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Crystal and frequency control glossary

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Satellite

A radio relay station that orbits the Earth. A complete satellite communications system also includes earth stations that communicate with each other via the satellite.

Satellite communications

A telecommunications service provided via one or more satellite relays and their associated uplinks and downlinks.

Satellite dish

A kind of antenna used to pick up transmissions broadcast from a satellite.

Satellite link

A radio link between a transmitting Earth station and a receiving Earth station through one satellite.

SAW

Abbreviation for surface acoustic wave.

S-band

The frequency spectrum near 2 GHz used for land-based microwave and some mobile satellite communications.

SC cut

A double rotated crystal cut good for ovenized application with good aging rates and low phase noise. SC stands for Stress Compensated. SC-cut crystals have an improved temperature and frequency characteristic for ovenized applications (OCXO). The frequency vs. temperature curve is a sine with the inflection temperature at ~ +95°C. This crystal operates in the thickness shear mode. Preferred for ovenized oscillators (OCXO) such as space systems, and Global Positioning Satellite Systems .

SCM

Abbreviation for signal code modulation.

Second

The basic unit of measure of time, equivalent to "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom." For our purposes, one "second" is 1/60th of a minute.

Secondary frequency standard

A frequency standard that does not have inherent accuracy, and therefore must be calibrated against a primary frequency standard.

Series resonance

The condition that exists when a crystal unit is operated without the presence of load capacitance. Series resonance is frequently shortened to the word series. See load resonance.

Series vs. parallel load resonance

A crystal can be used in an oscillator circuit to operate in either of two resonant modes: Series Resonance or Parallel Load Resonance (also known as antiresonance). The crystals used in these two types of modes are physically the same crystal, but calibrated to slightly different frequencies.

When a crystal is placed into an oscillator circuit, they oscillate together at a tuned frequency. This frequency is dependent upon the crystal design and the amount of load capacitance, if any, the oscillator circuit presents to the crystal. Specified in picoFarads (pF), load capacitance is comprised of a combination of the circuit’s discrete load capacitance, stray board capacitance, and capacitance from semiconductor Miller effects.

Short messaging service (SMS)

A service for sending messages of up to 160 characters (224 characters if using a 5-bit mode) to mobile phones that use Global System for Mobile (GSM) communication.

Shunt capacitance

Abbreviated as C0. A parameter associated with a quartz crystal unit, used to identify the capacitance resulting from the presence of the electrodes plus stray capacitance associated with the holder. The static capacitance between the crystal terminals. Measured in picoFarads (pF), shunt capacitance is present whether the device is oscillating or not (unrelated to the piezoelectric effect of the quartz). Shunt capacitance is derived from the dielectric of the quartz, the area of the crystal electrodes, and the capacitance presented by the crystal holder.

Sideband

The bands of frequency above and below a carrier frequency that are produced by its modulation.

SiGe

Abbreviation for silicon-germanium.

Signal

Detectable transmitted energy that can be used to carry information. As applied to electronics, any transmitted electrical impulse.

Signal frequency shift

Any change in frequency. Any change in the frequency of a radio transmitter or oscillator.

Signal to noise ratio (S/N)

Relative power of the signal to the noise. As the ratio decreases on a line, it becomes more difficult to distinguish between information and non-information (noise). S/N deteriorates with distance because the noise builds every time the signal is repeated.

Signal to noise ratio (SNR)

The ratio of the amplitude of the desired signal to the amplitude of noise signals at a given point in time. SNR is usually expressed in dB.

Sine wave

A periodic wave that can be represented by a sine curve. The amplitude of such a wave is a function of the sine of a linear quantity such as phase or time.

Single-frequency interference

Interference caused by a single-frequency source.

SiO₂

Abbreviation for silicon dioxide.

Smart antenna

An antenna system whose technology enables it to focus its beam on a desired signal to reduce interference. A wireless network would employ smart antennas at its base stations in an effort to reduce the number of dropped calls, improve call quality and improve channel capacity.

SMD

Abbreviation for surface mount device. See surface mount.

SMF

Abbreviation for surface-mount filter.

SMP

Abbreviation for surface-mount package.

SOIC

Abbreviation for small-outline integrated circuit.

SPDT

Abbreviation for single-pole double-throw.

Special cut crystals

Special cut crystals are those crystals that have been cut at a different angle of orientation to enhance performance for specific needs. Typical special cuts would include BT cut crystals, SC cut crystals, IT cut crystals, and FC cut crystals.

