. 17
( 42)


floating zero A control system in which the refer- fluid damping Use of a viscous fluid to damp a me-
ence point is easily moved. chanical member™s movement.
floating zone In a semiconductor ingot undergoing fluid-flow alarm An electronic circuit that actuates
purification, a molten zone in which impurities an alarm when fluid flowing through pipes or other
float. The material in the zone is melted by the channels changes from a predetermined rate.
radio-frequency (RF) field of an external heating fluid-flow control A servo system that automati-
coil, which is passed along the ingot to move the cally maintains or adjusts liquid flow through
molten zone to one end, picking up impurities pipes or other channels.
along the way and concentrating them at the end fluid-flow gauge See FLUID-FLOW METER.
that is later sawed off. fluid-flow indicator See FLUID-FLOW METER.
float switch A switch operated by a float, such as fluid-flow meter An instrument that indicates
in a sump pump. fluid flow rate through pipes or other channels.
flocking 1. Particulate felt used on phonograph fluid-flow switch In a fluid-cooled system, a
turntables to protect disks from being scratched. switch that actuates an alarm when the fluid
2. To coat with flocking. slows or stops.
flood gun In a storage (image-holding) oscillo- fluidics 1. A form of digital logic in which circuits
scope, the electron gun that sprays the storage operate by means of fluid flow. 2. A branch of
target with low-velocity electrons and makes the physics concerned with the behavior of fluids;
image visible on the viewing screen. The gun is more commonly called fluid dynamics.
mounted next to one pair of deflection plates. fluid-level control A servo system that automati-
Compare WRITING GUN. cally maintains the level of a fluid in a tank.
floor stand A support for a microphone, consisting fluid-level gauge An electronic system that provides
of a heavy base that rests on the floor, and an ad- direct readings of the level of a fluid in a tank.
justable, vertical boom that allows the micro- fluid-level indicator See FLUID-LEVEL GAUGE.
phone to be set at various heights. fluid logic Logic operations carried out by varying
floppy disk A flexible magnetic disk used in the flow and pressure of a gas or liquid in a cir-
recording, as in computer and data system stor- cuit of channels. Also see FLUID COMPUTER.
age. It usually refers to a 5.25-inch diskette. fluid ounce (U.S.) Abbreviation, fl. oz. A unit of vol-
ume equal to 2.957 — 10“5 cubic meters, or
flow 1. The movement of current carriers under
the influence of an electric field. 2. See ANGLE 0.02957 liter. A quart is 32 ounces; a gallon is
OF CONDUCTION. 3. A series of interrelated 128 ounces.
events in a time sequence. fluid-pressure alarm An electronic circuit that ac-
flow angle See ANGLE OF CONDUCTION. tuates an alarm when fluid pressure rises or falls
flowchart 1. A diagram depicting the logic steps in beyond set limits.
a digital-computer program. 2. A diagram show- fluid-pressure control A servo system that auto-
ing the flow of material through a sequence of matically maintains or adjusts fluid pressure in
processes. pipes or other channels.
flow direction The method of delineating an- fluid-pressure gauge See FLUID-PRESSURE ME-
tecedent and successor events on a flowchart; TER.
usually arrows and flowlines connecting the fluid-pressure indicator See FLUID-PRESSURE
events in the way a page is read (top to bottom, METER.
left to right). fluid-pressure meter An instrument that indicates
flowed-wax disk A form of recording disk, in which the pressure of a fluid in a pipe or other channel.
wax is melted onto a plastic or metal base. The fluid valve See ELECTROMECHANICAL VALVE.
grooves are cut in the wax layer. fluorescence The property of some materials to
flowline A line showing flow direction on a glow when excited by a stimulus, such as ultravi-
flowchart. olet, X rays, or an electron beam. Compare
flowmeter An instrument for measuring liquid PHOSPHORESCENCE.
flow rate. fluorescent lamp See FLUORESCENT TUBE.
flow relay A relay that is actuated by a predeter- fluorescent materials Materials that glow when
mined rate of fluid flow. irradiated, but cease to glow when the source of
fluctuating current See COMPOSITE CURRENT. excitation is removed. An example is the phos-
fluctuating voltage See COMPOSITE VOLTAGE. phor coating on the screen of a cathode-ray tube
fluid absorption See LIQUID ABSORPTION. (CRT).
292 fluorescent screen • flyback time

fluorescent screen A transparent or translucent fluxgate A device that controls the azimuth bear-
plate (such as the end of a cathode-ray tube or ing of a directional system by means of interac-
fluoroscope) coated with phosphors that glow tion with the geomagnetic field.
when struck by an electron beam, or by high- fluxgate magnetometer A magnetic compass for
energy electromagnetic radiation, such as ultravi- robot guidance. Uses coils to sense changes in ar-
olet or X rays. tificially generated reference fields. Output from
fluorescent tube A mercury-vapor glow lamp dis- the sensors is sent to a computer that calculates
tinguished by having a glass tube whose inner the robot™s position, based on the orientation and
wall is coated with a phosphor that emits light intensity of the lines of flux in the reference fields.
when excited by the ultraviolet glow discharge in flux graph A device that graphically records the in-
the vapor. tensity of a magnetic field around a permanent
fluorescent X rays X rays reradiated by the atoms magnet or electromagnet, or around an inductor
of a material that has absorbed X radiation. Dur- carrying a current.
ing initial exposure, energy absorbed from the ra- flux leakage See MAGNETIC LEAKAGE.
diation raises the energy level of electrons in the flux lines The theoretical lines of force in an elec-
atoms; when the electrons return to their normal tric or magnetic field.
energy levels, they reradiate some of the absorbed flux linkage The passage of lines of force set up by
energy. one component through another component, so
fluorine Symbol, F. A gaseous element of the halo- as to enclose most of the penetrated component™s
gen family. Atomic number, 9. Atomic weight, volume.
fluoroscope A device used for viewing the internal
structures of objects. A screen coated with mate-
rial that fluoresces when exposed to X rays is
mounted in one end of a light-tight viewing hood.
When an object is placed between the screen and Flux
an X-ray tube, an image is produced on the lines
screen. In medical applications, this device has
been supplanted by methods that do not use ion-
izing radiation; nuclear magnetic resonance imag-
ing (NMRI) is one example. In Out
fluoroscopy The art of using a fluoroscope in the
inspection of materials and parts or in medical flux linkage
flush A form of mounting in which there is little or
no protrusion from the panel surface. fluxmeter An instrument for measuring magnetic
flutter 1. In a high-frequency superheterodyne re- flux density. Also called gaussmeter.
ceiver, a rapid fluctuation in signal strength, flux refraction The tendency for magnetic lines of
caused by tuning and detuning of the oscillator flux to change direction at the boundary between
stage. This usually results from poor direct- substances having different permeability. Flux
current (dc) power-supply regulation. 2. Repeti- refraction resembles refraction of electromagnetic
tive, rapid fluctuations in the output of a sound radiation in or at a boundary between substances
reproducer. Also see WOW. 3. An echo effect having different indices of refraction.
sometimes observed in rooms or auditoriums of flyback 1. The abrupt drop or reversal of a current
poor acoustic design. or voltage that was previously increasing (e.g., the
flutter bridge A bridge-type instrument for mea- rapid fall of a sawtooth wave). Also see KICK-
suring flutter in constant-speed machines, such BACK. 2. The duration of the drop of a current or
as sound recording and reproducing devices. voltage that was previously increasing, for a saw-
flutter rate The frequency of flutter, in cycles per tooth or similar wave. 3. In an oscilloscope or pic-
second (Hertz). ture tube, the rapid return of the beam to its
flux 1. Theoretical lines of force that extend in all starting position.
directions from an electric charge (electric flux) flyback checker An apparatus that senses the
or from a magnetic pole (magnetic flux). 2. A presence of short or open circuits in motors,
material that makes metals more amenable to transformers, and generators, by measuring the
being joined by soldering. 3. The number of amount of flyback (kickback).
photons that pass through a surface for a given flyback power supply See KICKBACK POWER
time. SUPPLY.
flux density Symbol, B. Unit, tesla. The degree of flyback time The time taken for the electron beam
concentration of magnetic lines of force. One tesla in an oscilloscope tube, picture tube, or camera
represents a flux density of one volt-second per tube to return to its starting point after it has
square meter (V•s/m2). reached the point of maximum deflection.
flyback transformer • focal length

