18WuD2x

544 polymer • position
polymer A compound that is the product of polymerization,
resulting from the chemical union of
monomers. Also see POLYMERIZE.
polymerize To unite monomers or polymers of the
same kind to form a molecule having a higher
molecular weight.
polyphase In alternating-current circuits, pertaining
to the existence or generation of two or more
specific electrical phases. Compare SINGLE
PHASE.
polyphase antenna An antenna consisting of two
dipole radiators mounted perpendicular to each
other at their midpoint and excited 90 degrees
out of phase. The radiation pattern is approximately
circular in the plane of the elements. Also
called TURNSTILE ANTENNA.
90° Phase shift
polyphase antenna
polyphase generator 1. A dynamo-type generator
of polyphase power (two-phase, three-phase,
etc.). 2. See POLYPHASE OSCILLATOR.
polyphase oscillator An oscillator circuit that generates
polyphase alternating current. The circuit
contains separate oscillators for each phase. A
three-phase circuit, for example, has three symmetrical
oscillators with matched inductance and
capacitance values.
polyphase power 1. The total dissipated power in
a polyphase alternating-current circuit. 2. Polyphase
alternating current provided for utility purposes.
polyphase rectifier A rectifier of polyphase alternating
current generally obtained from a threephase
power line through a transformer. The
several common circuits usually contain a diode
for each phase. Such rectifiers offer the advantage
of higher ripple frequency than is obtainable
by single-phase operation. For a three-phase rectifier,
for example, the ripple frequency is three
times the line frequency; for a six-phase rectifier,
it is six times the line frequency.
polyphase system An alternating-current circuit
in which voltages or currents are normally out of
phase with each other by some fixed amount. Familiar
types are two-phase and three-phase.
polyphase transformer An alternating-current
transformer specifically designed for use in circuits
that have two or more simultaneous current
phases.
polypropylene A plastic material commonly used
as an electrical insulator. Dielectric constant,
2.0. Dielectric strength, 600 V/mil.
polyrod antenna A tapered dielectric antenna,
usually made of polystyrene, for directional microwave
transmission.
polysilicon A polycrystalline form of silicon (see
POLYCRYSTALLINE MATERIAL).
polystyrene A clear, colorless thermosetting-type
plastic. It is widely used as an insulating material
in radio-frequency circuits and, to some extent,
as a dielectric film in fixed capacitors. Dielectric
constant, 2.4 to 2.9. Dielectric strength, 20 to 28
kV/mm.
polystyrene capacitor A high-Q capacitor in
which the dielectric film is polystyrene.
polyvinyl chloride Abbreviation, PVC. A plastic
insulating material. Dielectric constant, 3.6 to
4.0. Dielectric strength, 800 V/mil.
pool cathode In an industrial electron tube, a
cathode consisting of a pool of mercury.
pool-cathode tube An industrial electron tube using
a pool cathode. Examples: excitron, ignitron,
and mercury-arc rectifier.
popcorn noise A temperature-dependent, randomshot
electrical noise. In a radio receiver or audio
circuit, this noise resembles the sound of popping
corn. It occurs in some operational amplifiers.
population In statistical analysis, the total group
of items, quantities, or values under consideration.
Sometimes called universe.
porcelain A hard, white, usually glazed ceramic
used as a dielectric and insulant. Dielectric constant,
6 to 7.5. Dielectric strength, 40 to 100
V/mil. Also called china.
porcelain capacitor A ceramic-dielectric capacitor
in which the dielectric is composed of porcelain or
a related substance.
porcelain insulator An electric insulator fabricated
from porcelain.
porch See BACK PORCH and FRONT PORCH.
port 1. In a circuit, device, or system, a point at
which energy or signals can be introduced or extracted
in a particular manner (e.g., two-port circulator
and I/O port). 2. An aperture in a
loudspeaker enclosure.
portable-mobile station See MOBILE STATION.
portable station A communications station that
can be carried from one location to another. A
portable station differs from a mobile station in
that a portable station does not usually operate
while in motion, whereas a mobile station does.
ported reflex enclosure A loudspeaker cabinet
with openings that facilitate bass (low-frequency)
sound reproduction.
pos 1. Abbreviation of POSITIVE. 2. Abbreviation
of POSITION.
position 1. The location of a point or object with respect
to one or more (usually fixed) references.
2. The setting of an adjustable device, such as a
potentiometer, rotary switch, or variable capacitor.