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36 result(s) found where the letter starting with "S"

S-PHM
Space Passive Hydrogen Maser.
 

SA
Selective Availability (GPS accuracy limits for civilian users)
 

SDH
Synchronous Digital Hierarchy
 

SDN
Integrated Services Digital Network
 

SDV
Switch Digital Video (=BMFB or BMFS)
 

Second
The basic unit of time or time interval in the International System of Units (SI) which is equal to 9 192 631 770 periods of radiation corresponding to the transition between the two hyperfine levels of the ground state of cesium-133.
 

Secondary Server
Another name for a stratum 2 server.
 

Shock
A specification referring to the ability of the oscillator to withstand, without performance degradation, a non-repetitive acceleration. A specification is given for three mutually perpendicular axes.
 

Short term frequency stability
An oscillator will change frequency over time due to internal or external causes in a temporary manner. That is, there are no permanent frequency changes due to this type of instability. Short term stability can usually be measured in terms of the period of the signal frequency. Causative factors include thermal noise in active components, shock and vibration, construction parameters, and external electrical fields.
 

Short term stability
Short term stability usually involves measurement averages from a few tenths of a second to 100s. Also called Sigma Tau and Allan Variance or Allan Deviation. See also Allan Variance and Allan Deviation
 

Sidereal time
The measure of time defined by the apparent diurnal motion of the vernal equinox; hence, a measure of the rotation of the Earth with respect to the reference frame that is related to the stars rather than the sun. Two types of sidereal time are used in astronomy: mean sidereal time and apparent sidereal time. One sidereal day is equal to about 23 hours, 56 minutes, and 4.090 seconds of mean solar time. Also, 366.2422 mean sidereal days equal 365.2422 mean solar days.
 

Sine wave
An output waveform described by a sine curve. A voltage or decibel value and tolerance must be included to complete the specification.
 

Slew
To adjust gradually the time of a clock until it tells the correct time. Compare with "step"
 

SNR
Signal to Noise Ratio
 

Solar time
SOH section overhead; a group of management communications facilities in SDH
Universal Time is the mean solar time of the prime meridian plus 12 hours, determined by measuring the angular position of the Earth about its axis. The UT is sometimes designated GMT, but this designation should be avoided.
 

SONET
synchronous optical network; the North American variant of SDH.
 

SPE
Synchronous Payload Envelope.
 

Spurious
These extra vibration modes produce additional, unwanted electrical responses which distort the filters response. These are commonly called 'spurious responses'. The most troublesome spurious responses fall on the high side of the passband, generally from 100 kHz to 1 MHz above center frequency.
 

Spurious responses
See Non-harmonic distortion.
 

Square wave
A rectangular wave output waveform having a 50% symmetry. If specified, the tolerance to the symmetry must be specified. TTL, LSTTL, CMOS and HCMOS outputs are described as square wave and comply to the wave form drawing at right.
 

SRO
Synchronized Rubidium Oscillator.
 

SSU
Synch Supply Unit.
 

Start-up time
The maximum time that the oscillator requires to reach stable operation within specifications after application of the supply voltage.
 

Step
To change the time of a clock to the correct time with no intermediate adjustments. Compare with "slew".
 

STM
synchronous transport module; the basic unit of transmission in SDH.
 

Storage temperature
The temperature range over which the oscillator may be stored, non-powered, without damage.
 

Stratum
The term "stratum" is referenced in both the network world and the telecommunications world. Dr. Davis Mills, University of Delaware, is the author of the RFC 1305 that is NTP (Network Time Protocol). He developed a hierarchical structure in which Stratum 0 is the USNO clock. Stratum 1 is a radio receiver that receives the time from Stratum 0. Stratum 2 is a client that receives the time over a network connection from a Stratum 1 clock. Stratum 3 is a client that gets the time from Stratum 2... and so on to a theoretical Stratum 15.
In the telecommunication world, stratum refers to the holdover performance of an oscillator in the event of loss of synchronization. Stratum 1, Stratum 2, Stratum 3, Stratum 4 are the most typical.

Stratum clocks Accuracy requirements placed on clocks in four strata. Accuracy of stratum clocks refers to clock performance when the clock receives no input reference.
 

STS-n
Synchronous Transport Signal level n.
 

Supply Current
The maximum operating current of the oscillator at the nominal supply voltage.
 

Supply voltage
The operating voltage (or range) of the oscillator.
 

Supply voltage stability
See frequency voltage tolerance.
 

SVN
Satellite Vehicle Number.
 

Symmetry
The ratio of the positive portion of the output signal to the entire period of the output signal. This applies only to rectangular wave outputs. The voltage at which to measure the symmetry is 1.4v for TTL and 50% of supply voltage for CMOS/HCMOS. Other rectangular output formats should include a voltage at which to measure symmetry.
 

Synchronization
The process of measuring the difference in time of two time scales such as the output signals generated by two clocks. In the context of timing, synchronization means to bring two clocks or data streams into phase so that their difference is 0 (see time scales in synchronism).
 

Synchronize clocks
To set two clocks to the same time and ensure that they are running at the same "speed". The speed at which a clock runs is determined by its frequency, that is, how often it "ticks" to the next fraction of a second. The design of a particular clock determines how small that fraction is.
 

Syntonization
Relative adjustment of two frequency sources with the purpose of cancelling their frequency difference but not necessarily their phase difference.