flyback transformer In a television receiver circuit, flywheel synchronization A form of television
the horizontal output transformer. The unit sup- scanning synchronization used when the re-
plies horizontal scanning voltage and kickback ceived signal is very weak. The synchronization
voltage, which is rectified to produce the high- signals from the transmitter are sensed by the re-
voltage direct-current (dc) anode potential. Also ceiver, which then produces its own local pulses
see FLYBACK and KICKBACK POWER SUPPLY. based on the rate of received pulses.
flying eyeball An undersea exploration robot con- flywheel tuning A tuning dial mechanism in
sisting of a television camera, illumination lamps, which the control shaft has a flywheel for the
and thrusters (such as jets or propellers). A cable, smoother tuning action afforded by the added
which also serves as a tether, sends data to a hu- momentum.
man operator, and allows the operator to control Fm Symbol for FERMIUM.
the movements of the robot. In some cases, the FM Abbreviation of FREQUENCY MODULATION.
tether/cable can be replaced by an infrared or fm Abbreviation of MODULATION FREQUENCY.
visible-light laser data link. FM-AM Pertaining to equipment that will operate
flying-spot tube A tube, such as a camera tube, in with either amplitude-modulated or frequency-
which a rapidly deflected spot of light scans an modulated signals.
image on a transparent screen; the spot is pro- FM-AM multiplier A method of frequency multipli-
jected through the picture to a photomultiplier. cation using both amplitude and frequency mod-
fly™s-eye lens A lens consisting of hundreds of ulation of a carrier wave.
much smaller lenses. Used in microelectronic cir- FM broadcast band The 88- to 108-MHz frequency
cuit fabrication to produce many images of the band, within which channels spaced 200 kHz
same circuit. apart occupy positions from 88.1 to 107.9 MHz.
flywheel effect 1. In an inductance-capacitance FM detector See DISCRIMINATOR, RATIO DE-
(LC) tank circuit, the completion of a partial input TECTOR, and SLOPE DETECTOR.
wave cycle at the resonant frequency, resulting FM-FM Frequency modulation by one or more FM
from the storage and release of energy. This pro- subcarriers.
vides a nearly perfect sine-wave output for class- FM limiter In a frequency-modulation circuit, a
AB, class-B, and class-C radio-frequency (RF) stage which holds the amplitude of the FM signal
power amplifiers. 2. In an LC tank circuit, the ac- to a constant value. The limiter can be active
tion in which energy continues to oscillate be- (e.g., an amplifier-limiter transistor) or passive
tween the capacitor and inductor after an input (e.g., a diode clipper).
signal has been removed. The oscillation stops FM multiplex See MULTIPLEX ADAPTER.
when the tank-circuit finally loses the energy ab- FM noise Unintentional modulation of a fre-
sorbed. The lower the inherent resistance of the quency-modulated transmitter, resulting from
circuit, the longer the decrement (decay time). noise in the audio-input stages.
FM-PM A system of modulation in which a carrier
is phase modulated by frequency-modulated sub-
Input waveform carriers.
FM radar A radar system in which the signal is fre-
quency modulated; the distance to the target is
measured in terms of the beat note between
transmitted and reflected waves.
FM repeater A two-way radio system composed
of a simultaneously operating receiver and
transmitter, the latter of which retransmits
(usually on a different frequency) all signals
picked up by the receiver. The system is usually

tower- or hilltop-mounted, and is used to extend
the range of two-way units in a communications
Time FM stereo The use of multiplex methods to trans-
mit and receive stereophonic programs in an FM
channel. Also see MULTIPLEX ADAPTER.
FM tuner A compact radio receiver that handles
frequency-modulated (FM) signals, and delivers
its low-amplitude audio output to a high-fidelity
system. Compare AM TUNER and AM-FM
Filled in by TUNER.
flywheel effect focal length Symbol, F. The distance from the cen-
ter of a lens or dish antenna to the principal fo-
flywheel effect, 1. cus. Also see PRINCIPAL FOCUS.
294 focus • folded pattern

focus 1. The point at which rays converge. Also see protects both the power supply and the powered
PRINCIPAL FOCUS. 2. To bring rays to a point of equipment.
convergence. folded dipole A half-wavelength, center-fed an-
focus coil See FOCUSING COIL. tenna constructed of two parallel wires with their
focus control In an oscilloscope or television cir- ends connected together. It has the same length
cuit, the potentiometer that controls the voltage as a simple dipole antenna, but the feed-point
on the focusing electrode of the cathode-ray tube impedance is four times that of the ordinary
and, accordingly, the sharpness of the image. dipole. Instead of approximately 73 ohms, the
focus grid 1. The focusing electrode in an electro- folded dipole presents a resistive impedance of
static cathode-ray tube. 2. The focusing electrode about 300 ohms. This makes the folded antenna
in an oscilloscope tube. desirable for use with high-impedance, parallel-
focusing Bringing a ray of particles or energy to a wire transmission lines. It also can be used to
common point. This can be done using lenses, obtain a good match with 75-ohm coaxial cable
deflecting coils, deflecting plates, or reflecting de- when four antennas are connected in phase, or
vices. Focusing can be done with acoustic waves, with 50-ohm coaxial cable when six antennas
electromagnetic waves, and theoretically with any are connected in phase. Compare DIPOLE
kind of disturbance propagated through any ANTENNA.
focusing anode See FOCUSING ELECTRODE.
focusing coil An external coil used to focus an »
electron beam in a cathode-ray tube. Also see
focusing electrode The internal electrode (grid or
ring) used to focus the electron beam in a cath-
ode-ray tube. Also called focus electrode. Also see
1, 2.
focusing magnet A permanent magnet assembly
for focusing the electron beam in a cathode-ray
300-„¦ Feeder
foil 1. The thin conductive strips on a printed-
circuit board. 2. Also known as tape. Thin metal
folded dipole
supplied in strips, intended for use in certain se-
curity systems. It can be installed in closed loops
at potential points of entry. folded horn A loudspeaker having a horn whose
foil capacitor A capacitor whose plates are sheets flare is divided into several zigzagging chambers;
or strips of metal foil separated by a dielectric that is, the horn is, in effect, folded to squeeze a
film. required length into a small cabinet.
foil coil See FOIL-WOUND COIL. folded-horn enclosure See LABYRINTH SPEAKER.
foil conductor A conductor that is a strip of metal folded pattern An oscilloscope image having an
foil, rather than wire. Also see FOIL PATTERN. elongated time axis obtained by successive hori-
foil electroscope See LEAF ELECTROSCOPE. zontal sweeps”each placed slightly lower on the
foil pattern The pattern of thin metal circuit paths
that constitute the “wiring” of a printed circuit.
foil-wound coil A coil wound with metal foil (usu-
ally aluminum or copper) instead of wire. Such
coils substantially reduce the weight of large
transformers and filter chokes.
2. In audio recording, the routing of sound (via an
audio mixer) to some other destination in addi-
tion to the recording medium. Example: playing
an electronic organ while singing, recording the
arrangement on tape, and also listening to it (or-
gan and voice) in a headset.
foldback current limiting In a power supply, a
method of automatically reducing the output cur-
rent to a safe level when the load current exceeds
folded pattern
the maximum recommended value. This action
folded pattern • fork oscillator

screen than the preceding one. The folded- recording system on and off. Often used for tak-
pattern technique provides a time axis several ing dictation.
times longer than the screen width. forbidden band See ENERGY GAP.
folding frequency In a system where sampling is forbidden character code An error-finding code
made at uniform frequency increments, the fre- using forbidden characters: combinations of pro-
quency corresponding to half the sampling rate in hibited bits. Also called forbidden combination.
hertz. forbidden energy band See ENERGY GAP.
foldover Distortion characterized by the horizontal force 1. Symbol, F. Units: newton, dyne, poundal.
or vertical overlapping of a television picture. The agency or influence that accomplishes work.
follower A single-stage, active circuit characterized 2. An operator interjection made during a pro-
by zero phase reversal, and voltage gain less than gram run that causes the computer to execute a
unity. The emitter follower is also called a com- branch instruction; it is usually necessary when
mon-collector circuit; the source follower is also a condition responsible for halting a program
known as a common-drain circuit. Characterized must be bypassed.
by moderate to high input impedance, and low forced coding Programming that minimizes the
output impedance over a wide band of frequen- time required to retrieve information from stor-
cies. age. Also called minimum latency programming or
follower drive In a servo system, the drive that minimum access programming.
mechanically follows the master drive. forced oscillations Oscillations in a circuit, such as
following blacks In a television picture, the effect in an inductance-capacitance (LC) tank, that re-
in which a moving white object has a black border sult from continuously applied alternating-current
following it. (ac) excitation. Compare FREE OSCILLATIONS.
following whites In a TV picture, the effect in foreground job A relatively high-priority, short-
which a moving dark object has a white border running program that is carried out by inter-
following it. rupting a low priority, long-running program.
follow-up motor See SERVOMOTOR. Compare BACKGROUND JOB.
font The physical shape and size of the letters and force pump In a multistage vacuum system, the
numbers in an alphanumeric system. first pump that reduces the pressure consider-
font reticle In optical character recognition, an ably below atmospheric pressure. Also see DIF-
overlay reference pattern of lines used to check FUSION PUMP and VACUUM PUMP.
the size and configuration of an input character, force summing device A transducer element that
the size of punctuation marks, and spacing be- is physically moved by a force being transduced.
tween lines and characters. foreshortened addressing In control computers,
food-service robot Any robot that is used for the the mixing of available storage by using simplified
purpose of packaging, preparing, and/or serving addressing instructions.
food. fork oscillator An audio-frequency oscillator con-
foot Abbreviation, ft. A unit of linear measure in trolled by a tuning fork. The dimensions of the
the English system equal to 0.3048 meter. fork determine its vibration frequency and, ac-
foot-candle Abbreviation, fc. A unit of illuminance; cordingly, the frequency of the oscillator.
1 fc is the amount of direct light emitted by 1 can-
dela (see CANDLEPOWER) that falls on 1 square
foot of a surface on which every point is 1 foot
away from the source. In the International Sys-
tem of Units, the unit is lux (lumens per square
meter). Compare METER-CANDLE.
foot-candle meter A light meter whose scale reads
AF output
directly in foot-candles.
foot-lambert Abbreviation, fL. A unit of lumi- Tuning
nance; the average brightness of a surface that fork
emits or reflects 1 lumen per square foot. The
Standard International (S.I.) unit is the candela
per square meter (cd/m2); 1 fL = 3.426 cd/m2.
foot-pound Abbreviation, ft-lb. In the English sys-
tem, a unit of energy equal to 1 pound displaced
through 1 foot in the direction of the exerting
force. The Standard International (S.I.) unit is the
joule (j); 1 ft-lb = 1.356 j.
foot-pound-second system See FPS SYSTEM OF
foot switch A switch operated by the foot, gener-
ally used for the purpose of turning a playback or fork oscillator
296 form • forward voltage drop

