Electromagnetic interference
[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).
CISPR subsequently produced technical publications covering measurement and test techniques and recommended emission and immunity limits.
[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.
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.
The energy is usually broadband by nature, although it often excites a relatively narrow-band damped sine wave response in the victim.
Sources of isolated EMP events include: Sources of repetitive EMP events, sometimes as regular pulse trains, include: 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).
The basic arrangement of noise emitter or source, coupling path and victim, receptor or sink is shown in the figure below.
Conducted noise is also characterised by the way it appears on different conductors: Inductive coupling occurs where the source and victim are separated by a short distance (typically less than a wavelength).
In the United States, the 1982 Public Law 97-259 allowed the Federal Communications Commission (FCC) to regulate the susceptibility of consumer electronic equipment.
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 2 A.
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.
Radio frequency signal quality has declined throughout the 21st century by roughly one decibel per year as the spectrum becomes increasingly crowded.
[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.
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 VCC and GND pins.
[citation needed] 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).
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.
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.
RQZ is a well-defined area surrounding receivers that has special regulations to reduce RFI in favor of radio astronomy observations within the zone.
[24] Prior to the introduction of Wi-Fi, one of the biggest applications of 5 GHz band was the Terminal Doppler Weather Radar.
[25][26] The decision to use 5 GHz 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.
[26][29] Transmissions on adjacent bands to those used by passive remote sensing, such as weather satellites, have caused interference, sometimes significant.
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.
