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 RadioShack Consumer Electronics Glossary: S

Acronym: Super Audio CompactDisc
Audio: a high-resolution digital audio format. The advantage of SACD over standard compact discs is that it uses a new method of encoding audio, called Direct Stream Digital (DSD), rather than Pulse Code Modulation or PCM. Super Audio CD can support high-resolution stereo recordings as well as high-resolution multi-channel (up to 6) discrete audio channels. Super Audio CD discs can be played back on dedicated Super Audio CD players or combination SACD/DVD-Video players. Certain SACD discs feature a conventional audio CD layer (hybrid SACDs) which can be played back by any CD player or computer with a CD-ROM drive.
Acronym: Specific Area Message Encoding
Weather: A six-digit code indicating a particular state and county. The first three digits indicate the state; the second three digits indicate the county.
Sample Rate
Audio: The rate per second at which an audio sample is recorded, measured in Hertz (Hz: cycles per second) and Kilohertz (kHz: thousand cycles per second).
Audio, Video, Satellite: A piece of equipment which is placed in orbit.
Satellite Antenna: see Antenna, Satellite.
Satellite System
Audio, Video, Satellite: A satellite antenna and a corresponding satellite receiver. Older C-band systems may also include a decoder.
Video: The degree to which a color is undiluted by white light. If a color is 100 percent saturated, it contains no white light. If a color has no saturation, it is a shade of gray. For example, a lightly saturated red looks pink, while a fully saturated red is a pure red.
Radar Detectors: A frequency band which extends approximately from 2 gigahertz to 4 gigahertz (1 gigahertz = 1 billion hertz, or cycles per second).
Satellite: A frequency band which extends approximately from 1700 megahertz to 3000 megahertz (1 megahertz = 1 million hertz, or cycles per second).
Acronym: Subsidiary Communications Authorization
Communications: A frequency band which contains the frequencies from 50 to 100kHz.
Communications: To use a radio scanner to listen to radio conversations.
Digital Video: To use an image scanner to convert a picture, photo or other document into an electronic image which can be stored on your computer. Flat bed scanners have become very reasonably priced in the past few years.
Metal Detectors: 1) The effective search coil detection width.
2) The movement of the search coil over the ground.
Communications: A radio that can tune quickly /automatically to a wide range of frequencies used by hobbyist to monitor police, fire, and other emergency services.
Digital Video: A device that uses light to read printed information and converts it into the computer in a digital form for editing.
Scanning, Conventional
Communications: Following conversations that are broadcast on a radio system which operates on only a single channel. Trunking is not used and the radio channel is selected manually.
Scanning, Trunked
Communications: Following conversations that are broadcast on radios automatically tuned by computer to change frequencies based on the data channel.
Scan, Wide
Metal Detectors: A search head where the transmit and receive coils are arranged in the form of 2 D's back to back. This type of coil offers different characteristics to the concentric. It will cover a larger area than a concentric coil of equivalent size and is less affected by mineralization. Also called Double D or 2D.
Schottky Diode: see Diode, Schottky.
Acronym: Silicon-Controlled Rectifier
Electronics: A three-terminal active component that acts as a gated diode. The gate terminal is used to turn the device on allowing current to pass from cathode to anode.
Plug 'n Power: A light-bulb module that is screwed into a light-fixture and responds to X-10 commands
Metal Detectors: A search technique in which the search coil is pressed and held in contact with the ground in order to maintain an even audio threshold. With newer detectors, this technique is used to gain depth.
Acronym: Subsidiary Communications Service
Communications: Another name for the SCA (Subsidiary Communications Authorization).
Acronym: Small Computer System Interface
Computers: A high-speed input/output bus which is faster than serial and parallel ports but slower (and harder to configure) than USB and Firewire ports.
Scuff Cover: see Skid Plate.
Audio: The effective surface area of the speaker driver.
SD Card
Acronym: Secure Digital Card
Digital Audio, Digital Video, Telephony, Computers: A flash memory card identical in size and shape to the MultiMedia Card (MMC) flash cards.
Acronym: Secure Digital Music Initiative
Digital Audio: A forum for the recording industry and certain technology companies to develop a protected framework for playing, recording and distributing digital music.
