. 34
( 42)


TANCE. smaller unit described in 1, when self-contained
secondary kVA The kilovolt-amperes in the sec- and operated independently (e.g., filter section).
ondary circuit of an operating transformer. Com- 3. See PROGRAM SEGMENT.
pare PRIMARY KVA. sectionalized antenna A set of collinear radiating
secondary power The power in the secondary cir- elements, placed end-to-end with reactances be-
cuit of a transformer. Also see SECONDARY KVA tween them, for the purpose of modifying the ra-
and SECONDARY VA. Compare PRIMARY POWER. diation pattern.
secondary radiation 1. The (sometimes random) sectionalized winding 1. A method of winding a
reradiation of electromagnetic waves, as from a coil in complete, multilayer sections that are
receiving antenna. 2. Rays emitted by atoms or stacked side by side or top to bottom, a technique
molecules when the latter are struck by other ra- that reduces distributed capacitance. 2. A coil
diation. wound, as defined in 1.
secondary rays Rays emitted by atoms or mol- sector On a magnetic disk, a specific portion of a
ecules that have been bombarded by other rays of track.
the same general nature. Examples: secondary X sectoral horn antenna An (usually sheetmetal)
rays and secondary beta rays. antenna with the shape of a horn of rectangular
secondary resistance The direct-current resis- cross section. It is flared in one dimension only.
tance of the secondary winding of a transformer.
secondary standard An accurate source of a
quantity (capacitance, frequency, inductance, re-
sistance, etc.), that is referred periodically to a
primary standard for correction.
secondary storage In computer and data-process-
ing operations, storage that is auxiliary to the
main storage. Also called backing storage.
secondary turns The number of turns in the sec-
ondary winding of a transformer. Compare PRI-
secondary utilization factor For a transformer in
a rectifier circuit, the utility factor of the sec-
ondary winding (ratio of direct-current power out-
put to secondary volt-amperes). Maximum
secondary VA The volt-amperes in the secondary radiation/response
circuit of a transformer. Compare PRIMARY VA.
secondary voltage The voltage across the sec- Flared
ondary winding of a transformer. Also called
secondary winding The normal output winding of
sectoral horn antenna
a transformer. Also called SECONDARY COIL.
second breakdown In a large-area power transis- sector display In a radar, a display that allows the
tor, a destructive breakdown caused by thermal continuous observation of a portion of the
runaway. scanned area.
second-breakdown voltage The collector voltage at secular equilibrium The state in which a radioac-
which second breakdown occurs in a transistor. tive substance changing into another substance
secular equilibrium • selective fading

is decaying as fast as the second substance is be- segment mark A character indicating the division
ing formed. between tape file sections.
secular variation A slow change in the intensity of segue (Pronounced SEG-way.) A smooth transition
the terrestrial magnetic field. from one sound or channel to another (e.g., be-
secure mode In a security system, the condition of tween musical selections in a radio broadcast).
being fully activated. The first selection decreases in volume as the sec-
securite In radiotelephony, a spoken word (pro- ond selection increases. There is some overlap.
nounced say-kyoor-ee-tay) identifying a trans- Seignette salt See ROCHELLE SALT.
mission concerning safety. Equivalent to TT in seismic detector A vibration sensor used in some
radiotelegraphy. types of intrusion-detection systems.
security code 1. A set of alphanumeric characters seismogram A record produced by a SEISMO-
(letters and/or numbers) or switch settings that GRAPH.
activates or deactivates a security system. 2. See seismograph An instrument for detecting and
PASSWORD. recording earth tremors. Indicates the direction,
security robot In a smart home, a robot that as- magnitude, and time of a quake.
sists in protection of a home or business, and its seismometer See SEISMOGRAPH.
occupants, from intrusion, burglary, or attack. If seismoscope An instrument that shows the occur-
an intruder enters the property, the security rence and time of an earthquake. Compare SEIS-
robot might drive the offender away or detain the MOGRAPH.
offender until police arrive. The robot might em- select To accept or separate a unit, quantity, or
ploy iris-print detection or facial feature detection course of action from all those available (in a
to identify an intruder from a distance. The robot group, mixture, or series).
would be linked to the home computer via a selectance 1. For a resonant circuit, the ratio
broad-bandwidth, high-speed wireless system. Er/Ex, where Er is the voltage at resonance, and
Compare SENTRY ROBOT. Also see SMART Ex is the voltage at a specified nonresonant fre-
HOME OR BUSINESS. quency. 2. For a receiver, the figure S2/S1, where
security system A set of electronic (and some- S1 is the sensitivity of the receiver in a given fre-
times also electromechanical) devices designed to quency channel, and S2 is the sensitivity in an-
do one or more of the following: restrict access to other specified channel.
a premises or computer system, detect abnormal selected mode In an encoder, a mode in which one
conditions, detect unauthorized entry, alert hu- output is read and the others are ignored.
man operators of abnormal conditions, alert own- selective Pertaining to a device or system, such as
ers and/or authorities of unauthorized entry to a a radio receiver, with a high degree of SELECTIV-
premises, and (in some cases) provide physical ITY.
protection of property. selective absorption The attenuation or absorp-
Seebeck effect The development of an electromo- tion of some frequencies or bands of frequencies,
tive force in a junction of two dissimilar metals with little or no attenuation at other frequencies
(a thermocouple) when the temperature of the or bands of frequencies.
junction is different from that of the rest of the selective amplifier An amplifier that can be
metal. tuned, with the desired degree of sharpness, to a
Seebeck emf The electromotive force resulting single frequency or band of frequencies. Radio-
from the Seebeck effect. frequency amplifiers are generally tuned by
seed crystal A small single crystal from which a means of inductance-capacitance (LC) circuits;
larger single crystal (e.g., germanium or silicon) is audio-frequency amplifiers are usually tuned by
grown. Also see CZOCHRALSKI METHOD. means of resistance-capacitance (RC) circuits.
seeing-eye robot A robot that serves in the capac- selective calling The calling, alerting, or alarming
ity of a seeing-eye dog, to help visually impaired of a desired station without interfering with other
people in their daily activities. stations.
seek See SEARCH. selective compliance assembly robot arm Abbre-
seek area An area of direct-access storage to which viation, SCARA. An electromechanical device de-
are assigned specific records and from which the signed especially for use in assembly lines. It
records can be accessed quickly. uses cylindrical coordinate geometry to allow pre-
segment 1. The portion of a line or curve lying be- cise, programmable movements in three dimen-
tween two points. 2. See PROGRAM SEGMENT. sions.
segmental meter An expanded-scale meter (see selective dump In computer operations, a dump
SCALE EXPANSION). (see DUMP) affecting a small, specific memory
segmented encoding law An approximation of a area.
smooth encoding law, done by means of linear selective fading Fading caused by propagation
partitions or segments. The greater the number of conditions, whose effects differ at slightly differ-
segments, the more accurate the approximation. ent frequencies. In an amplitude-modulated sig-
segmenting See PARTITIONING. nal, this effect causes the sidebands and carrier
616 selective fading • self-excited oscillator

to arrive in various phase relationships, with re- selenium rectifier A disk- or plate-type power rec-
sulting distortion in the received signal. tifier utilizing the junction between selenium and
selective interference Interference confined to a aluminum or selenium and iron.
narrow band of frequencies. self-bias For a transistor or vacuum tube, input-
selective polarization See POLARIZATION SE- electrode bias voltage resulting from the flow of
LECTIVITY. output-electrode current through a resistor com-
selective reflection In the reflection of electrons mon to both circuits. Also called AUTOMATIC
directed into a crystal by means of an electron BIAS.
gun, the tendency of the electrons to be reflected
more readily when they strike the crystal at cer-
tain speeds.
selective relay 1. A relay or relay circuit tuned to
open or close at one signal frequency. 2. A relay
or relay circuit adjusted to open or close at one
value of current or voltage.
selective trace In computer operations, a diagnos-
tic program used to analyze certain areas of
memory or specific kinds of program instruc-

tions, for debugging purposes.
selectivity 1. The ability of a circuit or device to

pass signals of one frequency and reject signals
at other frequencies. 2. The degree to which a cir- self-bias
cuit or device passes signals of one frequency and
rejects signals at other frequencies.
selectivity control In some equipment (such as self-capacitance The inherent internal capaci-
receivers, crystal filters, wave analyzers, and vi- tance of a device other than a capacitor.
bration meters) an adjustment that permits vari- self-checking number A number whose digits
ation of selectivity. have a value that determines the check digit at-
Selectoject A fully electronic, continuously tun- tached to it; thus, it can be verified following its

