7E Communications
   

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.