Recording of US House of Representatives debate on October 8, 2002, interrupted and distorted by electromagnetic interference from a solar flare at approximately 2:30p.m.[citation needed]Electromagnetic interference in analogue TV signal
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, electrostatic coupling, or conduction.[1] The disturbance may degrade the performance of the circuit or even stop it from functioning. In the case of a data path, these effects can range from an increase in error rate to a total loss of the data.[2] Both human-made and natural sources generate changing electrical currents and voltages that can cause EMI: ignition systems, cellular network of mobile phones, lightning, solar flares, and auroras (northern/southern lights).[citation needed] EMI frequently affects AM radios. It can also affect mobile phones, FM radios, and televisions, as well as observations for radio astronomy and atmospheric science.
Interference by 5GHz Wi-Fi seen on Doppler weather radar
History
Since the earliest days of radio communications, the negative effects of interference from both intentional and unintentional transmissions have been felt and the need to manage the radio frequency spectrum became apparent.[3]
In 1933, a meeting of the International Electrotechnical Commission (IEC) in Paris recommended the International Special Committee on Radio Interference (CISPR) be set up to deal with the emerging problem of EMI. CISPR subsequently produced technical publications covering measurement and test techniques and recommended emission and immunity limits. These have evolved over the decades and form the basis of much of the world's EMC regulations today.[4]
In 1979, legal limits were imposed on electromagnetic emissions from all digital equipment by the FCC in the US in response to the increased number of digital systems that were interfering with wired and radio communications. Test methods and limits were based on CISPR publications, although similar limits were already enforced in parts of Europe.[5]
In the mid 1980s, the European Union member states adopted a number of "new approach" directives with the intention of standardizing technical requirements for products so that they do not become a barrier to trade within the EC. One of these was the EMC Directive (89/336/EC)[6] and it applies to all equipment placed on the market or taken into service. Its scope covers all apparatus "liable to cause electromagnetic disturbance or the performance of which is liable to be affected by such disturbance".[5]
This was the first time there was a legal requirement on immunity, as well as emissions on apparatus intended for the general population. Although there may be additional costs involved for some products to give them a known level of immunity, it increases their perceived quality as they are able to co-exist with apparatus in the active EM environment of modern times and with fewer problems.[5]
Many countries now have similar requirements for products to meet some level of electromagnetic compatibility (EMC) regulation.[5]
Types
Electromagnetic interference divides into several categories according to the source and signal characteristics.
The origin of interference, often called "noise" in this context, can be human-made (artificial) or natural.
Continuous, or continuous wave (CW), interference arises where the source continuously emits at a given range of frequencies. This type is naturally divided into sub-categories according to frequency range, and as a whole is sometimes referred to as "DC to daylight". One common classification is into narrowband and broadband, according to the spread of the frequency range.
Audio frequency, from very low frequencies up to around 20kHz. Frequencies up to 100kHz may sometimes be classified as audio. Sources include:
Mains hum from: power supply units, nearby power supply wiring, transmission lines and substations.
An electromagnetic pulse (EMP), sometimes called a transient disturbance, arises where the source emits a short-duration pulse of energy. The energy is usually broadband by nature, although it often excites a relatively narrow-band damped sine wave response in the victim.
Sources divide broadly into isolated and repetitive events.
Sources of isolated EMP events include:
Switching action of electrical circuitry, including inductive loads such as relays, solenoids, or electric motors.
Nuclear electromagnetic pulse (NEMP), as a result of a nuclear explosion. A variant of this is the high altitude EMP (HEMP) nuclear weapon, designed to create the pulse as its primary destructive effect.
Electrical ignition systems, such as in gasoline engines.
Continual switching actions of digital electronic circuitry.
Conducted electromagnetic interference is caused by the physical contact of the conductors as opposed to radiated EMI, which is caused by induction (without physical contact of the conductors). Electromagnetic disturbances in the EM field of a conductor will no longer be confined to the surface of the conductor and will radiate away from it. This persists in all conductors and mutual inductance between two radiated electromagnetic fields will result in EMI.[7]
Coupling mechanisms
The four electromagnetic interference (EMI) coupling modes
Some of the technical terms which are employed can be used with differing meanings. Some phenomena may be referred to by various different terms. These terms are used here in a widely accepted way, which is consistent with other articles in the encyclopedia.