form 1. The core or frame upon which an inductor forward breakover voltage 1. For a semiconduc-
is wound. 2. A vessel, such as a mold, used in the tor pn junction, the smallest forward voltage at
shaping stage of a manufacturing process. which appreciable conduction occurs. This is
formaldehyde Formula, HCHO. A colorless, pun- about 0.3 V for germanium and 0.6 V for silicon.
gent gas that is a constituent of many well-known 2. For a silicon-controlled rectifier, the forward
plastic insulating materials (see PHENOLFORM- voltage value at which the device abruptly
ALDEHYDE PLASTICS). switches on.
formant 1. The audio-frequency range in which forward characteristic The current-voltage re-
the sound of a spoken syllable is concentrated. 2. sponse of a semiconductor junction that is biased
Any general group of audio frequencies. in the forward (high-conduction) direction. Com-
formant filter In an electronic organ, an audio fil- pare REVERSE CHARACTERISTIC.
ter that changes the waveshape of a tone so that forward compatibility standards Standards devel-
the tone will have the desired characteristics. oped to make programs for one computer system
format 1. The form in which data is presented usable for additional or replacement equipment.
(e.g., the arrangement of characters, fields, forward conduction The increased current con-
words, totals, etc.). 2. To prepare a computer disk duction through a pn junction that is forward bi-
or tape so that it will accept data. ased. Compare REVERSE CONDUCTION.
form factor 1. The SHAPE FACTOR for a filter or forward current Symbol, If. The increase in cur-

tuned circuit. 2. For a half-cycle of an alternat- rent flow through a pn junction that is forward bi-
ing-current (ac) quantity, the ratio of the root- ased. Compare REVERSE CURRENT.

mean-square (rms) value to the average value. forward current-transfer ratio The current gain of
form feed 1. A mechanical system that positions a bipolar transistor (alpha for the common-base
paper being supplied to a line printer. 2. The FF connection and beta for the common-emitter con-
character that initiates advancement of printout nection).
paper in a printer. 3. The advancement of print- forward power 1. In a transmission line, the power
out paper in a printer. leaving the generating source, as measured by a
form feed character In a control loop, a character directional wattmeter at that location. 2. The
(symbol, FF) used on printing devices for control- power arriving at the load at the terminating end
ling form feed. of a transmission line.

forming See ELECTROFORM, 1. forward propagation by ionospheric scatter See
form stop An automatic device that stops a printer FORWARD SCATTER.
when the paper runs out. forward propagation by tropospheric scatter Ab-
FORTH A high-level computer programming lan- breviation, FPTS. A method of transmitting part
guage used in certain robots, automated facto- of a radio signal beyond the horizon using the
ries, medical electronic devices, and electronic scattering effect of the troposphere. Also see FOR-
games. It was originally developed in the 1970s to WARD SCATTER and TROPOSPHERE.
facilitate computer control of equipment in astro- forward resistance Symbol, Rf. The resistance of a
nomical observatories. forward-biased pn junction. Also see FORWARD
FORTRAN A high-level computer programming BIAS. Compare REVERSE RESISTANCE.
language developed in the 1950s, and still used forward-reverse ratio See FRONT-TO-BACK RA-
in some scientific and mathematical applications. TIO.
It is not especially useful for the control of elec- forward scatter Also called forward propagation by
tronic or mechanical devices. ionospheric scatter. The scattering of a radio wave
fortuitous conductor A medium that creates an in the normal direction of propagation to points
unwanted electrical path. beyond the skip zone. The phenomenon occurs
fortuitous distortion Waveform distortion that re- because of waves returned from regions in the
sults from causes other than characteristic ef- ionosphere. Compare BACK SCATTER.
fects or bias effects. forward transconductance Symbol, gfs. For a
forward AGC Automatic gain control provided by common-source-connected FET, the ratio of a
special transistors whose transconductance de- drain-current differential to the differential of
creases with increasing emitter current, and vice gate-to-source voltage that produces it; gfs =
versa. Compare REVERSE AGC. 1000(dID/dVGS), where gfs is in microsiemens, ID is
forward-backward counter A counter that runs the drain current in milliamperes, and VGS is the
forward to perform addition and backward to per- gate-to-source voltage in volts.
form subtraction. forward voltage Symbol, Ef or Vf. Voltage whose
forward bias Forward voltage or current in a tran- polarity causes maximum current to flow through
sistor or semiconductor diode. a pn junction. Compare REVERSE VOLTAGE.
forward-blocking state For a silicon-controlled forward voltage drop The voltage across a semi-
rectifier, the off state, during which the forward conductor junction that is biased in the forward
bias is so much less than the forward breakover (high-conduction) direction. Compare REVERSE
voltage that only small off-state current flows. VOLTAGE DROP.

FOSDIC • fps system of units

FOSDIC Acronym for film optical scanning devices four-layer diode A dual-terminal npnp device that
for input to computer. is usable as a bistable switch, sawtooth or pulse
Foster-Seeley discriminator A discriminator cir- generator, memory device, etc.
cuit in which the diodes are operated from a four-layer transistor A transistor in which the
single-tuned, center-tapped secondary of the input wafer or block has four processed regions; how-
transformer. The center tap is also capacitively ever, the device might have only three terminals.
coupled to the top of the transformer™s primary Some examples are the silicon-controlled recti-
coil. Compare TRAVIS DISCRIMINATOR. fier, silicon-controlled switch, and thyristor.
four-level laser A laser identical to the three-level
laser, except for the addition of one excited state.
Ep four-phase system A two-phase system in which
From A Audio
the center taps of the coils are interconnected.
T1 R2 four-terminal network A network having two in-
’ put terminals and two output terminals. One in-
C1 C3 put terminal can be internally connected to one
output terminal (as when a common ground is
present), but this is not mandatory.
E2 R3
four-space 1. A mathematical space in which four
coordinates (w,x,y,z) are necessary to uniquely
B+ define a point. 2. Three-dimensional space with
the addition of time as a fourth dimension; coor-
Foster-Seeley discriminator dinates are, for example, (x,y,z) for space and t for
four-space coordinates 1. A system of coordinates
Foucault currents See EDDY CURRENTS.
for uniquely determining points in four-space.
four-address instruction A computer instruction
Such a system can be Euclidean or non-
in which the address is comprised of four ad-
Euclidean, as with space of any number of
dresses: two for operands, one for the result of
dimensions. 2. The set of numbers that defines a
the operation, and one for the upcoming instruc-
particular point uniquely in four-space; for exam-
ple, P = (3,“15,0,“7).
four-channel sound system Also called quadra-
four-sphere The set of all points equidistant from a
phonic sound system. A high-fidelity, stereo-
given point P in four-space. Formula is w2 + x2 +
phonic sound reproduction system, in which
y2 + z2 = r2, where r is the radius and the coordinates
there are four channels, rather than the usual
are (w,x,y,z) in the Euclidean, Cartesian system.
two. The channels are generally designated left
four-track recording A tape recording in which
front, left rear, right front, and right rear. The
four channels are recorded in two adjacent tracks
four-channel system is an enhancement of two-
on the tape. Usually, tracks number 1 and 3 are
channel stereo.
in the forward direction, and tracks number 2
four-dimensional continuum 1. In relativistic
and 4 are in the reverse direction.
theory, the space-time continuum. There are
four-track tape A magnetic tape with four parallel
three spatial dimensions and one time dimen-
sound paths.
sion. A point in the continuum can be uniquely
four-wire wye system A three-phase system in
defined by three space coordinates and one time
which three wires supply the respective phases, a
coordinate. 2. Any continuum that requires four
fourth being the neutral conductor.
and only four coordinates to uniquely determine
the position of a point.
fp Abbreviation of FREEZING POINT.
Fourier analysis Use of the FOURIER SERIES to
FPC Abbreviation of Federal Power Commission.
evaluate the components of a complex wave, or to
define a complex wave in terms of its components.
FPIS Abbreviation of forward propagation by iono-
Fourier series An infinite mathematical series that
spheric scatter. See FORWARD SCATTER.
shows any periodic function to be a combination
fpm Abbreviation of feet per minute.
of sine terms and cosine terms. Any complex
fps 1. Abbreviation of feet per second. 2. Abbrevia-
wave (e.g., a square wave) consists of fundamen-
tion of frames per second. 3. Abbreviation of foot-
tal and harmonic sine-wave components. In sim-
pound-second (fps), a chiefly British system of
plified form, the series is:
f(x) = A0/2 + A1 cos x + B1 sin x + A2 cos 2x + B2 fps system of units The British system of units of
sin 2x + A3 cos 3x + B3 sin 3x + . . . measurement that uses the foot for length, the
pound for mass, and the second for time. Com-
In general, the more terms to which the series is
calculated, the better the approximation of a
complex waveform.
298 FPTS • Fraunhofer region

