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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 [17].


SATELLITE-SUN CONJUNCTION

A period when the satellite and sun are close together and the noise from the sun prevents or hampers communications [17].


SATURABLE-CORE REACTOR

A coil in which the reactance is controlled by changing the permeability of the core [8].


SATURATION

(1) The condition existing in any circuit in which an increase in the input signal produces no further change in the output [13]. (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 [6] [7]. (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 [8].


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 [15].


SCANNING

(1) The process of subdividing a picture in an orderly manner into segments. This is used in facsimile transmission [17]. (2) Systematic movement of a radar beam to cover a definite pattern or area in space [18].


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 [16].


SCATTER ANGLE

The angle at which the receiving antenna must be aimed to capture the scattered energy of tropospheric scatter [10].


SCHEMATIC

A diagram which shows, by means of graphic symbols, the electrical connections and functions of a specific circuit arrangement [1] [4].


SCHEMATIC SYMBOLS

A letter, abbreviation, or design used to represent specific characteristics or
components on a schematic diagram [1].


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 [18].


SCREEN GRID

A grid placed between a control grid and the plate and usually maintained at a fixed positive potential [6].


SCREENING

Process of applying nonconductive or semiconductive materials to a substrate to form thick film components [14].


SEA CLUTTER

Unwanted echoes from the irregular surface of the sea that appear on a radar indicator [18].


SEARCH RADAR SYSTEM

An early-warning device that searches a fixed volume of space [18].

SECAS

SHIP EQUIPMENT CONFIGURATION ACCOUNTING SYSTEM —The Navy system that
keeps track of the configuration of equipment in the fleet [16].


SECOND DETECTOR

The part of the receiver that separates the audio or video component from the modulated intermediate frequency [18].


SECOND-SWEEP ECHOES

See AMBIGUOUS RETURNS [18].

SECONDARY

The output coil of a transformer [2].

SECONDARY CELL

A cell that can be recharged by a current being passed through the cell in a
direction opposite to the discharge current [1].


SECONDARY EMISSION

The liberation of electrons from an element, other than the cathode, as a
result of being struck by other high-velocity electrons [6].


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 [18].


SELECTIVITY

The ability of a receiver to select the desired signal and reject unwanted signals [9] [17].

SELENIUM

A chemical element with light-sensitive properties that makes it useful as a semiconductor material in metallic rectifiers [7].


SELF-BIAS

In a vacuum tube circuit, the voltage developed by the flow of current through a resistor in the grid or cathode leads [6].


SELF-EXCITED GENERATORS

DC generators in which the generator output is fed to the field to produce field excitation [5].


SELF-EXCITED METER

A term used to describe meters that operate from their own power sources
[16].


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]. (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 [10].


SELF-LUMINOUS BODIES

Objects that produce their own light [10].

SELF-SYNCHRONIZED RADAR

A type of radar in which the timing pulses are generated within the transmitter [18].


SENDING END

See INPUT END [10].

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] [16]. (3) The ability of a receiver to reproduce very weak signals. The greater the receiver sensitivity, the weaker the signal that can be reproduced [17]. (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 [12].


SENSITIVITY TIME CONTROL

(STC)—A circuit that varies the gain of a receiver as a function of time [18].


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 [1].


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 [9].


SERIES PEAKING

A technique used to improve high-frequency response in which a peaking coil is
placed in series with the output signal path [8].


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 [18].


SERIES-DIODE DETECTOR

The semiconductor diode in series with the input voltage and the load
impedance. Sometimes called a VOLTAGE-DIODE DETECTOR [12].


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 [9].


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 [9].


SERIES-PARALLEL CIRCUIT

A circuit that consists of both series and parallel networks [1] [9].

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 [9].


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 [9] [10].


SERIES-WOUND MOTORS AND GENERATORS

Machines in which the armature and field windings are connected in series with each other [5].


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 [15].


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 [15].


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 [15].


SET

A unit or units and the assemblies, subassemblies, and parts connected or associated together to perform a specific function [17].


SEXADECIMAL

Same as HEXADECIMAL [13].