There are four basic coupling mechanisms: conductive, capacitive, magnetic or inductive, and radiative. Any coupling path can be broken down into one or more of these coupling mechanisms working together. For example the lower path in the diagram involves inductive, conductive and capacitive modes.
Conductive coupling occurs when the coupling path between the source and victim is formed by direct electrical contact with a conducting body, for example a transmission line, wire, cable, PCB trace or metal enclosure. Conducted noise is also characterised by the way it appears on different conductors:
Common-mode coupling: noise appears in phase (in the same direction) on two conductors.
Differential-mode coupling: noise appears out of phase (in opposite directions) on two conductors.
Inductive coupling occurs where the source and victim are separated by a short distance (typically less than a wavelength). Strictly, "Inductive coupling" can be of two kinds, electrical induction and magnetic induction. It is common to refer to electrical induction as capacitive coupling, and to magnetic induction as inductive coupling.
Capacitive coupling occurs when a varying electrical field exists between two adjacent conductors typically less than a wavelength apart, inducing a change in voltage on the receiving conductor.
Inductive coupling or magnetic coupling occurs when a varying magnetic field exists between two parallel conductors typically less than a wavelength apart, inducing a change in voltage along the receiving conductor.
EMI filter for conducted emission suppression
Radiative coupling or electromagnetic coupling occurs when source and victim are separated by a large distance, typically more than a wavelength. Source and victim act as radio antennas: the source emits or radiates an electromagnetic wave which propagates across the space in between and is picked up or received by the victim.
ITU definition
Interference with the meaning of electromagnetic interference, also radio-frequency interference (EMI or RFI) is– according to Article 1.166 of the International Telecommunication Union's (ITU) Radio Regulations (RR)[8]– defined as "The effect of unwanted energy due to one or a combination of emissions, radiations, or inductions upon reception in a radiocommunication system, manifested by any performance degradation, misinterpretation, or loss of information which could be extracted in the absence of such unwanted energy".
Conducted EMI is caused by the physical contact of the conductors as opposed to radiated EMI which is caused by induction (without physical contact of the conductors).
For lower frequencies, EMI is caused by conduction and, for higher frequencies, by radiation.
EMI through the ground wire is also very common in an electrical facility.
Interference tends to be more troublesome with older radio technologies such as analogue amplitude modulation, which have no way of distinguishing unwanted in-band signals from the intended signal, and the omnidirectional antennas used with broadcast systems. Newer radio systems incorporate several improvements that enhance the selectivity. In digital radio systems, such as Wi-Fi, error-correction techniques can be used. Spread-spectrum and frequency-hopping techniques can be used with both analogue and digital signalling to improve resistance to interference. A highly directional receiver, such as a parabolic antenna or a diversity receiver, can be used to select one signal in space to the exclusion of others.
The most extreme example of digital spread-spectrum signalling to date is ultra-wideband (UWB), which proposes the use of large sections of the radio spectrum at low amplitudes to transmit high-bandwidth digital data. UWB, if used exclusively, would enable very efficient use of the spectrum, but users of non-UWB technology are not yet prepared to share the spectrum with the new system because of the interference it would cause to their receivers (the regulatory implications of UWB are discussed in the ultra-wideband article).
Potential sources of RFI and EMI include:[12] various types of transmitters, doorbell transformers, toaster ovens, electric blankets, ultrasonic pest control devices, electric bug zappers, heating pads, and touch controlled lamps. Multiple CRT computer monitors or televisions sitting too close to one another can sometimes cause a "shimmy" effect in each other, due to the electromagnetic nature of their picture tubes, especially when one of their de-gaussing coils is activated.
Switching loads (inductive, capacitive, and resistive), such as electric motors, transformers, heaters, lamps, ballast, power supplies, etc., all cause electromagnetic interference especially at currents above 2A. The usual method used for suppressing EMI is by connecting a snubber network, a resistor in series with a capacitor, across a pair of contacts. While this may offer modest EMI reduction at very low currents, snubbers do not work at currents over 2A with electromechanical contacts.[13][14]
Another method for suppressing EMI is the use of ferrite core noise suppressors (or ferrite beads), which are inexpensive and which clip on to the power lead of the offending device or the compromised device.