FPTS Abbreviation of FORWARD PROPAGATION modulation (PCM), a signal used to identify an in-
Fr Symbol for FRANCIUM. framing 1. Synchronization of the vertical compo-
fr Abbreviation of FRANKLINE. nent of a video signal so that the top and bottom
fractional exponent An exponent indicating that a of the transmitted and received pictures line up.
number is to be raised to a fractional power (e.g., 2. The process of lining up the top and bottom of
104/3). The numerator of the exponent indicates a movie picture. 3. Alignment of the characters in
the power to which the base number must be a digital alphanumeric transmission.
raised; the denominator of the exponent indicates francium Symbol, Fr. A radioactive metal element
the root that must be taken of the result. Thus, of the alkali-metal group. Produced artificially
na/b is equal to the bth root of na. through radioactive disintegration. Atomic num-
fractional gain Amplification less than unity. A ber, 87. Atomic weight, 223.
notable example is the transfer function of a Frankenstein scenario A theme often depicted in
source follower or emitter follower. science fiction, in which intelligent machines
fractional horsepower Any power rating lower seize power from their human creators. With the
than one horsepower (1 hp). Also see HORSE- rapid advance of technology, especially in
POWER. robotics and artificial intelligence (AI), some peo-
fractional uncertainty See RELATIVE UNCER- ple, including a few educated researchers, believe
TAINTY. this scenario is within the realm of possibility.
frame 1. A single, complete video image, scanned Most scientists think it is highly improbable.
in 1„30 second in conventional television receivers. Franklin antenna A vertical collinear array that
2. A single motion-picture (film) image. 3. In produces omnidirectional gain because of phas-
packet communications, a fundamental unit of ing among the individual components.
data. The three types are called information (I) frankline (Benjamin Franklin, 1706“1790) Abbre-
frame, supervisory (S) frame, and unnumbered (U) viation, fr. A name that has been suggested for
frame. 4. One of a recurring cycle of pulses. 5. In the unit of electric charge; 1 fr is the charge that
pulse-code modulation (PCM), a cyclic word exerts a force of 1 dyne on an equal charge at a
group including a sync signal. 6. A complete com- distance of 1 centimeter in a vacuum.
mutator cycle. 7. A digital representation of a set Franklin oscillator A dual-terminal, audio/radio-
of objects, useful in robotics and artificial intelli- frequency (AF/RF) oscillator circuit. Consists of a
gence (AI).
frame alignment The condition in which the re-
ceiver, or receiving apparatus, is in correct align- B’ B+
ment with the signal to be received. In television,
for example, this results in true rendition of the
picture. Incorrect frame alignment (misalign-
ment) might result in the picture being split with
the top and bottom interposed. For other types of
signals, misalignment would result in garbled re-
frame-alignment signal In television, a transmit-
ted signal that is used to ensure that frame align-
ment occurs in the receiver. It is a form of
synchronizing pulse.
frame-alignment time slot In a transmitted tele-
vision frame, an interval of time that is used for Output
the purpose of transmitting a frame-alignment
signal. There might or might not be other signal
information transmitted during this time interval.
frame frequency The number of frames of a mo-
tion-picture film that come into position per unit
of time in a camera, projector, or pickup. Franklin oscillator
frame of reference Geometric relationships used
to describe the location of a body in space.
frame rate See FRAME FREQUENCY. two-stage, resistance-capacitance (RC) coupled
frame-repetition rate See FRAME FREQUENCY. amplifier, with a tuned inductance-capacitance
frame roll Momentary vertical roll in a television (LC) tank in the input gate circuit, and with ca-
picture. pacitive feedback from the second drain to the
frame synchronizing signal 1. In pulse amplitude tank.
modulation (PAM), a coded pulse indicating initi- Fraunhofer region The area surrounding a radiat-
ation of a commutation frame. 2. In pulse-code ing antenna, throughout which the energy ap-
Fraunhofer region • frequency band

pears to come from a single point located near the or self-excited oscillator, will operate when the
actual antenna. synchronizing voltage is removed.
free air resonance For a speaker, the resonant fre- free-running multivibrator See ASTABLE MULTI-
quency or frequencies exhibited when the device VIBRATOR and UNCONTROLLED MULTIVIBRA-
is not mounted in a cabinet. TOR.
free carrier A free electron or, in a semiconductor free space Empty space; a theoretical ideal.
material, the equivalent hole. Also see ELEC- free-space loss Radio transmission loss disregard-
TRON and HOLE. ing variable factors (a theoretical condition).
free charge The portion of a charge on a conductor free-space pattern The ideal directivity pattern of
that, being unaffected by a neighboring charge, an antenna that is situated many wavelengths
will escape to ground when the conductor is above ground. In use, this pattern is modified by
grounded. Compare BOUND CHARGE. reflections from ground.
free electron 1. An electron situated in one of the free speed The angular velocity of an unloaded
outer orbits of an atom, held loosely by the nu- motor.
cleus. Because free electrons can easily escape free-standing display In a computer system, a re-
the attraction of atomic nuclei, they will drift mote display unit for prompting peripheral oper-
among atoms if the material is subjected to an ators.
electric potential. The result is electric current. freezing point Abbreviation, fp. The temperature
Also see ELECTRON and BOUND ELECTRON. 2. at which a liquid starts becoming a solid at nor-
An electron that is not associated with any atomic mal pressure. Compare MELTING POINT.
nucleus. F region Also called F layer. A region of the iono-
free field Data organized in a storage medium in sphere with an altitude at night of approximately
such a way that a data item or field can be any- 175 miles. In daytime, the region splits into the
where in the medium. Compare FIXED FIELD. lower F1 region and the higher F2 region. This
free impedance For a transducer, the input layer is primarily responsible for long-distance
impedance produced by a perfectly short- propagation of radio waves at high frequencies
circuited load. (3 MHz to 30 MHz). At times it returns waves at
free magnetic pole A magnetic pole that is so well frequencies as high as about 70 MHz.
isolated from its opposing pole that it experiences Fremodyne detector A frequency-modulation
little or no influence from the latter. (FM) detector that is essentially a conventional
free magnetism A theoretical medium or fluid to amplitude-modulation (AM) circuit detuned to
which magnetic effects are conventionally given. one side of resonance (slope-tuned) to demodu-
The sum of free magnetism in any given object is late a frequency-modulated signal. Also see
always zero. Within any small part of the field, the SLOPE DETECTOR.
free magnetism is thought of as flux lines. This French phone See CRADLEPHONE.
theoretical medium can be any nonmagnetic ma- freqmeter Contraction of FREQUENCY METER.
terial. frequency Symbol, f. The rate at which a phe-
free net In radio communications, a network in nomenon is repeated. The basic unit of fre-
which stations are free to communicate with quency is the Hertz (Hz), which represents one
other stations in the net without constant su- complete cycle per second. Common units en-
pervision by the net control station. Such com- countered in electronics are the kilohertz (kHz),
munication is carried out on a frequency megahertz (MHz), and gigahertz (GHz), where
1 kHz = 103 Hz, 1 MHz = 106 Hz, and 1 GHz = 109
slightly above or below that of the net™s formal
operation. Hz. Occasionally, the terahertz (THz) is used;
1 THz = 1012 Hz.
free oscillations Oscillations in a circuit, such as
an inductance-capacitance (LC) tank, that con- frequency-agile radar A radar system in which the
tinue after excitation has been removed. Also see transmitter frequency is shifted in a predeter-
FLYWHEEL EFFECT. Compare FORCED OSCIL- mined pattern for the purpose of avoiding detec-
LATIONS. tion. A frequency-agile radar system, with a
free path In a gas tube, the path taken by an elec- complex frequency control program, is very diffi-
tron as it collides with atoms. Also see MEAN cult to jam.
FREE PATH. frequency allocation 1. The assignment of fre-
free-power supply 1. A simple tuned radio-fre- quencies to radio and allied services by the li-
quency (RF) detector diode, used to rectify a radio censing authority (in the United States, the
signal and supply small amounts of direct cur- Federal Communications Commission). 2. A spe-
rent for the operation of low-powered transistor cific assignment of a frequency or a band of fre-
circuits. 2. See SOLAR BATTERY. quencies. Also see RADIO SPECTRUM.
free reel The supply reel of a magnetic-tape frequency band A given range of frequencies, usu-
recorder. ally specified for some application (e.g., the band
free-running frequency The frequency at which a allocated for standard radio broadcast service).
synchronized generator, such as a multivibrator Also see BAND.
300 frequency bias • frequency drift

