S/NR

Signal-to Noise Ratio. A measure of how clean (noise-free) the recovered baseband signal is.

S-band

Satellite downlinks in the region of 2.6 GHz.

Scalar Feed

The wide flare corrugated horn antenna feed, commonly used in C-band home satellite TV receiving systems.

Satellite Receiver

The indoors electronic component of an earth station which downcoverts, processes and prepares satellite signals, for viewing or listening.

Saturation - (1)

Operating point of a non-liner amplifier when drive level is adjusted to obtain maximum osutput.

Saturation - (2)

colour intensity parameter in a video signal.

SAW (Surface Acoustic Wave) Filter

A solid state filter that yields a sharp transition between regions of transmitted and attenuated frequencies.

Scanning

The organized process of moving the electron beam in a television picture tube so an entire scene is drawn as a sequential series of horizontal lines connected by horizontal and vertical retraces.

SCPC

Single Channel Per Carrier. A narrowband transmission mode used to relay audio and data information.

Scrambling

A method of altering the identity of a video or audio signal in order to prevent its reception by persons not having authorized decoders.

Screening

A metal, concrete or natural material that screens, out unwanted TI from entering an antenna or a metal shield that prevents the ingress of unwanted RF signals in an electronic circuit.

Secam

Sequence Couleur a Memorie. French-designed color TV encoding system.

Serrated Vertical Pulse

The television vertical sync pulse which is subdivided into six serrations. These sub-pulses occur at twice the horizontal scanning frequency.

Servo Hunting

An oscillatory searching of the feedhorn probe when use of inadequate quage control cables results in insufficient voltage at the feedhorn.

Shaped Beam

Beam of irregular cross-section, produced by multiple feed or shaped reflector techniques.

Shaped Reflector

Techniquesfor controlling beam pattern, aperture illumination, noise, and side lobe power, and for increasing antenna efficiency, by variation of antenna (and subreflector) shape from the true paraboloid, hyperboloid etc.

Sheath

The outer covering or jacket of a multiconductor cable.

Shield Effectiveness

The relative ability of a shield to screen out undesirable radiation. Frequently confused with the term shield percentage, which it is not.

Shield

In cables, a metallic layer placed around a conductor or group of conductors to prevent electrostatic or electromagnetic interference between the enclosed wires and external fields.

Shortwave

Transmissions on frequencies of 6-25 MHz.

SHF

Super high frequency.

Side Lobe

A parameter used to describe an antenna's ability to detect off-axis signals. The larger the side lobes, the more noise and interference an antenna can detect.

Signal-to-noise ratio

The ratio of signal power to noise power in a specified bandwidth, usually expressed in decibels.

Single Channel Per Carrier (SCPC)

A satellite transmission system that employs a separate carrier for each channel, as opposed to frequency division multiplexing that combines many channels on a single carrier.

SiS

Sound-in-Syncs (audio/video multiplexing system). Strictly referes to digital version used by E.

Skew

A term used to describe the adjustment necessary to fine tune the feedhorn polarity detector when scanning between satellites.

Skin Effect

The phenomenon in which the depth of penetration of electric currents into a conductor decreases as the frequency increases.

Slant Range

The distance that a signal travel from a satellite to a TVRO.

SMATV

Satellite Master Antenna Television.

Snow

Video noise or sparkiies caused by an insufficient signal-to- noise input ratio to a television set or monitor.

Solar Eclipse

When the Earth shadows the satellite's solar array from the Sun.

Solar Array

A network of solar cells which generate electricity when exposed to sunlight.

Solar Outage

The loss of reception that occurs when the sun is positioned directly behind a target satellite. When this occurs, solar noise downs out the satellite signal and reception is lost.

SPADE

Single channel per carrkier, PCM multiple - Access Demand - Assignment Equipment (SCPC phony sys).

Spark Test

A test designed to locate pin-holes in the insulation of a wire or cable by application of a voltage for a very short period of time while the wire is being drawn through the electrode field.

Sparklies

Small black andlor white dashes in a television picture indicating an insufficient signal-to-noise ratio. Also known as "snow".

Specific Gravity

The ratio of the density (mass per unit volume) of a material to that of water.

Spectrum

The range of electromagnetic radio frequencies used in transmission of voice, data and television.

SPELDA

Dual paylond lanuch adapter for Ariance.

Spherical

Simple geometry for feed-steerable multiple beam antenna.

Spherical Antenna

An antenna system using a section of a spherical reflector to focus one or more satellite signals to one or a series of local areas.

Spillover

Usable (but often unwanted) signal reaching locations beyond defined Edge of Coverage.

Spin stabilization

A form of satellite attitude control which is achieved through spinning the exterior of spacecraft about its axis at a fixed rate.

Spiral Wrap

The helical wrap of a tape or thread over a core.

Splashplate

Component of a backfire feed system - an unshaped (or arbitrarily shaped) subreflector.

Splitter

A device that takes a signal and splits into two or more identical but lower power signals.

Spot Beam

Beam of circular or elliptical cross-section, covering a defined region of the Earth's surface, small in relation to a global beam.

SS-TDMA

Satellite-Switched Time Division Multiple Access.

SSB

Single Side Band. A form of amplitude modulation (AM) whereby one of the sidebands and the carrier are supperssed.

SSPA

Solid-State Power Amplifier. A transistor or FETHPA now increasingly replacing TVVTs in satellite transponder

Stairstep (UK Stircase)

A video test waveform, included in ITS.

Stationkeeping

Orbital adjustments to maintain satellite accurately at desired geostationary location.

Statsionar

Russian geostationary communications satellite systems.

Step-Track

Software-based automatic antenna tracking system.

STL

Studio - Transmitter Link.

Strand

A single uninsulated wire.

Stranded Conductor

A conductor composed of groups of wires twistea together.

Strip Force

The force required to remove a small section of insulating material from the conductor it covers. Usually measured in pounds.

STS

Space Transportation System (the Shuttle).

Subcarrier

An information-carrying-wave, which in turn modulates the main carrier in a communications system. Subcarriers are used for color information, TV audio, independent audio, and data transmission.

Subsatellite point

The unique spot over the Earth's equator assigned to every geostationary satellite.

Subscription television

Television programming/channels that can be viewed in your home only if you pay for them. The signal of subscription satellite television channels is scrambled and beamed down. Only subscribers who have an IRD for those particular subscription services have access to them.

Surface Resistivity

The resistance of a material between two opposite sides of a unit square of its surface. It is usually expressed in ohms.

Surface Acoustic Wave

A sound or acoustic wave traveling on the surface of the optically polished surface of a pie zoelectric material. This wave travels the speed of sound but can pass frequencies as high as several gigahertz.

Sweep Test

Pertaining to cable, checking frequency response by generating an rf voltage whose frequency is varied back and fort through a given frequency range at a rapid constant rate and observing the results of an oscilloscope.

Sync Suppression

Type of Video scrambling (e.g., Oak Orion, Nimrod)

Synchronization(Sync)

The process of orienting the transmitter and receiver circuits in the proper manner in order that they can be synchronized . Home television sets are synchronized by an incoming sync signal with the television cameras in the studios 60 times per second. The horizontal and vertical hold controls on the television set are used to set the receiver circuits to the approximate sync frequencies of incoming television picture and the sync pulses in the signal then fine tune the circuits to the exact frequency and phase.

Synchronizing Pulses

Pulses imposed on the composite baseband video signal used to keep the television picture scanning in perfect step with the scanning at the television, camera.