Acronym: Symmetric Digital Subscriber Line
Internet: A technology which allows high-speed Internet connections on standard telephone lines (POTS). It is called symmetric because the data rate when receiving (downstream rate) is the same as the data rate when transmitting (upstream rate). SDSL supports data rates of up to 3 Mbps. Compare to ADSL.
Acronym: Standard-definition Digital Television
Digital Video: A digital video format with 480 lines of resolution.
Sea Level
Weather: The height or level of the sea surface at any time. It is used as a reference for elevations above and below.
Search Coil: see Coil, Search.
Search Coil Cable
Metal Detectors: An electrostatically shielded cable containing multiple conductors which carry signals to and from the search coil and control housing.
Search Engine
Internet: 1) A web site which collects names and/or data about other web sites, and presents them to you when you run a search or query.
2) A service on a web site which allows you to search that site for specific keywords.
Batteries: A rechargeable battery designed to deliver the rated capacity, and then be recharged and re-used.
Electronics: The second winding of a transformer, which is the output winding connected to a load. Compare to Primary, which is the input winding connected to the source.
Secondary Cell
Batteries: A rechargeable battery designed to deliver the rated capacity, and then be recharged and re-used.
Secure Digital Music Initiative: see SDMI.
Secure Digital Card: see SD Card.
Self Discharge
Batteries: The rate at which a battery will lose energy while in storage.
DIY, Electronics: 1) A material which is neither a good conductor or a good insulator, such as germanium, lead sulfide, lead telluride, selenium, silicon, and silicon carbide.
2) A component constructed using a semicondutor material, such as a diode, photocell, thermistor, transistor, etc.
Semiconductor, n-type
Acronym: Negative-type Semiconductor
Electronics: A semiconductor that carries current in the form of electrons (negative).
Semiconductor, p-type
Acronym: Positive-type Semiconductor
Electronics: A semiconductor that carries current in the form of electron deficiencies or "holes" (positive).
Audio: A rating obtained by applying a standard input value and measuring the resulting output. The standard input values are given in the chart below.
Sensitivity for... Is measured by applying... And measuring...
Speakers 1 watt the sound pressure level (SPL) at one meter.
Headphones 1 milliwatt the sound pressure level at the earpiece.
Microphones 1 pascal the output level.
Amplifiers a given impedance (usually 4 or 8 ohms) the input level required to output one watt.
Receivers an audio signal the input level required to obtain a given signal-to-noise ratio.
Metal Detectors: The measure of the capacity of a detector to perceive changes in conductivity within the detection pattern. Generally, the more sensitivity a detector can smoothly provide, the more depth it will achieve.
Digital Video: An electronic device that converts the light allowed in by the shutter to an electrical signal.
Sensor, CCD
Acronym: Charge-Coupled Device Sensor
Digital Video: An image sensor that reads the charges from the sensor's photosites one row at a time.
Sensor, CMOS
Acronym: Complementary Metal Oxide Semiconductor Sensor
Digital Video: An image sensor which can incorporate processing circuitry on the same chip as the sensor.
Sensor, Hall Effect
Electronics: A contactless sensor which is triggered in response to either an external magnet or a ferrous object.
Sensor, Shock
Electronics: A sensor which is triggered in response to physical shock.
Audio: A specification (in dB) describing the amount of isolation between the left and right channel stereo signals. The higher the dB rating, the better the isolation.
Digital Video: The shades of brown found in the pictures from very early in photography. Also used as a special effect on some digital cameras, which converts the existing image into shades of brown.
Serial Bus: see IEEE-1394.
Serial Port
Computers: Standard, but extremely slow, connection port found on most computers. Also called RS-232. Both Macintosh and PC computers can have serial ports.
Electronics: A method of making multiple electrical connections in which the positive lead of each component is connected to the negative lead of the next component and only the first and last components are connected to the power terminals, so that the current has a single path to follow through the circuit. Compare to Parallel.
Service Band
Communications: A frequency range that is used for a particular purpose, such as aircraft or police communications.
Service Maintenance Repeater: see SMR (Communications).
Severe Weather: see Weather, Severe.
Severe Thunderstorm: see Thunderstorm, Severe.
