SATELLITE ECLIPSE - An eclipse where the rays of the sun do not reach the satellite.
This prevents recharging of the solar cells of the satellite and decreases the power to
the transmitter .
SATELLITE-SUN CONJUNCTION - A period when the satellite and sun are close together and
the noise from the sun prevents or hampers communications .
SATURABLE-CORE REACTOR - A coil in which the reactance is controlled by changing the
permeability of the core .
SATURATION - (1) The condition existing in any circuit in which an increase in the
input signal produces no further change in the output . (2) The operating point of a
vacuum tube or transistor at which a further increase in grid or base current no longer
produces an increase in plate or collector current . (3) In a magnetic core, the condition
in which a magnetic material has reached a maximum flux density and the permeability has
decreased to a value of (approximately) 1 .
SATURATION FLUX DENSITY - (1) The maximum intrinsic flux density possible in a sample
of magnetic material. (2) The intrinsic flux density asymptotically approaches the
saturation flux density as the magnetizing field strength increases.
SATURATION NOISE - (See noise.)
SCALING FACTOR - The term used to describe the use of unequal resistors in a servo's
summing network to compensate for differences between input and output signal levels .
SCANNING - (1) The process of subdividing a picture in an orderly manner into segments.
This is used in facsimile transmission . (2) Systematic movement of a radar beam to cover
a definite pattern or area in space .
SCAT CODE - A four-digit subcategory code used to identify the functional measurement
parameters that can be satisfied by any one of many pieces of test equipment .
SCATTER ANGLE - The angle at which the receiving antenna must be aimed to capture the
scattered energy of tropospheric scatter .
SCHEMATIC - A diagram which shows, by means of graphic symbols, the electrical
connections and functions of a specific circuit arrangement .
SCHEMATIC SYMBOLS - A letter, abbreviation, or design used to represent specific
characteristics or components on a schematic diagram .
SCINTILLATION - Apparent change in target reflectivity. Motion of the target causes
successive radar pulses to bounce off different parts of the target, such as fuselage and
wingtip .
SCRATCH - A long, narrow, straight defect in the top surface of a head track or a tape.
SCREEN GRID - A grid placed between a control grid and the plate and usually maintained
at a fixed positive potential .
SCREENING - Process of applying nonconductive or semiconductive materials to a
substrate to form thick film components .
SEA CLUTTER - Unwanted echoes from the irregular surface of the sea that appear on a
radar indicator .
SEARCH RADAR SYSTEM - An early-warning device that searches a fixed volume of space .
SECAS (SHIP EQUIPMENT CONFIGURATION ACCOUNTING SYSTEM) - The Navy system that keeps
track of the configuration of equipment in the fleet .
SECONDARY - The output coil of a transformer .
SECONDARY CELL - A cell that can be recharged by a current being passed through the
cell in a direction opposite to the discharge current .
SECONDARY STORAGE - See storage, secondary.
SECONDARY EMISSION - The liberation of electrons from an element, other than the
cathode, as a result of being struck by other high-velocity electrons .
SECONDARY LOOP - In a cooling system, the loop that transfers the heat from the heat
source, such as electronic equipment, to the primary loop; usually distilled water .
SECOND DETECTOR (DEMODULATOR) - The part of the receiver that separates the audio or
video component from the modulated intermediate frequency .
SECOND-SWEEP ECHOES - See AMBIGUOUS RETURNS .
SECTORS - The pie-shaped segments of a disk's recording surface.
SELECTIVITY - The ability of a receiver to select the desired signal and reject
unwanted signals .
SELENIUM - A chemical element with light-sensitive properties that makes it useful as a
semiconductor material in metallic rectifiers .
SELF-BIAS - In a vacuum tube circuit, the voltage developed by the flow of current
through a resistor in the grid or cathode leads .
SELF-EXCITED GENERATORS - Dc generators in which the generator output is fed to the
field to produce field excitation .
SELF-EXCITED METER - A term used to describe meters that operate from their own power
sources .
SELF-INDUCTION - (1) The production of a counterelectromotive force in a conductor when
its own magnetic field collapses or expands with a change in current in the conductor .
(2) The phenomenon caused by the expanding and collapsing fields of an electron that
encircle other electrons and retard the movement of the encircled electrons .
