Electromagnetic interference (or EMI, also called radio frequency interference or RFI) is a (usually undesirable) disturbance caused in a radio receiver or other electrical circuit by electromagnetic radiation emitted from an external source. ^[1] The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit. The source may be any object, artificial or natural, that carries rapidly changing electrical currents, such as an electrical circuit, the Sun or the Northern Lights. Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... An electrical network or electrical circuit is an interconnection of analog electrical elements such as resistors, inductors, capacitors, diodes, switches and transistors. ... Sol redirects here. ... The Aurora Borealis, or Northern Lights, shines above Bear Lake Aurora Borealis as seen over Canada at 11,000m (36,000 feet) Red and green Aurora in Fairbanks, Alaska Aurora Borealis redirects here. ...

EMI can be induced intentionally for radio jamming, as in some forms of electronic warfare, or unintentionally, as a result of spurious emissions and responses, intermodulation products, and the like. It frequently affects the reception of AM radio in urban areas. It can also affect cell phone, FM radio and television reception, although to a lesser extent. Radio jamming is the (usually deliberate) transmission of radio signals that disrupt communications by decreasing the signal to noise ratio. ... // Electronic warfare (EW) is the use of the electromagnetic spectrum to effectively deny the use of this phenomena by an adversary, while optimizing its use by friendly forces. ... Intermodulation or intermodulation distortion (IMD), or intermod for short, is the result of two or more signals of different frequencies being mixed together, forming additional signals at frequencies that are not, in general, at harmonic frequencies (integer multiples) of either. ... Mediumwave radio transmissions (sometimes called Medium frequency or MF) are those between the frequencies of 300 kHz and 3000 kHz. ... Motorola T2288 mobile phone A mobile phone is a portable electronic device which behaves as a normal telephone whilst being able to move over a wide area (compare cordless phone which acts as a telephone only within a limited range). ... FM radio is a broadcast technology invented by Edwin Howard Armstrong that uses frequency modulation to provide high-fidelity sound over broadcast radio. ...

Sound

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EMI sound sample. A Wi-Fi signal interferes with a speaker system.

Image File history File links 802_11bg_interference. ... Official Wi-Fi logo Wi-Fi (pronounced wye-fye, IPA: ), also unofficially known as Wireless Fidelity, is a wireless technology brand owned by the Wi-Fi Alliance intended to improve the interoperability of wireless local area network products based on the IEEE 802. ...

EMI/RFI types

EMI or RFI may be broadly categorized into two types; narrowband and broadband. Narrowband (narrow bandwidth) refers to a signal which occupies only a small amount of space on the radio spectrum -- the opposite of broadband or wideband. ... Broadband in telecommunications is a term that refers to a signaling method that includes or handles a relatively wide range of frequencies, which may be divided into channels or frequency bins. ...

Narrowband interference usually arises from intentional transmissions such as radio and TV stations, pager transmitters, cell phones, etc. Broadband interference usually comes from incidental radio frequency emitters. These include electric power transmission lines, electric motors, thermostats, bug zappers, etc. Anywhere electrical power is being turned off and on rapidly is a potential source. The spectra of these sources generally resembles that of synchrotron sources, stronger at low frequencies and diminishing at higher frequencies, though this noise is often modulated, or varied, by the creating device in some way. Included in this category are computers and other digital equipment as well as televisions. The rich harmonic content of these devices means that they can interfere over a very broad spectrum. Characteristic of broadband RFI is an inability to filter it effectively once it has entered the receiver chain. ^{[2][3] [4]} Broadcasting is the distribution of audio and/or video signals which transmit programs to an audience. ... Motorola T2288 mobile phone A mobile phone is a portable electronic device which behaves as a normal telephone whilst being able to move over a wide area (compare cordless phone which acts as a telephone only within a limited range). ... For other uses, see Frequency (disambiguation). ... Power line redirects here. ... For other kinds of motors, see motor. ... Bi-metallic thermostat for buildings A thermostat is a device for regulating the temperature of a system so that the systems temperature is maintained near a desired setpoint temperature. ... General Electric synchrotron accelerator built in 1946, the origin of the discovery of synchrotron radiation. ... In telecommunications, modulation is the process of varying a periodic waveform, i. ... This article is about the machine. ... For other uses, see Digital (disambiguation). ... This article is about the components of sound. ... Radio frequency, or RF, is a frequency or rate of oscillation within the range of about 3 Hz and 300 GHz. ... For the device which is a tuner (radio) and a amplifier and/or loudspeaker, see receiver (home stereo). ...

