radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a tr ...

reception, radio noise is unwanted random

radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the up ...

electrical signals, fluctuating voltages, always present in a

radio receiver In radio communications, a radio receiver, also known as a receiver, a wireless, or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. Th ...

in addition to the desired radio signal. Radio noise near in

frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

to the radio signal being received (in the receiver's

passband A passband is the range of frequencies or wavelengths that can pass through a filter. For example, a radio receiver contains a bandpass filter to select the frequency of the desired radio signal out of all the radio waves picked up by its antenn ...

) interferes with it in the receiver's circuits. Radio noise is a combination of natural electromagnetic

atmospheric noise Atmospheric noise is radio noise caused by natural atmospheric processes, primarily lightning discharges in thunderstorms. On a worldwide scale, there are about 40 lightning flashes per second – ≈3.5 million lightning discharges ...

("spherics", static) created by electrical processes in the atmosphere like

lightning Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an average ...

, manmade

radio frequency interference Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrost ...

(RFI) from other electrical devices picked up by the receiver's

antenna Antenna ( antennas or antennae) may refer to: Science and engineering * Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves * Antennae Galaxies, the name of two collid ...

, and

thermal noise A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

present in the receiver input circuits, caused by the random thermal motion of molecules. Atmosphericnoise

The level of noise determines the maximum sensitivity and reception range of a radio receiver; if no noise were picked up with radio signals, even weak transmissions could be received at virtually any distance by making a radio receiver that was sensitive enough. With noise present, if a radio source is so weak and far away that the radio signal in the receiver has a lower amplitude than the average noise, the noise will drown out the signal. The level of noise in a communications circuit is measured by the

signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in de ...

(S/N), the ratio of the average amplitude of the signal voltage to the average amplitude of the noise voltage. When this ratio is below one (0 dB) the noise is greater than the signal, requiring special processing to recover the information. The limiting noise source in a receiver depends on the frequency range in use. At frequencies below about 40 MHz, particularly in the

mediumwave Medium wave (MW) is the part of the medium frequency (MF) radio band used mainly for AM radio broadcasting. The spectrum provides about 120 channels with more limited sound quality than FM stations on the FM broadcast band. During the dayt ...

and

longwave In radio, longwave, long wave or long-wave, and commonly abbreviated LW, refers to parts of the radio spectrum with wavelengths longer than what was originally called the medium-wave broadcasting band. The term is historic, dating from the e ...

bands and below,

and nearby radio frequency interference from electrical switches,

motors An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power g ...

, vehicle ignition circuits,

computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations ( computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These prog ...

s, and other man-made sources tends to be above the

floor in the receiver's circuits. These noises are often referred to as static. Conversely, at

very high frequency Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves ( radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VH ...

and

ultra high frequency Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter ...

and above, these sources are often lower, and thermal noise is usually the limiting factor. In the most sensitive receivers at these frequencies,

radio telescope A radio telescope is a specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency ...

s and

satellite communication A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. C ...

antennas, thermal noise is reduced by cooling the

RF front end RF is an abbreviation for radio frequency. Rf or RF may also mean: Arts and entertainment * ''Red Faction (series)'', a series of revolution video games * Rinforzando, , in music notation * ''RF Online'', an online RPG made by CCR Businesses * A ...

of the receiver to

cryogenic In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cr ...

temperatures. 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 In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visib ...

that electronic equipment is permitted to radiate. These standards are aimed at ensuring what is referred to as

electromagnetic compatibility Electromagnetic compatibility (EMC) is the ability of electrical equipment and systems to function acceptably in their electromagnetic environment, by limiting the unintentional generation, propagation and reception of electromagnetic energy whic ...

(EMC).

References

Radio noise
ITU-R Recommendation P.372,

International Telecommunication Union The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...

, Geneva. * Blackard, K.L.; et al.
Measurements and models of radio frequency impulsive noise for indoor wireless communications
IEEE Journal on Selected Areas in Communications 11 (7), September 1993. * Dalke, R.; et al.
Measurement and analysis of man-made noise in VHF and UHF bands
Wireless Communications Conference, 1997. * Lauber, W.R.; Bertrand, J.M.
Statistics of motor vehicle ignition noise at VHF/UHF
IEEE Trans. Electromagn. Compat. 41 (3), August 1999. * Sanchez, M.G.; et al.
Impulsive noise measurements and characterization in a UHF digitalTV channel
IEEE Trans. Electromagn. Compat. 41 (2), May 1999. * Blankenship, T.K.; Rappaport, T.S.
Characteristics of impulsive noise in the 450-MHz band in hospitals and clinics
IEEE Transactions on Antennas and Propagation 46 (2), February 1998. {{Noise

Radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a tr ...

tr:Parazit (elektronik)

See also

References