able, notcher-peaker that is resistance-capaci- transfer between storage locations or peripherals.
tance tuned. The name is an acronym for select or self-cleaning contacts Switch or relay contacts
reject. that clean themselves automatically by means of
selector 1. A channel switch in a radio or televi- wiping action.
sion receiver. 2. See SELECTOR SWITCH. self-contained device A device containing all
selector channel In data-processing and com- parts and sections (e.g., main circuit, power sup-
puter systems, a data transmission channel con- ply, meter, loudspeaker, etc.) needed for full oper-
trolling the information flow between peripherals ation (i.e., no auxiliary equipment is needed).
and a central processing unit. self-controlled oscillator See SELF-EXCITED OS-
selector pulse In digital communications, an iden- CILLATOR.
tifying pulse that represents a certain group of self discharge The tendency of an electrochemical
bits or data. cell or battery to gradually lose stored energy
selector relay A device, such as a stepping switch, when not in use.
that actuates one of a number of available cir- self-discharge rate A quantitative expression of
cuits on receipt of a predetermined number of the speed with which SELF DISCHARGE occurs
pulses. in an electrochemical cell or battery when it is
selector switch A (usually rotary) multiposition stored without being used.
self-energy Symbol, E. The energy mc2, in joules,
switch that allows an operator to select from
among several options (such as frequency chan- of a particle traveling at the speed of light c
(2.9979 — 108 meters per second) and whose
nels, frequency bands, or selective filters).
selenium Symbol, Se. A nonmetallic element. mass is m kilograms.
Atomic number, 34. Atomic weight, 78.96. It is self erasing In a magnetic tape, the unwanted
used in the manufacture of some diodes, recti- erasing of data near a highly magnetized region.
fiers, and photocells. self-excited generator An alternating-current
selenium cell A photoelectric cell that uses spe- generator in which the field coils are supplied
cially processed selenium as the light-sensitive with direct current produced by the machine it-
material. It can be operated as a photoconductive self. Compare SEPARATELY EXCITED GENERA-
cell or a photovoltaic cell. TOR.
selenium diode A junction diode in which the self-excited oscillator An oscillator consisting of
semiconductor material is specially processed se- an amplifier that supplies its own input signal
lenium. Also see JUNCTION DIODE. through positive feedback, and whose oscillation
selenium photocell See SELENIUM CELL. frequency depends entirely on circuit constants,

self-excited oscillator • self-sustained oscillations

such as the capacitance and inductance in a tank self-organizing Pertaining to a computer or sys-
circuit. Compare CRYSTAL OSCILLATOR, FORK tem that can change the arrangement of data files
OSCILLATOR, HUMMER, and MAGNETOSTRIC- for particular purposes.
TION OSCILLATOR. self-powered device A device that requires no ex-
ternal source of power (i.e., it is equipped with a
self-contained battery or a generator).
self-pulsing blocking oscillator A blocking oscil-
lator that produces a train of radio-frequency
self-quenching detector A super-regenerative de-
which the low-frequency quenching voltage is
supplied by the regenerative detector itself. Also
self-quenching oscillator A circuit, such as a
+ blocking oscillator, in which oscillation is period-
ically switched off automatically, resulting in a
self-interrupted wave train.
self-excited oscillator
self-rectifying vibrator A vibrator-type power
supply in which one vibrator reed chops the di-
rect-current input to the primary winding of the
self-focus picture tube A television picture tube in
transformer, and a second vibrator reed rectifies
which the electron gun has an automatic, electro-
the alternating-current output delivered by the
static focusing arrangement.
secondary winding. Also see VIBRATOR RECTI-
self-generating photocell See PHOTOVOLTAIC
self-rectifying X-ray tube An X-ray tube operated
self-generating transducer A voltage-producing
with alternating-current anode voltage.
transducer, such as a piezoelectric pickup or dy-
self-regulation The ability of a circuit or device to
namic microphone.
control its output automatically, according to
self-healing capacitor A capacitor, such as a wet
some predetermined plan, by using output error
electrolytic unit, in which the dielectric is re-
to correct operation or to vary the input.
stored to its normal condition after a high-voltage
self reset 1. The action of a circuit breaker to reap-
ply power after a certain elapsed time. 2. The ac-
self-heated thermocouple A thermocouple in
tion of any device, returning a circuit or system to
which the passage of an applied current produces
normal automatically.
the heat necessary for the activation of the ther-
self-resetting loop In a computer program, a loop
in which instructions cause locations used in the
self-heating thermistor A thermistor heated to
loop to assume their condition prior to the loop™s
above ambient temperature by the current pass-
ing through it. Also called DIRECTLY HEATED
self-resistance The inherent internal resistance of
a device other than a resistor.
self-resonant frequency The frequency at which a
self impedance The effective or measured im-
device will resonate naturally (without external
pedance at a circuit point.
tuning). Thus, an inductor will self-resonate with
self-inductance 1. The inductance of an inductor.
its distributed capacitance; similarly, a capacitor
2. The inherent internal inductance of a device
will resonate with its stray inductance.
other than an inductor.
self-saturation In a magnetic amplifier, saturation
self-induction Induction that occurs in a single
resulting from rectification of the saturable-
circuit. An instance is the generation of an op-
reactor output current.
posing voltage across a coil by an alternating cur-
self-starting motor An alternating-current motor
rent flowing through it. Compare INDUCTION.
that starts running as soon as voltage is applied
(i.e., no external mechanical force is needed). Also
self-latching relay A relay that remains in the
state that it has been switched (i.e., locked open
self-sustained oscillations Oscillations main-
or closed) until a subsequent signal is received.
tained by means of positive feedback (inductive
self-modulated oscillator A circuit, such as a
or capacitive) from the output to the input
blocking oscillator, in which oscillation occurs
of a circuit. See, for example, SELF-EXCITED
simultaneously at two frequencies, one modulat-
ing the other.
618 self-test • semiresonant line

self-test Any arrangement whereby a device or semiconductor photosensor A semiconductor
system determines, without the aid of an external photodiode or phototransistor, as opposed to a
operator, whether or not it is operating correctly. phototube.
self-ventilated motor See OPEN MOTOR. semiconductor rectifier A heavy-duty semicon-
self-wiping contacts See SELF-CLEANING CON- ductor diode (or assembly of such diodes) de-
TACTS. signed primarily to change alternating current to
selsyn See AUTOSYN and SYNCHRO. direct current in power-supply units. Rectifiers
SEM 1. Abbreviation of SINGLE-ELECTRON MEM- commonly are made from copper oxide, germa-
ORY. 2. Abbreviation of SCANNING ELECTRON nium, magnesium-copper sulfide, selenium, or
semantic network A reasoning scheme sometimes RECTIFIER.
used in artificial intelligence. Logical state-ments semiconductor resistor A tiny resistor manufac-
or sentences are broken down into nodes (gener- tured from semiconductor material, especially one
ally nouns) and relationships (generally verbs that is etched onto the chip of an integrated circuit
and modifiers). This allows statements to be (IC). The thickness, and the types and concentra-
mapped in a way that is easy for computers to tions of impurities added, determine the resis-
store and modify. tance of the component. Such resistors can handle
semiautomatic key Also called bug. A telegraph only a tiny amount of power because of their small
key that mechanically produces a string of size. But because IC circuits are designed to con-
Morse-code dots (short pulses) when its lever is sume minimal power, this is not a problem. The
pressed to one side (usually toward the right), small signals produced by ICs can be amplified,
and continuous circuit closure when the lever is using circuits made from discrete components, if it
pressed to the opposite side (usually toward the is necessary to obtain higher signal power. See
left). Dashes are manually sent by the operator. also INTEGRATED CIRCUIT.
semiconductor A material whose natural resistiv- semidirectional Pertaining to a transducer that
ity lies between that of conductors and insulators exhibits different directional characteristics at
(e.g., GERMANIUM, SILICON, SELENIUM, and different frequencies.
GALLIUM ARSENIDE). semiduplex operation A two-frequency communi-
semiconductor capacitor A miniaturized com- cation system that operates in duplex at one end
ponent that takes advantage of reverse biasing of the link, and in simplex at the other end. Also
in a semiconductor P-N junction. When a volt- see DUPLEX OPERATION and SIMPLEX TELEG-
age source is connected across a diode so that it RAPHY.
does not conduct, the diode acts as a capacitor. semilogarithmic graph Also called semilog graph.
The capacitance varies depending on how much A graph in which one axis is logarithmic and the
reverse voltage is applied to the diode. The other axis is linear.
greater the reverse voltage, the smaller the ca-
pacitance. Some diodes are especially manufac-
tured to serve this function. This phenomenon
can be useful in the fabrication of integrated cir-
cuits (ICs). See also INTEGRATED CIRCUIT, 7
Logarithmic scale

semiconductor counter A device for measuring
the intensity of ionizing radiation (such as alpha
particles, beta particles, or gamma rays) using a
photodiode and sensing circuit.
semiconductor device A component (such as a
diode, photocell, rectifier, or transistor) that ex-
ploits the properties of a semiconductor.
semiconductor diode A solid-state diode, as op-
0 2 4 6 8 10
posed to a vacuum-tube diode or gas-tube diode.
Examples: germanium diode, selenium diode, and linear scale
silicon diode.
semiconductor junction Within a body of semi- semilogarithmic graph
conductor material, the area of physical contact
between two regions (usually n and p) having op-
posite electrical properties. semimetal An elemental substance that exhibits
semiconductor laser See LASER DIODE. some, but not all, of the properties of a metal (e.g.,
semiconductor material See SEMICONDUCTOR. antimony and arsenic). Also called METALLOID.
semiconductor-metal junction The area of semiresonant line An open-wire transmission line
physical contact between a metal and a semi- cut approximately to resonant length at the fre-
conductor. quency of operation.
semitone • sequential