Most countries have legal requirements that mandate electromagnetic compatibility: electronic and electrical hardware must still work correctly when subjected to certain amounts of EMI, and should not emit EMI, which could interfere with other equipment (such as radios).
Radio frequency signal quality has declined throughout the 21st century by roughly one decibel per year as the spectrum becomes increasingly crowded.[additional citation(s) needed] This has inflicted a Red Queen's race on the mobile phone industry as companies have been forced to put up more cellular towers (at new frequencies) that then cause more interference thereby requiring more investment by the providers and frequent upgrades of mobile phones to match.[15]
The International Special Committee for Radio Interference or CISPR (French acronym for "Comité International Spécial des Perturbations Radioélectriques"), which is a committee of the International Electrotechnical Commission (IEC) sets international standards for radiated and conducted electromagnetic interference. These are civilian standards for domestic, commercial, industrial and automotive sectors. These standards form the basis of other national or regional standards, most notably the European Norms (EN) written by CENELEC (European committee for electrotechnical standardisation). US organizations include the Institute of Electrical and Electronics Engineers (IEEE), the American National Standards Institute (ANSI), and the US Military (MILSTD).
Integrated circuits are often a source of EMI, but they must usually couple their energy to larger objects such as heatsinks, circuit board planes and cables to radiate significantly.[16]
On integrated circuits, important means of reducing EMI are: the use of bypass or decoupling capacitors on each active device (connected across the power supply, as close to the device as possible), rise time control of high-speed signals using series resistors,[17] and IC power supply pin filtering. Shielding is usually a last resort after other techniques have failed, because of the added expense of shielding components such as conductive gaskets.
The efficiency of the radiation depends on the height above the ground plane or power plane (at RF, one is as good as the other) and the length of the conductor in relation to the wavelength of the signal component (fundamental frequency, harmonic or transient such as overshoot, undershoot or ringing). At lower frequencies, such as 133MHz, radiation is almost exclusively via I/O cables; RF noise gets onto the power planes and is coupled to the line drivers via the VCC and GND pins. The RF is then coupled to the cable through the line driver as common-mode noise. Since the noise is common-mode, shielding has very little effect, even with differential pairs. The RF energy is capacitively coupled from the signal pair to the shield and the shield itself does the radiating. One cure for this is to use a braid-breaker or choke to reduce the common-mode signal.
At higher frequencies, usually above 500MHz, traces get electrically longer and higher above the plane. Two techniques are used at these frequencies: wave shaping with series resistors and embedding the traces between the two planes. If all these measures still leave too much EMI, shielding such as RF gaskets and copper or conductive tape can be used. Most digital equipment is designed with metal or conductive-coated plastic cases.[citation needed]
RF immunity and testing
Any unshielded semiconductor (e.g. an integrated circuit) will tend to act as a detector for those radio signals commonly found in the domestic environment (e.g. mobile phones).[18] Such a detector can demodulate the high frequency mobile phone carrier (e.g., GSM850 and GSM1900, GSM900 and GSM1800) and produce low-frequency (e.g., 217Hz) demodulated signals.[19] This demodulation manifests itself as unwanted audible buzz in audio appliances such as microphone amplifier, speaker amplifier, car radio, telephones etc. Adding onboard EMI filters or special layout techniques can help in bypassing EMI or improving RF immunity.[20] Some ICs are designed (e.g., LMV831-LMV834,[21] MAX9724[22]) to have integrated RF filters or a special design that helps reduce any demodulation of high-frequency carrier.