Special emergency radio service

A Private Land Mobile Radio Service employed by persons or organizations engaged in emergency medical and rescue service, health care or similar activity.

Specialized mobile radio (SMR)

A two-way radio service provided within a designated portion of the 800 and 900 MHz frequency bands.

Specified frequency

The frequency specified by the customer.

Spectrum

The electromagnetic radio spectrum. The FCC grants authorizations and licenses to private and governmental entities to use specified portions under certain conditions.

Spectrum assignment

Federal government authorization for use of specific frequencies or frequency pairs within a given allocation, usually at stated a geographic location(s). Mobile communications authorizations are typically granted to private users, such as oil companies.

Spread spectrum

Telecommunications techniques in which a signal is transmitted in a bandwidth considerably greater than the frequency content of the original information.

SPICE

Abbreviation for Simulation Program with Integrated Circuit Emphasis.

Spur

A substitution for the term spurious frequency response. The word "spur" is used to refer to a frequency occurring at some point higher than the desired mode, but lower than the next overtone.

Spurious frequency response

In radio reception, a response in the receiver intermediate frequency (IF) stage produced by an undesired emission in which the fundamental frequency (or harmonics above the fundamental frequency) of the undesired emission mixes with the fundamental or harmonic of the receiver local oscillator.

SSB

Abbreviation for single sideband. Single-sideband modulation is a communications system in which one of the two sidebands used in amplitude-modulation is suppressed.

SSPA

Abbreviation for solid state power amplifiers.

Stability

The change in the oscillator frequency, referred to the desired oscillator frequency, caused by temperature changed.

Standard calibration tolerance

The allowable deviation from nominal, expressed in parts per million — ppm, at a specific temperature at +25 °C.

Start-up time

The specified time from oscillator power-up to the time the oscillator reaches steady state oscillation.

Starting resistance

The non-linear change in the resistance of a crystal as a function of the power level used to drive the crystal.

Static capacitance

See shunt capacitance.

Stone (quartz)

A term used to describe a quartz crystal before any machining operations have been done. The synthetic single crystals grown in the Hydrothermal Process are referred to as a "Stone".

Stopband

The part of the frequency spectrum that is subjected to specified attenuation of signal strength by a filter. See attenuation.

Storage temperature range

The minimum and maximum temperatures that the device can be stored or exposed to when in a non-oscillation state. After exposing or storing the device at the minimum or maximum temperatures for a length of time, all of the operating specifications are guaranteed over the specified operating temperature range.

Strip resonator

A small AT cut crystal whose width is much smaller than its length. The crystal is a finite plate design requiring exact mathematical analysis to achieve good performance. The length of the resonator can be parallel to either the X or Z axis of quartz.

Superheterodyne receiver

The most widely used type of radio receiver, in which all incoming modulated radio-frequency signals are converted to a common intermediate-frequency or IF carrier value for additional amplification and selectivity prior to demodulation. The advantage to this method is that most of the radio's signal path has to be sensitive to only a narrow range of frequencies. The diagram below shows the basic elements of a single conversion superheterodyne receiver.

Supply voltage

The DC input voltage necessary for oscillator operation, specified in volts.

Surface mount (SM)

A component, either active or passive, having no separate leads but which is part of the component body to permit direct mounting on a printed circuit board.

Surface-mount technology or surface-mount toroidal (SMT)

A surface mount device is a component, either active or passive, having no separate leads but which is part of the component body to permit direct mounting on a printed circuit board.

Symmetry

Symmetry is defined as the ratio of amount of time the voltage is in the logic "1" state compared to the time in the logic "0" state. The measurements are taken at the 50% points of the voltage transition between the two logic states. The time period of one cycle of the waveform is calculated first as below.

1/Frequency in Hertz = Time Period in Seconds

Next, the time period of the logic "1" state is measured from the 50% point of the waveform's positive voltage transition to the 50% point of the waveform’s negative voltage transition, then compared to the total waveform period. The calculation for symmetry is shown below:

Logic "1" Time in Symmetry/Period of One Cycle X 100 = % Symmetry

For the % symmetry of the logic "0" state, subtract the logic "1" symmetry from 100%. For example, 40/60% means that the waveform is in its logic "1" state 40% and in the logic "0' state 60% of the total waveform time period.

Synchronous digital hierarchy (SDH)

A standard technology for synchronous data transmission on optical media. It is the international equivalent of Synchronous Optical Network.

Synchronous optical network (SONET)

Abbreviation for synchronous optical network. An interface standard for synchronous optical-fiber transmission, applicable to the Physical Layer of the OSI Reference Model.

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