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Crystal and frequency control glossary

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Q

Abbreviation for quality factor. It is the ratio of energy stored in a system divided by the energy dissipated in the system. Used to characterize the acoustic loss in quartz crystal resonators.

QASK

Abbreviation for quadrature amplitude shift keying.

QRP

In amateur radio, QRP operation means transmitting at reduced power levels. The term QRP derives from the Q code where "QRP?" was used to mean, "Should I reduce Power?”.

Quadrature amplitude modulation (QAM)

Quadrature modulation in which the two carriers are amplitude modulated. In analog communications, the representation (i.e., transmission) of digital information by encoding bit sequences of fixed, specified length (number of bits), and representing these bit sequences as a function of (a) the amplitude of an analog carrier; or (b) a phase shift of the analog carrier with respect to the phase that represented the preceding bit sequence, and where the permissible phase shift is an integral multiple of /2 radians (90°, or one-quarter unit interval); or (c) both.

Quadrature phase shift keying (QPSK)

Abbreviation for quadrature phase shift keying.Phase-shift keying in which four different phase angles are used. Each of the angles is usually 90° out of phase.

Quartz

The crystalline form of Silicon Dioxide (SiO₂). Quartz is the material from which a blank is made.

Quartz blank

See blank.

Quartz clock

A clock containing a quartz oscillator that determines the accuracy and precision of the clock.

Quartz crystal

Synthetic quartz is composed of Silicon and Oxygen (Silicon Dioxide SiO₂) and is cultured in autoclaves under high pressure and temperature. Quartz exhibits piezoelectric properties that generate an electrical potential when pressure is applied on the surfaces of the crystal. Conversely, when an electrical potential is applied to the surfaces of a crystal, mechanical deformation or vibration is generated. These vibrations occur at a frequency determined by the crystal design and oscillator circuit. Under proper conditions, quartz can be used to stabilize the frequency of an oscillator circuit.

Quartz crystal microbalance (QCM)

A piezoelectric quartz crystal that utilizes the Converse Piezoelectric Effect to determine mass changes as a result of frequency change of the crystal. Material is coated onto the crystal that attracts a certain other material. When this other material becomes attached, it lowers the crystal frequency, the amount being directly related to its mass. The Sauerbrey equation relates the frequency change to the mass change. The mass change can be in the nanogram range.

Sauerbrey equation: Df = -Dm_df²/__qv_q

where:

Df = change in frequency

Dm_d = change in mass density (m_d, mass per surface area)

f² = frequency squared

__q = density of quartz = 2650 kg m^-3

v_q = propagation of sound in quartz = 3340 m s^-1

Quartz crystal oscillator

A timing device that consists of a crystal and an oscillator circuit, providing an output waveform at a specified reference frequency.

Quartz crystal unit

A completed quartz crystal, including a resonator plate with electrodes, a holder with suitable mounting structures, and a permanently sealed cover. Usually called a crystal.

Quartz oscillator

An oscillator in which a quartz crystal is used to stabilize the frequency.

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