semitone See HALF STEP. warning signal to human operators and/or com-
sender See TRANSMITTER, 1, 3. puters.
sending-end impedance See DRIVING-POINT sentry robot In a smart home or business, a robot
IMPEDANCE. that alerts the owner to abnormal conditions. It
sending set 1. See RADIO TRANSMITTER. 2. An can detect fire, burglars, or water in places it
equipment for transmitting electromagnetic should not be. It might also detect abnormal tem-
waves. Also see TRANSMITTER, 1. perature, barometric pressure, wind speed, hu-
sensation level The level of sound that produces a midity, or air pollution. A wireless link alerts the
tingling or noticeable sensation in the ear. owner via a device similar to a common beeper.
sense 1. To check the condition of a switching de- Compare SECURITY ROBOT. Also see SMART
vice, such as a gate. 2. See READ. HOME OR BUSINESS.
sense amplifier A device that produces a control separately excited generator An alternating-
signal when some characteristic of the input sig- current generator whose field coils are supplied
nal changes. with direct current from another generator or from
sense determination In a direction finder that a battery. Compare SELF-EXCITED GENERATOR.
provides an ambiguous indication (two readings separately quenched detector A superregenera-
180 degrees apart), the process of deducing, or tive detector (see SUPERREGENERATIVE CIR-
the ability of the apparatus to deduce, the true di- CUIT) in which the quenching voltage is supplied
rection from which the signal is coming. by a separate low-frequency oscillator. Also see
sense resistor A (usually low-value) resistor used QUENCHING ACTION and QUENCH OSCILLA-
to sense current in a circuit without introducing TOR. Compare SELF-QUENCHED OSCILLATOR.
a significant loss. The voltage drop across this re- separation See CHANNEL SEPARATION.
sistor is proportional to the current and can be separation energy The energy required to remove
applied to a voltmeter, oscilloscope, or other in- a proton or neutron from the nucleus of an atom.
strument for measurement or observation. The separation energy depends on the atomic
sensing circuit 1. A circuit that samples a quan- number.
tity. 2. In a voltage regulator, the circuit that separator 1. See FILTER, 1. 2. A perforated or
monitors the output voltage and delivers a con- porous plate of insulating material (usually plas-
trol voltage proportional to the output-voltage er- tic or wood) for holding active plates apart in a
ror. storage cell. 3. In computer operations, a charac-
sensing window See WINDOW, 2. ter marking the division between logical data
sensitive communications Two-way communica- units. Also called data delimiter.
tions of an emergency or priority nature, or in- septate cavity A coaxial cavity containing a SEP-
volving the security of government operations. TUM between the inner and outer conductors.
sensitive device A device that responds to a signal septate waveguide A waveguide containing one or
of low amplitude. more septa (see SEPTUM) to control power trans-
sensitivity 1. The ability of a circuit or device to mission.
respond to a low-level applied stimulus. 2. For a septum A thin metal vane used as a reflector in a
receiver, the input-signal (in microvolts or milli- waveguide or cavity.
volts) required for a specified output level. 3. For sequence 1. A succession of objects, parameters,
a galvanometer, microamperes or milliamperes or numbers. 2. An ordered set of numbers”each
per scale division. 4. The ohms-per-volt rating of of which is related to its predecessor by a specific
a voltmeter. Also see VOLTMETER SENSITIVITY. mathematical function.
sensitivity adjustment 1. An input gain control in sequence checking routine In computer opera-
an amplifier circuit. 2. The radio-frequency gain tions, a routine that verifies the order of items of
control of a receiver. 3. A control or switch that is data.
used to select the range or threshold of a piece of sequence control register In a computer memory,
test equipment. a register whose contents determine the instruc-
sensitivity control A manual or automatic device tion to be implemented next.
for adjusting the sensitivity of a circuit or device. sequence programmer A timing device that can be
sensitometer An instrument used to measure the preset to start or stop various operations at pre-
sensitivity of certain materials to light. determined times.
sensor 1. A device that samples a phenomenon, sequencer A device that initiates or terminates
and delivers a proportionate current or voltage in events in a desired sequence.
terms of which the intensity of the phenomenon sequence relay A relay whose several contacts
can be measured, or with which control action close in a predetermined order.
can be initiated. 2. An electronic device that de- sequence timer A timer in which separate delay
tects abnormal conditions (e.g., smoke and heat) circuits are actuated in a predetermined se-
and delivers a warning signal to human operators quence.
and/or computers. 3. An electronic device that sequential In computer operations, a term denot-
detects intrusion to a premises and delivers a ing operations on data items in which the items
620 sequential • series equivalent of parallel circuit

(e.g., records in a file) are taken in an order deter- available only in the same order. Compare PAR-
mined by key values, rather than in the order in ALLEL STORAGE.
which the items are physically arranged. serial transfer The propagation of information
sequential access memory Any semiconductor along a single path, in which data bits are sent
memory in which data can be recalled or ad- one after the other.
dressed only in a certain specified order. series 1. The sum of a mathematical sequence (see
sequential analysis In statistics, using an unspec- SEQUENCE, 2). 2. Pertaining to the connection
ified number of observations as samples from of elements or components end-to-end (see SE-
which a result is derived. Each observation is RIES CIRCUIT).
accepted or rejected, or another observation is series addition See SERIES-AIDING.
made. series-aiding The condition in which two series
sequential color television The successive trans- voltages or magnetic fields are added together.
mission of the three primary colors in a television Compare SERIES-BUCKING.
system, and their reproduction at the receiver in series antenna tuning Antenna-feeder tuning in
the same order. Also see DOT-SEQUENTIAL SYS- which a separate tuning capacitor is connected in
TEM, FIELD-SEQUENTIAL SYSTEM, and LINE- series with each wire. Compare PARALLEL AN-
sequential control Computer operation in which
the order of instruction implementation is the
same as the order of instruction storage. Two-wire
sequential relay See SEQUENCE RELAY. line
sequential scanning Rectilinear television scan-
ning in which the center-to-center distance be-
tween successive lines is the same as the nominal
line width.
sequential switch 1. A switch that provides selec-
tion of two or more ports in a rotating succession.
2. In a television system, a switch that allows the
monitoring technician to select any of the cam-
eras for viewing.
sequential timer See SEQUENCE TIMER.
series antenna tuning
ser 1. Abbreviation of SERIES. 2. Abbreviation of
serial 1. Pertaining to the performance of steps, or
the occurrence of elements (such as data items series bucking The condition in which two series
on magnetic tape), in succession. 2. An order, voltages or magnetic fields oppose each other.
row, or sequence in which one item follows an- Compare SERIES-AIDING.
other (as opposed to parallel). series capacitance Capacitance acting, or con-
serial access Access to data file records in their or- nected, in series with another capacitance or
der in a storage medium. other quantity.
serial adder See SERIAL ARITHMETIC UNIT. series capacitors Capacitors connected in series.
serial arithmetic unit In computer operations, an If the individual capacitors have values C1, C2,
arithmetic unit in which digits are handled in or- . . . , Cn, then the total capacitance Ct is equal to
der. Compare PARALLEL ADDER. 1/(1/C1 + 1/C2 + . . . + 1/Cn). Also see SERIES
serial bit Data in which the bits of each byte or CIRCUIT.
word are sent or received one at a time. series circuit A circuit whose components are, in
serial memory A register in which the input and effect, connected in a string (i.e., end-to-end).
output data is stored and retrieved one bit at a Compare PARALLEL CIRCUIT.
time. series-diode half-wave rectifier See SERIES-
serial-parallel 1. Pertaining to data transfer that is DIODE RECTIFIER.
serial in one sense and parallel in another sense. series-diode rectifier A rectifier circuit in which
For example, entire words might be serially trans- the diode is connected in series with the source
mitted within a system, but the constituent bits and load. Compare SHUNT-DIODE RECTIFIER.
of each word might be transferred in parallel. series dropping resistor See DROPPING RESIS-
serial processing In computer operations, the se- series equivalent impedance A series impedance
quential processing of several different programs that will draw the same current (magnitude and
through a single channel. Compare PARALLEL phase) drawn by a given parallel circuit con-
PROCESSING. nected across the same single-phase source.
serial storage In computer operation, storage in series equivalent of parallel circuit See SERIES
which elements are entered in order and are EQUIVALENT IMPEDANCE.
series-fed amplifier • serrated rotor plate

