increases the internal resistance of the cell . (2) The magnetic orientation of molecules
in a magnetizable material in a magnetic field, whereby tiny internal magnets tend to line
up in the field .
POLAR ORBIT - An orbit that has an angle of inclination of or near 90 degrees .
POLE - (1) The number of points at which current can enter a switch; for example,
single pole, double pole, and three pole . (2) The sections of a field magnet where the
flux lines are concentrated; also where they enter and leave the magnet .
POLE PIECE - (1) A piece of ferromagnetic material used to control the distribution of
magnetic lines of force; that is, it concentrates the lines of force in a particular place
or evenly distributes the lines of force over a wide area . (2) The shaped magnetic
material upon which the stator windings of motors and generators are mounted or wound .
POLYESER - (1) An acronym for polyethylene glycol terephthalate. (2) The material most
commonly used as a base film for precision magnetic tape.
POLYMER FUME FEVER - A flu-like condition caused by a person breathing the vapors of
fluorocarbons when they are heated. Sometimes called FOUNDRYMAN'S FEVER .
POLYPHASE - A term that describes systems or units of a system that are activated by or
which generate separate out-of-phase voltages. Typical polyphase systems are 2-phase and
3-phase; their voltages are 90- and 120-degrees out of phase, respectively. This term
means the same as MULTIPHASE .
POSITIONAL NOTATION - A numbering system in which a number is represented by means of a
stated set of symbols or digits, such that the value contributed by each symbol or digit
depends upon its position as well as upon its value .
POSITIONAL WEIGHTING - The value given a digit based on the digit's position within a
given number .
POSITION SENSOR - A component in a servosystem that measures position and converts the
measurement into a form convenient for transmission as a feedback signal .
POSITION SERVOSYSTEM - A servosystem whose end function is to control the position of
the load it is driving .
POSITIVE ALTERNATION - The part of a sine wave that is above the reference line .
POSITIVE CLAMPER - A circuit that clamps the lower extremity of the output waveshape to
a dc potential of 0 volts .
POSITIVE FEEDBACK - Feedback in which the feedback signal is in phase with the input
signal. Also called REGENERATIVE FEEDBACK .
POSITIVE LOGIC - The form of logic in which the more positive logic level represents 1
and the more negative level represents 0 .
POSITIVE TEMPERATURE COEFFICIENT - The characteristic of a conductor in which the
resistance increases as temperature increases .
POTENTIAL ENERGY. - Energy caused by the position of one body with respect to another
body or to the relative parts of the same body .
POTENTIOMETER - A variable resistor, used as a position sensor in servosystems, having
a terminal connected to each end of a resistive element and a third terminal connected to
a wiper contact. The output is a voltage that is variable depending upon the position of
the wiper contact. The potentiometer is commonly referred to as a variable voltage
divider. It, in effect, converts mechanical information into an electrical signal .
POWER - The rate of doing work or the rate of expending energy. The unit of electrical
power is the watt .
POWER AMPLIFIER - An amplifier in which the output-signal power is greater than the
input-signal power .
POWER-AMPLIFIER (CHAIN) TRANSMITTER - Transmitter that uses a series of power
amplifiers to create a high level of power .
POWER FACTOR - The ratio of the actual power of an alternating or pulsating current, as
measured by a wattmeter, to the apparent power, as indicated by ammeter and voltmeter
readings. The power factor of an inductor, capacitor, or insulator is an expression of
their losses .
POWER GAIN - In an antenna, the ratio of its radiated power to that of a reference .
POWER LOSS - (1) The electrical power, supplied to a circuit, that does no work and is
usually dissipated as heat . (2) The heat loss in a conductor as current flows through it
.
POWER PENTODE - A special purpose tube used to provide high-current gain or power
amplification. Each grid wire is directly in line with the one before and after it, a fact
which allows more electrons to reach the plate .
POWER RATIO - See POWER GAIN .
POWER STANDING-WAVE RATIO (PSWR) - The ratio of the square of the maximum and minimum
voltages of a transmission line .
POWER SUPPLY - A unit that supplies electrical power to another unit. It changes ac to
dc and maintains a constant voltage output within limits .
PREAMPLIFIER (PREAMP) - An amplifier that raises the output of a low-level source for
further processing without appreciable degradation of the signal-to-noise ratio .
PRECESSION - The rotation of the spin axis of a gyro in response to an applied force.