GPS: An instrument used for measuring the angle between the horizon and a celestial body (such as the moon, a star or the sun) in order to determine longitude and/or latitude.
Software: A method of software distribution in which the author requests some payment, usually in the accompanying documentation files or in an announcement made by the software itself. Such payment may or may not buy additional support or functionality. Compare to Freeware.
Shelf Life
Batteries: A rating that indicates how long the battery will last in storage until it is dead by self-discharge.
Acronym: Super High Frequency
Electronics: The frequency band between 3 GHz and 30 GHz.
Electronics, Cables: A metal grounded cover used to protect a wire, component or piece of equipment from stray magnetic and/or electric fields.
Electronics, Cables: The condition of being protected from passing magnetic waves to or from the shielded device.
Shield, Faraday
Metal Detectors: A metal foil wrapping of the search coil windings for the purpose of eliminating electrostatic interference caused by wet vegetation.
Short Circuit
Electronics: A low-resistance conection between two points in a circuit. Also called a short.
Short Message Service: see SMS.
Communications: The frequency band between 535 kHz and 30,000 kHz.
A parallel circuit branch.
Digital Video: The device in the camera that opens and closes to let light from the scene strike the image sensor and expose the image. The three primary shutter types used in digital photography are digital (or CCD) shutters, iris (or leaf) shutters and focal plane shutters.
Shutter, CCD: see Shutter, Digital.
Shutter, Digital
Digital Video: A digital or CCD shutter works by electronically limiting the sampling time of the sensor. Also called a CCD Shutter.
Shutter, Focal Plane
Digital Video: A shutter that uses two curtains to control the exposure. The first curtain exposes the film or sensor, and the second curtain moves after the first to cover the film or sensor.
Shutter, Iris
Digital Video: A continuously-adjustable shutter consisting of interposed metal leaves. See illustration. Also called a Leaf Shutter.
Shutter Lag
Digital Video: The time between pressing the shutter and actually capturing the image. This is due to the camera having to calculate the exposure, set the white balance and focus the lens.
Shutter, Leaf: see Shutter, Iris.
Shutter Speed
Digital Video: The length of time the shutter opens to let light pass through the lens to the focal plane.
Acronym: Système International d'Unités (French " International System of Units")
Measurement: An international system of measurement which incorporates the metric system and components of the cgs system.
Audio: Sibilance is the noise that is associated with the vocal pronunciation of "s" "sch" or "ch" and other words with syllables that have the same characteristics. The phrase "Sally sells seashells by the seashore" would emphasize sibilance. Overload in an unprotected microphone and any linked electronics can be caused by sibilance. A windscreen placed on the microphone can correct this problem.
Acronym: System Identification
Telephony: A unique digital code assigned to each cellular system. The home system of each mobile is stored in it's internal memory so that the mobile knows when it is a roamer (outside it's normal service area).
Communications: A frequency band, either higher or lower than the carrier, that is energized by the AM modulation process. Amplitude modulation creates two sidebands -- the upper sideband (the frequencies above the carrier) and the lower sideband (the frequencies below the carrier). Normal AM has both sidebands. When one sideband has been removed, it is SSB (Single side-band) AM.
Sideband, Lower
Communications: The frequency band which is lower than the carrier frequency but which is energized by the AM modulation process.
Sideband, Upper
Communications: The frequency band which is higher than the carrier frequency but which is energized by the AM modulation process.
Telephony: Line echoes that are allowed to bleed back into the earpiece in order to provide the user to hear themself talk, giving positive feedback that the telephone is working.
DIY, Electronics: An electrical quantity that conveys information.
Metal Detectors: An audio response or visual indication alerting the operator that a target has been detected.
Signal Bridge (Phase Coupler)
Electronics, Plug 'n Power: A device that connects two 110V phases together so that the Plug 'n Power X-10 signal can cross from one to the other. This allows Plug 'n Power units to work with each other even though they are on different phases.
Signal, Deep
Metal Detectors: A barely audible signal.
Signal, Faint
Metal Detectors: A sound characteristic of targets that are sometimes deeply buried or very small in size.
Signal, False
Metal Detectors: An erroneous signal created by over shoot, ground voids or highly-mineralized hot rocks. See also Back-Reading.