SELF-LUMINOUS BODIES - Objects that produce their own light .
SELF-SYNCHRONIZED RADAR - A type of radar in which the timing pulses are generated
within the transmitter .
SENDING END - See INPUT END .
SENSITIVITY - (1) For an ammeter, the amount of current that will cause full-scale
deflection of the meter. (2) For a voltmeter, the ratio of the voltmeter resistance
divided by the full-scale reading of the meter; expressed in ohms per volt . (3) The
ability of a receiver to reproduce very weak signals. The greater the receiver
sensitivity, the weaker the signal that can be reproduced . (4) Efficiency of a
microphone. Describes microphone power delivered to a matched-impedance load as compared
to the sound level being converted. Usually expressed in terms of the electrical power
level .
SENSITIVITY TIME CONTROL (STC) - A circuit that varies the gain of a receiver as a
function of time .
SEPARATION LOSS - The loss in output that occurs when the surface of the coating of a
magnetic tape fails to make perfect contact with the surface of the record or reproduce
head.
SEQUENTIAL ACCESS - A storage technique in which the stored items of information become
available only in a one after the other sequence, whether or not all the information or
only some of it is desired. Magnetic tape is an example.
SERIES CIRCUIT - An arrangement where electrical devices are connected so that the
total current must flow through all the devices; electrons have one path to travel from
the negative terminal to the positive terminal .
SERIES-CONNECTED DUPLEXER - A configuration in which the tr spark gap is connected in
series in one leg of the transmission line one-half wavelength away from the T-junction .
SERIES-DIODE DETECTOR - The semiconductor diode in series with the input voltage and
the load impedance. Sometimes called a VOLTAGE-DIODE DETECTOR .
SERIES-FED OSCILLATOR - An oscillator in which dc power is supplied to the amplifier
through the tank circuit or a portion of the tank circuit .
SERIES LIMITER - A diode connected in series with the output, in which the output is
taken across the resistor. Either the positive or negative alternation of the input wave
is eliminated .
SERIES-NEGATIVE LIMITER - A diode connected in series with the output, in which the
output is taken across the resistor. It eliminates the negative alternation of the input
wave .
SERIES-PARALLEL CIRCUIT - A circuit that consists of both series and parallel networks
.
SERIES PEAKING - A technique used to improve high-frequency response in which a peaking
coil is placed in series with the output signal path .
SERIES-POSITIVE LIMITER - A diode connected in series with the output, in which the
output is taken across a resistor. It eliminates the positive alternation of the input
wave .
SERIES-RESONANT CIRCUIT - A resonant circuit in which the source voltage is connected
in series with a capacitor and an inductor (also in series) to furnish a low impedance at
the frequency at which the circuit is resonant .
SERIES VOLTAGE REGULATOR - A regulator with a regulating device that is in series with
the load resistance .
SERIES-WOUND MOTORS AND GENERATORS - Machines in which the armature and field windings
are connected in series with each other .
SERVOAMPLIFIER - Either ac or dc amplifiers used in servosystems to build up signal
strength. These amplifiers usually have relatively flat gain versus frequency response,
minimum phase shift, low output impedance, and low noise level. .
SERVOMOTOR - An ac or dc motor used in servosystems to move a load to a desired
position or at a desired speed. The ac motor is usually used to drive light loads at a
constant speed, while the dc motor is used to drive heavy loads at varying speeds .
SERVOSYSTEM - An automatic feedback control system that compares a required condition
(desired value, position, and so forth) with an actual condition and uses the difference
to drive a control device to achieve the required condition .
SET - A unit or units and the assemblies, subassemblies, and parts connected or
associated together to perform a specific function .
SEXADECIMAL - Same as HEXADECIMAL .
SHADOW - A dead spot (minimum radiation) caused by the physical obstruction of
transmitted waves by a feed horn .
SHAPING CIRCUIT - A circuit that alters the shapes of input waveforms .
SHARP-CUTOFF TUBE - The opposite of a remote-cutoff tube. An electron tube that has
evenly spaced grid wires. The amplification of the sharp-cutoff tube is limited by the
bias voltage and tube characteristics .