SHADOW

A dead spot (minimum radiation) caused by the physical obstruction of transmitted waves by a feed horn [18].


SHAPING CIRCUIT

A circuit that alters the shapes of input waveforms [9].

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 [6].


SHELF LIFE

The period of time that a cell or battery may be stored and still be useful [1].

SHIELDED PAIR

A line consisting of parallel conductors separated from each other and surrounded by a solid dielectric [10].


SHIELDING

(1) A metallic covering used to prevent magnetic or electromagnetic fields from affecting an object [1]. (2) Technique designed to minimize internal and external interference [14].


SHORT CIRCUIT

An unintentional current path between two components in a circuit or between a component and ground; usually caused by a circuit malfunction [1] [3] [16].


SHORT-CIRCUITED LINE

A transmission line that has a terminating impedance equal to 0 [10].

SHUNT

A resistive device placed in parallel with another component. Appreciable current may flow through it and an appreciable voltage may exist across it [12].


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 [8].


SHUNT RESISTOR

A resistor in parallel. In an ammeter, shunt resistors are used to provide multiple ranges [3].


SHUNT VOLTAGE REGULATOR

A regulator whose regulating device is in parallel with the load resistance [7].


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 [12].


SHUNT-WOUND MOTORS AND GENERATORS

Machines in which the armature and field windings are connected in parallel (shunt) with each other [5].


SIGNAL

A general term used to describe any ac or dc of interest in a circuit; for example, input signal [8] [15].


SIGNAL DISTORTION

Any unwanted change to the signal [12].

SIGNIFICANT SIDEBANDS

Those sidebands with significantly large amplitude [12].

SILICON

A metallic element which, in its pure state, is used as a semiconductor [7].

SILICON-CONTROLLED RECTIFIER

A semiconductor device that functions as an electrically controlled switch [7].


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]. (2) The basic synchronous alternating waveform for all complex waveforms [12].


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 [4].


SINGLE, STATIONARY-LOBE SCANNING SYSTEM

Antenna (with a single, stationary beam) that is rotated to obtain 360-degree coverage [18].


SINGLE-ENDED MIXER

See UNBALANCED CRYSTAL MIXER [18].

SINK

See OUTPUT END [10].

SKIP DISTANCE

The distance from a transmitter to the point where the sky wave is first returned to earth [10].


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 [10].


SKY WAVES

Radio waves reflected back to earth from the ionosphere [10].

SLANT RANGE

See RANGE [18].

SLIP

The difference between rotor speed and synchronous speed in an ac induction motor [5].

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 [5]. 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 [12].


SLOT

Narrow opening in a waveguide wall used to couple energy in or out of the waveguide. Also called an aperture or a window [11].


SM & R CODE

SOURCE, MAINTENANCE, AND RECOVERABILITY CODE (SM & R CODE)—Specifies
maintenance level for repair of components or assemblies [14].


SNAP-ACTING

Changing position quickly with the aid of a spring [3].

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 [3].


SOLID

One of the three states of matter; it has definite volume and shape (ice is a solid) [1].

SOLID-STATE DEVICE

An electronic device that operates by the movement of elections within a solid
piece of semiconductor material [7].


SONIC

Pertaining to sounds capable of being heard by the human ear [10].

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 [10]. (3) The device which furnishes the electrical energy used by a load [1].


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 [12].


SPACE CHARGE

An electrical charge distributed throughout a volume or space [6].

SPACE DIVERSITY

Reception of radio waves by two or more antennas spaced some distance apart
[10].


SPACE WAVE

Radio waves that travel directly from the transmitter to the receiver and remain in the troposphere [10].


SPACING

The condition in teletypewriter operation where a circuit is open and no current flows [17].

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 [12].


SPECIFIC GRAVITY

The ratio between the density of a substance and that of pure water at a given
temperature [1].


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.) [4]


SPECTRUM

(1) The entire range of electromagnetic waves arranged in order of their frequencies. (2) The range of frequencies considered in a system [10].


SPECTRUM ANALYSIS

The display of electromagnetic energy arranged according to wavelength or
frequency [12].