Signal Level
Audio: The power rating of an audio signal. There are four general types: Mic-level, Line-level and Instrument-level, and Phono level.
Signal, Radio
GPS: An electromagnetic wave, such as light or X-ray. The speed of electromagnetic waves in vacuum, is 186,000 miles per second.
Signal to Noise Ratio
Audio: The ratio of the magnitude of the signal to the magnitude of noise, expressed in decibels.
Signal Width
Metal Detectors: The total distance of ground an audio signal is sustained during search coil travel or scan.
Silent Search
Metal Detectors: A detector capable of producing a target signal while operating below the audio threshold.
Silicon-Controlled Rectifier: see SCR.
Metal Detectors: A silver coin as opposed to a clad coin, usually dated pre-1965.
Acronym: Subscriber Identity Module
Telephony: A computer chip set in a handset that contains information which identifies the subscriber when connecting to the network.
Communications, Telephony, Computers: A form of communication or data transfer which occurs in only one direction at a time.
Sine Wave
Acronym: Sine Waveform
DIY, Electronics: A waveform that represents the variation of a signal over time at a single frequency. For example, household current in the United States has a sine waveform at 60 Hz.
Sine Waveform
Sine Wave, Modified
DIY, Electronics: "Modified sine wave" is a designation used to describe an inverter that produces AC power in a modified or squared-off sine wave (the red line in the image below traces a modified sine wave). A modified sine wave inverter can handle many devices, but can have problems with devices such as microwave ovens, laser printers, laptop computers, clocks and cordless tool chargers, as a modified sine wave produces a greater number of harmonics. Equipment such as these are particularly sensitive to harmonics, and devices that use capacitors in the circuit (such as some battery chargers) can also be damaged. Also called Square Sine Wave.
Modified (or Square) Sine Waveform
Sine Wave, True
Inverters: "True sine wave" is a designation used to describe an inverter that provides AC power in a true sine wave, rather than a modified or square sine wave. A true sine wave inverter can power most devices or household appliances. Also called Pure Sine Wave.
Single In-line Package: see SIP.
Single-lens Reflex: see SLR.
Single Pole Double Throw: see SPDT.
Single Pole Single Throw: see SPST.
Single Throw
Electronics: Refers to a switch or relay that contains only one set of contacts which can be either opened or closed.
Electronics: A device such as a load that consumes power or conducts away heat.
Batteries: A nickel-cadmium battery which uses a plate of sintered nickel powder.
Batteries: The process of bonding either a metal or powder by cold pressing it into a desired shape and then applying heat to weld the metal or powder without melting it.
Electronics: Having the shape or properties of a sine wave.
Acronym: Single In-line Package
Electronics: A component package containing several electronic components (generally resistors) with a single row of connecting pins.
Communications: A group of radio repeaters that are connected to the same high-speed data bus. Up to 20 LTR repeaters can be connected together in this way.
Internet: A collection of pages that are organized as a coherent whole.
Skid Plate
Metal Detectors: A protective cover for the bottom of the search coil. Also called Scuff Cover.
Software: A set of graphics that allows you to customize the look and feel of a software application.
Weather: Also known as ice pellets, it is winter precipitation in the form of small bits or pellets of ice that rebound after striking the ground or any other hard surface.
Acronym: Single-Lens Reflex
Digital Video: A camera that has one lens that is used for both composing the frame and capturing the image to memory, as opposed to using a Range Finder. Also called TTL.
Slow-blow Fuse: see Fuse, Slow-blow.
Slow Motion
Metal Detectors: A description of search coil speed required to operate the motion discriminate mode.
Small Computer System Interface: see SCSI.
Smart Card
Telephony: A card with a microprocessor and memory, approximately the size of a credit card.
Digital Audio, Digital Video, Telephony, Computers: A popular form of flash memory card, also called a SSFDC (Solid State Floppy Disc Card). Compare to MMC (Multimedia Card). The two types are not interchangeable.
Smart Telephone
Telephony: A telephone with a microprocessor, memory, screen and a built-in modem. The smart telephone combines the some of the capabilities of a PC on a handset.
Smiley: see Emoticon.
