EMI(Electromagnetic Interference)
Any electromagnetic disturbance, phenomenon, signal, or emission that causes, or is capable of causing, undesired responses or degradation of performance in electrical or electronic equipment. EMI is characterized by the following categories for test and measurement purposes: 1. Conducted Emissions, 2. Radiated Emissions, 3. Conducted Susceptibility, 4. Radiated Susceptibility
EMC(Electromagnetic Compatibility)
The capability of equipment or systems to be used in their intended environment within designed efficiency levels without causing or receiving degradation due to unintentional EMI. EMC generally encompasses all of the electromagnetic disciplines.
EMI/EMC terminology explanation
Absorbing Clamp Method
The absorbing clamp method of measurement is accepted by CISPR as a standard method of measuring the interference power levels on cables connected to electronic and electrical devices. Measurements can be made from 30 MHz to 1 GHz.
Air Discharge Method
A method for testing ESD-protection structures in which the ESD generator is discharged through an air gap between the generator and the device under test (DUT).
Anechoic Chamber
A room lined with absorbing material to reduce the reflection of electromagnetic waves. A full anechoic chamber is designed to simulate a free-space environment. It should have absorber material on all surfaces, including the floor. A semi-anechoic chamber should have absorbing material on the walls and ceiling only. The floor should be without absorbing material so that it is reflective to create a ground plane effect.
An antenna is a transducer through which electromagnetic waves are coupled from a transmitter to space and from space to a receiver. Some of the design parameters of an antenna include gain, bandwidth, beamwidth, directivity, radiation pattern, impedance, phase and polarization.
Antenna Factor (AF)
The term (AF) is used to define the antenna calibration relationship required for making accurate radiated emission measurements. The unknown electric field strength (E in V/m) is obtained by multiplying the voltage (V in Volts or uVolts) at the measuring r
Antenna Material
Material with surface conductivity between 109 and 1014 Ω/m2 resistant to electric charge buildup.
Antistatic Material
A material preventing or inhibiting the buildup of static electricity
Artificial Hand
An electric circuit network describing human impedance between the ground and a mobile electric device in normal state of use.
Artificial Mains Network
A network which is inserted into power supply path of UUT (Unit Under Test), provides the load impedance as prescribed by the given frequency range for the measurement of the interference voltage and to isolate UUT from the power supply.
Artificial Noise
Noises emitted from artificial sources: radio waves from broadcasts and radar; noises from engine spark plugs, switches, fluorescent tubes; noises from guided heating and welding; noises from the computer and its peripherals; and others.
Audio Rectification
Interference to electronic devices caused by a strong RF field that is rectified and amplified in the device.
Average Detect
Electrical charge/discharge time constant the cymoscope is set at the inverse of path bandwidth of 1/5 or lower and the output voltage is the average value of incoming signal modulation envelope detected.
Balanced Line
A transmission line consisting of two conductors in the presence of ground, capable of being operated in such a way that when the voltages of the two conductors at all transverse planes are equal in magnitude and opposite in polarity with respect to ground, the currents in the two conductors are equal in magnitude and opposite in direction.
Abbreviation for balanced to unbalanced. In radio frequency usage, a device used to couple a balanced device or line to an unbalanced device or line.
Biconical Antenna
Used for FCC, MIL-STD testing, receive/transmit. A broadband linear polarized dipole antenna used to measure and produce electric fields from approximately 30 MHz to 300 MHz.
To provide a fixed union between two objects that results in electrical conductivity between them. The union may occur either from physical contact between conducting surfaces of the objects or from the addition of a firm electrical connection.
Broadband EMI
Interference generated over a wide range of frequencies. For example, automotive ignition noise.
Reception of a signal for a few seconds via meteor scatter
Burst Noise
Burst noise is the noise which comes suddenly at high amplitude thus making the signal change its value. We can also say it to be the Impulse noise. It happens at low frequency
One or more conductors or optical fibers that serve as a common connection for a group of related devices
By-pass Capacitor
A capacitor that provides a path of low impedance - low resistance to AC signals.
Cabinet Radiation
Radiation from the cabinet containing the radiation source, exclusive of
radiation from the antenna or the cables attached to it
Electromagnetic interference of duration shorter than the defined time length, measured based on relevant rules.
