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 CELLAn electrochemical cell in which the chemical action eats away one of the electrodes,
usually the negative electrode .
PRIMARY LOOPIn a cooling system, the primary source of cooling for the distilled water .
PRIMARY WINDINGThe winding of a transformer connected to the electrical source .
PRIME MOVERThe 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 BOARDA flat, insulating surface upon which printed wiring and miniaturized
components are connected in a predetermined design and attached to a common base  .
PRISMA triangular-shaped glass that refracts and disperses light waves into component wavelengths
PROBE COUPLERA resonant conductor placed in a waveguide or cavity to insert or extract energy
PROGRAMMED TRACKINGThe method that uses known satellite orbital parameters to generate
antenna pointing angles .
PROPAGATIONWaves traveling through a medium .
PULSESignal 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 MODULATIONA form of modulation in which one of the characteristics of a pulse train is
PULSE OSCILLATORA 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 .