Digital Video: An editing tool which averages pixels with their neighbors to reduces contrast and simulate an out-of-focus image.
Acronym, Communications: Service Maintenance Repeater
Acronym, Telephony: Specialized Mobile Radio
Communications: A repeater maintained by a radio club that requires that radio operators be a member of that club in order to transmit to that repeater.
Telephony: A private business service that uses mobile radiotelephones and base stations, often in dispatch applications. See ESMR.
Acronym: Short Message Service
Telephony: A message service that allows the user to send short text-only messages between wireless telecommunications devices. SMS is the first phase of message service development and was introduced as part of the GSM standard. SMS information is sent through the network using open frequencies in the existing network. The next phase is EMS (Enhanced Messaging Service), which adds black-and-white image and basic sound capabilities, and MMS (Multimedia Messaging Service), which adds advanced video and voice capabilities.
Acronym: Signal/Noise
Audio: see Signal to Noise Ratio.
Acronym: Signal to Noise Ratio
Audio: see Signal to Noise Ratio.
Video: A reception problem occurring with analog video signals. It iscaused by poor reception or interference from another source.
Weather: Frozen precipitation in the form of white or translucent ice crystals in complex branched hexagonal form. It most often falls from stratiform clouds, but can fall as snow showers from cumuliform ones. It usually appears clustered into snowflakes.
Snow Advisory
Weather: A statement or advisory issued when snow is expected to create hazardous travel conditions. It warns of less severe weather conditions than a winter storm
Snow Grains
Weather: Frozen precipitation in the form of very small, white, opaque grains of ice. The solid equivalent of drizzle.
Snow Pellets
Weather: Frozen precipitation in the form of white, round or conical opaque grains of ice. Their diameter ranges from 0.08 to 0.2 inch (2 to 5 mm). They are easily crushed and generally break up after rebounding from a hard surface, unlike hail.
Solar Panel
Electronics: A panel that is made up of solar cells which are capable of collecting energy fromsunlight.
DIY: A metallic alloy designed to melt at relatively low temperatures and solidify quickly, used to join two metal surfaces.
Solder, Silver
DIY: A solder composed of silver, copper and zinc. It has a melting point lower than pure silver, but higher than lead-tin solder.
Electronics: An air-core coil which, when equipped with a movable iron core, will convert current into physical motion.
Solid Conductor: see Conductor, Solid.
Electronics: Refers to circuits where signals pass through a solid semiconductor material such as transistors and diodes as opposed to vacuum tubes where signals pass through a vacuum.
Solid State Floppy Disc Card: see SmartMedia™.
Sound Card
Audio, Computers: A PC circuit card that allows a computer to a) convert digital audio files to stereo sound through external sources such as amplified speaker systems or b) convert stereo sound from an external source to digital audio files. Sound cards are included with most PC computers. Macintosh computers almost always have built-in sound capabilities that do not require a sound card.
Sound Pressure Level: see SPL.
Acronym: Single Pole Double Throw
Electronics: Refers to a three-terminal switch or relay in which one terminal can be connected to either one of the other terminals.
Audio: A device which converts electrical energy to sound energy. This can mean an entire loudspeaker system such as a woofer, midrange, tweeter, crossover network, and enclosure. It can also mean an individual speaker driver such as a woofer.
Speaker Driver
Audio: A single speaker element rather than an assembled loudspeaker. The primary parts of a driver are (1) the cone (or dome), which moves the air, and (2) the voice coil and (3) the magnet. The electrical signal from the audio source causes the voice coil to move toward or away from the magnet, and the movement of the voice coil moves the cone. Speaker drivers include tweeters, midrange, and woofers, and can be either standalone or horn loaded.
Specialized Mobile Radio: see SMR (Telephony).
Speed of Light
Measurement: The speed at which electromagnetic radiation travels in a vacuum (space) and measures 186,000 miles per second
A spherical surface is one on which every point is the same distance (radius) from a fixed point in the center. A three-dimensional circle.
Audio, Turntables: the in the center off the turntable platter onto which the record is placed. There are two areas of variation for spindles: size (either small, for playing standard-hole records, or large, for playing 45's) and single-play vs. stacking. There is also an adapter which can be placed over a small spindle to allow single-play of 45's.