Clock Signal
A signal used to coordinate the actions of two or more circuits. A clock signal oscillates between a high and a low state, normally with a 50% duty cycle, and is usually a square wave. A clock signal might also be gated, that is, combined with a controlling signal that enables or disables the clock signal for a certain part of a circuit.
Coherent Noise
A broadband noise definitively associated with the amplitude and phase of the neighboring frequency and its noise voltage is correlated with the bandwidth. It’s a prime example of indirect noise in the case of clock signal or radar being the noise source.
Common Impedance Coupling Noise
Noise generated by current from two different circuits being stranded in common impedance path.
Common-Mode Choke
An often used type of EMI filter which is wound in such a way that the phasing of the conductors will present a high impedance to common mode current (or noise) while presenting a low impedance to the desired signal.
Common-Mode Noise or Interference
This type of conducted emission travels in the same direction in both wires and returns through the ground plane or structure. In power and signal systems that have a single reference to ground or single-point ground, CM noise is capacitively coupled to the ground plane or structure. Because of this capacitive coupling, CM noises are generally high frequency (above approximately 2 MHz).
Commutation Notch
The change of cycle time to that much shorter than AC current in the process of AC-to-DC conversion by the converter which achieves the result by switching connections
Conducted Emission (CE)
The potential EMI generated inside equipment and carried through the I/O lines, the control leads, or power lines
Continous Wave
A wave of constant amplitude and constant frequency
Corner Frequency
The transition frequency range between the PASS-BAND and STOP-BAND.
A discharge of electricity appearing as a bluish-purple glow on the surface of, and adjacent to, a conductor when the voltage gradient exceeds a certain critical value. It is due to the ionization of surrounding air by high voltage.
Coupling Clamp
Coupling clamp enables coupling of the fast transients to the circuit under test without any galvanic connection to the circuit terminals, cable shielding, or any part of the EUT
Coupling Network
Electrical circuit for the purpose of transferring energy from one circuit to another.
Coupling Path
The path through which all or part of electronic energy from a source emitter is conducted to another circuit or equipment
Coupling Plane
A metal plate to promote discharge of antistatic buildup on the object in proximity to UUT (Unit Under Test).
A nonlinear interference where the modulation product of an interfering signal is present along with that of the desired signal. This is usually a type of adjacent channel interference.
Crosstalk results from the coupling of conducted emissions between two pairs of wires, one pair carrying emissions from a source and the other pair connected to a susceptible device. In a printed circuit board (PCB), crosstalk involves interaction between signals on two different electrical nets. The one creating crosstalk is called an aggressor, and the one receiving it is called a victim. Often, a net is both an aggressor and a victim.
Current Probe
A precision EMI measuring sensor which clamps onto a wire, wire pair, coaxial line, cable, harness or strap carrying current, intentional or interference. Snap-on current probes are used to measure the normal-mode current in a single wire or the common-mode current in a wire pair, coax or an entire bundle or harness. Current probes cover the 100 Hz to 1 GHz spectrum in two or three units.
Differential Mode Noise or Interference
This type of conducted emission is propagated out one wire and returned on the other. This noise is generated by clock signals or switching waveforms in power supplies. DM noise amplitudes are usually minimal above 2 MHz because line-to-line and line-to-ground capacitance and wiring inductance tend to filter this type noise.
Decibel (dB)
Logarithmic representation of a ratio measurement. Although it expresses the ratio of two power levels, it may be used for other electrical ratios across the same or equal impedances. It is most commonly used for expressing power, voltage and current ratios as follows: Power Ratio dB = 10 log (P1/P2), Voltage Ratio dB = 20 log (V1/V2), Current Ratio dB = 20 log (I1/I2).
Decoupling Circuit
Refers to a magnetic circuit where comparatively more of the flux generated by the MMF fringes around the magnetic material instead of entering it.
Degraded capability during immunity test is an undesirable implications for the operational performance of UUT (Unit Under Test), but it does not necessarily lead to operational problems or ultimate failure.
Differential Mode Voltage
The voltage that drives equal and oppositely directed currents to achieve an intended circuit function. The source of differential mode current.
Dipole Antenna
An antenna with its gain, radiation pattern, and impedance defined at or near resonance of one-half wavelength. The antenna is split at its electrical center for connection to a transmission line. The radiation pattern is maximum at right angles to the axis of the antenna.