Designers often need to carry out special tests for RF immunity of parts to be used in a system. These tests are often done in an anechoic chamber with a controlled RF environment where the test vectors produce a RF field similar to that produced in an actual environment.[19]
RFI in radio astronomy
Interference in radio astronomy, where it is commonly referred to as radio-frequency interference (RFI), is any source of transmission that is within the observed frequency band other than the celestial sources themselves. Because transmitters on and around the Earth can be many times stronger than the astronomical signal of interest, RFI is a major concern for performing radio astronomy.[23] Natural sources of interference, such as lightning and the Sun, are also often referred to as RFI.[citation needed]
Some of the frequency bands that are very important for radio astronomy, such as the 21-cm HI line at 1420MHz, are protected by regulation.[citation needed] However, modern radio-astronomical observatories such as VLA, LOFAR, and ALMA have a very large bandwidth over which they can observe.[citation needed] Because of the limited spectral space at radio frequencies, these frequency bands cannot be completely allocated to radio astronomy; for example, redshifted images of the 21-cm line from the reionization epoch can overlap with the FM broadcast band (88–108MHz), and therefore radio telescopes need to deal with RFI in this bandwidth.[23]
Techniques to deal with RFI range from filters in hardware to advanced algorithms in software. One way to deal with strong transmitters is to filter out the frequency of the source completely. This is for example the case for the LOFAR observatory, which filters out the FM radio stations between 90 and 110MHz. It is important to remove such strong sources of interference as soon as possible, because they might "saturate" the highly sensitive receivers (amplifiers and analogue-to-digital converters), which means that the received signal is stronger than the receiver can handle. However, filtering out a frequency band implies that these frequencies can never be observed with the instrument.[citation needed]
A common technique to deal with RFI within the observed frequency bandwidth, is to employ RFI detection in software. Such software can find samples in time, frequency or time-frequency space that are contaminated by an interfering source. These samples are subsequently ignored in further analysis of the observed data. This process is often referred to as data flagging. Because most transmitters have a small bandwidth and are not continuously present such as lightning or citizens' band (CB) radio devices, most of the data remains available for the astronomical analysis. However, data flagging can not solve issues with continuous broad-band transmitters, such as windmills, digital video or digital audio transmitters.[citation needed]
Another way to manage RFI is to establish a radio quiet zone (RQZ). RQZ is a well-defined area surrounding receivers that has special regulations to reduce RFI in favor of radio astronomy observations within the zone. The regulations may include special management of spectrum and power flux or power flux-density limitations. The controls within the zone may cover elements other than radio transmitters or radio devices. These include aircraft controls and control of unintentional radiators such as industrial, scientific and medical devices, vehicles, and power lines. The first RQZ for radio astronomy is United States National Radio Quiet Zone (NRQZ), established in 1958.[24]
RFI on environmental monitoring
Prior to the introduction of Wi-Fi, one of the biggest applications of 5GHz band was the Terminal Doppler Weather Radar.[25][26] The decision to use 5GHz spectrum for Wi-Fi was finalized at the World Radiocommunication Conference in 2003; however, meteorological authorities were not involved in the process.[27][28] The subsequent lax implementation and misconfiguration of DFS had caused significant disruption in weather radar operations in a number of countries around the world. In Hungary, the weather radar system was declared non-operational for more than a month. Due to the severity of interference, South African weather services ended up abandoning C band operation, switching their radar network to S band.[26][29]
Transmissions on adjacent bands to those used by passive remote sensing, such as weather satellites, have caused interference, sometimes significant.[30] There is concern that adoption of insufficiently regulated 5G could produce major interference issues. Significant interference can impair numerical weather prediction performance and incur negative economic and public safety impacts.[31][32][33] These concerns led US Secretary of Commerce Wilbur Ross and NASA Administrator Jim Bridenstine in February 2019 to urge the FCC to cancel a proposed spectrum auction, which was rejected.[34]
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 which may cause unwanted effects such as electromagnetic interference (EMI) or even physical damage to operational equipment. The goal of EMC is the correct operation of different equipment in a common electromagnetic environment. It is also the name given to the associated branch of electrical engineering.
In telecommunications, especially radio communication, spread spectrum are techniques by which a signal generated with a particular bandwidth is deliberately spread in the frequency domain over a wider frequency band. Spread-spectrum techniques are used for the establishment of secure communications, increasing resistance to natural interference, noise, and jamming, to prevent detection, to limit power flux density, and to enable multiple-access communications.
