In electrical engineering

Electrical engineering

Electrical engineering is a field of engineering that generally deals with the study and application of electricity, electronics and electromagnetism. The field first became an identifiable occupation in the late nineteenth century after commercialization of the electric telegraph and electrical...

, and particularly in telecommunications, frequency drift is an unintended and generally arbitrary offset of an oscillator from its nominal

Real versus nominal value

In economics, nominal value refers to a value expressed in money terms in a given year or series of years. By contrast, real value adjusts nominal value to remove effects of price changes over time...

 frequency

Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

. Causes may include changes in temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

, which can alter the piezoelectric effect in a quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

 crystal

Crystal

A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

, or problems with a voltage regulator

Voltage regulator

A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. A voltage regulator may be a simple "feed-forward" design or may include negative feedback control loops. It may use an electromechanical mechanism, or electronic components...

 which controls the bias voltage to the oscillator. It is traditionally measured in Hz/s.

On a radio

Radio

Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

 transmitter

Transmitter

In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...

, frequency drift can cause a radio station

Radio station

Radio broadcasting is a one-way wireless transmission over radio waves intended to reach a wide audience. Stations can be linked in radio networks to broadcast a common radio format, either in broadcast syndication or simulcast or both...

 to drift into an adjacent channel

Adjacent channel

In broadcasting an adjacent channel is an AM, FM, or TV channel that is next to another channel. First-adjacent is immediately next to another channel, second-adjacent is two channels away, and so forth. Information on adjacent channels is used in keeping stations from interfering with one...

, causing illegal interference

Adjacent-channel interference

Adjacent-channel interference is interference caused by extraneous power from a signal in an adjacent channel. ACI may be caused by inadequate filtering , improper tuning or poor frequency control .ACI is distinguished from crosstalk.Broadcast...

. Because of this, Frequency allocation

Frequency allocation

Use of radio frequency bands of the electromagnetic spectrum is regulated by governments in most countries, in a Spectrum management process known as frequency allocation or spectrum allocation. Radio propagation does not stop at national boundaries...

 regulations specify the allowed tolerance

Tolerance (engineering)

Engineering tolerance is the permissible limit or limits of variation in# a physical dimension,# a measured value or physical property of a material, manufactured object, system, or service,# other measured values ....

 for such oscillators in a type-accepted device. A temperature-compensate

Compensation (engineering)

In engineering, compensation is planning for side effects or other unintended issues in a design. The design of an invention can itself also be to compensate for some other existing issue or exception....

d, voltage-controlled crystal oscillator (TCVCXO) is normally used for frequency modulation

Frequency modulation

In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...

.

On the receiver

Receiver (radio)

A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...

 side, frequency drift was mainly a problem in early tuners, particularly for analog

Analog signal

An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...

 dial tuning, and especially on FM, which exhibits a capture effect

Capture effect

In telecommunication, the capture effect, or FM capture effect, is a phenomenon associated with FM reception in which only the stronger of two signals at, or near, the same frequency will be demodulated....

. However, the use of a phase-locked loop

Phase-locked loop

A phase-locked loop or phase lock loop is a control system that generates an output signal whose phase is related to the phase of an input "reference" signal. It is an electronic circuit consisting of a variable frequency oscillator and a phase detector...

 (PLL) essentially eliminates the drift issue. For transmitters, a numerically controlled oscillator (NCO) also does not have problems with drift.

Drift differs from Doppler shift, which is a perceived difference in frequency due to motion of the source or receiver, even though the source is still producing the same wavelength

Wavelength

In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

. It also differs from frequency deviation

Frequency deviation

Frequency deviation is used in FM radio to describe the maximum instantaneous difference between an FM modulated frequency and the nominal carrier frequency...

, which is the inherent and necessary result of modulation

Modulation

In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...

 in both FM and phase modulation

Phase modulation

Phase modulation is a form of modulation that represents information as variations in the instantaneous phase of a carrier wave.Unlike its more popular counterpart, frequency modulation , PM is not very widely used for radio transmissions...

.