frequency bias An intentional change in the fre- frequency converter 1. An active or passive device
quency of a transmitted signal. for changing the frequency of a signal. 2. The
frequency bridge 1. Any alternating-current mixer in a superheterodyne circuit.
bridge, such as the Wien bridge or resonance frequency correction Manual or automatic reset-
bridge, that can be nulled at only one frequency ting of a deviated frequency to its original value.
for a given set of bridge-arm values. 2. Any alter- frequency counter An instrument that counts sig-
nating-current bridge that is used to measure nal cycles or pulses over a standard time base (a
unknown frequencies. frequency measurement). Often used to accu-
frequency calibrator A device, such as a crystal os- rately measure the frequencies of radio or televi-
cillator, that provides a signal of precise frequency sion signals; in this application, it is a precision
with which other signals can be compared. Also FREQUENCY METER.
frequency changer 1. A superheterodyne con- frequency detector See FREMODYNE DETEC-
verter (see CONVERTER). 2. A motor-generator in TOR.
which the output voltage has the same value as frequency deviation 1. The degree to which a fre-
the input voltage, but is of a different frequency. quency changes from a prescribed value. Thus, if
3. See FREQUENCY-MULTIPLYING TRANS- the frequency of a 1000-Hz oscillator drifts be-
FORMER. 4. See FREQUENCY MULTIPLIER. tween 990 and 1010 Hz, the deviation is ±10 Hz.
frequency-change signaling See FREQUENCY- 2. In a frequency-modulated (FM) signal, the
SHIFT KEYING. amount of instantaneous frequency shift above
frequency channel A relatively narrow segment of and below the unmodulated carrier frequency.
a frequency band allocated to a station in a par- frequency-deviation meter In frequency-modula-
ticular service. The bandwidth of the channel de- tion (FM) communications operations, a meter
pends on the type of modulation used, the type of that gives a direct reading of frequency deviation
data to be transmitted, and the speed or fidelity of resulting from a modulating signal. It uses either
the data to be transmitted. a tuned circuit or a frequency comparator.
frequency comparator A device, such as an oscil- frequency difference 1. In a superheterodyne cir-
loscope or zero-beat indicator, used to check one cuit, the difference between the signal frequency
frequency against another. Also see FREQUENCY and the oscillator frequency. 2. In any beat-
COMPARISON. frequency operation, the quantity f2 “ f1, where f2
frequency comparison The observation of a cur- is the higher frequency and f1 is the lower
rent or voltage of one frequency for similarities in frequency. Compare FREQUENCY SUM.
that of another frequency. Comparisons (as in frequency discriminator See DISCRIMINATOR.
frequency matching) can be made by audio frequency distortion A form of distortion in which
means, by visual means, or both. Common in- the amplification of some frequencies is different
struments used are oscilloscopes, beat-note de- from that of others.
tectors, and beat-note meters. frequency distribution See DISTRIBUTION, 2.
frequency-compensated attenuator An attenua- frequency diversity The transmission and recep-
tor, such as one in an electronic voltmeter or tion of signals at two or more frequencies for the
wideband oscilloscope, that has been modified by purpose of reducing the effects of fading. It is gen-
the addition of capacitors or inductors to achieve erally used in long-distance, high-frequency cir-
reasonably flat response over a wide range of fre- cuits.
quencies. frequency divider A circuit or device whose out-
frequency compensation The modification of a put frequency is a fraction of the input frequency.
circuit, such as an amplifier or attenuator, by the Compare FREQUENCY MULTIPLIER.
addition of capacitors or inductors to tailor its re- frequency-dividing network See CROSSOVER
sponse at specified frequencies. NETWORK.
frequency control 1. An adjustable component frequency-division multiplex A form of multiple-
(potentiometer, variable capacitor, or variable in- signal parallel transmission in which a single car-
ductor) with which the frequency or frequency re- rier is modulated by two or more signals
sponse of a circuit is adjusted. 2. A device, such simultaneously.
as a quartz crystal or tuning fork, that automati- frequency doubler A circuit that multiplies an in-
cally sets the frequency of an oscillator. put frequency by two. If a doubler™s input circuit
frequency conversion The process of changing a is tuned to frequency f, then its output circuit is
signal from one frequency to another, usually generally tuned to 2f. Frequency doubling is per-
without altering the signal bandwidth. In some formed by various nonlinear devices, including
cases, a signal is turned “upside down” by this transistors, varactors, and biased diodes.
process [e.g., an upper-sideband (USB) signal frequency drift An undesired, usually gradual,
might be changed to a lower-sideband (LSB) sig- change in the frequency of a signal from its in-
nal]. Generally accomplished by means of a tended frequency or channel; expressed in hertz
MIXER. or kilohertz.
frequency function • frequency response

Tuned Tuned cast stations or a frequency meter used in elec-
to to tric-generating stations).
2f 2f frequency multiplier A circuit or device whose out-
put frequency is a multiple of the input frequency.
See, for example, FREQUENCY DOUBLER.
frequency-multiplying amplifier See MULTI-
frequency-multiplying transformer A magnetic
amplifier that generates harmonics of the supply
frequency. The effect results from the nonlinear-
ity of the transformer core material.
frequency offset 1. The difference between an ac-
tual frequency and the desired frequency. 2. In a
communications transceiver, the difference be-
tween the receiver frequency and the transmitter
frequency. In some modes, such as single-side-
frequency doubler band (SSB), the offset is normally zero. In other
modes, notably continuous-wave (CW) Morse
code, the offset is normally several hundred Hz.
frequency function See PROBABILITY DENSITY
frequency overlap 1. A common band of frequen-
frequency indicator 1. A device that indicates
cies between two adjacent channels in a commu-
when a phase or frequency is common to two al-
nications system. 2. A common frequency region
ternating currents. 2. The display or dial that
between two assigned bands. 3. A condition in
shows the operating frequency of a radio re-
which parts of the sidebands of two signals oc-
ceiver or transmitter. 3. See FREQUENCY ME-
cupy the same range of frequencies.
frequency pulling A change in the frequency of a
frequency keying See FREQUENCY-SHIFT KEY-
circuit, especially of a self-excited oscillator, re-
sulting from the detuning effects of an external
frequency meter An instrument for measuring the
circuit, device, or condition (such as body capac-
frequency of an alternating current. The several
itance or a change in the temperature).
different types are used in different applications.
frequency pushing An effect in which a current
change in a source oscillator causes a shift in
source frequency.
frequency quadrupler See QUADRUPLER, 2.
frequency-modulated radar See FM RADAR.
frequency quintupler See QUINTUPLER, 2.
frequency modulation Abbreviation, FM. A
frequency range 1. A communication system™s fre-
method of conveying intelligence in wireless com-
quency transmission limits, beyond which the
munications and broadcasting. The amplitude of
power output is attenuated below a specified
the carrier remains constant, and the instanta-
amount. 2. The frequency band or bands within
neous frequency varies. One scheme for obtain-
which a radio transmitter, receiver, or transceiver
ing this type of modulation is to apply the
is designed to operate.
modulating signal to a varactor in an oscillator.
frequency ratio counter See FREQUENCY RATIO
Another method is to modulate the phase of the
oscillator signal. This causes small fluctuations
frequency ratio meter A meter that indicates the
in the frequency as well, because any instanta-
ratio between two frequencies, and is useful in
neous phase change shows up as an instanta-
the quick identification of harmonics.
neous frequency change (and vice versa). Also
frequency record A phonograph test disk contain-
ing recordings of various frequencies at specified
frequency modulation deviation 1. In frequency
frequency rejection The elimination, usually by a
modulation (FM), the largest difference between
filter, of a single frequency (or narrow band of fre-
the instantaneous signal frequency and the un-
quencies) from a mixture of frequencies. Compare
modulated carrier frequency. 2. The maximum
bandwidth of an FM signal at its audio modula-
frequency relay A frequency-sensitive relay (see
tion amplitude peak.
frequency modulator 1. A circuit or device that
frequency response A performance characteristic
modulates the frequency of an oscillator. 2. The
that describes the operation of a device or circuit
modulator section of an FM transmitter.
over a specified range of signal frequencies (e.g.,
frequency monitor A device used (often continu-
the gain-versus-frequency characteristic of an
ously) to check the frequency of a signal (e.g., a
frequency-deviation meter used in radio broad-
302 frequency-response recorder • frequency-variation method