Dropout Voltage
The voltage at which all contacts return to their “normal”, unoperated positions. (Applicable only to non-latching relays.)
Ductive Coating
The coating of low-resistance material applied as a thin film on the surface of the case made from material such as plastics with the aim to minimize emissions from the interior of the equipment. Highly conductive fillers such as silver, copper, nickel, and carbon are normally used mixed with binders for this purpose
The length of time the surge stay at least 50% above the peak value.
A material which at room temperature stretches under low stress to at least twice its length and snaps back to original length upon release of stress.
Electrical Application Voltage
A series of laws and regulations issued by Ministry of Communication of Japan in 1960 aimed at preventing dangers such as electrocution and fire as well as electrical failures.
Electro Conductive Plastics
Plastics made mixed with metallic or carbon fillers. They are often used in the casings for electronics products to shield against electromagnetic radiation and as anti-static counter-measures.
Electromagnetic Pulse (EMP)
A broadband, high-intensity, short-duration burst of electromagnetic energy. In the case of nuclear detonations, the electromagnetic pulse signal consists of a continuous spectrum with most of its energy distributed throughout the lower frequencies of 3 Hz to 30 kHz. Such an intense single-pulse transient electromagnetic wave may be generated when a nuclear device is detonated or it may be generated by non-nuclear means. This intense wave may damage semiconductor components and signal processing circuitry that is found in electronic and electrical equipment.
Electromagnetic Vulnerability (EMV)
The characteristics of electrical or electronic equipment/systems that cause it to suffer degradation or failure in performance as a result of electromagnetic interference.
Electromagnetic Wave
A wave produced by the interaction of time-varying electric and magnetic fields
Electromagnetic Wave Absorber
An absorbing material which convert electromagnetic energy into another form to reduce the reflection of electromagnetic waves in enclosures such as anechoic chamber.
EMI Receiver
An EMI Receiver is a tunable, sensitive voltmeter used to measure electric and magnetic field strengths. Most are similar to specialized spectrum analyzers, but are characterized by having preselectors, several detector functions, a housing shielding effectiveness of at least 90 dB and other unique additions. The frequency coverage of high-end receivers is typically 30 Hz to 22 GHz. Measurement bandwidths are variable to cover broadband and narrowband measurements. For EMI testing, they are used to measure conducted emissions (via LISN or R-F current probe) and radiated emissions (via antennas).
Electromagnetic energy propagated from a source by radiation or conduction. Note: The emission may be either desired or undesired and may occur anywhere in the electromagnetic spectrum
ESD Simulator
A Simulator for ESD test
EUT (Equipment under Test)
The test article(s) or item(s) being tested.
External immunity
The ability of equipment, units and system to function well without resistance against electromagnetic interference introduced through antenna or other input connections from the outside.
Far Field Region
Far from the source, field properties depend mostly on the medium through which the field propagates while near the source, field properties are determined primarily by source characteristics. Farthest from the source is the fraunhoffer region or far field (where radiated field components decrease as 1/r where r is the field interface distance).
Ferrite Beads
A small circular ferrite material structure that will increase the inductance of a wire that runs through the bead. It is used to reduce radiation
Ferrite Material
Powdered magnetic (permeable) material in the form of beads, rods and blocks used to absorb conducted interference on wires, cables and harnesses. Made by calcining a combination of metal oxides sintered into tiles. Material only a few millimeters thick absorbs low frequencies. Tiles may be used with dielectric materials or as a hybrid combination with dielectric pyramids.
Field Strength (FS)
The radiated voltage per meter (V/m) or current per meter (A/m) corresponding to electric (E) or magnetic (H) fields, respectively.
A device for blocking the flow of EMI current while passing the desired 50/60/400-Hz current. In communications circuits, it suppresses unwanted frequencies, noise, or separates channels.
A video error that occurs when the frame rate is too low, allowing the human eye to distinguish a flickering effect.
Frame Ground
Grounding of the case for safety’s sake.
Frequency Band
A particular frequency range, either those between a low and high cut-off or those used for a particular purpose.
A material that maintains shielding effectiveness across a seam or gap in an electronic enclosure. It is made from a variety of materials including fabric-wrapped foam, wire mesh, stamped metal, and elastomer.
A secondary image or signal resulting from echo, envelope delay distortion, or multipath reception.