Acronym: Sound Pressure Level
Audio: The RMS sound pressure in dB re 20 microPa; used as a technical indication of loudness.
Electronics, Audio, Video, Satellite: A device with one input and two or more outputs which splits the signal into two or more identical signals.
Electronics, Video, Satellite: A device which consists of a combiner and a splitter in the same package. The combiner is used to combine two different signals which operate on different frequencies (such as local broadcast antenna output and satellite antenna outputs) into a single signal carried on a single cable, to simplify the cable run. The splitter in this device is used to to split the combined signal back into the two original signals to allow each signal to be connected to the correct input on the receiver.
Splitter, Passive
Electronics, Video, Satellite: A splitter that divides a signal into two or more identical signals without any amplification of the signal to counteract the signal loss due to splitting the signal. If the signal loss affects reception, it can be corrected by adding a signal amplifier. A splitter which does amplify the signal is called a distribution amplifier.
Spot Metering
Digital Video: A method of autoexposure based on a meter reading of a small circle in the center of the viewfinder.
Spread Spectrum
Telephony: A modulation technique, also known as frequency hopping, used in wireless systems. The data is converted into packets, which are spread over a range of bandwidth.
Acronym: Single Pole Single Throw
Electronics: Refers to a two-terminal switch or relay thet can open or close one circuit.
Communications: 1) A knob or switch on a communications receiver that allows you to set the minimum strength signal that will be received.
2) To use the squelch knob or switch.
Acronym: Single SideBand
Electronics: An AM tranmission format in which the transmitter suppresses one sideband (either the upper sideband or the lower sideband).
Acronym: Solid State Floppy Disc Card
Computers, Digital Audio, Digital Video, Telephony: see SmartMedia™.
Metal Detectors: The ability of a metal detector to maintain a manually-adjusted tuning threshold under the effects of outside interference. See also Drift.
Standard Atmosphere: see Atmosphere, Standard.
Standard-definition Digital Television: see SDTV.
Standard Surface Pressure: see Pressure, Standard Surface.
Standby Charge
Batteries: A low overcharge current rate continuously applied to a battery to keep it at a full charge. Also known as trickle charge.
Standby Time
Telephony: The amount of time you can leave your fully charged cordless, cellular, portable or transportable telephone turned on (without actually being used) before the current drain required to maintain the telephone will completely discharge the batteries.
Standing Wave Ratio: see SWR
Computers, Networking: A network topology in which the computers are connected as illustrated below. See also Bus, Ring, Mesh, Tree.
Star Topology
Start, Cold
GPS: The power-on sequence where the GPS receiver downloads almanac data before establishing a position fix.
Start, Warm
GPS: Used to describe state where a GPS receiver is powered on and still has valid almanac data available. This shortens the time required to locate satellites and arrive at the first position solution.
Measurement: Cgs unit for charge; equal to 3.336*10-10 coulombs.
Statement (Weather)
Weather: "A message containing follow up information to a warning, watch, or emergency."
(taken from NWR's "Detailed SAME Specification File" (
Audio, Video, Communications: A crackling noise heard on AM radio receivers, caused by electric storms or electric devices.
Static Electricity
Electronics: Stationary electric charges.
Measurement: Cgs unit for electrical potential; equal to (erg/esu) and 299.8 volts.
Steady Pix™:
Video: A feature on RCA® camcorders which digitally stabilizes the images before recording them on tape, minimizing video "jitters" caused by camera motion.
Step-down Transformer: see Transformer, Step-down.
Step-up Transformer: see Transformer, Step-up.
Acronym: (short for) Stereophonic
Audio: Refers to multi-channel sound (combined sound from more than one microphone) which is sent to mutiple speakers (usually, but not limited to, two).
Weather: An individual low pressure disturbance, complete with winds, clouds, and precipitation. The name is associated with destructive or unpleasant weather. Storm-scale refers to disturbances the size of individual thunderstorms.
Storm, Winter
Weather: Any one of several storm systems that develop during the late fall to early spring and deposit wintry precipitation, such as snow, freezing rain, or ice. Types of winter storms include blizzards, ice storms, and nor'easters.