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 20 kHz to around 300 GHz. This is roughly between the upper limit of audio frequencies and the lower limit of infrared frequencies, and also encompasses the microwave range. These are the frequencies at which energy from an oscillating current can radiate off a conductor into space as radio waves, so they are used in radio technology, among other uses. Different sources specify different upper and lower bounds for the frequency range.
In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna with the purpose of signal transmission up to a radio receiver. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating current, the antenna radiates radio waves.
This is an index of articles relating to electronics and electricity or natural electricity and things that run on electricity and things that use or conduct electricity.
A ferrite bead – also called a ferrite block, ferrite core, ferrite ring, EMI filter, or ferrite choke – is a type of choke that suppresses high-frequency electronic noise in electronic circuits.
In radio reception, radio noise is unwanted random radio frequency electrical signals, fluctuating voltages, always present in a radio receiver in addition to the desired radio signal. Radio noise near in frequency to the radio signal being received interferes with it in the receiver's circuits. Radio noise is a combination of natural electromagnetic atmospheric noise created by electrical processes in the atmosphere like lightning, manmade radio frequency interference (RFI) from other electrical devices picked up by the receiver's antenna, and thermal noise present in the receiver input circuits, caused by the random thermal motion of molecules.
A radio transmitter or receiver is connected to an antenna which emits or receives the radio waves. The antenna feed system or antenna feed is the cable or conductor, and other associated equipment, which connects the transmitter or receiver with the antenna and makes the two devices compatible. In a radio transmitter, the transmitter generates an alternating current of radio frequency, and the feed system feeds the current to the antenna, which converts the power in the current to radio waves. In a radio receiver, the incoming radio waves excite tiny alternating currents in the antenna, and the feed system delivers this current to the receiver, which processes the signal.
In electronics, noise is an unwanted disturbance in an electrical signal.
In electronics, electric power and telecommunication, coupling is the transfer of electrical energy from one circuit to another, or between parts of a circuit. Coupling can be deliberate as part of the function of the circuit, or it may be undesirable, for instance due to coupling to stray fields. For example, energy is transferred from a power source to an electrical load by means of conductive coupling, which may be either resistive or direct coupling. An AC potential may be transferred from one circuit segment to another having a DC potential by use of a capacitor. Electrical energy may be transferred from one circuit segment to another segment with different impedance by use of a transformer; this is known as impedance matching. These are examples of electrostatic and electrodynamic inductive coupling.
In telecommunication, a measuring receiver or measurement receiver is a calibrated laboratory-grade radio receiver designed to measure the characteristics of radio signals. The parameters of such receivers can be adjusted over a much more comprehensive range of values than other radio receivers. Their circuitry is optimized for stability and enables calibration and reproducible results. Some measurement receivers also have exceptionally robust input circuits that can survive brief impulses of more than 1000 V, as they can occur during measurements of radio signals on power lines and other conductors.
A line impedance stabilization network (LISN) is a device used in conducted and radiated radio-frequency emission and susceptibility tests, as specified in various electromagnetic compatibility (EMC)/EMI test standards.
In the field of EMC, active EMI reduction refers to techniques aimed to reduce or to filter electromagnetic noise (EMI) making use of active electronic components. Active EMI reduction contrasts with passive filtering techniques, such as RC filters, LC filters RLC filters, which includes only passive electrical components. Hybrid solutions including both active and passive elements exist. Standards concerning conducted and radiated emissions published by IEC and FCC set the maximum noise level allowed for different classes of electrical devices. The frequency range of interest spans from 150 kHz to 30 MHz for conducted emissions and from 30 MHz to 40 GHz for radiated emissions. Meeting these requirements and guaranteeing the functionality of an electrical apparatus subject to electromagnetic interference are the main reason to include an EMI filter. In an electrical system, power converters, i.e. DC/DC converters, inverters and rectifiers, are the major sources of conducted EMI, due to their high-frequency switching ratio which gives rise to unwanted fast current and voltage transients. Since power electronics is nowadays spread in many fields, from power industrial application to automotive industry, EMI filtering has become necessary. In other fields, such as the telecommunication industry where the major focus is on radiated emissions, other techniques have been developed for EMI reduction, such as spread spectrum clocking which makes use of digital electronics, or electromagnetic shielding.