SPECTRUM ANALYZER

A test instrument that provides a visual display of the frequency distribution
of an RF signal such as a transmitter output [18].


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 [16].


SPHERICAL WAVEFRONTS

Waves of energy that spread out in concentric circles [18].

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 [15].


SPLATTER

Unwanted sideband frequencies that are generated from overmodulation [12].

SPLICE

A joint formed by the connecting of two or more conductors [4].

SPORADIC E LAYER

Irregular, cloud-like patches of unusually high ionization. Often forms at heights near the normal E layer [10].


SPREADER

Insulator used with transmission lines and antennas to keep the parallel wires separated [10].

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 [11].


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 [4].


SQUELCH

A circuit that cuts off the output of a receiver when there is no input [17].

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 [5].


STABILITY

In a magnetron, the ability to maintain normal operating characteristics [18].

STAGE

One of a series of circuits within a single device; for example, first stage of amplification [8].

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 [11].


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 [10].


START

The first unit of a teletypewriter signal. It is always a space [17].

STATIC

(1) A fixed nonvarying condition, without motion [13]. (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 [1].


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 [5]. (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 [15].


STATUTE MILE

5,280 feet [18].

STEP-BY-STEP COUNTER

A counter that provides an output for each cycle of the input in one-step
increments [9].


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 [15].


STICKOFF VOLTAGE

A low voltage used in multispeed synchrosystems to prevent false synchronizations [15].


STOP

The last unit of a teletypewriter signal. It is always a mark [17].

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 [4].


STRANDS

Fine metallic filaments twisted together to form a single wire [4].

STRATOSPHERE

Located between the troposphere and the ionosphere; it has little effect on radio waves [10].


STROBOSCOPE

An instrument that allows viewing of rotating or reciprocating objects by producing the optical effect of a slowing down or stopping motion [16].


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 [10] [18].


SUBASSEMBLY

Consists of two or more parts that form a portion of an assembly or a unit [17].

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 [17].


SUBSTRATE

Mounting surface for integrated circuits. May be semiconductor or insulator material depending on type of IC [14].


SUDDEN IONOSPHERIC DISTURBANCE

An irregular ionospheric disturbance that can totally blank out hf radio communications [10].


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 [15].


SUPERHETERODYNE RECEIVER

A type of receiver that uses a mixer to convert the RF echo to an IF signal for amplification [18].


SUPERHIGH FREQUENCY

The band of frequencies from 3 gigahertz to 30 gigahertz [17].

SUPERSONIC

(1) Speed greater than the speed of sound [10]. (2) Ultrasonic.

SUPPORT SYSTEM

For a radar, a system that provides an auxiliary input, such as dry air, electrical
power, or liquid cooling [18].


SUPPRESSION

The process of eliminating an undesired portion of a signal [17].

SURFACE WAVE

Radio waves that travel along the contours of the earth, thereby being highly
attenuated [10].


SWAMPING RESISTOR

A resistor used to increase or "broaden" the bandwidth of a circuit [8].

SWITCH

(1) A device used to connect, disconnect, or change the connections in an electrical circuit [1]. (2) A device used to open or close a circuit [3].


SWR

(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 [10] [11].


SYMPTOM ELABORATION

Using built-in indicating instruments or other aids to define equipment
malfunction [16].


SYMPTOM RECOGNITION

Recognition of a situation in equipment operation that is not normal [16].

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 [15].


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 [15].


SYNCHRO SYSTEM

Two or more synchros interconnected electrically. The system is used to transmit data among equipments and stations [15].


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 [15].


SYNCHRONIZER

A circuit that supplies timing signals to other radar components [18].

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 [15].


SYNCHRONOUS

A type of teletypewriter operation where both transmitter and receiver operate
continuously [17].


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 [5].


SYNCHRONOUS ORBIT

An orbit in which the satellite moves or rotates at the same speed as the earth
[17].


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 [5].


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 [11].


SYSTEM

A combination of sets, units, assemblies, subassemblies, and parts joined together to form a specific operational function or several functions [17].



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