series-fed amplifier An amplifier circuit in which series regulator A voltage regulator circuit in
the operating voltages are applied in series with which the controlled device is in series with the
the alternating-current signal voltages. Also see load. Compare SHUNT REGULATOR.
SERIES FEED. series resistance 1. Resistance acting in series
series-fed oscillator An oscillator circuit in which with another resistance or with another quantity
the direct-current operating voltage is applied in (e.g., capacitance and inductance). 2. The inher-
series with the alternating-current output volt- ent resistance that acts effectively in series with
age. Also see SERIES FEED. the plates of a capacitor. 3. The resistance of the
series feed The application of alternating-current wire in a coil, acting effectively in series with the
(ac) and direct-current (dc) voltages in series to a inductance.
device. Example: the presentation of the dc op- series resistors Resistors connected in series with
erating voltages for an amplifier in series with each other. If the individual resistors have values
the ac signal voltages (see SERIES-FED AMPLI- R1, R2, . . . , Rn, then the total resistance Rt is
FIER). equal to R1 + R2 + . . . + Rn. Also see SERIES
series feedback A feedback system in which the CIRCUIT.
feedback signal is presented to the input point in series resonance Resonance in a circuit consisting
series with the input signal. Compare SHUNT of a capacitor, inductor, and an alternating-
FEEDBACK. current generator in series. At the resonant fre-
series field A magnetic field produced by a series quency, the inductive reactance and the
winding in a motor or generator. capacitive reactance cancel, so the net reactance
series generator An electric generator in which the is zero. The capacitor current and inductor
armature and field windings are connected in se- current are maximum and equal, and the circuit
ries. Compare SHUNT GENERATOR. impedance is minimum. Compare PARALLEL
series inductance 1. Inductance acting, effec- RESONANCE.
tively, in series with some other quantity (e.g., the series-resonant circuit A resonant circuit in
inherent inductance of a wirewound resistor). which the capacitor, inductor, and generator are
2. An inductance connected in series with other connected in series. Also see SERIES RESO-
inductances, or with some other quantity (e.g., NANCE. Compare PARALLEL-RESONANT CIR-
capacitance and resistance). CUIT.
series inductors Inductors connected in series, series-resonant trap A wavetrap consisting of a
and separated or oriented in a way that mini- series-resonant inductance-capacitance (LC) cir-
mizes the effects of mutual inductance. Assuming cuit. Compare PARALLEL-RESONANT TRAP.
zero mutual inductance, if the individual induc- series-resonant wavetrap See SERIES-RESO-
tors have values L1, L2, . . . , Ln, then the total in- NANT TRAP.
ductance Lt is equal to L1 + L2 + . . . + Ln. Also see series-shunt circuit See PARALLEL-SERIES.
series limiter A limiter (clipper) circuit in which series tracking capacitor See OSCILLATOR PAD-
the diode is essentially in series with the signal. DER.
Compare PARALLEL LIMITER. series-type frequency multiplier A varactor fre-
series loading The series insertion of reactances quency-multiplier circuit in which the varactor is
in a circuit for the purpose of impedance in series with the input and output. Compare
series magnetic circuits A combination of several series-type resonance bridge A resonance bridge
magnetic paths in line so that flux extends in which the impedance arm is a series-resonant
through each path in sequence; this is analogous circuit. Compare SHUNT-TYPE RESONANCE
to the passage of electric current successively BRIDGE.
through series-connected resistors. series winding 1. In a motor or generator, a wind-
series motor An electric motor whose armature ing connected in series with the armature. 2. A
and field windings are connected in series. Com- method of motor or generator construction in
pare SHUNT MOTOR. which the field winding is connected in series
series operation The operation of units in succes- with the armature.
sion, necessitating sequential current flow series-wound generator See SERIES GENERA-
through each. Also see SERIES CIRCUIT. TOR.
series opposition See SERIES BUCKING. series-wound motor See SERIES MOTOR.
series-parallel See PARALLEL-SERIES. serrated pulse A pulse having a notched or slotted
series-parallel capacitors See PARALLEL-SERIES top. An example is the vertical sync pulse in tele-
series-parallel inductors See PARALLEL-SERIES serrated rotor plate In a variable capacitor, an ex-
INDUCTORS. ternal rotor plate that is slotted radially. This al-
series-parallel resistors See PARALLEL-SERIES ters the capacitance-variation curve of the
RESISTORS. capacitor to allow alignment of sensitive apparatus
622 serrated rotor plate • sexadecimal number system

(e.g., the tracking of radio-frequency tuned nals, supplied by the controlled electronic device,
circuits in a radio receiver). cause the motor to run in such a way as to opti-
serrated vertical sync pulse In television, the ver- mize or stabilize the system.
tical sync pulse notched at twice the horizontal servomotor A motor operated by the output signal
sweep frequency. of a servo amplifier. Depending on the end appli-
service 1. To maintain or repair electronic equip- cation of the servo system, the motor signal might
ment. 2. To provide maintenance or repair of elec- or might not be corrected.
tronic equipment. servo oscillation In a servo system, a back-and-
serviceability ratio For a device or system, the ra- forth movement or fluctuation, relative to the
tio ts/(ts + td), where ts is serviceable (opera- optimum setting or position. It Results from im-
tional) time, and td is downtime (non-operational proper system adjustment. Sometimes the sys-
time). tem stabilizes at the optimum after a short period
serviceable time The cumulative time during of oscillation; in some cases, the oscillation con-
which an operator-monitored (but not necessarily tinues indefinitely.
operated) device or system is capable of normal servo robot A (usually industrial) robot whose mo-
operation. tion sequence is programmed into a computer.
service area For a broadcast or communications The robot follows the instructions given by the
station, the useful coverage area. computer, and makes precise, timed movements
service band 1. For a communications system, the on that basis. Different computer programs allow
band of frequencies in which operation is nor- different motion sequences, so a single robot can
mally carried out. 2. A band of frequencies specif- be used for various tasks.
ically assigned, by government regulation, to a servo system An automatic control system using
certain communications service or services. one or more servomechanisms.
service channel The band of frequencies that a set 1. A piece of equipment or a system (e.g., radio
particular broadcast or communications station set). 2. In a flip-flop circuit, an input that is not
occupies, when the carrier frequency is held con- controlled by the clock. 3. To adjust a circuit or
stant. device, such as a flip-flop, to a desired operating
service charge The amount charged by a techni- point or condition. 4. A class of numbers, things,
cian for installation, maintenance, or repair of or events. 5. In computer programming, to initial-
equipment. It is often performed on a per-hour ize a variable (i.e., to assign a label to a location).
basis. set analyzer A combination test instrument de-
service maintenance For a cell or battery, the rel- signed originally for troubleshooting radio re-
ative amount of energy capacity (percentage of ceivers. It consists of a multimeter and transistor
full-charge capacity) available at a given time, or tester or vacuum-tube tester.
after a certain length of time in normal use. set noise Electrical noise arising inside a radio or
service meter 1. An energy (“power”) meter. Also television receiver, as opposed to that picked up
see KILOWATT-HOUR METER. 2. A rugged mul- from the outside.
timeter used by a service technician. set pulse A pulse used to adjust a device to a cer-
service oscillator A signal generator designed ex- tain state (see SET, 3).
pressly for troubleshooting and repair service. set terminal In a flip-flop, the one-input terminal.
service switch 1. The main switch controlling the Compare RESET TERMINAL.
electric service to a building or other place of in- setting The position or value to which an ad-
stallation. 2. In television repair, a switch on the justable device is set for a particular purpose.
rear of a chassis. The switch facilitates adjust- settling time 1. In a digital voltmeter, the time re-
ment of screen controls by removing vertical de- quired between the application of a test voltage
flection temporarily. and the final display of an accurate readout. 2. In
service-type instrument An instrument having a digital-to-analog converter, the time between
reasonable accuracy and a degree of rugged- half of the level change over all inputs and the ar-
ness so that it is suitable for field or shop use. rival of the output to a level within a certain tol-
Examples: SERVICE METER and SERVICE OS- erance of its specified final level. It is defined for
CILLATOR. Compare LABORATORY-GRADE either full-scale to zero or zero to full-scale.
INSTRUMENT. set up To arrange and prepare equipment for oper-
servo amplifier A highly stable amplifier designed ation.
expressly for use in a SERVOMECHANISM. setup See SET, 1.
servo loop In a control system (particularly a servo set-up time 1. The time required to install and test
amplifier), the output-to-input feedback loop, an electronic system, and to ready the system for
through which automatic control is performed. operation. 2. In a digital gate, the length of time
servomechanism Also called servo. A self-correct- that a pulse must be held to produce a change of
ing, closed-loop control system. It usually uses state.
an electromechanical device, such as a motor, sexadecimal number system See HEXADECIMAL
that controls some electronic device. Error sig- NUMBER SYSTEM.
sexagesimal number system • shaft-position indicator

sexagesimal number system A number system pole of a motor. Current induced in the coil
whose radix is 60. causes a momentary flux shift that approximates
SF 1. Abbreviation of SAFETY FACTOR. 2. Abbre- a rotating field that self-starts a simple single-
viation of SINGLE FREQUENCY. 3. Abbreviation phase induction motor. 2. A coil used in a simple
of STANDARD FREQUENCY. 4. Abbreviation of ac relay to prevent chatter.
SFA Abbreviation of SINGLE-FREQUENCY AMPLI- shading signal In a television camera, a signal that
FIER. increases the gain of the amplifier while the beam
SF band A section of the S BAND extending from scans a dark part of the image.
1650 to 1850 MHz. shadow area A region in which signal attenuation
sferics In wireless broadcast or communications or the absence of a signal results from the
reception, random electromagnetic noise gener- SHADOW EFFECT.
ated by the earth™s atmosphere. Some of this
noise is thermal in origin; some originates in thun-
derstorms. Sometimes this noise is called static.




