The Illustrated Dictionary of Electronics - Loscha

524 personal communications service • phase coincidencepersonal communications service Abbreviation,PCS. Also called digital cellular. An enhancedwireless network using digital modulation,cellular repeaters, and facilitating telephone andInternet connections. Emphasis is on maximizinguser mobility and portability, and minimizingblind zones. Compare CELLULAR COMMUNICA-TIONS.personal computer A small computer equippedwith a keyboard, display, hard disk, diskettedrive(s), a modem or fax/modem, one or more serialdata ports, and one or more parallel dataports. They are used extensively by individualsand businesses for record keeping, data processing,communications, word processing, graphics,etc.; they are also used in schools as an educationalaid.personal digital assistant Abbreviation, PDA. SeeHANDHELD COMPUTER.personal equation The value of systematic errorfor a person observing specific phenomena ormaking measurements.personality Characteristics that make an intelligentcomputer or robot human-like. In general,the more powerful the computer, the more personalityit can have, depending on the installedsoftware. In some cases, certain malfunctions ina computer can produce personality quirks.personal robot A usually autonomous robot intendedfor use by individuals. The most commonexamples are robot toys, programmable with aPERSONAL COMPUTER, intended for the educationand entertainment of children. More sophisticateddevices can perform domestic tasks, suchas cleaning floors and mowing lawns.peta- Abbreviation, P. A prefix meaning 10 15 .petagram Abbreviation, Pg. A large unit of mass orforce, 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 12kilometers.pF Abbreviation of PICOFARAD.pf Symbol for POWER FACTOR.PFET Abbreviation of P-CHANNEL JUNCTIONFIELD-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 effectivehydrogen-ion concentration in gramequivalents per liter. The scale runs from zero to14, on which 7 denotes neutrality relative to acidityvs. alkalinity; values between zero and 7 denoteacidity, and values between 7 and 14 denotealkalinity. 2. Abbreviation of PICOHENRY.phantom Radio interference in the form of a beatnote (heterodyne), resulting from interference betweentwo strong carriers, often from local radiostations. When the phantom frequency lieswithin the tuning range of a receiver, the phantomcan be tuned in as a separate signal. Butwhen the phantom corresponds to the intermediatefrequency (IF) of the receiver, it will ride intothe IF amplifier and be present as an untunableinterferential signal.phantom channel In a properly phased highfidelitystereo sound system, the apparent soundsource centered between the left- and right-channelloudspeakers.phantom circuit In wire telephony, a third circuitthat has no wires; it results from a method (usingrepeating coils) of making two other circuits dothe work of (this third) one.phantom signal Also called bogey. In a radar system,a signal that does not correspond to an actualtarget. The origin of the phantom signal orecho 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 betweenthe instant that one alternating quantity reachesits maximum value and the instant that anotheralternating quantity reaches its maximum value.It is usually given in degrees (a complete cycle being360 degrees) along the horizontal axis of thetime-versus-magnitude graph of the ac quantity.phase-angle voltmeter An instrument that indicatesboth the magnitude and phase of a voltage.phase coincidence For signals having the samefrequency, the condition of their coinciding interms of instantaneous amplitudes, so positivepeaks of the first signal correspond to positivepeaks of the second signal, and negative peaks ofthe first signal correspond to negative peaks ofthe second signal. For periodic waves that do notchange their characteristics with time, this is thesame thing as being shifted by an integral multipleof 360 degrees in phase. Compare PHASEOPPOSITION.