frequency-response recorder A graphic recorder frequency split 1. The difference between the re-
that automatically plots a frequency-response ceiver frequency and the transmitter frequency in
curve for a device under test. a communications repeater. 2. See FREQUENCY
frequency run A test, or test sequence, that deter- OFFSET, 2.
mines the loss characteristics of a circuit as a frequency spotting The setting-up of signals at
function of the operating frequency. reference frequencies (usually harmonics of a
frequency scanning 1. A controlled fluctuation of standard-frequency oscillator), and their use in
the transmitter frequency in a frequency-agile identifying unknown frequencies. Also see FRE-
radar or communications system. 2. In a pro- QUENCY CALIBRATOR.
grammable, digital communications receiver or frequency spread The ratio f2/f1, where f1 is the
transceiver, a form of simultaneous digital moni- lowest frequency in a given range of frequencies
toring of two or more channels. 3. The frequency- and f2 is the highest frequency. Compare FRE-
response change in a spectrum analyzer. QUENCY SPAN.
frequency scaler See SCALER. frequency stability The degree to which a fre-
frequency-selection sensor A sensor that passes quency remains constant during variations in
or rejects phenomena at certain frequencies while temperature, current, voltage, and similar fac-
ignoring those at other frequencies. tors. It is specified in Hertz (Hz), kilohertz (kHz),
frequency-selective relay See SELECTIVE RE- or megahertz (MHz), or in parts per million per
LAY, 1. unit of the variable parameter.
frequency-sensitive bridge A bridge, such as the frequency standard A signal source of a precise
Wien bridge or resonance bridge, that can be bal- frequency, against which other signal sources
anced at only one frequency for a given set of can be calibrated. See specifically PRIMARY FRE-
bridge-arm values. QUENCY STANDARD and SECONDARY FRE-
frequency separator In a television receiver, the QUENCY STANDARD.
circuit that separates horizontal- and vertical- frequency sum In a beat-frequency system, the
scanning sync pulses. quantity f1 + f2, where f1 is the lower frequency
frequency-shift keying Abbreviation, FSK. A and f2 is the higher frequency. Compare FRE-
method of digital signal transmission. The logic 1 QUENCY DIFFERENCE, 2.
(high or mark) pulses are sent at a specific carrier frequency swing See FREQUENCY DEVIATION, 1,
frequency, and the logic 0 (low or space) pulses 2.
are transmitted at another frequency slightly frequency synthesizer A generator of signals at a
higher or lower than the logic 1 pulses. This is precise frequency or set of frequencies, generally
the most primitive form of frequency modulation adjustable in discrete frequency steps. It is used
(FM). The difference between the mark and space for test or communications purposes. The signals
frequencies is called the shift, and is usually are derived from a single-frequency source, usu-
between 100 and 1000 Hz. Compare ally a crystal oscillator. Also see SIGNAL SYN-
frequency tolerance The acceptable amount by
which a frequency can vary from its intended
value. The tolerance can be specified as a per-
centage of the stated frequency, a certain number
of parts per million, or a certain number of hertz
(Hz), kilohertz (kHz), or megahertz (MHz). Exam-
ple: 3.675000 MHz ±10 Hz.
frequency-to-voltage converter A device or cir-
cuit that delivers an output voltage that is pro-
portional to the input frequency.
frequency translation 1. The conversion of a
given frequency band from one part of the elec-
tromagnetic spectrum to another, without chang-
ing the actual separation of channels or the
overall width of the band. 2. See FREQUENCY
frequency transmission The passage of a fre-
frequency-shift radar See DOPPLER RADAR.
quency or band of frequencies from a mixture of
frequency span The difference f2 “ f1, where f1 is
frequencies through a filter or other circuit. Com-
the lowest frequency in a given range of frequen-
cies and f2 is the highest frequency. Compare
frequency tripler See TRIPLER, 2.
frequency-variation method A method of deter-
frequency spectrum All electromagnetic radia-
mining the figure of merit (Q) of a tuned circuit by
tion, from longest to shortest wavelengths, within
varying the frequency of the applied test voltage
a set of specified limits.
frequency-variation method • ft

from resonance (fr ) to a high point (f2) and a low verter portion of a superheterodyne communica-
point (f1). At the high and low points, the circuit tions receiver (i.e., the RF amplifier, first detector,
voltage is 0.707 times the voltage at resonance. and local oscillator). Compare REAR END.
The figure of merit then is calculated from the for- front layer photocell See RECTIFIER PHOTO-
mula Q = fr/(f2 “ f1). CELL.
frequency-voltage converter See FREQUENCY- front porch In a television horizontal sync pulse,
TO-VOLTAGE CONVERTER. the interval between the end of the sync pulse
frequency-wavelength conversion See WAVE- and the fall of the blanking pedestal. Compare
fresnel (A.J. Fresnel, 1788“1827) A unit of fre- front projection In big-screen video, a scheme in
quency equal to 1012 Hz. Also called terahertz and which the images from a set of bright cathode-ray
abbreviated THz. tubes (CRTs) are projected onto a reflective
fresnel lens A usually square plastic sheet with screen, in a manner similar to the way the film is
progressively thicker concentric areas; its effect is projected in a movie theater.
similar to that of an automotive headlight lens. front-surface mirror Also called first-surface mir-
Fresnel number A measure of the relative effects of ror. A mirror that has its reflective material on the
diffraction in an optical lens. The Fresnel number front, instead of on the back.
is equal to the radius of the lens divided by the front-to-back ratio Abbreviation, f/b. An ex-
product of the light wavelength and the lens focal pression of the ability of a unidirectional an-
length, all measured in the same units. tenna to concentrate its radiation or response in
Fresnel region For a radio-frequency transmitting its favored direction. This specification is nearly
antenna, the zone between the antenna and the always given in decibels (dB). The field strength
FRAUNHOFER REGION. The size of the Fresnel in the favored direction is compared with the
region depends on the wavelength of the radiated field strength exactly opposite the favored direc-
energy. tion at the same distance from the antenna in
friction The resistance to mechanical motion when free space, at the same frequency, and with the
one material is rubbed against another. Friction same power applied to the antenna feed point.
was one of the earliest sources of human-made Measurements can be made with a calibrated
electricity (see FRICTIONAL ELECTRICITY and field-strength meter. Compare FRONT-TO-
ELECTRIC MACHINE). Electrical resistance, op- SIDE RATIO.
posing the flow of current, is analogous to fric- front-to-side ratio Abbreviation, f/s. An expres-
tion. sion of the directivity of a unidirectional or bidi-
frictional electricity Static electricity generated rectional antenna system. This specification is
by rubbing one material against another. nearly always given in decibels (dB). The field
frictional electric machine See ELECTRIC MA- strength in the favored direction(s) is compared
CHINE. with the field strength at right angles to the fa-
frictional error The change in parameters of a vored direction(s) at the same distance from the
phonograph pickup, resulting from friction with antenna in free space, at the same frequency, and
the disk surface. with the same power applied to the antenna feed
frictional loss A decrease or impairment in the ef- point. Measurements can be made with a cali-
ficiency with which energy is converted into use- brated field-strength meter. Compare FRONT-
ful work, caused by friction between moving TO-BACK RATIO.
parts. frost alarm A device or circuit that responds to the
fringe area The region in which a signal falls to the presence of frost and actuates an alarm. Such
minimum field strength necessary for satisfactory alarms are sensitive to temperature, moisture, or
communication. both.
fringe howl In a regenerative detector, a howling FRUGAL Acronym for FORTRAN rules used as a
sound that occurs when the transistor first be- general applications language.
gins to oscillate, obscuring the signal. The term is FRUSA Acronym for flexible rolled-up solar array,
used because the circuit is operated at the fringe such as the type used in spacecraft and commu-
of oscillation. nications satellites.
fringing See EDGE EFFECT. F scan In radar operations, a display in which a
Fritch Trade name (American Telephone & Tele- central blip represents the target at which the
graph Co.) for frequency-selective switch. antenna is pointed; horizontal and vertical
fritting A condition in which electrical contact cor- displacement of the blip indicate corresponding
rosion creates a small hole, through which horizontal and vertical aiming errors.
molten contact material passes to form a conduc- FSK Abbreviation of FREQUENCY-SHIFT KEYING.
tive bridge. FSM Abbreviation of FIELD-STRENGTH METER.
front contact The movable contact of a relay. FS meter See FIELD-STRENGTH METER.
front end 1. The first radio-frequency (RF) amplifier FSR Abbreviation of feedback shift register.
stage in a radio or television receiver. 2. The con- ft Abbreviation of foot or feet.
304 FT-cut crystal • full-scale sensitivity

tank, and/or the extent to which the tank is full
FT-cut crystal A piezoelectric plate cut from a
(fraction or percentage).
quartz crystal at an angle of +57°, with respect to
fuel meter See FUEL GAUGE.
the z-axis. Also see CRYSTAL AXES and CRYS-
fuel-pressure indicator An instrument for mea-
suring fuel pressure in pipes or other channels.
ft-Lb Abbreviation of FOOT-LAMBERT.
fuel-pressure meter See FUEL-PRESSURE INDI-
ft-lb Abbreviation of FOOT-POUND.
Fuchs antenna A simple antenna consisting of a
full adder In a digital computer, an adder circuit
single-wire radiator without feeder or transmis-
that can handle the carry signal, as well as the bi-
sion line, connected directly to the transmitter. It
nary elements that are to be added. Also see
is usually an odd multiple of 0.25 wavelength
long. When a good radio-frequency (RF) ground is
full bridge A bridge-rectifier circuit in which each
used, this antenna can be effective at high fre-
of the four arms contains a diode. By comparison,
quencies, although part of its radiated field is of-
the three-quarter bridge contains a resistor in
ten inside the transmitter building.
one arm; the half bridge, resistors in two arms;
and the quarter bridge, resistors in three arms.
full-duplex system In data communications, a
system that transmits data in both directions si-
multaneously and continuously. Compare HALF-
full-focus yoke See COSINE YOKE.
fullhouse A multichannel radio-control model
plane system that allows the use of a realistic
complement of working control surfaces.
full-load current The output current from a
source when the load is maximum (that is, the
element: load resistance is minimum).
odd multiple full-load power The power drawn from a source
of »/4 when the load is maximum (that is, the load re-
sistance is minimum).
full-load voltage The output voltage of a source
when full power is drawn [i.e., when the load is
maximum (that is, the load resistance is mini-
Fuchs antenna
full-load wattage See FULL-LOAD POWER.
full-power frequency response The highest fre-
quency at which a signal can fluctuate at full volt-
fuel alarm A sensing circuit that actuates an
age (peak-to-peak) without causing distortion of
alarm when the fuel in a tank or reservoir falls to
more than a certain specified amount.
a prescribed level.
full-range speaker See MONORANGE SPEAKER.
fuel cell A generator that produces electricity di-
full scale 1. The operating range of an instrument.
rectly from a reaction between fuel substances,
2. In an analog meter, the quantity indicated by
such as hydrogen and oxygen.
maximum deflection of the needle (usually at the
fuel-flow alarm An electronic circuit that actuates
extreme right-hand end of the calibrated scale).
an alarm when fuel flow changes from a pre-
3. Transducer output as a function of highest al-
scribed value.
lowable input stimulus.
fuel-flow control A servo system that automati-
full-scale current Symbol, IFS. In a digital-to-
cally maintains or corrects the flow rate of a fuel.
analog converter, the maximum current that can
fuel-flow gauge See FUEL-FLOW METER.
occur at the output.
fuel-flow indicator See FUEL-FLOW METER.
full-scale error For an electrical indicating instru-
fuel-flow meter An instrument for measuring fuel
ment, the rated full-scale input signal minus the
flow rate.
actual input signal that causes a full-scale deflec-
fuel-flow switch A switch that is actuated by fuel
tion. Thus, the predictable error in an instrument,
flowing in pipes or other channels.
expressed as a percentage of the full-scale reading.
fuel gauge An instrument consisting of a trans-
full-scale frequency Generally expressed in Hertz
ducer that senses the level of liquid fuel in a tank
(Hz) or kilohertz (kHz). The maximum frequency
and delivers a proportional output current or
at which a voltage-to-frequency converter can op-
voltage, and an electric meter whose needle is de-
erate while remaining within its specifications.
flected in proportion to the current or voltage
full-scale sensitivity The current, voltage, or
and, therefore, to the fuel level. Alternatively, the
power required to deflect a meter mechanism to
meter can be a direct-readout digital device,
full scale.
showing the number of gallons remaining in the
full-scale symmetry • function generator