shadow area

shadow attenuation 1. The attenuation of electro-
magnetic energy caused by an obstacle. It is gen-
erally measured in decibels. 2. The attenuation of
electromagnetic energy produced by the curva-
SFO 1. Abbreviation of SINGLE-FREQUENCY ture of the earth.
OSCILLATOR. 2. Abbreviation of STANDARD- shadow effect The obstruction of radio waves by
FREQUENCY OSCILLATOR. objects in their path.
SFR Abbreviation of SINGLE-FREQUENCY RE- shadow mask See APERTURE MASK.
SFR-Chireix-Mesny antenna See CHIREIX- shadow region See SHADOW AREA.
MESNY ANTENNA. shadow tuning indicator A tuning meter in which
SG Abbreviation of SCREEN GRID. the indicating medium is a shadow whose width
SG band A section of the S BAND extending from is proportional to meter current.
2700 to 2900 MHz. shaft The rodlike part of an adjustable component
SGCS Abbreviation of silicon gate-controlled switch (such as a potentiometer or variable capacitor) to
(see SILICON-CONTROLLED SWITCH). which a rotating (or turning) member is attached.
shaded-pole motor An induction-type alternating- shaft-angle encoder An electronic system for con-
current motor using shading coils on the field verting shaft rotation into direct binary or deci-
poles for self-starting with a single-phase supply. mal readings.
shading Electronic enhancement of a television shaft lock A device for fastening the shaft of an ad-
picture, resulting in a different brightness over justable component (such as a potentiometer, ro-
various portions of the background, as compared tary switch, or variable capacitor) in position at a
with the actual situation. It can be used, for ex- particular setting.
ample, to make certain subjects stand out from shaft-position encoder See SHAFT-ANGLE EN-
the background. CODER.
shading coil 1. A single, short-circuited turn (cop- shaft-position indicator A device that delivers an
per ring) encircling the tip of the core of a coil that analog or digital output signal proportional to the
carries alternating current (ac), such as the field arc of rotation of a shaft.
624 shaker • shock-excited oscillator

shaker See VIBRATOR, 2. shield box A shield having a general box shape,
shake table A platform, actuated by a vibrator, on and which is usually enclosed on all sides.
which components can be mounted for a vibra- shield braid Tubing woven from wire, through
tion test. which an insulated wire is passed and thus
shallow-diffused junction A pn junction made by shielded.
diffusing the impurity material for a short dis- shield can A cylindrical shield, usually enclosed
tance into the semiconductor wafer. Compare on all sides.
DEEP-DIFFUSED JUNCTION. shield disk A flat shield having a disk shape. Also
shape factor 1. For a tuned circuit, the ratio of the see BAFFLE, 2; SHIELD BAFFLE; and SHIELD
60-dB bandwidth to the 6-dB bandwidth. 2. For a PARTITION.
filter, the ratio of bandwidth at high attenuation shielded cable Cable completely enclosed within a
to that at low attenuation. metal sheath that is either flexible or rigid.
shaping network A combination of components for shielded wire A single strand of insulated wire
changing the natural response of a circuit to a de- completely enclosed in a flexible or rigid shield.
sired response (i.e., a curve-changing circuit). shield partition A wall-type shield usually con-
shared file A data file that is available for use by sisting of a single, flat sheet of metal, sometimes
more than one system simultaneously. bent into an angle. Also called BAFFLE SHIELD
shared files system A data-processing system (see BAFFLE, 2).
having one direct-access storage device from shield plate See BAFFLE, 2; SHIELD BAFFLE;
which information can be accessed by more than SHIELD DISK; and SHIELD PARTITION.
one computer. shield room See CAGE.
sharpener 1. A circuit or device for increasing the shield wire A (usually grounded) wire, near and
selectivity of another circuit or device. 2. A circuit parallel to another wire that it shields.
or device for decreasing the rise or fall time of a shift 1. To move from one operating point to an-
pulse or square wave. 3. A circuit or device for other in a characteristic curve, or in the operation
steepening the response of a filter. of an equipment. 2. To transfer data from one
sharpness See SELECTIVITY. point to another in a system, or move it left or
sharp pulse A pulse having extremely fast rise and right in a register.
fall times and narrow width (i.e., a spike). shift flip-flop circuit A flip-flop designed espe-
shaving The physical modification of a phono- cially as a stage in a shift register.
graph disc, or other permanent recording sur- shift pulse In a shift register, a drive pulse that ini-
face, in preparation for rerecording. tiates the shifting of characters.
SH band A section of the S BAND extending from shift register In computers, calculators, and stor-
3700 to 3900 MHz. age systems, a circuit (usually composed of flip-
sheath See POSITIVE-ION SHEATH. flops in cascade) in which pulses can be shifted
shelf corrosion In a dry cell in storage, deteriora- from stage to stage and finally out of the circuit.
tion of the negative electrode because of local ac- shingle-type photocell A device in which several
tion in the zinc. separate photocells are series connected by
shelf life 1. The longest period of time that elec- slightly overlapping the ends of adjacent cells.
tronic equipment can be continuously kept in ship station A radio or radar station installed
storage before deterioration of materials or degra- aboard a ship that is not in port.
dation of performance occurs. 2. The longest pe- ship-to-shore communication Radio communica-
riod of time that a battery can be stored without tion between a ship at sea and a land-based sta-
use before it must be discarded or recharged. tion.
shell 1. An electronic orbit (imaginary shell) in an shock 1. See ELECTRIC SHOCK. 2. A signal ap-
atom. 2. The envelope of a component (e.g., the plied momentarily to a circuit, as in the shock ex-
outer casing of a power transistor or the housing citation of a tank. 3. A sudden, dramatic change
of a plug). 3. The rigid case in an audio or video in an environmental variable (such as tempera-
tape cassette. ture). 4. Physical blows or vibration.
shell-type choke See SHELL-TYPE INDUCTOR. shock absorber Any object or device intended for
shell-type core A core that completely surrounds reducing physical vibration of a component, set of
the coil(s) of a choke or transformer. components, circuit, or system.
shell-type inductor An inductor in which the core shock device 1. A device for administering shock
completely surrounds the coil. therapy (see ELECTROSHOCK, 1). 2. An induc-
shell-type transformer A transformer in which tion coil and associated primary supply for apply-
the core completely surrounds the coils. ing high voltage to a wire fence.
shf Abbreviation of SUPERHIGH FREQUENCY. shock excitation Driving an inductance-capaci-
shield A metallic partition or box for confining an tance (LC) tuned circuit into damped oscillation
electric or magnetic field. by momentarily applying a pulse.
shield baffle A sheet-type shield. Also see BAFFLE, shock-excited oscillator A type of self-excited os-
2 and SHIELD PARTITION. cillator in which the transistor is suddenly cut off
shock-excited oscillator • short skip


RG Transmitter


L C Output

shock-excited oscillator

by applying a cutoff voltage to the gate or base
electrode. This abrupt interruption of steady
drain or collector current shocks the tank into
damped oscillations.
shock hazard 1. Any situation that presents the
Land Water
danger of electric shock to attendant personnel.
2. The existence of a potential difference that will
cause a current of at least 5 mA to flow through a
resistance of 500 ohms or more, for a prolonged
period of time.
Shockley diode See FOUR-LAYER DIODE.
shore effect
shock mount A structure that secures a micro-
phone while minimizing the pickup of vibrations
cuit under consideration. The current amplifica-
through the table, floor, or other surface on
tion factor (alpha) of a common-base-connected
which the microphone is placed.
transistor is such a parameter because its collec-
shock therapy See ELECTROSHOCK, 1.
tor load resistance is assumed to be zero.
shoran Contraction of SHORT-RANGE NAVIGA-
shorted-stub tuning Tuning a stub to match a
feeder to an antenna by sliding a short-circuiting
shore effect The tendency of radio waves traveling
bar along the two wires of the feeder.
along a shore to be bent either toward or away
shorting bar A thick, metal strap for short-circuit-
from the shore. It can occur because of differ-
ing two binding posts.
ences in surface conductivity and/or atmo-
shorting link A sheet-metal strip for connecting
spheric temperature over land, as compared with
together two binding posts.
shorting loop In a telephone system, a device that
shore station A fixed, land-based radio station
short-circuits two specified points for the purpose
that communicates with ships at sea.
of testing or line fault location.
shore-to-ship communication See SHIP-TO-
shorting stick A metal rod with an insulating han-
dle, used to short-circuit a charged capacitor to
short circuit An often unintended low-resistance
remove the shock hazard.
path through which current bypasses a compo-
shorting switch See SHORT-CIRCUITING
nent or circuit.
short-circuit current In a power supply, the cur-
short-line tuning Use of a parallel capacitance to
rent that flows when the output is directly
tune a transmission line that is less than a quar-
shorted. Many power supplies have shutdown de-
ter-wave long.
vices that cause the current to stop flowing when
short-range navigation Contraction, shoran. Nav-
the output terminals are short-circuited; other
igation by means of SHORT-RANGE RADAR.
supplies effectively insert resistance in series
short-range radar A radar having a 50- to 150-
with the load, if necessary, to limit the current.
mile maximum line-of-sight range for a 1-square-
short-circuiting switch A rotary selector switch in
meter reflecting target that is perpendicular to
which unused contacts are automatically short-
the radar beam.
short skip Skip of only a few hundred miles range.
short-circuit parameter A parameter for which
zero resistance is assumed in the part of the cir-
626 short-skip communication • SI

short-skip communication Radio communica- between two specific points in a device or system.
tion via the ionosphere over relatively short dis- 4. To deliberately bypass some part of a system
tances (400 to 1300 miles). See, for example, by means of a short circuit.
short-term drift The gradual change in the value shunt-diode rectifier A rectifier circuit in which
of a quantity, such as frequency or voltage, ob- the diode is connected in parallel with the source
served over a comparatively brief interval, as op- and load. Compare SERIES-DIODE RECTIFIER.
posed to change occurring over a long period. shunt-fed 1. Pertaining to a circuit or device in
Compare LONG-TERM DRIFT. which the direct-current operating voltage and al-
short-term effect The variation of any electrical ternating-current signal voltage are applied in
parameter over a relatively brief time interval. Ex- parallel to an electrode. 2. Pertaining to a base-
ample: frequency drift over a short time period. grounded vertical antenna excited at some point
Also called short-time effect. above ground.
short-term stability Stability reckoned over a shunt feed See PARALLEL FEED.
comparatively brief time interval, as opposed to shunt feedback A feedback system in which the
stability for a long period. Compare LONG-TERM fed-back signal is presented to the input of the
STABILITY. network in parallel with the input signal. Com-
short-time effect See SHORT-TERM EFFECT. pare SERIES FEEDBACK.

shortwave 1. Pertaining to wavelengths shorter shunt generator An electric generator in which the
than 200 meters (i.e., frequencies higher than armature and field windings are connected in