Stranded Conductor: see Conductor, Stranded.
Weather: Clouds composed of water droplets that exhibit no or have very little vertical development. The density of the droplets often blocks sunlight, casting shadows on the earth's surface. Bases of these clouds are generally no more than 6,000 feet above the ground. They are classified as low clouds, and include all varieties of stratus and stratocumulus. The opposite in type are the vertical development of cumuliform clouds.
Weather: A low cloud composed of layers or patches of cloud elements. It can form from cumulus clouds becoming more stratiformed and often appears as regularly arranged elements that may be tessellated, rounded, or roll-shaped with relatively flat tops and bases. It is light or dark gray in color, depending on the size of the water droplets and the amount of sunlight that is passing through them.
Weather: The boundary zone or transition layer between the stratosphere and the mesosphere. Characterized by a decrease in temperature with increasing altitude.
Weather: The layer of the atmosphere located between the troposphere and the mesosphere, characterized by a slight temperature increase and absence of clouds. It extends between 11 and 31 miles (17 to 50 kilometers) above the earth's surface. It is the location of the earth's ozone layer.
Weather: One of the three basic cloud forms (the others are cirrus and cumulus. It is also one of the two low cloud types. It is a sheetlike cloud that does not exhibit individual elements, and is, perhaps, the most common of all low clouds. Thick and gray, it is seen in low, uniform layers and rarely extends higher than 5,000 feet above the earth's surface. A veil of stratus may give the sky a hazy appearance. Fog may form from a stratus cloud that touches the ground. Although it can produce drizzle or snow, it rarely produces heavy precipitation. Clouds producing heavy precipitation may exist above a layer of stratus.
Stratus Fractus
Weather: Stratus clouds that appear in irregular fragments, as if they had been shred or torn. Also appears in cumulus clouds (called cumulus fractus), but not in cirrus clouds.
Digital Audio, Digital Video: To begin playback before the entire file has been downloaded, or to play an audio or video file which is not located on the user's computer without downloading that file or creating a copy of the file on the user's computer.
Stylus, Styli (plural)
Audio, Turntables: The mechanical component that connects to the cartridge and contacts the record. Also called Needle.
Video: A secondary signal containing additional information to be added to the main signal.
Telephony: A mobile cellular user.
Subscriber Identity Module: see SIM.
Subsidiary Communications Service: see SCS.
Audio: A speaker driver similar to the woofer, except that it is designed to reproduce only the low end of bass frequencies, usually from 80 Hz downward.
Subwoofer, Active
Audio: A subwoofer or speaker system that includes a dedicated amplifier to increase the subwoofer signal.
Subwoofer, Passive
Audio: A subwoofer that does not amplify the subwoofer signal.
Electronics: Refers to a radio receiver that converts all radio frequencies to a fixed intermediate frequency to maximize gain and bandwidth before demodulation.
Communications: A transmitting encoding method which mixes the carrier and oscillator frequency.
Super High Frequency: see SHF.
Surface Area
Metal Detectors: Refers to the area of a target closest to the search coil where eddy current generation can take place.
Surface-barrier Diode: see Diode, Schottky.
Surface-Microphone: see Microphone, Boundary.
Surface Mount
Metal Detectors: The art of mounting electronic components on the surface of a printed circuit board rather than using the "through board" method. This allows more technology in a much smaller space and with much higher tolerances.
Surround Material
Audio: The material used for the outer suspension of a speaker cone. The surround material holds the diaphragm in place but allows it to move when activated.
Surround Sound
Audio: A multi-channel sound format which is used to reproduce the full quality of recorded sound by providing multi-directional audio. The most common type of surround sound is the 5.1 channel system (referring to 2 front channels, 1 center channel, 2 rear channels, and a subwoofer channel). The subwoofer is the ".1" channel. There are several 5.1 formats: Dolby® Stereo Digital (DSD) by Dolby® (theater), Dolby® Digital (AC-3) by Dolby®, DTS® by Digital Theater Systems, Sony® Dynamic Digital Sound (SDDS®) by Sony® (for movies), Super Audio CD (SACD®) by Sony® (for audio), and THX by THX Ltd.