In electrical engineering, a common-mode signal is the identical component of voltage present at both input terminals of an electrical device. In telecommunication, the common-mode signal on a transmission line is also known as longitudinal voltage.
Capacitors have many uses in electronic and electrical systems. They are so ubiquitous that it is rare that an electrical product does not include at least one for some purpose. Capacitors allow only AC signals to pass when they are charged blocking DC signals. The main components of filters are capacitors. Capacitors have the ability to connect one circuit segment to another. Capacitors are used by Dynamic Random Access Memory (DRAM) devices to represent binary information as bits.
Electrical noise can disrupt DSL internet connections. The interference can be detected as electrical impulses on the physical telephone line on which the internet connection operates. The noise causes interference which in turn causes a DSL modem to mount up CRC errors. This eventually causes DSL synchronisation to drop.
An electromagnetic pulse (EMP), also referred to as a transient electromagnetic disturbance (TED), is a brief burst of electromagnetic energy. The origin of an EMP can be natural or artificial, and can occur as an electromagnetic field, as an electric field, as a magnetic field, or as a conducted electric current. The electromagnetic interference caused by an EMP can disrupt communications and damage electronic equipment. An EMP such as a lightning strike can physically damage objects such as buildings and aircraft. The management of EMP effects is a branch of electromagnetic compatibility (EMC) engineering.
Switching Control Techniques address electromagnetic interference (EMI) mitigation on power electronics (PE). The design of power electronics involves overcoming three key challenges:
power losses
EMI
harmonics
Common mode current is the portion of conductor currents that are unmatched with the exactly opposite and equal magnitude currents. Common mode current cause multiconductors to act or behave like a single conductor. In electromagnetic compatibility (EMC), there are two common terms that will be found in many electromagnetic interference discussions or considered as fundamental concepts, those are Differential Mode and Common Mode. Those terms are related to coupling mechanisms. Many electrical systems contain elements that are capable to act like an antenna. Each element is capable of unintentionally emitting Radio Frequency energy through electric, magnetic, and electromagnetic means. Common Mode coupling as well as Differential Mode coupling can occur in both a conducted and radiated way.
References
↑ Based on the "interference" entry of The Concise Oxford English Dictionary, 11th edition, online
↑ Sue, M.K. (15 June 1981). Radio frequency interference at the geostationary orbit. NASA Technical Reports Server (Report). Jet Propulsion Laboratory. hdl:2060/19810018807.
↑ Sue, M.K.; Sue, M K. (15 June 1981), "NASA", Radio frequency interference at the geostationary orbit, Jet Propulsion Laboratory, hdl:2060/19810018807, retrieved 2023-05-10
↑ Paglin, Max D.; Hobson, James R.; Rosenbloom, Joel (1999), The Communications Act: A Legislative History of the Major Amendments, 1934-1996, Pike & Fischer– A BNA Company, p.210, ISBN0-937275-05-0
1 2 Saltikoff, Elena (2016). "The Threat to Weather Radars by Wireless Technology". Bulletin of the American Meteorological Society. 97 (7): 1159–1167. Bibcode:2016BAMS...97.1159S. doi:10.1175/BAMS-D-15-00048.1. ISSN0003-0007. Since 2006, interference to C-band radars from RLAN is increasingly experienced by most OPERA members. ... The South African weather services initially tried to implement specific software filtering to improve the situation but then decided in 2011 to move its meteorological radar network to S band.
↑ Touw, Ron (Nov 16, 2016). "Radar Detection and DFS on MikroTik"(PDF). Radar Detect and DFS on MikroTik. MikroTik. Retrieved 4 December 2019– via YouTube. Decision ERC/DEC/(99)23 adds 5250–5350MHz and 5470–5725MHz with more Tx power but with the added caveat that DFS was required to protect legacy users (Military Radar and Satellite uplinks)
↑ Tristant, Philippe (16–18 September 2009). "RLAN 5GHz interference to weather radars in Europe"(PDF). International Telecommunication Union. Retrieved 4 December 2019. More than 12 European countries experienced such interference cases (other cases have now been reported in number of countries in the world). Definitively harmful interference (in Hungary, the radar was declared as non-operational for more than 1 month)
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