Ground Loop
The condition of having two or more ground references in a common system. When two or more grounds have a potential difference between them, current can flow. This flow of current is a new circuit or loop which can interfere with the normal operation of the system.
The connection of an electric circuit or equipment to Earth or a conductive body of relatively large extent in place of Earth. The connection or bonding of an equipment case, chassis, bus, or frame to a conductive object or structure to ensure a common potential.
Ground Reference Plane
A conducting surface or plate used as a common electrical reference point for circuits.
Guide Shield
A shield including reception circuitry in an amplifier
A sinusoidal component of an AC voltage that is a multiple of the fundamental waveform frequency
The ability of equipment and/or system to perform without degradation in the presence of an electromagnetic disturbance.
Transient voltage or current condition of positive or negative amplitude.
Incoherent Noise
Broadband noise from discharge plate or corona discharge are prime examples of incoherent noise. The noise voltage is correlated to the square root of the bandwidth.
Induction Field
Very close to the source, the field is called the induction field (reactive or quasi-static field, non-radiating E or H field may provide strong coupling at low frequency and close proximity to source
Interface Port
(1) The point at which two systems or pieces of equipment are connected.
(2) A connection between two systems or devices. A shared boundary defined by common physical interconnection characteristics, signal characteristics, and meanings of interchanged signals.
It is the result of two radio signals of different frequencies being mixed together. The cause for intermodulation is the existence of non-linear characteristics of the according equipment. Intermodulation is rarely desirable in radio, as it essentially creates spurious emissions, which can create minor to severe interference to other operations on the resulting frequency
Internal Immunity
The ability of equipment and/or system to perform without degradation in the presence of an electromagnetic disturbance.
Internal Noise
Undesirable electrical signals that are present in a circuit or equipment. This becomes interference if the result is a degradation in performance. Whenever possible, noise should be controlled at the source to avoid extensive interference problems.
Inter-system Interference
Obstruction to the system caused by electromagnetic interference generated by another system.
Intra-system Interference
Obstruction to the system caused by electromagnetic interference generated from within the system itself.
Isolation Transformer
A transformer with a 1:1 turns ratio. It does not step voltage up or down. It serves as a safety device, isolating the grounded conductor of a power line from a chassis or any portion of a circuit load.
1. Pertaining to a material with properties, such as density, electrical conductivity, electric permittivity, magnetic permeability, or refractive index that do not vary with distance or direction. 2. Pertaining to a material with magnetic, electrical, or electromagnetic properties that do not vary with the direction of static or propagating magnetic, electrical, or electromagnetic fields within the material.
The absolute or relative voltage, current, or power at a particular point in a circuit or system.
Line impedance stabilization network (LISN) is an electrical network used between the power mains and the test article for isolation in measuring conducted emissions. It ensures test measurement repeatability by stabilizing the power line and test article input impedances (which vary with frequency) at 50 ohms.
Magnetic Shield
A screen using magnetic substance which localize magnetism and prevent magnetic field having effects elsewhere.
Mains Terminal Interface Voltage
Electromagnetic interference transmitted from inside of equipment and carried outside is measured as voltage at power cable terminal. This measurement referred to as Mains Terminal Interface Voltage need to follow LISN procedures.
Mini Bus
A low-impedance bus which is separated by an insulating material with one side as path for current in-flow and the other side as path for the out-flow and which is used in high-speed logical circuits to ensure uninterrupted supply of quality power.
Monopole Antenna
A monopole antenna is a type of radio antenna formed by replacing one half of a dipole antenna with a ground plane at right-angles to the remaining half. If the ground plane is large enough, the monopole behaves exactly like a dipole, as if its reflection in the ground plane formed the missing half of the dipole.
Narrow-Band EMI
An emission that has a spectral energy distribution that is narrow compared to a referenced bandwidth, such as that of the susceptible receptor or the measuring receiver. This is usually defined using the 3 dB bandwidths. The unit for narrowband signal measurements using EMI receivers is usually dBuV
Natural Noise
Electronic noises generated from causes attributed to nature, such as physical phenomenon from space, earth and atmosphere.
Near Field Region
The close-in region of an antenna wherein the angular field distribution is dependent upon distance from the antenna
Normal Mode Noise
A noise signal which appears between a set of phase conductors irrespective of their associated ground conductor.
