In
electrical engineering
Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems that use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...
, and particularly in
telecommunications
Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...
, frequency drift is an unintended and generally arbitrary offset of an
oscillator from its
nominal frequency. Causes may include component aging,
changes in
temperature
Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
that alter the
piezoelectric effect in a
crystal oscillator, or problems with a
voltage regulator
A voltage regulator is a system designed to automatically maintain a constant voltage. It may use a simple feed-forward design or may include negative feedback. It may use an electromechanical mechanism or electronic components. Depending on the ...
which controls the
bias voltage to the oscillator. Frequency drift is traditionally measured in Hz/s. Frequency stability can be regarded as the absence (or a very low level) of frequency drift.
On a
radio
Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connec ...
transmitter
In electronics and telecommunications, a radio transmitter or just transmitter (often abbreviated as XMTR or TX in technical documents) is an electronic device which produces radio waves with an antenna (radio), antenna with the purpose of sig ...
, frequency drift can cause a
radio station
Radio broadcasting is the broadcasting of audio (sound), sometimes with related metadata, by radio waves to radio receivers belonging to a public audience. In terrestrial radio broadcasting the radio waves are broadcast by a land-based rad ...
to drift into an
adjacent channel, causing illegal
interference. Because of this,
Frequency allocation regulations specify the allowed
tolerance for such oscillators in a
type-accepted device. A temperature-compensated, voltage-controlled crystal oscillator (
TCVCXO) is normally used for
frequency modulation.
On the
receiver side, frequency drift was mainly a problem in early
tuners, particularly for
analog dial
tuning, and especially on FM, which exhibits a
capture effect. However, the use of a
phase-locked loop (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. It also differs from
frequency deviation, which is the inherent and necessary result of
modulation
Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information.
The process encodes information in form of the modulation or message ...
in both FM and
phase modulation.
See also
*
Allan variance
*
Clock drift
*
Phase noise
*
Automatic frequency control (AFC)
*
Phase-locked loop (PLL)
References
Communication circuits
Broadcast engineering
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