Noise (radio)
Encyclopedia
In radio
reception, noise is the superposition of white noise
(also called "static") and other disturbing influences on the signal, caused either by thermal noise and other electronic noise
from receiver input circuits or by interference from radiated electromagnetic noise picked up by the receiver's antenna
. If no noise was picked up with radio signals, even weak transmissions could be received at virtually any distance by making a radio receiver that was sensitive enough. In practice, this doesn't work, and a point is reached where the only way to extend the range of a transmission is to increase the transmitter power.
Thermal noise can be made lower by cooling the circuits, but this is only usually worthwhile on radio telescope
s. In other applications the limiting noise source depends on the frequency range in use. At low frequencies
(longwave
or mediumwave
) and at high frequencies
(shortwave
), interference caused by lightning
or by nearby electrical impulses in electrical switches
, motors
, vehicle ignition circuits
, computer
s, and other man-made sources tends to swamp transmissions with thermal noise. These noises are often referred to as static
. Atmospheric noise
is radio noise caused by natural atmospheric processes, primarily lightning discharges in thunderstorms. At very high frequency
and ultra high frequency
these sources can still be important, but at a much lower level, such that thermal noise is usually the limiting factor. Cosmic background noise
is experienced at frequencies above about 15 MHz when highly directional antennas are pointed toward the sun or to certain other regions of the sky such as the center of the Milky Way Galaxy.
Electromagnetic noise can interfere with electronic equipment in general, causing malfunction, and in recent years standards have been laid down for the levels of electromagnetic radiation
that electronic equipment is permitted to radiate. These standards are aimed at ensuring what is referred to as electromagnetic compatibility
, or EMC.
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...
reception, noise is the superposition of white noise
White noise
White noise is a random signal with a flat power spectral density. In other words, the signal contains equal power within a fixed bandwidth at any center frequency...
(also called "static") and other disturbing influences on the signal, caused either by thermal noise and other electronic noise
Electronic noise
Electronic noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects...
from receiver input circuits or by interference from radiated electromagnetic noise picked up by the receiver's antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
. If no noise was picked up with radio signals, even weak transmissions could be received at virtually any distance by making a radio receiver that was sensitive enough. In practice, this doesn't work, and a point is reached where the only way to extend the range of a transmission is to increase the transmitter power.
Thermal noise can be made lower by cooling the circuits, but this is only usually worthwhile on radio telescope
Radio telescope
A radio telescope is a form of directional radio antenna used in radio astronomy. The same types of antennas are also used in tracking and collecting data from satellites and space probes...
s. In other applications the limiting noise source depends on the frequency range in use. At low frequencies
Low frequency
Low frequency or low freq or LF refers to radio frequencies in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon,...
(longwave
Longwave
In radio, longwave refers to parts of radio spectrum with relatively long wavelengths. The term is a historic one dating from the early 20th century, when the radio spectrum was considered to consist of long, medium and short wavelengths...
or mediumwave
Mediumwave
Medium wave is the part of the medium frequency radio band used mainly for AM radio broadcasting. For Europe the MW band ranges from 526.5 kHz to 1606.5 kHz...
) and at high frequencies
High frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
(shortwave
Shortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
), interference caused by lightning
Lightning
Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
or by nearby electrical impulses in electrical switches
Switch
In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another....
, motors
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
, vehicle ignition circuits
Ignition system
An ignition system is a system for igniting a fuel-air mixture. Ignition systems are well known in the field of internal combustion engines such as those used in petrol engines used to power the majority of motor vehicles, but they are also used in many other applications such as in oil-fired and...
, computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
s, and other man-made sources tends to swamp transmissions with thermal noise. These noises are often referred to as static
Static
Static has several meanings:* Static electricity, a net charge of an object** The triboelectric effect, e.g. from shoes rubbing carpet* White noise, a random signal with a flat power spectral density** Noise , a type of radio interference...
. Atmospheric noise
Atmospheric noise
Atmospheric noise is radio noise caused by natural atmospheric processes, primarily lightning discharges in thunderstorms. On a worldwide scale, eight million lightning discharges per day — about 100 lightning flashes per second.-History:...
is radio noise caused by natural atmospheric processes, primarily lightning discharges in thunderstorms. At very high frequency
Very high frequency
Very high frequency is the radio frequency range from 30 MHz to 300 MHz. Frequencies immediately below VHF are denoted High frequency , and the next higher frequencies are known as Ultra high frequency...
and ultra high frequency
Ultra high frequency
Ultra-High Frequency designates the ITU Radio frequency range of electromagnetic waves between 300 MHz and 3 GHz , also known as the decimetre band or decimetre wave as the wavelengths range from one to ten decimetres...
these sources can still be important, but at a much lower level, such that thermal noise is usually the limiting factor. Cosmic background noise
Cosmic noise
Cosmic noise and galactic radio noise is random noise that originates outside the Earth's atmosphere. It can be detected and heard on radio receivers.- Elaboration :Cosmic noise characteristics are similar to those of thermal noise...
is experienced at frequencies above about 15 MHz when highly directional antennas are pointed toward the sun or to certain other regions of the sky such as the center of the Milky Way Galaxy.
Electromagnetic noise can interfere with electronic equipment in general, causing malfunction, and in recent years standards have been laid down for the levels of electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
that electronic equipment is permitted to radiate. These standards are aimed at ensuring what is referred to as electromagnetic compatibility
Electromagnetic compatibility
Electromagnetic compatibility is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects that such energy may induce...
, or EMC.