full-scale symmetry Expressed in microamperes sionally some odd shape. The most efficient con-
(mA). The mathematical difference between the figuration is the circular loop. Maximum radia-
full-scale current outputs in a complementary- tion occurs perpendicular to the plane of the loop.
output digital-to-analog converter. full-wave rectifier A rectifier that delivers a half-
full track A recording track covering the full width cycle of pulsating direct-current (dc) output
of a magnetic tape. voltage for each half-cycle of applied alternating-
full-track head A tape-recorder head having a gap current (ac) voltage. The successive output
that covers the full width of the tape. half-cycles have the same polarity. See, specifi-
full-track recording Usually applicable to quarter- cally, BRIDGE RECTIFIER and FULL-
inch or narrower magnetic recording tape, a one- WAVE, CENTER-TAP RECTIFIER. Compare
track recording made by a head that magnetizes HALF-WAVE RECTIFIER.
essentially the entire width of the tape. full-wave vibrator 1. In a vibrator-type power sup-
full-wave bridge rectifier See BRIDGE RECTI- ply, an interrupter that closes contacts on both
FIER. ends of its swing, thus causing direct current (dc)
full-wave, center-tap rectifier A circuit in which to flow through the transformer in alternate di-
the center-tapped secondary winding of a trans- rections. 2. A vibrator-type rectifier that closes in
former operates two rectifier diodes, each on an both directions.
alternate half-cycle of secondary voltage. The fre- full-wave voltage doubler A voltage-doubler cir-
quency of the ripple in the direct-current (dc) out- cuit whose direct-current (dc) output has a ripple
put is equal to twice the alternating-current (ac) of twice the alternating-current (ac) supply fre-
input frequency. Compare BRIDGE RECTIFIER. quency. Compare HALF-WAVE VOLTAGE DOU-
function 1. A mapping between two sets of quanti-
ties or points A and B, such that: (1) For each y in
Pulsating B, there exists at least one corresponding x in A;
dc out and (2) For each x in A, there exists exactly one y
ac in B. In this case y is said to be a function of x;
in this can be written as y = f (x). The set A is called
the domain of f; the set B is called the range of f.
2. A mathematical expression, using symbols, re-
lating variables (e.g., the expression x - y = z is a
full-wave, center-tap rectifier function of variables x, y, and z). 3. The behavior
and application for which a device or system is
designed. 4. Part of a computer instruction spec-
full-wave detector A detector circuit using two
ifying the operation to be done.
diodes in a full-wave, center-tap rectifier configu-
functional blocks Combinations of substances or
components that perform specific tasks in an
full-wave doubler See FULL-WAVE VOLTAGE
electronic circuit. An example is a tuned circuit,
containing inductive reactance, capacitive reac-
full wavelength Symbol, ». The distance that cor-
tance, and resistance.
responds to 360 degrees of phase as an electro-
functional character See CONTROL CHARACTER.
magnetic (EM) field is propagated. In free space, it
functional design Design specifications encom-
is related to the frequency by a simple equation:
passing a description of how system elements will
L ft = 984/f interrelate, and what their logic design will be.
where L ft represents » in feet, and f represents the functional diagram FUNCTIONAL DESIGN repre-
frequency in megahertz. If » is expressed in me- sented in graphic form; that is, as an illustration
or set of illustrations.
ters, then the formula is:
functional electronic block Abbreviation, FEB. A
L m = 300/f
complete integrated circuit. See INTEGRATED
Where L m represents the displacement in meters. CIRCUIT.
In general, if ν is the velocity factor (expressed as functional end (FE) point In a system operating
a ratio) in a given medium, then: from a battery power supply, the lowest voltage at
which the equipment will properly operate. As a
L ft = 984ν/f
battery discharges, the voltage decreases; when
the voltage drops to the FE point, the battery
L m = 300ν/f must be replaced or recharged.
functional test A performance test of a device or
circuit, to see that it behaves as intended in the
environment in which it is to be used.
full-wave loop antenna A loop antenna with a cir-
function generator 1. A signal generator whose
cumference of one wavelength, fed at a break. The
output is any of several selectable waveforms
loop can be circular, square, triangular, or occa-
306 function generator • fV

(e.g., sine, square, triangular, step-pulse) and fre- fuse A safety device consisting of a wire of low-
quencies (or repetition rates). 2. An analog com- melting-point metal. When current passing
puter circuit that produces a variable based on a through the wire exceeds a prescribed (safe) level,
mathematical function and one or more input the resulting heat melts the wire and opens the
variables. circuit, protecting equipment from damage. See
function key 1. In digital communications, a key- PROXIMITY FUSE.
board key used to control the form in which a fuse box A set of electrical fuses, usually enclosed
message will be received. 2. On a computer key- in a metal box.
board, any of 12 keys (usually designated F1 fused junction In a semiconductor, a junction pro-
through F12) that activates special functions. duced by alloying metals to the semiconductor
The precise action of a given key depends on the material.
program being run. fused junction See ALLOY JUNCTION.
function polling A polling technique in which a fuse resistor See FUSIBLE RESISTOR.
disabled device signals its condition and specifies fuse wire The low-melting-point wire used in
the remedy. fuses. See FUSE.
function switch In a multifunction instrument, fusible resistor A low-value resistor that also
such as a voltohm-milliammeter, the switch that serves as a fuse in certain appliances, such as
permits selection of the various functions. television receivers.

function table 1. A table of mathematical function fusing current The specified current level at which
values. 2. Hardware or software that translates a wire of a given diameter and material composi-

one representation of information into another. tion will melt.
3. A routine that allows a computer to use the fusion 1. In acoustics, pertaining to delayed or
values of independent variables to determine the reflected waves that arrive within approximately
value of a dependent variable. „25 of a second of the direct wave. So called be-
fundamental Contraction of FUNDAMENTAL FRE- cause the human ear/brain “fuses” (blends)
QUENCY. sounds together when they are separated by
less than about 1„25 second. If the delay is longer,
fundamental component The FUNDAMENTAL
FREQUENCY of a complex wave. the ear/brain usually perceives an echo in-
fundamental frequency 1. The lowest frequency stead. 2. In a nuclear reaction, the uniting of

in a complex wave containing harmonic energy. two atomic nuclei, accompanied by the release
2. In a radio or television transmitter, the in- of energy.
tended frequency of operation. 3. In acoustics future labels In a computer system, program in-
and audio applications, the predominant pitch of struction labels that refer to locations not desig-
a musical tone. nated as absolute addresses by a compiler or
fundamental group A set of trunk lines in a tele- assembler.
phone system, through which zone centers are futurist A person who tries to anticipate or predict,
interconnected. based on current technology and trends, what
fundamental mode See DOMINANT MODE. will be accomplished in a given field in the next
fundamental suppression Removal of the funda- several years or decades.
mental frequency from a complex wave, leaving fuzz A form of deliberate distortion in the waveform
only the harmonics, as in the operation of a null produced by an electric guitar.
network adjusted to the fundamental frequency. fuzzbox A circuit that distorts the waveform pro-
fundamental units Base units of an absolute sys- duced by an electric guitar, for the purpose of cre-
tem of units. Example: the meter (m), the kilo- ating various musical sound effects.
gram (kg), and the second (s) in the mks system. fuzz buster Slang for a specialized mobile radio re-
fundamental wavelength The wavelength that ceiver, used by drivers of vehicles to signal the
corresponds to the FUNDAMENTAL FREQUENCY presence of law-enforcement radar equipment.
of a wave or signal. fV Abbreviation of femtovolt.

