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sound wave
Pressure waves propagated through air or other plastic media. Sound waves are generally audible to the human ear if the frequency is between approximately 20 and 20,000 vibrations per second. (hertz)

source
Device that provides signal power or energy to a load.

source follower
FET amplifier in which signal is applied between gate and drain with output taken between source and drain. Also called "common drain."

source impedance
Impedance through which output current is taken from a source.

south pole
Pole of a magnet into which magnetic lines of force are assumed to enter.

spark
Momentary discharge of electrical energy due to ionization of air or other dialectric material separating two charges.

SPDT
Single pole double throw.

speaker
Also called "loudspeaker." Transducer that converts electrical energy into mechanical energy at audio frequencies.

spectrum
Arrangement or display of light or other forms of electromagnetic radiation separated according to wavelength, energy or some other property.

spectrum analyzer
Instrument used to display the frequency domain of a waveform plotting amplitude against frequency.

speed-up capacitor
Capacitor added to the base circuit of a BJT switching circuit to improve the switching time of the device.

SPST
Abbreviation for "single pole single throw."

square wave
Wave that alternates between two fixed values for an equal amount of time.

static
Crackling noise heard on AM radio receivers. Caused by electric storms or electric devices.

static electricity
Stationary electric charges.

static reverse current
Reverse current through a zener diode when the reverse voltage across the diode is less than the zener voltage rating of the device.

stator
Stationary part of some rotary device such as a variable capacitor.

step-down transformer
Transformer in which the output AC voltage is less than the input AC voltage.

step-up transformer
Transformer in which the output AC voltage is greater than the input AC voltage.

stereo sound
System in which reproduced sound is delivered through two or more channels to give a sense of direction to the source.

stop band
Range of frequencies outside the pass band of a tuned amplifier.

storage time
In a BJT switching circuit, it is the time required for collector current to drop from 100% to 90% of its maximum value.

stranded conductor
Conductor composed of a group of strands of wire twisted together.

stray capacitance
Undesirable capacitance that exists between two conductors such as two leads or one lead and a metal chassis.

subassembly
Components contained in a unit for convenience in assembling or servicing equipment.

subatomic
Particles such as electrons, protons and neutrons that are smaller than atoms.

substrate
Mechanical insulating support upon which a device is fabricated.

summing amplifier
An op-amp circuit whose output is proportional to the sum of its instantaneous voltages.

superconductor
Metal such as lead or niobium that, when cooled to within a few degrees of absolute zero, can conduct current with no resistance.

superheterodyne receiver
Radio receiver that converts all radio frequencies to a fixed intermediate frequency to maximize gain and bandwidth before demodulation.

super high frequency
(SHF) Frequency band between 3 GHz and 30 GHz. So desiganted by Federal Communications Comission (FCC).

superposition theorem
Theorem designed to simplify networks containing two or more sources. It states that in a network containing more than one source, the current at any one point is equal to the algebraic sum of the currents produced by each source acting separately.

supply voltage
Voltage provided by a power source.

surface-barrier diode
(Schottky diode)High speed diode that has very little junction capacitance. Also known as a "hot-carrier diode."

surface leakage current
Diode reverse current that passes along the surface of the semiconductor materials.

surge current
High charging current that flows into a power supply filter capacitor as the power is first turned on.

sweep generator
Test instrument designed to produce a voltage that continously varies in frequency over a band of frequencies. Used as a souce to display frequency response of a circuit on an oscilloscope.

switch
Electrical device having two states, on (closed) or off (open). Ideally having zero impedance when closed and infinite impedance when open.

switching transistor
transistor designed to change rapidly between saturation and cut-off.

synchronization
Also called sync. Precise matching of two waves or functions.

synchronous
Two or more signals in step or in phase.

sync pulse
Pulse used as a reference for synchronization.

system
Combination of several pieces of equipment to perform in a particular manner.

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