The direction of precession is always perpendicular to the direction of applied force .
PRECESSION VECTOR - In a gyro, a vector representing the angular change of the spin
axis when torque is applied. The precession vector represents the axis about which
precession occurs .
PRESTANDARD NAVY SYNCHROS - Synchros that are designed to meet Navy, rather than
servicewide, specifications .
PREVENTIVE MAINTENANCE - Visual, mechanical, electrical, and electronic checks that are
made to determine whether or not equipment is functioning properly .
PRIMARIES (OF LIGHT) - The three primary colors of light from which all other colors
can be derived. The colors are red, green, and blue .
PRIMARY CELL - An electrochemical cell in which the chemical action eats away one of
the electrodes, usually the negative electrode .
PRIMARY LOOP - In a cooling system, the primary source of cooling for the distilled
water .
PRIMARY STORAGE - See storage, primary.
PRIMARY WINDING - The winding of a transformer connected to the electrical source .
PRIME MOVER - The source of the turning force applied to the rotor of a generator. This
may be an electric motor, a gasoline engine, a steam turbine, and so forth .
PRINTED CIRCUIT BOARD - A flat, insulating surface upon which printed wiring and
miniaturized components are connected in a predetermined design and attached to a common
base .
PRINTER - A device used with a computer to produce hard copy, printed output.
PRISM - A triangular-shaped glass that refracts and disperses light waves into
component wavelengths .
PROBE COUPLER - A resonant conductor placed in a waveguide or cavity to insert or
extract energy .
PROGRAM - (1) Verb - The act of writing instructions for computer execution. (2) Noun -
The set of instructions that tells the computer the steps to execute to automatically
solve a problem.
PROGRAM FLOWCHART - See flowchart.
PROGRAMMED TRACKING - The method that uses known satellite orbital parameters to
generate antenna pointing angles .
PROPAGATION - Waves traveling through a medium .
PROM - Acronym for programmable read-only memory.
PULSE - Signal characterized by a steep rise from and decay toward an initial level .
PULSE-AMPLITUDE MODULATION (PAM) - Pulse modulation in which the amplitude of the
pulses is varied by the modulating signal .
PULSE-CODE MODULATION (PCM) - A modulation system in which the standard values of a
quantized wave are indicated by a series of coded pulses .
PULSE DURATION (PD) - The period of time during which a pulse is present .
PULSE-DURATION MODULATION (PDM) - Pulse modulation in which the time duration of the
pulses is changed by the modulating signal .
PULSE-FORMING NETWORK (PFN) - An lc network that alternately stores and releases energy
in an approximately rectangular wave .
PULSE-FREQUENCY MODULATION (PFM) - Pulse modulation in which the modulating voltage
varies the repetition rate of a pulse train .
PULSE MODULATION - A form of modulation in which one of the characteristics of a pulse
train is varied .
PULSE OSCILLATOR - A sine-wave oscillator that is turned on and off at specific times.
Also known as a ringing oscillator .
PULSE-POSITION MODULATION (PPM) - Pulse modulation in which the position of the pulses
is varied by the modulating voltage .
PULSE-REPETITION FREQUENCY (PRF) - The rate, in pulses per second, at which the pulses
occur .
PULSE-REPETITION RATE (PRR) - Same as PULSE-REPETITION FREQUENCY (PRF) .
PULSE-REPETITION TIME (PRT) - Interval between the start of one pulse and the start of
the next pulse; reciprocal of pulse-repetition frequency .
PULSE-TIME MODULATION (PTM) - Pulse modulation that varies one of the time
characteristics of a pulse train (pwm, pdm, ppm, or pfm) .
PULSE WIDTH - Duration of time between the leading and trailing edges of a pulse .
PULSE-WIDTH MODULATION (PWM) - Pulse modulation in which the duration of the pulses is
varied by the modulating voltage .
PULSING - Allowing oscillations to occur for a specific period of time only during
selected intervals .
PUMP - Electrical source of the energy required to vary the capacitance of a parametric
amplifier .
PUNCHED CARD - A card punched with hole patterns that represent data or program
instructions. Punched cards can be read by an input device (card reader) to a computer.
PUNCHED TAPE - A tape punched with hole patterns that represent data or program
instructions. Tape can be read by an input device to a computer.
PUSH-PULL AMPLIFIER - An amplifier that uses two transistors (or electron tubes) whose
output signals are in phase opposition .