gain bandwidth product Symbol, fT. The fre-
G 1. Symbol for CONDUCTANCE. 2. Abbreviation
quency at which the gain of a bipolar transistor is
of GIGA-. 3. Symbol for DEFLECTION FACTOR.
equal to 1 (no amplification or loss) in the
4. Symbol for PERVEANCE. 5. Symbol for GRAV-
common-emitter configuration. The f T represents
an absolute upper limit for the frequency at
TOR. 7. Symbol for GATE. 8. Abbreviation for
which a bipolar transistor will works as an
amplifier. Any attempt to design an amplifier
g 1. Symbol for CONDUCTANCE. 2. Abbreviation
using a bipolar transistor at a frequency higher
of GRAM. 3. Subscript for GATE. 4. Subscript for
than its fT will inevitably fail. Compare ALPHA
GA Radiotelegraph abbreviation of “Go ahead.”
gain control 1. To adjust the gain of an amplifier.
G/A Abbreviation of ground-to-air.
2. A potentiometer used to adjust amplifier gain.
Ga Symbol for GALLIUM.
GaAs 1. Formula for gallium arsenide. 2. Pertain-
ing to semiconductor devices based on gallium +
GA coil A special form of coil, wound with extra
space among the turns to reduce the distributed
gadget 1. A device or component. 2. A superfluous
or makeshift device.
gadolinium Symbol, Gd. A metallic element of the
rare-earth group. Atomic number, 64. Atomic
weight, 157.25.
gage See GAUGE.
gain The extent to which a component, circuit, de-
vice, or system increases current, voltage, or
power. Applicable especially to active devices,
gain control
such as transistors and integrated circuits (ICs),
and to amplifiers and filters that use them. Also
gain function A function between two currents or
used to express the directional properties of some
voltages in a circuit with gain.
antenna systems. Usually specified in decibels
gain-level linearity The quantitative measure of
the extent to which the gain of a device depends
on the signal level. The level is found by compar-

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308 gain-level linearity • gamma rays

ing the output to the input level over a range of human) skin. This phenomenon is a useful indi-
input signal levels. cator in physiology, psychology, and criminology.
gain reduction The drop in gain of an amplifier at galvanic taste A sharp, metallic taste experienced
high- and low-frequency extremes. when a small electric current is passed through
gain sensitivity control See DIFFERENTIAL GAIN the tip of the tongue.
CONTROL. galvanism (After Luigi Galvani, 1737“1798) The
gain stability The degree to which the gain of a production of an electric current by chemical ac-
system remains constant during changes in re- tion, as in a battery.
lated factors, such as temperature, supply power, galvanize To coat steel with zinc to forestall corro-
and loading. sion.
gain temperature coefficient The extent to which galvanometer A sensitive, bi-directional current
the full-scale current varies over a certain tem- meter. Used in various electrical tests”especially
perature range, expressed in parts per million per as a null indicator in bridge operation. Also see
degree Celsius (ppm/°C). MICROAMMETER.
galactic noise Radio noise propagated from the galvanometer constant The number by which a
plane of our galaxy, and especially from the cen- galvanometer reading must be multiplied in order
ter, located in the direction of the constellation to obtain the current in microamperes, mil-
Sagittarius. It is of significance in space commu- liamperes, or amperes.
nications and radio astronomy. galvanometer recorder A graphic recorder in
galena Formula, PbS. Natural lead sulfide, which which a mirror in a movable-coil galvanometer re-
in nature takes the form of bluish-gray, cubical flects a beam of light to a passing strip of photo-
crystals. graphic film.
gallium Symbol, Ga. Atomic number, 31. Atomic galvanometer shunt A resistor placed in parallel
weight, 69.72. One of the constituents of the with a galvanometer to decrease its sensitivity.
semiconductor compound GALLIUM ARSENIDE. Also see SHUNT RESISTOR.
gallium arsenide Formula, GaAs. A compound of galvanometry The use of galvanometers to deter-
gallium and arsenic, used as a semiconductor mine the intensity and direction of electric cur-
material. It is noted for its low-noise characteris- rents.
tics. galvanoplastics The science of ELECTROPHO-
gallium-arsenide diode A diode in which the semi- RESIS and ELECTROPLATING.
conductor material is processed gallium ar- galvanoscope An instrument for detecting and
senide. showing the direction of very weak electric cur-
gallium-arsenide varactor A low-noise, micro- rents.
wave varactor in which the semiconductor mate- galvanotherapy The use of electric currents to
rial is gallium arsenide. produce heat in the body of a human or animal.
gallium-phosphide diode A light-emitting diode in gamma ferric oxide A form of coating used in for-
which the semiconductor material is processed mulation of magnetic recording tape.
gallium phosphide. gamma match A linear transformer for matching
galloping ghost A form of radio-control system in an unbalanced (usually coaxial) feed line to a bal-
which the elevation and rudder can be moved to anced (usually half-wave) antenna. The outer
the desired extent. conductor of the cable is connected to the center
Galton whistle A device for producing high- of the radiator, and an extension of the center
frequency acoustic waves (ultrasound), similar to conductor runs for a short distance parallel to the
a common dog whistle. radiator, making a right-angle bend before con-
galvanic cell Generic term for any electrochemical necting to the radiator.
primary voltaic cell.
galvanic corrosion Corrosion that occurs on one Radiator
of two dissimilar metals when they are immersed
in an electrolyte. Caused by battery action be-
tween them. Compare ELECTROLYTIC CORRO-
galvanic couple See VOLTAIC COUPLE.
galvanic current A very small direct current such
as that produced by dissimilar metals in acid or section
feed line
by nervous reaction in living tissue.
galvanic pile See VOLTAIC PILE.
gamma match
galvanic series A list of metals and alloys arranged
in order of the most to least likely to oxidize in a
gamma rays High-energy, ionizing radiation emit-
given environment.
ted by radioactive substances; similar to X rays,
galvanic skin response Abbreviation, GSR. The
but of a shorter wavelength.
variations in electrical resistance of the (usually
gamma section • gaseous voltage regulator

gamma section See GAMMA MATCH. the M-valence band and the N-conduction band
gang To mechanically couple components (pots, in a material).
switches, etc.) for operation by a single knob. gap filling Modification of an antenna for the
gang capacitor A variable capacitor consisting of purpose of eliminating nulls in the directional
sections mounted on the same shaft for simulta- pattern.
neous variation. It is usually specified by the gap insulation See SLOT INSULATION, 1, 2.
number of sections (e.g., four-gang capacitor). gap loss In a reproducing head, the loss that oc-
Compare GANGED CAPACITORS. curs because of the GAP DEPTH.
ganged capacitors Separate variable capacitors gap-type protector A spark gap used to protect
mechanically connected together (e.g., by belt or equipment from high-voltage transients.
gear drive) for simultaneous variation. Compare gap voltmeter See NEEDLE GAP and SPHERE
ganged potentiometers Separate potentiometers gap width In a magnetic recording head, the width
mechanically connected together (e.g., by belt or of the gap (taken parallel with the face). Compare
gear drive) for simultaneous variation. Compare GAP DEPTH.
GANG POTENTIOMETER. garbage 1. In digital computer operations, a collo-
ganged rheostats See GANGED POTENTIOME- quialism for useless or incorrect data. 2. Collo-
TERS. quialism for unreadable signals or severe
ganged switches Separate switches mechanically intermodulation in a radio communications cir-
connected together for simultaneous operation. cuit. 3. Colloquialism for an unsound theory.
Compare MULTISWITCH. garble 1. Garbled matter. 2. Also called scramble.
ganged tuning Simultaneous tuning of separate To purposely render communications or data un-
circuits by means of ganged capacitors or ganged intelligible to everyone, except the intended recip-
potentiometers. ient(s). See SCRAMBLER CIRCUIT.
gang potentiometer A potentiometer consisting garbled matter Confused communications or
of sections mounted on the same shaft for si- data, usually resulting from distortion in a circuit
multaneous variation. Usually specified accord- or system. Also called GARBLE.
ing to the number of sections (e.g., dual garbler See SCRAMBLER CIRCUIT.
potentiometer). garnet maser A maser that uses natural or syn-
gang printer In digital computer and data process- thetic garnet as the stimulated material. Also see
ing operations, an electromechanical printer ca- YTTRIUM-IRON-GARNET.
pable of printing an entire line at one time. gas One of the states of matter, characterized by
gang punch 1. To punch identical or nonvarying molecules that are widely separated and are in
information into the cards of a group. 2. A ma- continual, relatively rapid motion. Because it is a
chine for this operation. fluid, a gas will readily conform to a container of
gang rheostat See GANG POTENTIOMETER. any shape. Gases can readily be compressed and
gang switch See MULTISWITCH. liquefied. Compare LIQUID, PLASMA, and SOLID.
Gantt chart A chart of activity versus time used in gas amplification In a radiation-counting device,
industry as an aid in making decisions regarding the ratio, in decibels, of the charge collected to
the allocation of resources for specific activities the charge produced in the gas.
[e.g., as applied to PERT (project evaluation and gas breakdown The ionization of a gas by means of
review techniques)]. high voltage. The intensity of the electric field pre-
gap 1. A space between electrodes or magnetic vents recombination of ions. Collisions among
poles. 2. A device consisting essentially of sepa- atoms cause further ionization. Thus, the gas be-
rated electrodes (e.g., spark gap). 3. A relatively comes a good conductor of current.
narrow space cut in iron cores to provide a break gas cell A cell whose operation depends on gas ab-
in a magnetic circuit. Also see SLOT, 1. 4. The sorption by the electrodes.


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