1.50 MHz). 2. Pertaining to the frequencies above parallel. Compare SERIES GENERATOR.
the standard amplitude-modulation broadcast shunting effect The condition in which a quantity,
band (above 1.605 MHz), but below 30 MHz. such as stray capacitance or resistance, acts in
shortwave converter A superheterodyne con- parallel with another quantity. Example: the
verter for adapting a longwave receiver (such as a shunting (parallel) resistance of an electrolytic
broadcast receiver) for shortwave reception. capacitor.
shortwave listener Abbreviation, SWL. A radio shunt leads Interconnecting wires used for the
hobbyist who receives, but does not transmit, purpose of attaching a shunting component to a
shortwave signals. test instrument.

shortwave receiver Any radio receiver capable of shunt limiter See PARALLEL LIMITER.
intercepting and demodulating signals in the shunt loading The parallel insertion of reactance
range 1.705 MHz to 30 MHz. in a circuit, for the purpose of impedance match-
shortwave transmitter Any radio transmitter ca- ing.
pable of producing energy in the range 1.705 MHz shunt motor An electric motor whose armature
to 30 MHz. and field windings are connected in parallel.
shot-effect noise Electrical noise caused by ran- Compare SERIES MOTOR.
dom fluctuations in a current, as in a diode or shunt regulator A voltage-regulator circuit in
transistor. Also see EQUIVALENT NOISE RESIS- which the controlled transistor or vacuum tube is
TANCE. Compare THERMAL NOISE. in parallel with the output (load) terminals. Com-
shotgun microphone A highly directional micro- pare SERIES REGULATOR.
phone sensitive only to sounds coming from a shunt resistor 1. A resistor connected in parallel
specific direction; the response pattern has a nar- with a meter or recorder to increase its current
row main lobe. It name results from its long, range. 2. A resistor connected in parallel with a
cylindrical configuration. voltmeter to convert it into a current meter. Com-
shot noise Electrical noise arising from intermit- pare MULTIPLIER RESISTOR.
tent impulses, such as those produced by spark shunt-series circuit See PARALLEL-SERIES CIR-
discharges, make-and-break contacts, etc. Its CUIT.
name results from its resemblance to pistol shots. shunt tee junction A waveguide H-PLANE TEE
shrink The amount by which a material being mea- JUNCTION.
sured with an electronic instrument decreases in shunt-type frequency multiplier A varactor fre-
surface dimension. Compare STRETCH. quency multiplier circuit in which the varactor is
shrink tubing Plastic sleeving placed over a con- in parallel with the input and output. Compare
ductor or at a conductor/connector joint, and SERIES-TYPE FREQUENCY MULTIPLIER.
made to shrink tightly with the application of shunt-type resonance bridge A resonance bridge
heat. in which the impedance arm is a parallel-reso-
shunt Synonym, parallel. 1. Pertaining to the nant circuit. Compare SERIES-TYPE RESO-
connection of one component across (in parallel NANCE BRIDGE.
with) another (e.g., shunt resistor). 2. Pertaining shunt-wound generator See SHUNT GENERATOR.
to connection of components in such a manner shunt-wound motor See SHUNT MOTOR.
that they each (or all) are subjected to identical SI Abbreviation of (Standard) INTERNATIONAL
voltages. 3. A deliberately produced short circuit SYSTEM OF UNITS.

S/I • sidetone

S/I Abbreviation of signal-to-intermodulation ratio. sideband technique A method of using, for com-
Si Symbol for SILICON. munications or other purposes, one or both of the
sibilants 1. High-frequency (hissing) components sidebands of a modulated signal without the car-
of speech. 2. High-frequency sounds or audio sig- rier.
nals. side-chain amplifier An auxiliary amplifier that is
SIC Abbreviation of specific inductive capacity (see external to a main amplifier. Such an amplifier
DIELECTRIC CONSTANT). might be used, for example, in a feedback chan-
SiC Formula for SILICON CARBIDE. nel or in a volume-compression or volume-
sideband 1. With respect to a carrier, one of the expansion channel.
additional frequencies generated by the modula- side frequency See SIDEBAND.
tion process. In simple amplitude modulation, side lobe In certain directional antenna systems, a
the two sidebands are fc + fm and fc “ fm, where minor lobe in the horizontal-plane directivity pat-
fc is the carrier frequency, and fm is the modula- tern that appears at right angles, or nearly at
tion frequency. 2. Pertaining to sidebands as de- right angles, to the main lobe. Such a lobe repre-
fined in 1. sents reduced sensitivity and/or power gain rela-
tive to the main lobe. Also see MAIN LOBE,
(channel center)
Relative amplitude (V)

Lower Upper
sideband sideband

Relative Relative
modulating modulating
frequency frequency


sideband attenuation See SIDEBAND CUTTING.
sideband cutting Elimination or attenuation of the
sidebands of a modulated signal by a circuit hav-
ing insufficient bandwidth.
sideband frequency The frequency of the modula-
tion-generated signal accompanying a carrier.
One sideband frequency is that of the carrier mi-
nus that of the modulating signal; another is the sidelobe suppression Elimination of the side-
sum of the carrier and the modulation frequency. lobe(s) from the radiation pattern of an antenna.
See also SIDEBAND, 1. sidestacked antennas Antennas mounted in a
sideband interference 1. Interference arising from horizontal line, parallel to each other, and con-
one or both of the normal sidebands of a modu- nected by a common coupler to a transmitter or
lated signal. 2. Interference caused by spurious receiver.
sidebands, resulting from overmodulation. sideswiper A manual telegraph key operated by
sideband power The power contained in the side- moving the lever sideways, rather than up and
band(s) of a signal. down.
sideband slicing See SIDEBAND CUTTING. sidetone 1. In wire telephony, the reproduction by
sideband splatter In an amplitude-modulated or the receiver of sounds picked up by the transmit-
single-sideband signal, the emission of side- ter of the same telephone. 2. In radiotelegraphy,
band energy at frequencies other than within an audible tone actuated when the carrier is
the designated channel. Also simply called transmitted. It allows the sending operator to
splatter. hear Morse code elements as they are sent.
628 sidetone telephone • signal rectification

sidetone telephone A telephone set with no provi- signal gain The gain of an amplifier circuit”espe-
sion for canceling the sidetone. cially if used in small-signal applications. See
siemens Symbol, S. The SI unit of conductance. also AMPLIFICATION, and GAIN.
The conductance of a component or medium in signal generator An instrument that produces sig-
siemens is equal to the reciprocal of the resis- nals of precise frequency and amplitude, usually
tance in ohms. over a wide range.
Siemen™s electrodynamometer A spring-tension signal ground 1. Any circuit point that remains at
meter that operates by means of torque, with zero zero signal potential. 2. A connection to a point
current through the device representing zero that is deliberately maintained at zero signal po-
torque. It can be used for measurements of cur- tential.
rent, voltage, or power. signal/image ratio See SIGNAL-TO-IMAGE RA-
Sierra Phonetic alphabet code word for the letter S. TIO.
sig Abbreviation of SIGNAL. signaling In a communications system, the ex-
sign 1. Any indicator denoting whether a value is change of data in electrical form, either analog or
positive or negative. 2. A graphic device indicat- digital.
ing an operation. Examples: + (addition), — (mul- signaling rate In data communications, the speed
tiplication). 3. Any symbol. An ampersand, for at which data is transmitted. It is commonly ex-
example, is an “and” sign. 4. A characteristic pressed in bits per second (bps). Also, it is some-
symptom of malfunction or improper operation times expressed in baud or in words per minute
(e.g., a high standing-wave ratio in an antenna (wpm).
system is a sign of an impedance mismatch). signaling time slot In a communications signal, a
signal An electrical quantity, such as a current or specified interval of time, starting at a certain in-
voltage, that can be used to convey information stant in each signal frame. This interval is used
for communication, control, calculation, etc. exclusively for the purpose of signaling.
signal-actuated voice recorder Abbreviation, SA- signal injection 1. The introduction of a signal
VOR. A recorder that goes into operation auto- into a circuit. 2. A method of troubleshooting in
matically when the speaker starts talking and communications receivers. A signal generator is
stops when the speaker finishes. used to introduce a test signal into each stage,
signal amplitude The intensity of a signal quantity starting with the output and proceeding stage-by-
(see SIGNAL). stage toward the input, until the defective stage
signal booster See PREAMPLIFIER. or component is located.
signal channel In a system, a channel through signal injector A simple (usually single-frequency)
which only signals flow, control and modifying im- signal generator used in troubleshooting to intro-
pulses being accommodated by other channels. duce a test signal at selected points in a circuit,
signal circuit A circuit handling signal currents to locate malfunctioning stages or components.
and voltages to the exclusion of control and oper- Also see SIGNAL INJECTION, 2.
ating currents and voltages. signal intensity See SIGNAL STRENGTH.
signal conditioner Any accessory device (such as a signal inversion Phase reversal of a signal passing
peak probe, demodulator probe, current shunt, through a circuit, device or medium.
etc.) used to modify or change the function of a ba- signal level At a given point in a circuit, the
sic instrument (such as an electronic voltmeter). strength of a signal, with respect to a reference
signal converter See CONVERTER, 1. amplitude.
signal current The current component of a signal, signal loss 1. A reduction in the amplitude of a sig-
as opposed to operating current in a system. nal as it passes through a system. 2. The
signal diode A diode designed primarily for light- complete disappearance of a signal. 3. See
duty signal applications (detection, demodula- FRACTIONAL GAIN.
tion, modulation, curve changing), as opposed to signal mixer See MIXER.
the heavy-duty applications of power diodes and signal/noise ratio See SIGNAL-TO-NOISE RATIO.
rectifiers. signal notcher See NOTCH FILTER.
signal distance In two words (bit groups) of the signal peaker See PEAK FILTER.
same length, the number of corresponding bit po- signal power The amplitude of a signal expressed
sitions whose states differ. For example, the sig- in watts, milliwatts, or microwatts, as opposed to
nal distance between 01001 and 10011 is 3. amplitude expressed as a current or voltage.
signal-flow analysis A graphic method of analyz- signal processor Any device, (e.g., preamplifier,
ing circuits, particularly those using feedback, expander, amplitude limiter, delay network) in-
through the use of diagrams in which straight ar- serted into or added onto a system to modify an
rows represent transmission paths, dots repre- input or output signal.
sent nodes, and curved arrows represent signal rectification The conversion of an alternat-
feedback paths. ing-current signal into a proportionate direct-
signal-flow diagram The transmission-path dia- current signal, usually by means of a diode
gram used in SIGNAL-FLOW ANALYSIS. circuit.
signal rectifier • silicon capacitor

