Spectral splatter
Encyclopedia
In radio electronics
or acoustics
, spectral splatter (also called switch noise) refers to spurious emission
s that result from an abrupt change in the transmitted signal, usually when transmission is started or stopped.
For example, a device transmitting a sine wave
produces a single peak in the frequency spectrum; however, if the device abruptly starts or stops transmitting this sine wave, it will emit noise at frequencies other than the frequency of the sine wave. This noise is known as spectral splatter.
When the signal is represented in the time domain
, an abrupt change may not be visually apparent; in the frequency domain
, however, the abrupt change causes the appearance of spikes at various frequencies.
A sharper change in the time domain usually results in more spikes or stronger spikes in the frequency domain. Spectral splatter can thus be reduced by making the change more smooth. Controlling the power ramp
shape (i.e. the way in which the signal increases ("power-on ramp") or falls off ("power-down ramp")) can help reduce the splatter. In some cases one can use a filter
to remove unwanted emissions. Note that a completely abrupt change (in the mathematical sense) is not possible in physical reality; the change is always somewhat smoothed naturally, for example due to the capacitance
(in electronics) or inertia
(in acoustics) of the components involved.
In radio electronics, the need to minimize spectral splatter arises because signals are usually required by government regulations to be contained in a particular frequency band, defined by a spectral mask
. Spectral splatter can cause emissions that violate this mask.
Radio electronics
*For the magazine, see Radio-ElectronicsRadio electronics is the sub-field of electrical engineering concerning itself with the class of electronic circuits which receive or transmit radio signals....
or acoustics
Acoustics
Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...
, spectral splatter (also called switch noise) refers to spurious emission
Spurious emission
A spurious emission is any radio frequency not deliberately created or transmitted, especially in a device which normally does create other frequencies...
s that result from an abrupt change in the transmitted signal, usually when transmission is started or stopped.
For example, a device transmitting a sine wave
Sine wave
The sine wave or sinusoid is a mathematical function that describes a smooth repetitive oscillation. It occurs often in pure mathematics, as well as physics, signal processing, electrical engineering and many other fields...
produces a single peak in the frequency spectrum; however, if the device abruptly starts or stops transmitting this sine wave, it will emit noise at frequencies other than the frequency of the sine wave. This noise is known as spectral splatter.
When the signal is represented in the time domain
Time domain
Time domain is a term used to describe the analysis of mathematical functions, physical signals or time series of economic or environmental data, with respect to time. In the time domain, the signal or function's value is known for all real numbers, for the case of continuous time, or at various...
, an abrupt change may not be visually apparent; in the frequency domain
Frequency domain
In electronics, control systems engineering, and statistics, frequency domain is a term used to describe the domain for analysis of mathematical functions or signals with respect to frequency, rather than time....
, however, the abrupt change causes the appearance of spikes at various frequencies.
A sharper change in the time domain usually results in more spikes or stronger spikes in the frequency domain. Spectral splatter can thus be reduced by making the change more smooth. Controlling the power ramp
Power ramp
In telecommunications, power ramp is the way in which the signal increases or falls off , which may result in spectral splatter....
shape (i.e. the way in which the signal increases ("power-on ramp") or falls off ("power-down ramp")) can help reduce the splatter. In some cases one can use a filter
Linear filter
Linear filters in the time domain process time-varying input signals to produce output signals, subject to the constraint of linearity.This results from systems composed solely of components classified as having a linear response....
to remove unwanted emissions. Note that a completely abrupt change (in the mathematical sense) is not possible in physical reality; the change is always somewhat smoothed naturally, for example due to the capacitance
Capacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...
(in electronics) or inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
(in acoustics) of the components involved.
In radio electronics, the need to minimize spectral splatter arises because signals are usually required by government regulations to be contained in a particular frequency band, defined by a spectral mask
Spectral mask
In telecommunications, a spectral mask, also known as a channel mask or transmission mask, is a mathematically-defined set of lines applied to the levels of radio transmissions. The spectral mask is generally intended to reduce adjacent-channel interference by limiting excessive radiation at...
. Spectral splatter can cause emissions that violate this mask.