Power line noise

Virtually all power-line noise, originating from utility company equipment, is caused by a spark or arcing across some power-line related hardware. A breakdown and ionization of air occurs, and current flows between two conductors in a gap. The gap may be caused by broken or loose hardware such as a cracked insulator. Typical culprits include insufficient and inadequate hardware spacing such as a gap between a ground wire and a staple. Once an ionized path is established in the gap, current flows at all parts of the cycle where the voltage is higher than the breakdown voltage of the gap. This typically occurs only at the positive and negative voltage peaks -- the times of highest instantaneous voltage throughout the cycle.

As an example for a 60Hz system (i.e.power-lines carrying 60 Hz AC, such as in the US), the voltage on them passes through two peaks each cycle (one positive and one negative) and pass through zero twice each cycle. This gives 120 peaks and 120 zero crossings in each second (50Hz: 100 peaks and crossings correspondingly). Power-line noise follows this pattern, generally occurring in bursts at a rate of 120 bursts per second. This gives power-line noise a characteristic sound that is often described as a harsh and raspy hum or buzz. Because the peaks occur twice per cycle, true power-line noise has a strong 120-Hz modulation on the signal (50Hz system: 100Hz).^[5]

Mitigation

On integrated circuits, the most 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), risetime control of high-speed signals using series resistors, and V_CC filtering. Shielding is usually a last resort after other techniques have failed because of the added expense of RF gaskets and the like. Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... See Capacitor (component) for a discussion of specific types. ... Almost all integrated circuits (ICs) have at least two pins which connect to the power rails of the circuit they are installed in. ... It has been suggested that this article or section be merged with Radio waves. ...

The efficiency of the radiation depends on the height above the ground 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, harmonic or transient (overshoot, undershoot or ringing)). At lower frequencies, such as 133 MHz, radiation is almost exclusively via I/O cables; RF noise gets onto the power planes and is coupled to the line drivers via the V_CC and ground 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. A megahertz (MHz) is one million (106) hertz, a measure of frequency. ... Differential pair is a pair of conductors with special characteristics, used for differential signaling. ... The braid breaker is a term for one of the best filters for preventing TVI. It is the case that in many cases of Television interference caused by a high field strength of a nearby HF transmitter that the aerial down lead plugged into the back of the TV acts... A Choke is an inductor designed to have a high reactance to a particular frequency when used in a signal-carrying circuit. ...

At higher frequencies, usually above 500 MHz, 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 tape can be used. Most digital equipment is designed with metal, or conductive-coated plastic, cases. A megahertz (MHz) is one million (106) hertz, a measure of frequency. ...

Switching power supplies can be a source of EMI, but have become less of a problem as design techniques have improved.

Most countries have legal requirements that mandates 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). Electromagnetic Compatibility (EMC) 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 an energy may induce. ...

Susceptibilities of different radio technologies

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 dipole antennas used with broadcast systems. Newer radio systems incorporate several improvements that improve 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. Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. ... A simple half-wave dipole antenna that a shortwave listener might build. ... The word selectivity has more meanings: Selectivity, the ability to notice/distinguish small differences. ... Official Wi-Fi logo Wi-Fi (pronounced wye-fye, IPA: ), also unofficially known as Wireless Fidelity, is a wireless technology brand owned by the Wi-Fi Alliance intended to improve the interoperability of wireless local area network products based on the IEEE 802. ... In computer science and information theory, error correction consists of using methods to detect and/or correct errors in the transmission or storage of data by the use of some amount of redundant data and (in the case of transmission) the selective retransmission of incorrect segments of the data. ... Spread-spectrum techniques are methods by which energy generated at one or more discrete frequencies is deliberately spread or distributed in time or frequency domains. ... Frequency-hopping spread spectrum (FHSS) is a spread-spectrum method of transmitting signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. ... In electromagnetics, directivity is a figure of merit for an antenna. ... The Parabolic antenna is a high-gain, reflector antenna used for radio, television and data communications, and also for radiolocation (RADAR), on the UHF and SHF frequencies. ... Antenna Diversity is a transmission technique in which the information-carrying signal is transmitted along different propagation paths. ...

