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Crystal and frequency control glossary

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dB Bandwidth

The specified reference level for the difference between the frequency limits of a band containing the useful frequency components of a signal.

dB

Abbreviation for decibel. See decibel.

dBc

Decibels with respect to or relative to the carrier power.

dBm

Decibels with respect to 1 mW. dBm is used in communication work as a measure of absolute power values. Zero dBm equals one milliwatt.

dBW

Decibels with respect to 1 W. Watts of power expressed in decibels.

DC

Abbreviation for direct current.

DCS

Abbreviation for distributed communications system or digital cellular system.

DDS

Abbreviation for direct digital synthesis.

Decibel

Abbreviation = dB. A unit for describing the ratio of two powers or intensities, or the ratio of a power to a reference power.

DECT

Abbreviation for Digital European cordless telephone.

Desired frequency

See nominal frequency.

Deviation

The amount by which a quantity differs from its nominal value. The amount by which a frequency differs from the nominal or specified frequency.

Dew Point

The temperature at which a condensable component of a gas starts to condense into a liquid.

Dice (Quartz)

Pieces of quartz produced by sectioning quartz wafers into rectangular shapes. Dice are then further machined to produce crystal blanks.

Dielectric

Material that does not conduct electricity readily, i.e., an insulator. A good dielectric should also have other properties: It must resist breakdown under high voltages; it should not itself draw appreciable power from the circuit; it must have reasonable physical stability; and none of its characteristics should vary much over a fairly wide temperature range. One important application of dielectrics is as the material separating the plates of a capacitor.

Digital signal processor (DSP)

A specialized, programmable computer processing unit that is able to perform high-speed mathematical processing.

DIL

Abbreviation for dual in-line.

DIP

Abbreviation for dual in-line package.

Direct broadcast satellite (DBS)

A high-powered satellite that transmits or retransmits signals which are intended for direct reception by the public. The signal is transmitted to a small earth station or dish (usually 18-inches) mounted on homes or other buildings.

Direct piezoelectric effect

The generation of electricity (or electric polarity) in crystals subjected to mechanical stress.

Directional antenna

An antenna in which the radiation pattern is not omnidirectional, i.e., a nonisotropic antenna.

Disciplined oscillator (DO)

An oscillator whose output frequency is continuously steered (often through the use of a phase locked loop) to agree with an external reference. For example, a GPS disciplined oscillator (GPSDO) usually consists of a quartz or rubidium oscillator whose output frequency is continuously steered to agree with signals broadcast by the GPS satellites.

Dish

A circular antenna used to pick up transmissions broadcast from a satellite. See satellite dish.

DOD master clock

The master clock to which time and frequency measurements for the U.S. Department of Defense are referenced, i.e., are traceable. The U.S. Naval Observatory master clock is designated as the DOD Master Clock.

Double rotated quartz cut

SC cut, IT cut, and FC cuts are examples of double rotated quartz cuts. Double rotated quartz cut refers to the two rotations from two reference planes needed for these cuts.

Downlink

A link from a satellite to an earth station.

Drive level

The amount of power dissipation in the crystal, expressed in microwatts or milliwatts. Maximum power is the most power the device can dissipate while still maintaining operation with all electrical parameters guaranteed. Drive level should be maintained at the minimum levels necessary to initiate proper start-up and assure steady state oscillation. Excessive drive level can cause poor aging characteristics and crystal damage.

Dry Nitrogen

Moisture free nitrogen.

DTCXO

Abbreviation for Digitally Temperature Compensated Crystal Oscillator.

DUT

Abbreviation for device under test.

Duty cycle

The measure of output waveform uniformity. This term, also referred to as symmetry, is a measurement of the time that the output waveform is in a logic high state, expressed as a percentage (%). This parameter is measured at a specified voltage threshold or at a percentage of the output waveform amplitude.

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