SHEDDING - The loss of oxide or other particles from the coating or backing of a tape,
usually causing contamination of the tape transport and, by redeposit, of the tape itself.
SHELF LIFE - The period of time that a cell or battery may be stored and still be
useful .
SHIELDED PAIR - A line consisting of parallel conductors separated from each other and
surrounded by a solid dielectric .
SHIELDING - (1) A metallic covering used to prevent magnetic or electromagnetic fields
from affecting an object . (2) Technique designed to minimize internal and external
interference .
SHORT CIRCUIT - An unintentional current path between two components in a circuit or
between a component and ground; usually caused by a circuit malfunction .
SHORT-CIRCUITED LINE - A transmission line that has a terminating impedance equal to 0
.
SHORT-TERM TAPE SPEED - (See tape speed.)
SHUNT - A resistive device placed in parallel with another component. Appreciable
current may flow through it and an appreciable voltage may exist across it .
SHUNT-DIODE DETECTOR - A diode detector in which the diode is in parallel with the
input voltage and the load impedance. Also known as a current detector because it operates
with smaller input levels .
SHUNT-FED OSCILLATOR - An oscillator that receives its dc power for the transistor or
tube through a path both separate from and parallel to the tank circuit .
SHUNT PEAKING - A technique used to improve high-frequency response in which a peaking
coil is placed in parallel (shunt) with the output signal path .
SHUNT RESISTOR - A resistor in parallel. In an ammeter, shunt resistors are used to
provide multiple ranges .
SHUNT VOLTAGE REGULATOR - A regulator whose regulating device is in parallel with the
load resistance .
SHUNT-WOUND MOTORS AND GENERATORS - Machines in which the armature and field windings
are connected in parallel (shunt) with each other .
SIEMANS - The new and preferred term for mho .
SIGNAL. - A general term used to describe any ac or dc of interest in a circuit; for
example, input signal .
SIGNAL DISTORTION - Any unwanted change to the signal .
SIGNAL-TO-NOISE RATIO - (1) The ratio of the power output of a given signal to the
noise power in a given bandwidth. (2) Is usually measured by the corresponding root mean
square signal and noise voltages appearing across a constant output resistance.
SIGNIFICANT SIDEBANDS - Those sidebands with significantly large amplitude .
SILICON - A metallic element which, in its pure state, is used as a semiconductor .
SILICON-CONTROLLED RECTIFIER (SCR) - A semiconductor device that functions as an
electrically controlled switch .
SINE WAVE - (1) The curve traced by the projection on a uniform time scale of the end
of a rotating arm, or vector. Also known as a sinusoidal wave . (2) The basic synchronous
alternating waveform for all complex waveforms .
SINGLE-ENDED MIXER - See UNBALANCED CRYSTAL MIXER .
SINGLE LINE DIAGRAM - A diagram which shows, by means of single lines and graphic
symbols, the course of an electric circuit or system of circuits and the component devices
or parts used therein .
SINGLE, STATIONARY-LOBE SCANNING SYSTEM - Antenna (with a single, stationary beam) that
is rotated to obtain 360-degree coverage .
SINK - See OUTPUT END .
SKEW - A deviation of a line connecting the average displacement of the read or write
track gaps from a line perpendicular to the reference edge of the tape in the direction of
tape motion.
SKEW TAPE - (1) The continuous strings of "1" values written on a properly
adjusted tape drive for the entire recoverable length of the tape. (2) An "all '1'
pattern" on all tracks. (3) The write head, the write delays, and the tape drive
adjusted to write with minimum physical skew and gap scatter.
SKIN EFFECT - The tendency for alternating current to concentrate in the surface layer
of a conductor. The effect increases with frequency and serves to increase the effective
resistance of the conductor .
SKIP DISTANCE - The distance from a transmitter to the point where the sky wave is
first returned to earth .
SKIP ZONE - A zone of silence between the point where the ground wave becomes too weak
for reception and the sky wave is first returned to earth .
SKY WAVES - Radio waves reflected back to earth from the ionosphere .
SLANT RANGE - See RANGE .
SLIP - The difference between rotor speed and synchronous speed in an ac induction
motor .