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. Spread-spectrum techniques are methods by which energy generated at one or more discrete frequencies is deliberately spread or distributed in time or frequency domains. ... Ultra-wideband (also UWB, and ultra-wide-band, ultra-wide band, etc. ... Ultra-wideband (also UWB, and ultra-wide-band, ultra-wide band, etc. ...

Interference to consumer devices

Complex electronic circuitry is found in all sorts of devices used in the home. This results in a vast interference potential that didn't exist in earlier, simpler decades. In the US, Public Law 97-259, enacted in 1982, gave the FCC the authority to regulate the susceptibility of consumer electronic equipment sold in the United States. The FCC, working with equipment manufacturers, decided to allow them to develop standards for EMI immunity and implement their own voluntary compliance programs.^[6] United States may refer to: Places: United States of America SS United States, the fastest ocean liner ever built. ... The abbreviation FCC can refer to: Face-centered cubic (usually fcc), a crystallographic structure Federal Communications Commission, a US government organization Farm Credit Corporation/Farm Credit Canada, a Canadian government organization Families with Children from China, an adoption support organization Florida Christian College, a college in central Florida Fresno City...

Broadcast transmitters, two-way radio transmitters, paging transmitters, and cable TV are potential sources of RFI and EMI. Other possible sources of interference include a wide variety of devices, such as doorbell transformers, toaster ovens, electric blankets, ultrasonic pest controls (bug zappers), heating pads, and touch controlled lamps.^[7] The word broadcast can refer to: Broadcasting, the transmission of audio and video signals. ... Antenna tower of Crystal Palace transmitter, London A transmitter (sometimes abbreviated XMTR) is an electronic device which with the aid of an antenna propagates an electromagnetic signal such as radio, television, or other telecommunications. ... Motorola HT1000 hand-held two-way radio A two-way radio is a radio that can both transmit and receive (a transceiver), unlike a broadcast receiver which only receives content one way. ... Cable television or Community Antenna Television (CATV) (and often shortened to cable) is a system of providing television, FM radio programming and other services to consumers via radio waves transmitted directly to people’s televisions through fixed coaxial cables as opposed to the over-the-air method used in... Ultrasound is sound with a frequency greater than the upper limit of human hearing, approximately 20 kilohertz. ...

Standards

The Special International Committee on Radio Interference (CISPR) sets standards for radiated and conducted electromagnetic interference. The CISPR is the Comite International Special des Perturbations Radioelectriques (Special International Comitee on Radio Interference). ...

See also

• Radio receiver

For the device which is a tuner (radio) and a amplifier and/or loudspeaker, see receiver (home stereo). ...

References

1. ^ Based on the "interference" entry of The Concise Oxford English Dictionary, 11th edition, online
2. ^ http://www.radiosky.com/journal0901.html RadioSky Jornal
3. ^ Radio frequency interference / editors, Charles L. Hutchinson, Michael B. Kaczynski ; contributors, Doug DeMaw ... [et al.]. 4th ed. Newington, CT American Radio Relay League c1987. 
4. ^ Radio frequency interference handbook. Compiled and edited by Ralph E. Taylor. Washington Scientific and Technical Information Office, National Aeronautics and Space Administration; [was for sale by the National Technical Information Service, Springfield, Va.] 1971. 
5. ^ http://www.arrl.org/tis/info/powerline-FAQ.html#tutorial ARRL, The Power Line Noise FAQ
6. ^ http://www.arrl.org/tis/info/rfigen.html RadioFrequency Interference/ElectroMagnetic Interference, ARRL
7. ^ http://www.kyes.com/antenna/interference/tvibook.html INTERFERENCE HANDBOOK

External links

• ARRL, RFI
• Interference Handbook