Glossary Terms Beginning S

0-9 : A : B : C : D : E : F : G : H : I : J : K : L : M

N : O : P : Q : R : S : T : U : V : W : X : Y : Z

S point: See S-interface.
S/N: Signal-to-noise ratio - typically expressed in dB.
S/T bus; S/T interface: See S0 bus/interface.
S0 bus; S0 interface: Converts the ISDN data from the format used between the exchange and the socket to the type used in the subscriber's premises.
Sampling frequency (rate): Rate at which samples are taken.
Sampling: Instantaneous measurement of the picture at a particular point in time; the value of the signal at that instant is typically converted to a binary number.
Satellite link: Microwave link between a transmitting earth station and receiving earth station through a satellite.
Satellite newsgathering: SNG: the means by which news is gathered for television and radio broadcast using satellite communications.
Satellite system operator: Organization which operates and controls one or more satellite spacecraft.
Satellite, artificial: Electronic communications relay station orbiting the Earth.
Satellite, geostationary: An electronic communications relay station orbiting 35 785 km (22 237 miles) above the Equator, moving in a fixed orbit at the same speed and direction as the Earth, i.e. approximately 11 000 kph (7000 mph).
Satphone: Generic term for satellite telephone, usually used on the INMARSAT system.
Saturated flux density: SFD: the power required to achieve saturation of a single channel on a satellite.
Saturation: Where a high power amplifier is driven into the non-linear part of its power transfer characteristic, such that an increase in input power results in little or no increase in output power.
Scope: See Oscilloscope
SCPC: Single channel per carrier.
SDI: Serial digital interface.
SDTV: Standard definition television.
SDV: Serial digital video.
Sensitivity: Ability of an electronic device (typically a receiver) to detect and process very small signals satisfactorily.
Serial digital video: Digital video transmitted serially, typically at a data rate of 270 Mbps.
Sidelobes: A parabolic antenna does not produce a completely perfect radiation pattern, which would be a single focused beam, but has a main 'lobe' (centred on the boresight) and a number of 'sidelobes' radiating out from the antenna.
Sidereal cycle: The Earth rotates once in every 23 hours, 56 minutes and 4.1 seconds, rather than exactly 24 hours - equivalent to one sidereal day.
SIF: Standard interchange format: format for exchanging video images of 240 lines × 352 pixels for NTSC, and 288 lines × 352 pixels for PAL and SECAM.
Signal-to-noise ratio: S/N: ratio of the signal power and noise power in analogue systems; a video S/N of 54-56 dB is considered to be of full broadcast quality.
Simplex: Transmission in one direction only between sending and receiving station.
Single channel per carrier: SCPC: a transmission of single programme signal on one carrier.
S-interface: The ISDN subscriber interface where the connection to the ISDN network is through another network termination device such as an ISDN switchboard.
Skew: An adjustment that compensates for slight variance in angle within the same sense of polarity.
Slice: Sequence of macroblocks across the picture in a digital compression process.
Slot, orbital: Longitudinal position in the geosynchronous arc at which a communications satellite is located - allocated by the ITU.
Small signal suppression: Suppression effect seen on a relatively low-power carrier signal when a low-power carrier and a high-power carrier share the same transponder on a satellite.
SNG: Satellite newsgathering.
Solar eclipse: Event when the Earth moves between the satellite and the Sun, preventing the satellite from receiving energy from the Sun to provide solar power.
Solar noise: Description of the electromagnetic 'noise' generated from the Sun.
Solar outage: Event during the equinoxes when the satellite is on that part of its orbit where it is between the Sun and the Earth, causing a downlink receiving antenna pointed at a satellite to become 'blinded' as the Sun passes behind the satellite.
Solid state power amplifier: SSPA: a high-power amplifier using solid-state electronics as the amplifying element, as opposed to a vacuum tube device.
Space segment: Generic term for the part of the transmission system that is in the sky.
Spectrum: The full range of electromagnetic radio frequencies.
Spectrum analyser: A radio receiving instrument with the ability to repeatedly and automatically tune across a band of electromagnetic spectrum, showing the amplitude of signals present in that band on a display screen.
Spike: A voltage or energy surge; irregularities in the power supply waveform.
Splitter: Passive device (one with no active electronic components) which distributes a signal into two or more paths.
Spotbeam: High-power satellite signal with a focused antenna pattern that covers only a small region.
Spurious radiation: Any radiation outside a defined frequency band; potential source of interference.
SQIF: Sub-quarter common intermediate format: 128 × 96 pixels.
SSPA: Solid-state power amplifier.
Stand-up: Position where a reporter gives a news report; generic term for a short news report from the field.
Station-keeping: Small orbital adjustments regularly made to maintain the satellite's orbital position within its allocated 'box' on the geostationary arc.
Store and forward: Process by which high-quality video is digitized and compressed at the high bit-rate, stored, and later transmitted in non-real time through a low data rate circuit, e.g. INMARSAT.
Sun-out: See Solar outage.
Switched-56: 56 kbps digital telephony data service in the US, similar to ISDN, and now rapidly being superseded by ISDN.
Symbol; symbol rate: Used in connection with the transmitted data, where a defined number of bits represents a 'symbol' - a unit of information. One symbol per second is termed a 'baud'.
Synchronization: Process of achieving the same timing relationship at the transmitter and the receiver in order that information can be correctly conveyed.
System noise: Unwanted signals and artifacts generated within a receive system, typically expressed as a power figure to balance against the signal power.