SLIP RINGS - Contacts that are mounted on the shaft of a motor or generator to which
the rotor windings are connected and against which the brushes ride . Devices for making
electric connections between stationary and rotating contacts.
SLOPE DETECTOR - A tank circuit tuned to a frequency, either slightly above or below an
fm carrier frequency, that is used to detect intelligence .
SLOT - Narrow opening in a waveguide wall used to couple energy in or out of the
waveguide. Also called an aperture or a window .
SNAP-ACTING - Changing position quickly with the aid of a spring .
SOFT COPY - Output of a computer displayed on a display terminal or monitor (crt). It
is nonpermanent.
SOFT METAL LAMINATIONS - (See core material, soft.)
SOFTWARE - Programs, routines, codes, and other written information used to direct the
operation of a computer; as distinguished from hardware.
SOLENOID - An electromagnetic device that changes electrical energy into mechanical
motion; based upon the attraction of a movable iron plunger to the core of an
electromagnet .
SOLID - One of the three states of matter; it has definite volume and shape (ice is a
solid) .
SOLID-STATE DEVICE - An electronic device that operates by the movement of elections
within a solid piece of semiconductor material .
SONIC - Pertaining to sounds capable of being heard by the human ear .
SORT - The process of arranging data records in a predefined sequence by use of sort
keys; for example, to sequence personnel records by social security number (the sort key).
SOURCE - (1) The object that produces the waves or disturbance. (2) The name given to
them end of a two-wire transmission line that is connected to a source . (3) The device
which furnishes the electrical energy used by a load .
SOURCE DATA - The data in its initial state to be processed by a computer system.
SOURCE DOCUMENT - The document that contains the initial (raw) data for computer
processing.
SOURCE, MAINTENANCE, AND RECOVERABILITY CODE (SM & R CODE) - Specifies maintenance
level for repair of components or assemblies .
SOURCE PROGRAM - A computer program written in a language like COBOL, FORTRAN, or
assembly language. It must be translated into an object program before it can be executed
by a computer.
SPACE - Absence of an rf signal in cw keying. Key-open condition or lack of data in
communications systems. Also a period of no signal .
SPACE CHARGE - An electrical charge distributed throughout a volume or space .
SPACE DIVERSITY - Reception of radio waves by two or more antennas spaced some distance
apart .
SPACE WAVE - Radio waves that travel directly from the transmitter to the receiver and
remain in the troposphere .
SPACING - The condition in teletypewriter operation where a circuit is open and no
current flows .
SPARK-GAP MODULATOR - A modulator that consists of a circuit for storing energy, a
circuit for rapidly discharging the storage circuit (spark gap), a pulse transformer, and
a power source .
SPECIAL-PURPOSE COMPUTER - A computer designed to perform one specific function such as
a weather computer.
SPECIAL PURPOSE ELECTRONIC TEST EQUIPMENT (SPETE) - Test equipment that is specifically
designed to generate, modify, or measure a range of electronic functions of a specific or
peculiar nature on a single system or equipment .
SPECIFIC GRAVITY - The ratio between the density of a substance and that of pure water
at a given temperature .
SPECIFIC RESISTANCE - The resistance measured in ohms of a unit volume of a substance
to the flow of electric current. (The unit volume used is generally the circular
mil-foot.)
SPECTRUM - (1) The entire range of electromagnetic waves arranged in order of their
frequencies. (2) The range of frequencies considered in a system .
SPECTRUM ANALYSIS - The display of electromagnetic energy arranged according to
wavelength or frequency .
SPECTRUM ANALYZER - A test instrument that provides a visual display of the frequency
distribution of an rf signal such as a transmitter output .
SPIN VECTOR - In a gyro, a vector representing the angular velocity of the gyro rotor.
The spin vector lies along the spin axis of the rotor .
SPHERICAL WAVEFRONTS - Waves of energy that spread out in concentric circles .
SPLATTER - Unwanted sideband frequencies that are generated from overmodulation .
SPLICE - A joint formed by the connecting of two or more conductors .
SPOKING - A buckling in which the tape pack is deformed into a shape that approximates
a polygon.
SPOOL - (See reel.)
SPORADIC E LAYER - Irregular, cloud-like patches of unusually high ionization. Often
forms at heights near the normal E layer .
