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Glossary > Glossary Terms Beginning
Glossary Terms Beginning S
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: X : Y
- S point
- See S-interface.
- 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.
- 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).
- 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.
- 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.
- See Oscilloscope
- Single channel per carrier.
- Serial digital interface.
- Standard definition television.
- Serial digital video.
- 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.
- 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.
- 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.
- Transmission in one direction only between sending and receiving station.
- Single channel per carrier
- SCPC: a transmission of single programme signal on one carrier.
- The ISDN subscriber interface where the connection to the ISDN network is
through another network termination device such as an ISDN switchboard.
- An adjustment that compensates for slight variance in angle within the same
sense of polarity.
- 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.
- 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.
- 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.
- A voltage or energy surge; irregularities in the power supply waveform.
- Passive device (one with no active electronic components) which distributes
a signal into two or more paths.
- 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.
- Sub-quarter common intermediate format: 128 × 96 pixels.
- Solid-state power amplifier.
- Position where a reporter gives a news report; generic term for a short news
report from the field.
- 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.
- See Solar outage.
- 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
- 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.