18WuD2x

524 personal communications service • phase coincidence
personal communications service Abbreviation,
PCS. Also called digital cellular. An enhanced
wireless network using digital modulation,
cellular repeaters, and facilitating telephone and
Internet connections. Emphasis is on maximizing
user mobility and portability, and minimizing
blind zones. Compare CELLULAR COMMUNICA-
TIONS.
personal computer A small computer equipped
with a keyboard, display, hard disk, diskette
drive(s), a modem or fax/modem, one or more serial
data ports, and one or more parallel data
ports. They are used extensively by individuals
and businesses for record keeping, data processing,
communications, word processing, graphics,
etc.; they are also used in schools as an educational
aid.
personal digital assistant Abbreviation, PDA. See
HANDHELD COMPUTER.
personal equation The value of systematic error
for a person observing specific phenomena or
making measurements.
personality Characteristics that make an intelligent
computer or robot human-like. In general,
the more powerful the computer, the more personality
it can have, depending on the installed
software. In some cases, certain malfunctions in
a computer can produce personality quirks.
personal robot A usually autonomous robot intended
for use by individuals. The most common
examples are robot toys, programmable with a
PERSONAL COMPUTER, intended for the education
and entertainment of children. More sophisticated
devices can perform domestic tasks, such
as cleaning floors and mowing lawns.
peta- Abbreviation, P. A prefix meaning 10 15 .
petagram Abbreviation, Pg. A large unit of mass or
force, equal to 10 15 grams or 10 12 kilograms.
petameter Abbreviation, Pm. A large unit of (astronomical)
distance, equal to 10 15 meters or 10 12
kilometers.
pF Abbreviation of PICOFARAD.
pf Symbol for POWER FACTOR.
PFET Abbreviation of P-CHANNEL JUNCTION
FIELD-EFFECT TRANSISTOR.
PFM Abbreviation of PULSE-FREQUENCY MODU-
LATION.
PG Abbreviation of POWER GAIN.
Pg Abbreviation of PETAGRAM.
pH 1. Symbol for hydrogen-ion concentration. Numerically,
pH is the negative logarithm of the effective
hydrogen-ion concentration in gram
equivalents per liter. The scale runs from zero to
14, on which 7 denotes neutrality relative to acidity
vs. alkalinity; values between zero and 7 denote
acidity, and values between 7 and 14 denote
alkalinity. 2. Abbreviation of PICOHENRY.
phantom Radio interference in the form of a beat
note (heterodyne), resulting from interference between
two strong carriers, often from local radio
stations. When the phantom frequency lies
within the tuning range of a receiver, the phantom
can be tuned in as a separate signal. But
when the phantom corresponds to the intermediate
frequency (IF) of the receiver, it will ride into
the IF amplifier and be present as an untunable
interferential signal.
phantom channel In a properly phased highfidelity
stereo sound system, the apparent sound
source centered between the left- and right-channel
loudspeakers.
phantom circuit In wire telephony, a third circuit
that has no wires; it results from a method (using
repeating coils) of making two other circuits do
the work of (this third) one.
phantom signal Also called bogey. In a radar system,
a signal that does not correspond to an actual
target. The origin of the phantom signal or
echo cannot be readily determined.
phantom target See ECHO BOX.
phase angle Unit, degree or radian. In an alternating-current
(ac) circuit, the lag or lead between
the instant that one alternating quantity reaches
its maximum value and the instant that another
alternating quantity reaches its maximum value.
It is usually given in degrees (a complete cycle being
360 degrees) along the horizontal axis of the
time-versus-magnitude graph of the ac quantity.
phase-angle voltmeter An instrument that indicates
both the magnitude and phase of a voltage.
phase coincidence For signals having the same
frequency, the condition of their coinciding in
terms of instantaneous amplitudes, so positive
peaks of the first signal correspond to positive
peaks of the second signal, and negative peaks of
the first signal correspond to negative peaks of
the second signal. For periodic waves that do not
change their characteristics with time, this is the
same thing as being shifted by an integral multiple
of 360 degrees in phase. Compare PHASE
OPPOSITION.