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Crystal and frequency control glossary

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C

C Band

Certain high-frequency radio frequency bands between 3,900 and 6,545 MHz used by communications satellites in the fixed satellite service.

C.I.

The abbreviation for crystal impedance, sometimes used in place of the word resistance.

C.I.M.

Abbreviation for crystal impedance meter. See test set.

C0

Abbreviation for shunt capacitance.

C1

The abbreviation for motional capacitance. Motional capacitance is also often abbreviated as Cm.

Calibrated

The process of plating a crystal to the finished frequency.

Calibration

The setting tolerance is the maximum allowable deviation from the nominal frequency at 25°C. It is normally specified in parts per million (ppm).

Calibration Accuracy

See frequency tolerance.

Can

The upper portion, or cover, of a crystal holder. See cover and holder.

Can - illustration

Capacitance ratio

In applications (i.e. VCXO) where variations in the crystal parallel resonant frequency are desired, the capacitive ratio (r) may be specified. This ratio is an indicator of the change in a parallel load resonant frequency as a direct result of a given change in crystal load capacitance. Because the value of this ratio has physical limitations when it is realized in a quartz crystal design, please consult the factory for product specifications. r = C0/C1

Capacitance

The property exhibited by two conductors separated by a dielectric whereby an electric charge becomes stored between the conductors. Capacitance is measured in "farads" and is identified by the letter "C."

Capacitor

A passive electronic circuit component consisting, in its simplest form, of two metal electrodes separated by a dielectric.

Capacity

The average amount of traffic that a circuit or circuit group can handle.

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Carrier frequency

The nominal frequency of a carrier wave.

CCRR

Abbreviation for co-channel rejection ratio.

CDMA

Abbreviation for code-division multiple access. A coding scheme, used as a modulation technique, in which multiple channels are independently coded for transmission over a single wideband channel.

Note 1: In some communication systems, CDMA is used as an access method that permits carriers from different stations to use the same transmission equipment by using a wider bandwidth than the individual carriers. On reception, each carrier can be distinguished from the others by means of a specific modulation code, thereby allowing for the reception of signals that were originally overlapping in frequency and time. Thus, several transmissions can occur simultaneously within the same bandwidth, with the mutual interference reduced by the degree of orthogonality of the unique codes used in each transmission.

Note 2: CDMA permits a more uniform distribution of energy in the emitted bandwidth.

CDPD

Abbreviation for cellular digital packet data. CDPD is a specification for supporting wireless access to the Internet and other public packet-switched networks.

Cellemetry

Brand name for BellSouth Cellular Corp.'s telemetry service, which uses the cellular network to carry data messaging used for remote services such as utility meter reading, vending machine status and vehicle or trailer tracking.

Center Frequency or Nominal Frequency

The midpoint in the passband. The specified reference frequency of the crystal and is typically specified in megahertz (MHz) or kilohertz (kHz).

Central Processing Unit System (CPU)

The portion of a computer that includes circuits controlling the interpretation and execution of instructions and also the portion that executes programmed instructions, performs arithmetic and logical operations on data, and controls input / output functions.

Channel

A single path, either RF or voice, for transmitting electrical signals between a sending point and receiving point. Channels are often measured in terms of the amount of spectrum they occupy (bandwidth) measured in Hertz.

Channel elements

The frequency determining device in communications equipment. (i.e. oscillator, TCXO, and/or VCXO).

Channel spacing

The difference in frequency between successive radio or television channels.

Chemical etching process

Cleaning quartz resonators by removing some of the surface.

Circuit

Physical connection of channels, conductors and equipment required to provide a complete communications pathway.

Clear channel

A clear channel protects stations designated as Class A stations from objectionable interference within their primary and secondary service areas. To provide this wide service area, Class A stations operate within a power range of 10 to 50 kilowatts.

Clock

A device providing signals used in a transmission system to control the timing of certain functions such as the duration of signal elements or the sampling rate. A device that generates periodic, accurately spaced signals used for such purposes as timing, regulation of the operations of a processor, or generation of interrupts.

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Clock rate

The rate at which a clock issues timing pulses.

Cm

Abbreviation for motional capacitance.

 

Cold Weld

Welding in which a molecular bond is obtained by a cold flow of metal under extremely high pressures, without heat; widely used for sealing transistors and quartz crystal holders.

Co-location

Placement of multiple antennas at a common physical site to reduce environmental impact and real estate costs and speed zoning approvals and network deployment. Co-location can be affected by competitive and interference factors.

Colpitts oscillator

An oscillator in which a parallel-tuned tank circuit has two voltage-dividing capacitors in series, with their common connection going to the cathode in the electron-tube version and the emitter circuit in the transistor version.

Modified Colpitts oscillator - illustration

Common-Mode Rejection Ratio (CMRR)

The ratio of the common-mode interference voltage at the input of a circuit, to the corresponding interference voltage at the output.

Communications satellite

A satellite that is used to relay telecommunications information.

Complementary Metal-Oxide Semiconductor (CMOS)

The semiconductor technology used in the transistors that are manufactured into most of today's computer microchips.

COMSAT

Abbreviation for Communications Satellite Corporation. Corporations, chartered by Congress, as an exclusive provider of international telecommunications satellite channels to the US COMSAT also represents the US in INTELSAT.

Conductor

A material that easily conducts an electric current because some electrons in the material are free to move.

Contour

A modification to one or both of the major faces of a resonator plate in which the face is altered to have a completely spherical configuration. See bevel.

Coupled mode

An unwanted mode that becomes energized at the same frequency as the desired mode, thereby draining energy from the desired mode.

Cover

TThe upper portion of a crystal holder. See holder.

Cover - illustration

Covered SMR

A subset of specialized mobile radio operators subject to a particular set of regulations.

Crystal

A generic term used in place of the more complete expression piezoelectric quartz crystal unit. A homogenous solid formed by a repeating, three-dimensional pattern of atoms, ions, or molecules and having fixed distances between constituent parts. Usually a mineral, especially a transparent form of quartz, having a crystalline structure, often characterized by external planar faces.

Crystal blanks

Round or square wafers of quartz crystals.

Crystal calibration

See calibrated.

Crystal cut

The orientation of the crystal element with respect to crystallographic axis of the crystal.

Crystal element

Piezoelectric material cut to a given geometric shape, size and orientation with respect to the crystallographic axis of the crystal.

Crystal enclosure

The enclosure protecting the crystal vibrator(s) and mounting system.

Crystal filter

An electric wave filter employing pies-electric crystals for its reactive elements. In general, filters can be provided in a number of differing topologies, including bandpass, band reject or notch, low pass, and high pass.

Crystal oscillator

An oscillator in which the frequency is controlled by a piezoelectric crystal. A crystal oscillator may require controlled temperature because its operating frequency is a function of temperature. Types of crystal oscillators include voltage-controlled crystal oscillators (VCXO), temperature-compensated crystal oscillators (TCXO), oven-controlled crystal oscillators (OCXO), temperature-compensated-voltage controlled crystal oscillators (TCVCXO), oven-controlled voltage-controlled crystal oscillators (OCVCXO), microcomputer-compensated crystal oscillators (MCXO), and rubidium crystal oscillators (RbXO).

Crystal Unit Equivalent Circuit

The electrical circuit which has the same impedance as the unit in the immediate neighborhood of resonance.

Equivalent circuit of a resonator - illustration of crystal equivalent circuit

Current

The net transfer of electric charge per unit of time.

CW

A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency. Continuous wave is also the name given to an early method of radio transmission, in which a carrier wave is switched on and off.

Cycle

One complete repetition of an event.

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