SPREADER - Insulator used with transmission lines and antennas to keep the parallel
wires separated .
SPROCKET TUNER - A mechanical tuning device for magnetron tubes that changes the
frequency of the cavities by changing the inductance. Also called a CROWN-OF-THORNS TUNER
.
SQUARE MIL - The area of a square, the sides of which are each equal to 1 mil. One
square mil is equal to 1.2732 circular mils .
SQUEAL - (See stick-slip.)
SQUELCH - A circuit that cuts off the output of a receiver when there is no input .
SQUIRREL-CAGE WINDINGS - A type of rotor winding in which heavy conductors are imbedded
in the rotor body. The conductors are shorted together at the ends by continuous rings. It
is widely applied in ac induction motors. Physically, it appears as a rotating
squirrel-cage, thus the name .
STABILITY - In a magnetron, the ability to maintain normal operating characteristics .
STAGE - One of a series of circuits within a single device; for example, first stage of
amplification .
STAGGER TUNING - A method of klystron tuning in which the resonant cavities are tuned
to slightly different frequencies to increase the bandwidth of the amplifier .
STANDARD - An exact value of an electrical quantity (established by international
agreement), which serves as a model for measurement of that quantity.
STANDARD REFERENCE TAPE - A tape intended for daily calibration, the performance of
which has been calibrated to the amplitude reference tape.
STANDING WAVE - The distribution of voltage and current, formed by the incident and
reflected waves, that has minimum and maximum points on a resultant wave that appear to
stand still .
STANDING-WAVE RATIO (SWR) - The ratio of the maximum (voltage, current) to the minimum
(voltage, current) points of a transmission line. Indicates the impedance matching quality
of the termination of the line .
START - The first unit of a teletypewriter signal. It is always a space .
STATIC - (1) A fixed nonvarying condition, without motion . (2) Atmospheric noise, as
in a receiver.
STATIC ELECTRICITY - Stationary electricity that is in the form of a charge. The
accumulated electric charge on an object .
STATOR - (1) The stationary part of a rotating electrical machine. The stator may be
either the field or the armature, depending on the design of the machine . (2) The
stationary member of a synchro that consists of a cylindrical structure of slotted
laminations on which three Y-connected coils are wound with their axes 120 degrees apart.
Depending on the type of synchro, the stator's functions are similar to the primary or
secondary windings of a transformer .
STATUTE MILE-5,280 feet .
STEP-BY-STEP COUNTER - A counter that provides an output for each cycle of the input in
one-step increments .
STEP-TRANSMISSION SYSTEM - A data transmission system that operates on direct current.
It consists of a step transmitter (rotary switch) and a step motor interconnected to
transmit data (information) between remote locations .
STICKOFF VOLTAGE - A low voltage used in multispeed synchrosystems to prevent false
synchronizations .
STICK-SLIP - (1) A low-speed phenomenon. (2) A relationship between tension,
temperature, humidity, wrap angle, head material, tape binder, and elastic properties. (3)
When detected audibly, it is a squeal.
STICKTION - The tape's adhering to transport components, such as heads or guides.
STIFFNESS - (1) The resistance to bending the tape. (2) A function of tape thickness.
(3) A modulus of elasticity.
STOP - The last unit of a teletypewriter signal. It is always a mark .
STORAGE, PRIMARY (MAIN, INTERNAL) - The section of the cpu in which instructions and
data are held. Also called main memory.
STORAGE, SECONDARY (AUXILIARY, EXTERNAL) - Storage outside the cpu where programs and
data are stored for future computer processing; for example tapes, disks, and punched
cards.
STORED PROGRAM - The set of instructions stored in computer memory for execution.
STRANDED CONDUCTOR - A conductor composed of a group of wires. The wires in a stranded
conductor are usually twisted together and not insulated from each other .
STRANDS - Fine metallic filaments twisted together to form a single wire .
STRATOSPHERE - Located between the troposphere and the ionosphere; it has little effect
on radio waves .
STROBOSCOPE - An instrument that allows viewing of rotating or reciprocating objects by
producing the optical effect of a slowing down or stopping motion .
STUB - Short section of a transmission line used to match the impedance of a
transmission line to an antenna. Can also be used to produce desired phase relationships
between connected elements of an antenna .