Digital Video: An image resolution of 800 x 600 pixels.
S-VHS: see S-Video.
Video: Also called S-VHS and Y/C Video.
1) A video format which provides a higher-quality video signal over composite video, using a separate luma and chroma signal.
2) The specialized S-video cables for S-video connections.
3) The specialized S-video plugs or jacks used for S-video connections.
Metal Detectors: The motion used when moving the search coil over the ground.
Electronics: A component which is designed and used for making, breaking, or changing the connections in or among circuits.
Switch, DPDT
Acronym: Double-Pole, Double-Throw Switch
Electronics: see DPST.
Switch, DPST
Acronym: Double-Pole, Single-Throw Switch
Electronics: see DPST.
Switch, Mercury-type
Electronics: A switch which includes a small amount of mercury and which is activated by gravity or a physical shock that causes the mercury to bridge the internal contacts.
Switch, Momentary
Electronics: A spring-loaded switch that returns to a starting position after being triggered. The momentary setting is usually shown in parentheses in descriptions. A switch labeled OFF (ON) is a momentary switch with OFF as the fixed position.
Switch, Pushbutton
Electronics: A switch which is activated by pressing a button.
Switch, Dry Reed
Electronics: A switch which has ferromagnetic contact blades that can be triggered by an external magnetic field, such as from either a coil or permanent magnet.
Switch, Rocker
Electronics: A switch which is activated using a rocking mechanism. Rocker switches generally have three positions: the center position, and each of the rocker directions.
Switch, Rotary
Electronics: A switch which is activated using a rotary or turning mechanism.
Switch, Slave
Plug 'n Power: Wall switch used in conjunction with a master wall switch to control a light that is operated by two or more switches.
Switch, Slide
Electronics: A switch which is activated using a sliding mechanism.
Switch, Snap-action
Electronics: A switch which provides physical feedback (the "snap") when activated.
Switch, SPDT
Acronym: Single-Pole, Double-Throw Switch
Electronics: see SPDT.
Switch, SPST
Acronym: Single-Pole, Single-Throw Switch
Electronics: see SPST.
Switch, Tactile Pushbutton
Electronics: A pushbutton switch with two possible settings (on or off), which provides physical feedback when activated.
Switch, Toggle
Electronics: A spring-loaded switch with two possible settings (on or off).
Acronym: Standing Wave Ratio
Communications: A measure of the amount of signal lost due to poor antenna performance. A high SWR reduces the amount of signal that the antenna can actually transmit, reducing clarity and range. Because of this, in order to get the peak performance out of your system, we recommend that you tune the antenna using an SWR meter.
SWR Meter
Acronym: Standing Wave Ratio Meter
Communications: A testing device which measures the amount of signal lost due to poor antenna performance, allowing you to tune the antenna for optimum performance.
An ideal SWR reading is 1.0; however, this measurement is possible only under laboratory conditions or with a dummy load. Actual antenna installations have higher readings. In real-world operation, SWR of less than 3 is recommended. Use the following chart to interpret the readings you obtain.
1.0 to 1.5 Excellent The antenna cable and the antenna length match the transmitter's output requirements almost perfectly.
1.5 to 2.0 Very Good The antenna, the cable and the transmitter operate very efficiently.
2.0 to 3.0 Acceptable The antenna system easily puts out enough power for normal operation.
Above 3.0 Inefficient Adjust your antenna or antenna mounting system to improve operation.
Note: The SWR is different for different frequencies. If you measure the SWR on several different channels or frequencies, you get different readings. If you usually transmit on one channel more than the others, make your readings on the channel and fine-tune the system for that channel. If you use all the channels without preference, make your readings on a channel centered within the band you use.
The figures below the SWR values in the following chart indicate the percentage of power that reflected back to the transmitter. For example, an SWR reading of 1.5 also means that 4% of your signal power is lost. However, 96% of the transmitter power is more than enough for almost all applications.
SWR 1.0 1.1 1.2 1.5 2.0 2.5 3.0
REF POWER 0% 0.22% 0.8% 4.0% 11.1% 18.4% 25.0%
Video: The element of a video signal that tells the display where to display the picture, horizontally (HSYNC) and vertically (VSYNC).

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