(dB). Peak voltages are used to determine this ra-
+ tio in the case of pulse noise; root-mean-square
(rms) voltages are used in the case of random
RF dc noise.
In Out
signal-to-noise-and-distortion ratio Abbrevia-
tion, SINAD. In a receiver, the ratio of the desired
signal to the level of noise and distortion, other
than the specified signal. It is usually expressed
in decibels (dB).
signal tracer A tuned or untuned detector/ampli-
fier having an input probe and an output indica-
tor (meter, loudspeaker, or both), for following a
signal rectification
test signal through a circuit.
signal voltage The voltage component of a signal,
signal rectifier See SIGNAL DIODE. as opposed to the operating voltage of the circuit
signal regeneration See SIGNAL RESHAPING. generating or passing the signal.
signal reshaping 1. The processing of a signal so signal wave 1. Any electromagnetic disturbance of
that it acquires its original waveform. Also called a periodic nature that is modulated to convey in-
signal regeneration. 2. Passing a digital signal of formation. 2. The visual illustration or rendition
any type through a circuit that delivers a uni- of an electromagnetic disturbance that is modu-
form output pulse on a real-time one-to-one lated to convey information.
basis. signal winding In a magnetic amplifier or sat-
signal shifter 1. A device used for quickly chang- urable reactor, the coil that receives the control
ing the frequency of a transmitted signal. 2. A de- current.
vice that automatically causes a transmitted signal window See WINDOW, 2.
signal to be sent on a frequency that differs from signal wobbulator A frequency modulator used
the receiver frequency by a known and predeter- with an unmodulated signal generator to provide
mined amount. 3. See MIXER, 1. 4. See CON- sweep signals for visual alignment. Also see
signal squirter See SIGNAL INJECTOR. sign bit A one-bit SIGN DIGIT.
signal strength The amplitude of a signal, usually sign digit A character indicating the sign (positive
in terms of voltage. Current or power is specified or negative) of the value of the field or word to
in some applications. which it is attached (usually at the end).
signal-strength meter 1. See FIELD-STRENGTH signed field In a computer record, a field having a
METER. 2. See S-METER. number whose sign is indicated by a SIGN DIGIT.
signal synthesizer A special signal generator de- significant digits See SIGNIFICANT FIGURES.
livering signals whose frequency, amplitude, and significant figures In a numerical quantity, espe-
waveshape can be adjusted at will. cially one expressed in scientific (power of 10) no-
signal time delay The time required for an element tation, those figures (digits) that depict a quantity
of a signal to be transmitted through a circuit or to a required, relevant, or justifiable degree
network. This delay results in phase shift in an of precision. For example, 173,201 expressed
to three significant figures is 1.73 — 105;
signal-to-distortion ratio In a receiver, the ratio of 0.00477583 expressed to four significant figures
is 4.776 — 10“3. See also SCIENTIFIC NOTATION.
the desired signal to the level of distortion other
than the specified signal. Usually expressed in silencer See AUTOMATIC NOISE LIMITER.
decibels (dB). silent alarm In security systems, the transmission
signal-to-image ratio Abbreviation, S/I. In a re- of a warning signal to attendant human operators
ceiver, the ratio of signal amplitude to image am- and/or computers, without producing an audible
plitude, both being measured in the same units. or visible warning to intruders.
It is usually expressed in decibels (dB). silent alignment See VISUAL ALIGNMENT.
signal-to-noise-plus-noise ratio Abbreviation, silent piano See ELECTRONIC PIANO.
(S+N)/N. In a receiver, the ratio of the combined silica pencil A rod of silicon dioxide heated to emit
signal and noise amplitude to the amplitude of infrared rays.
the noise alone. It is usually expressed in decibels silicon Symbol, Si. A metalloidal element. Atomic
(dB). Peak voltages are used to determine this ra- number, 14. Atomic weight, 28.086. Silicon is
tio in the case of pulse noise; root-mean-square abundant in the earth™s crust. It is used in many
(rms) voltages are used in the case of random semiconductor devices, including integrated cir-
noise. cuits, diodes, photocells, rectifiers, and transis-
signal-to-noise ratio Abbreviations: S/N, SNR. In tors.
a receiver, the ratio of signal amplitude to noise silicon capacitor See VOLTAGE-VARIABLE CA-
amplitude. It is usually expressed in decibels PACITOR.
630 silicon carbide • silver-oxide cell

silicon carbide Formula, SiC. A compound of sili- is applied. When light falls on the P-N junction,
con and carbon valued as a semiconductor, an current flows. The current is proportional to the
abrasive material, and a refractory substance. intensity of the impinging energy, within certain
The commercial product is made by heating car- limits. The greatest sensitivity is in the near in-
bon and sand to a high temperature in an electric frared (IR). When energy of variable brightness
resistance furnace. Also called CARBORUNDUM. falls on the P-N junction under conditions of re-
silicon cell A type of photovoltaic cell using spe- verse bias, the output current follows the inten-
cially processed silicon as the light-sensitive ma- sity variations. This makes the device useful in
terial. This cell has a comparatively high voltage fiberoptic communications systems.
output. silicon point contact The contact between a
silicon-controlled rectifier Abbreviation, SCR. A pointed metal wire (cat whisker) and a silicon
four-layer semiconductor device commonly used wafer.
in power control applications (e.g., light dimmers silicon point-contact diode A diode in which a
and motor-speed controls). The electrodes are tungsten wire (cat whisker) contacts a wafer of
called the anode, the cathode, and the gate. The single-crystal silicon. It is useful at ultra high fre-
control signal is applied to the gate. quencies (UHF). Compare SILICON JUNCTION
silicon-controlled switch Abbreviation, SCS. A DIODE.
four-terminal semiconductor switching device silicon rectifier A semiconductor rectifier consist-
similar to the SILICON-CONTROLLED RECTI- ing essentially of a junction between n- and p-
FIER. It is used for light-duty switching. type silicon inside a specially processed wafer or
silicon crystal detector 1. See SILICON JUNC- plate of single-crystal silicon.
DIODE. 3. A point-contact diode in which a lump silicon solar cell A relatively heavy-duty photo-
of silicon is contacted by either a fine wire (cat voltaic cell using specially processed silicon as
whisker) or a blunt-tipped steel screw under the light-sensitive material.
pressure. silicon steel A high-permeability, high-resistance
silicon detector See SILICON CRYSTAL DETEC- steel containing 2 to 3 percent silicon. It is used
TOR. as core material in transformers and other elec-
silicon-diffused transistor A silicon bipolar tran- tromagnetic devices.
sistor fabricated by diffusion techniques. It is silicon transistor A transistor in which the semi-
characterized by high power-dissipation toler- conductor material is single-crystal silicon.
ance. silk-enameled wire Wire whose insulation is a
silicon diode A semiconductor diode in which the layer of silk on top of an enamel coating.
semiconductor material is specially processed sil- silver Symbol, Ag. A precious metallic element.
icon. Also see SILICON JUNCTION DIODE and Atomic number, 47. Atomic weight, 107.87. It is
SILICON POINT-CONTACT DIODE. used in circuits where low resistance and high Q
silicon dioxide Formula, SiO2. A compound of sil- are mandatory.
icon and oxygen. In the passivation of transistors silver arsenide trisulfide See PROUSTITE.
and integrated circuits, a thin layer of silicon silver-dollar construction Printed-circuit assem-
dioxide is grown on the surface of the wafer to bly on a disk-shaped board, about the size of a
protect the otherwise exposed junctions. U.S. silver dollar.
silicone A polymeric material characterized by a silver-mica capacitor A fixed capacitor made by
recurring chemical group containing oxygen and painting or depositing a silver layer (capacitor
silicon atoms in the main chain as links. Various plate) on both faces of a thin mica film (dielectric
silicone compounds have numerous uses in elec- separator).
tronics. silver migration The undesirable tendency of sil-
silicon junction diode A semiconductor diode us- ver to be removed from one location and de-
ing a pn junction in a silicon wafer. Compare SIL- posited in another under adverse environmental
silicon on sapphire Abbreviation, SOS. Pertaining silver-oxide battery A set of two or more silver-
to integrated-circuit fabrication in which a silicon oxide cells stacked one atop the other, electrically
epitaxial layer is grown on a sapphire substrate. connected in series. The resulting battery has a
silicon oxide A compound containing both silicon cylindrical shape. A set of four cells provides ap-
monoxide and silicon dioxide, and having dielec- proximately 6 volts under no-load conditions; a
tric properties. It is used in the manufacture of battery of six cells provides 9 volts; a battery of
metal-oxide-semiconductor (MOS) devices. eight cells provides 12 volts. See also SILVER-
silicon photocell A photocell using a silicon pn OXIDE CELL.
junction as the light-sensitive medium. silver-oxide cell An electrochemical cell having a
silicon photodiode A silicon diode constructed so button-like shape, small enough to fit inside a
that radiant energy can strike the barrier be- wristwatch. There are several available sizes and
tween the P- and N-type materials. A reverse bias thicknesses, all with similar appearance. The
silver-oxide cell • single cotton enameled wire