Noise Cut Transformer
This transformer will effectively eliminate reflected noise from the power source and is an excellent choice to condition the power supplied to sensitive production equipment
Noise Margin
(VIL min VOL max) or (VOH min VIH max) which ever is lowest.
Normal Mode Noise
A noise signal which appears between a set of phase conductors irrespective of their associated ground conductor
Open Site
A test facility location, free of reflecting objects except a ground plane, where radiated emission tests may be carried out per CISPR 22 (FCC, Parts.15B, EN55022 and other test standards). A site attenuation test must be carried out to confirm that radiated pickup from a source to a receiving antenna falls within 4 dB of the theoretical range.
Parallel Stripline
Parallel plates used as a current path so designed to generate electromagnetic waves for the purpose of conducting immunity rest
Peak-value Detection
Peak Detection is characterized by rapid charge and slow discharge characteristics. The rise time is generally less than the reciprocal of the widest IF bandwidth and the discharge time provides enough delay to allow for full response of the receiver output functions. This method is required for testing EMI emissions to Military Specifications.
Plane Wave
A wave whose surfaces of constant phase are infinite parallel planes normal to the direction of propagation.
Power Filter
A filter made of LC device to remove noise conducted through power cable while passing the desired 50/60/400-Hz current. It come in several forms: stand-alone type in casing, one-board type for attachment to PCB, and inlet socket type to be fitted at power input.
Power Line Filter
A filter to remove normal-mode and common-mode noise present on a power line. It is used to suppress conductive emissions and improve conducted susceptibility of the equipment.
Quasi-peak Detection
Quasi-Peak Dectection is characterized by controlled charge and discharge time constants along with controlled predetection bandwidths to provide weighted readings corresponding to the type of signal measured or the EMI degrading effects. This method is used by CISPR and through harmonization of ANSI and adoption by the FCC.
That feature of a housing, shell, or insert that permits the mating of plug and receptacle in only one specified alignment. Under certain circumstances, polarization and keying may be combined in a connector design. Mechanical features on mating components to prevent incorrect mating.
A direct current (dc) that changes in value at regular or irregular intervals.
Note: A pulsating direct current may change in value, i.e., be always present but at different levels, or it may be a current that is interrupted completely at regular or irregular intervals, but when present, is always in the same direction.
A current or voltage which changes abruptly from one value to another and back to the original value in a finite length of time. Used to describe one particular variation in a series of wave motions
Radiated Emission (RE)
Desired or undesired electromagnetic energy that is propagated into or across space, either as a transverse electromagnetic wave or by capacitive or inductive coupling.
Radio Frequency Interference (RFI)
RFI is considered as part of the EMI spectrum, with interference signals being within the radio frequency (RF) range. This term was once used interchangeably with EMI.
Random Noise
Noise consisting of a large number of transient disturbances with a statistically random time distribution
Reflection Loss
The part of transmission loss due to power reflected by a discontinuity (impedance mismatch) in a transmission line.
Ripple Content
The AC component of the output of a DC signal. The term typically refers to the residual line-frequency-related AC part in the output of a DC power supply that arises as a result of incomplete or inadequate filtering.
Rise Time
Risetime is the time required for the leading edge of a pulse to rise 10% to 90% of its final value.
A reduction in a voltage envelope. The duration is usually from one cycle to a few seconds. Usually, sags are caused by fault clearing or heavy load startup.
1. A nonferrous metallic mesh used to provide electromagnetic shielding. 2. To reduce undesired electromagnetic signals and noise by enclosing devices in electrostatic or electromagnetic shields.
The capability of the receiver to differentiate between desired signal and unwanted signal.
Shielded Room
A room made free from EMI by applying shielding to the floor, walls, and ceiling, and by suppressing interference entering through the power lines. Typical construction shields from 70 dB to 140 dB from 10 kHz to 10 GHz.
Shielding Effectiveness
The relative capability of a shield to screen out undesirable electric and magnetic fields and plane waves. The measurement is the ratio of the signal received without the shield to the signal received inside the shield.
Signal-to-Noise Ratio
SNR - The ratio of signal strength to noise level in an electronic system.
Site Attenuation
Method to check performance of radiated emission test site with the use of the calibrated antennas
Skin Effect
The higher the frequency the more the tendency of the current to flow through a conductor close to the surface of it. This is called Skin Effect.