SUBASSEMBLY - Consists of two or more parts that form a portion of an assembly or a
unit .
SUBHARMONIC - An exact submultiple of the fundamental frequency. Even subharmonics are
one-half, one-quarter, and so on. Odd subharmonics are one-third, one-fifth, and so on of
the fundamental frequency .
SUBROUTINE LIBRARY - A set of standard and proven computer routines that are kept on
file for use at any time.
SUBSTRATE - Mounting surface for integrated circuits. May be semiconductor or insulator
material depending on type of IC .
SUDDEN IONOSPHERIC DISTURBANCE - An irregular ionospheric disturbance that can totally
blank out hf radio communications .
SUMMING NETWORK - A combination of two or more parallel resistors used in servosystems
as an error detector. The output of the network is the algebraic sum of the inputs .
SUPERHETERODYNE RECEIVER - A type of receiver that uses a mixer to convert the rf echo
to an IF signal for amplification .
SUPERHIGH FREQUENCY - The band of frequencies from 3 gigahertz to 30 gigahertz .
SUPERSONIC - (1) Speed greater than the speed of sound . (2) Ultrasonic.
SUPPORT SYSTEM - For a radar, a system that provides an auxiliary input, such as dry
air, electrical power, or liquid cooling .
SUPPRESSION - The process of eliminating an undesired portion of a signal .
SURFACE TREATMENT - Any process by which the surface smoothness of the tape coating is
improved after it has been applied to the base film.
SURFACE WAVE - Radio waves that travel along the contours of the earth, thereby being
highly attenuated .
SWAMPING RESISTOR - A resistor used to increase or "broaden" the bandwidth of
a circuit .
SWEPT-FREQUENCY TESTING - Testing the frequency response of a component or system by
applying an rf signal, in which the frequency is varied back and forth through a set
frequency range at a steady rate, to the input of a device. The output is then monitored
to determine the amplitude of the output with respect to frequency.
SWITCH - (1) A device used to connect, disconnect, or change the connections in an
electrical circuit . (2) A device used to open or close a circuit .
SYMMETRICAL MULTIVIBRATOR - A circuit that generates square waves .
SYMPTOM ELABORATION - Using built-in indicating instruments or other aids to define
equipment malfunction .
SYMPTOM RECOGNITION - Recognition of a situation in equipment operation that is not
normal .
SYNCHRO - A small motorlike analog device that operates like a variable transformer and
is used primarily for the rapid and accurate transmission of data among equipments and
stations .
SYNCHRO CAPACITOR - A unit containing three delta-connected capacitors. The synchro
capacitor is used in synchro systems to increase the system's accuracy by cancelling or
reducing the phase shift introduced by synchro inductance .
SYNCHRONIZER - A circuit that supplies timing signals to other radar components .
SYNCHRONIZING NETWORK - A circuit, also called a crossover or switching network, used
in servosystems to sense how far the load is from the point of correspondence; it then
functions to switch the appropriate signal into control .
SYNCHRONOUS - A type of teletypewriter operation where both transmitter and receiver
operate continuously .
SYNCHRONOUS MOTOR - An ac motor whose rotor is activated by dc. It is characterized by
constant speed and requires squirrel-cage windings or some other method to be
self-starting .
SYNCHRONOUS ORBIT - An orbit in which the satellite moves or rotates at the same speed
as the earth .
SYNCHRONOUS SPEED - The speed at which the rotating field in an ac motor revolves. This
speed is a function of the number of poles in the field and the frequency of the applied
voltage .
SYNCHRONOUS TUNING - In a klystron amplifier, a method of tuning that tunes all the
resonant cavities to the same frequency. High gain is achieved, but the bandwidth is
narrow .
SYNCHRO SYSTEM - Two or more synchros interconnected electrically. The system is used
to transmit data among equipments and stations .
SYNCHRO TESTER - A synchro receiver with a calibrated dial. This receiver is used
primarily for locating defective synchros. It can also be used for zeroing synchros .
SYSTEM - A combination of sets, units, assemblies, subassemblies, and parts joined
together to form a specific operational function or several functions .
SYSTEM NOISE - (See noise.)