sin“1 Symbols for the inverse of the sine function,
generated potential difference under no-load con-
also called the arc sine.
ditions is 1.5 volts, with a high ratio of stored en-
sine Abbreviation, sin. The trigonometric function
ergy per unit mass. The cell has a flat discharge
a/c, the ratio of the opposite side of a right trian-
curve; the voltage remains essentially constant
gle to the hypotenuse.
until the charge is almost depleted, and then the
voltage drops rapidly.
silver solder A solder consisting of an alloy of sil-
sine galvanometer A galvanometer in which the
ver, copper, and zinc. It has a comparatively high
sine of the angle of deflection is proportional to
melting temperature. Also see HARD SOLDER.
the current. Compare TANGENT GALVANOME-
silverstat A multiconductor device used to adjust
the balance of a resistance or reactance bridge.
sine law The variation in radiation intensity in any
similar decimals Two or more decimal numbers
direction from a linear source is proportional to
that have the same number of digits to the right
the sine of the angle between the axis of the
of the radix point (e.g., 3.14 and 6.39, or 1.234
source and the direction of interest.
and 1.000).
sine potentiometer A POTENTIOMETER whose
simple quad A combination of two parallel paths”
output is proportional to the sine of the angle
each containing two elements in series.
through which the shaft has rotated.
simple tone A pure sine-wave tone (i.e., one hav-
sine wave A periodic wave that can be represented
ing negligible harmonic content).
by a sine curve (i.e., its amplitude is directly pro-
simplex channel An information channel for uni-
portional to the sine of a linear quantity, such as
directional transmission.
displacement or time). Compare COSINE WAVE.
simplex system 1. In data communications, a sys-
tem that transmits data in only one direction.
PLEX SYSTEM. 2. In voice communications via
radio, a direct path over a single channel, used
alternately for transmitting and receiving at each
station. 180° 360°
simplex telegraphy Wire telegraphy in which only

one message at a time can be sent over a line.
simplification of circuits See CIRCUIT SIMPLIFI-
simulation 1. Imitation of the performance of a
process, device, or system. 2. The use of a math-
ematical model to represent a physical process,
sine wave
device, or system. 3. The use of a computer,
sometimes with virtual reality hardware and soft-
ware, to mimic a real-life situation. singing Audible oscillation in a circuit or device,
simulator 1. A software or hardware system capa- such as the low-level buzz emanating from the fil-
ble of simulation (see SIMULATION, 2). 2. A com- ament of a lamp dimmed with a phase-control
puter program whose implementation allows circuit.
programs written for one computer to be compat- single-address coding In computer programming,
ible with another computer. 3. A system of equip- the use of instruction words that contain the ad-
ment for simulation (see SIMULATION, 1). dress for the location of the data to be operated
simulcast 1. To broadcast a program over two or on, and no other addresses.
more different channels at the same time. 2. To single-board computer Abbreviation, SBC. A com-
broadcast a program over two or more different puter built entirely on one circuit board.
types of mode, for example, television and radio, single-button microphone A carbon microphone
at the same time. 3. A program broadcast over having only one button attached to the di-
two or more channels or modes at the same aphragm. Also see BUTTON MICROPHONE.
time. single-channel codec A form of CODEC intended
simultaneous access See PARALLEL ACCESS. for operation on a single signal source, rather
simultaneous broadcasting See SIMULTANEOUS than in a multiplexed system.
TRANSMISSION. single-chip codec An integrated circuit contained
simultaneous computer See PARALLEL COM- entirely on one chip and in one package that can
PUTER. accomplish all CODEC functions. It can be a sin-
simultaneous transmission The transmission of gle-channel device or multiplexed.
the same information in two or more channels, or single-cotton-covered wire Wire insulated with
by means of two or more processes, at the same one layer of cotton.
time. single cotton enameled wire Wire insulated with
sin Abbreviation of SINE. one layer of cotton on top of an enamel coating.
632 single-crystal • single-layer solenoid

single-crystal Pertaining to the internal structure single-frequency duplex Two-way communica-
of a crystalline material, in which the character- tions over one medium or frequency. Voice-actu-
istic lattice is continuous throughout any size ated (VOX) or break-in devices are used at both
piece of the material. Also called MONOCRYS- ends of the circuit.
TALLINE. single-frequency oscillator An oscillator that nor-
single-crystal material A substance, such as a mally delivers a signal at only one frequency un-
semiconductor, of which a sample, regardless of til it is switched to another frequency (e.g.,
size, consists of only one crystal (i.e., there are no crystal-controlled oscillator).
grain boundaries). Also see SINGLE-CRYSTAL. single-frequency receiver A radio or television re-
Compare POLYCRYSTALLINE MATERIAL. ceiver that normally operates at one carrier
single-crystal pulling See CZOCHRALSKI frequency, rather than being tunable. Such re-
METHOD. ceivers are used in monitoring specific programs,
single-dial control Adjustment of a multistage picking up standard-frequency signals, and in
system via one rotatable, calibrated control at- similar applications.
tached to a ganged arrangement that tunes all single-gun color picture tube A color-television
stages simultaneously. picture tube in which the image is produced by a
single-diffused transistor A transistor in which single beam that scans the red, green, and blue
only one diffusion of an impurity substance is color-phosphor dots sequentially.
made. Thus, in a diffused-base transistor, a sin- single-hop propagation Long-distance radio-wave
gle diffusion provides the base region and at the propagation involving only one encounter with
same time creates the emitter-base and collector- the ionosphere, and involving no intermediate re-
base junctions. Compare DOUBLE-DIFFUSED flections from the earth™s surface.
TRANSISTOR. single-hop return distance The return distance,
single-electron memory Abbreviation, SEM. A as a function of the angle of departure from a ra-
computer memory in which the movement of one dio transmission, from a layer of the ionosphere.
electron can change a logic bit from 1 (high) to 0 The illustration shows the maximum possible
(low) or vice versa. distance under average conditions and assuming
single-element rotary antenna See ONE- an angle of departure of zero degrees.
single-ended circuit A circuit that has one end
grounded, as opposed to a double-ended circuit 80°
and push-pull circuit.
single-ended deflection In an oscilloscope or sim-
ilar device, horizontal or vertical deflection pro-
Angle of departure

vided by a single-ended deflection channel.
single-ended input An input circuit with one ter-
minal grounded (or the equivalent ungrounded F layer
input circuit). Also called unbalanced input. Com-
E layer
single-ended multiplexer A group of analog
switches that selects from several analog

single-ended output An output circuit with one
0 500 1000 1500 2000 2500 3000
terminal grounded (or the equivalent ungrounded
output). Also called unbalanced output. Compare
BALANCED OUTPUT. single-hop return distance (miles)
single-ended push-pull circuit An arrangement,
such as a complementary symmetry circuit, that
provides push-pull output with single-ended in- single-image response In an oscilloscope presen-
put, but does not require transformers. tation, a single pattern, as opposed to a double-
single-frequency Also called fixed-frequency. Per- trace pattern.
taining to circuits or devices that normally oper- single-inline package Abbreviation, SIP. A flat,
ate at one frequency only (e.g., single-frequency molded component package having terminal pins
oscillator). along one edge. All the pins lie along a common
single-frequency amplifier An amplifier that nor- line.
mally operates at only one frequency (or within a single-junction transistor See UNIJUNCTION
very narrow band of frequencies) (e.g., an inter- TRANSISTOR.
mediate-frequency amplifier, or a selective audio- single-layer coil A coil whose turns are wound
frequency amplifier used for harmonic analysis or side by side in one layer.
bridge balancing). single-layer solenoid See SINGLE-LAYER COIL.
single-line tap • single-track recorder

single-pole single-throw Abbreviation, SPST. De-
scriptive of an electrical, electronic, or mechani-
cal switch with a pole that can be connected to an
adjacent pole (or disconnected from it) at will. It is
used to provide the make and break function in a
single circuit.
single rail 1. A one-conductor communications
medium with a ground return. 2. A one-conduc-
tor data line, with a ground return.
single shot Also called one shot. Pertaining to circuit
single-inline package
operation in which a single input pulse applied to a
switching device (such as a multivibrator) causes it
single-line tap In a telephone system, a connec- to deliver a single output pulse, rather than switch
tion that provides or designates a separate line to a stable “on” state. A MONOSTABLE MULTIVI-
(e.g., to serve a single household). BRATOR operates in this mode.
single-loop feedback Feedback through only one single-shot multivibrator See MONOSTABLE
single phase Pertaining to the presence or genera- single sideband Abbreviation, SSB. Pertaining to a
tion of one alternating-current phase only. Com- system of modulation in which one of the side-
pare POLYPHASE. bands from an amplitude-modulated signal is at-


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