The range of frequencies of electromagnetic radiation from zero to infinity
Spectrum Analyzer
A spectrum analyzer is a laboratory instrument that displays signal amplitude (strength) as it varies by signal frequency. The frequency appears on the horizontal axis, and the amplitude is displayed on the vertical axis. To the casual observer, a spectrum analyzer looks like an oscilloscope and, in fact, some lab instruments can function either as oscilloscopes or spectrum analyzers. A spectrum analyzer can be used to determine whether or not a wireless transmitter is working according to federally defined standards for purity of emissions
A sharp momentary one-directional pulse.
Spurious Radiation
Any unintentional emission
Spurious Response
The spurious response is the ability of a receiver to prevent single unwanted signals from causing degradation to the reception of a desired signal
Stray Capacity
Refers to capacitance in between conductors or between a conductor and the ground.
A multi-layer transmission line that consists of two ground planes, separated by two layers of dielectric material that sandwich between them a thin center conductor that has a rectangular cross section. The impedance of stripline is determined by the thickness and dielectric constant of the dielectric layers and the width of the center conductor.
Surface Resistance
The ratio of DC voltage to the current flowing between two electrodes of specified configuration that contact the same side of a material. This measurement is expressed in ohms.
A short-term positive change in amplitude of a voltage.
The inability of equipment/systems to perform without degradation in the presence of an electromagnetic disturbance. Susceptibility is often characterized as a lack of immunity. The threshold of susceptibility is the level of interference at which the test article begins to show a degradation in performance. This is often frequency-dependent.
Continuous variation of frequency over a frequency band
Test Site
A site which meets the conditions for correct measurement of electromagnetic emissions from UUT (Unit Under Test) according to specified rules
Threshold Level
The minimum gate source voltage required for conduction of source drain current
A transmitter and a receiver combined in a single package.
Transfer Impedance
Transfer impedance is a fundamental value of a shield's performance, (It is not a test method.) Transfer impedance relates a current on one surface of the shield to the voltage drop generated by this current on the opposite surface of the shield. This value depends solely on the shield construction.
Pertaining to or designating a phenomenon or a quantity that varies between two consecutive steady states during a time interval short compared with the time-scale of interest.
A voltage sensitive breakdown device which is commonly used to limit overvoltage conditions (electrical surges) on power and data lines. When the applied voltage exceeds the breakdown point, the resistance of the device decreases from a very high level (thousands of ohms) to a very low level (a few ohms). The actual resistance of the device is a function of the rate of applied voltage and current.
Voltage Dip
A short-term decrease in line voltage, usually resulting from a short-circuit or a sudden increase in electrical load on the line
Voltage Surge
A sudden, sharp increase in the voltage or current lasting less than one cycle.
Voltage Unbalance
One or more of the three voltage levels in a polyphase system are unequal
Wave Impedance
The ratio of electric field to magnetic field of a radiating RF signal, at a point in space.
Umbrella Directive
An EU directive 89/336/EEC[Council Directive on the Approximation of the Law of the Member States relating to EMC] regarding electromagnetic emissions and susceptibility requirements.
Whistler Wave
wave in a plasma which propagates parallel to the magnetic field produced by currents outside the plasma at a frequency less than that of the electron cyclotron frequency, and which is circularly polarized, rotating in the same sense as the electrons in the plasma (about the magnetic field); also known as the electron cyclotron wave. Whistlers are so-named because of their characteristic descending audio-frequency tone, which is a result of the dispersion relation for the wave (higher frequencies travel somewhat faster
EMI/EMC International organization
EK : Electrotechnical Korea Stadards
UL : Underwriters Laborato-ries Standards
CCC : China Compulsory Certification
IEC : International Electrotechnical Commission.
ISO : International Standardization Organization
CISPR : Comite International Special des perturbation Radioelectrique.
CCIR : Comite Consuitatif International des Radio Communications.
CCITT : International Telegraph and Telephone Consultative Committee.
IEEE : Institute Electrical and Electronics Engineers,Inc
FCC : Federal Communications Committee
NEMA : National Electrical Manufactures Association.
NBS : National Bureau of Standard.
VDE : Verband Deutschen Elecetrotechniker
ANSI : American National Standard Institute.
EIA : Electronic Industries Association
FAA : Federal Aviation Administration.
NSA : National Security Agency.
VCCI : Voluntary Control Council for Interference by Information technology equipment.
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