Glossary

Absorption: The conversion of electromagnetic energy into heat within a material (e.g., ferrite tiles).

Active Antenna: An antenna with a built-in pre-amplifier to increase sensitivity for low-level emissions.

ALC (Automatic Level Control): A feedback loop in an RF amplifier used to maintain a constant output level during immunity testing.

AM (Amplitude Modulation): Varying the strength of a carrier wave to represent a test signal.

Ambient Level: Background electromagnetic noise present at a test site when the EUT is powered off.

Amplifier Saturation: The point where increasing input power no longer produces a linear increase in output.

Anechoic Chamber: A shielded room lined with RF-absorbent material to eliminate reflections and external noise.

Antenna Factor (AF): The ratio of the incident electric field to the voltage produced at the antenna terminals.

Aperture: An opening in a shielded enclosure (like a vent) that may allow RF leakage.

Attenuation: The reduction of RF power as it passes through a device, measured in decibels (dB).

Average Detector: A receiver setting that averages the signal envelope over a specific period.

B-Field: A measure of magnetic flux density, typically expressed in Tesla (T).

Bandwidth: The usable frequency range of a source, amplifier, or filter.

BCI (Bulk Current Injection): Injecting RF current into a cable bundle using a current clamp for immunity testing.

Beamwidth: The angle between the two directions where radiation intensity is at least half its maximum.

Broadband: A device or signal covering a wide range of frequencies simultaneously.

Calibration: The process of ensuring the accuracy and traceability of measurement instruments.

Capacitive Coupling: The transfer of energy between networks via mutual capacitance.

CE Marking: A certification mark indicating conformity with EEA health and safety standards.

CISPR: The International Special Committee on Radio Interference, responsible for global EMC standards.

Coaxial Cable: A shielded cable with a centre conductor, dielectric, and conductive braid.

Common Mode (CM): Noise flowing in the same direction and phase on all conductors of a cable.

Conducted Emissions (CE): Electromagnetic interference traveling along power or signal cables.

Conducted Immunity (CI): A device's ability to withstand interference entering through connected cables.

Coupling/Decoupling Network (CDN): A device used to inject disturbances into an EUT while protecting auxiliary equipment.

Damping: The reduction in the amplitude of an oscillation or wave over time.

dB (Decibel): A logarithmic unit used to express the ratio between two power or voltage levels.

DC Block: A component that prevents DC current from entering RF equipment while allowing RF signals to pass.

Decade: A frequency ratio of 10:1 (e.g., 30 MHz to 300 MHz).

Declaration of Conformity (DoC): A legal document signed by a manufacturer stating a product meets all regulations.

Designated Standard: A UK technical specification used to prove conformity for UKCA marking.

Differential Mode (DM): Noise flowing in opposite directions on a pair of conductors.

Dipole Antenna: A fundamental antenna consisting of two identical conductive elements.

Directivity: An antenna’s ability to focus radiated power in a specific direction.

DUT/EUT: Device Under Test or Equipment Under Test; the apparatus being evaluated.

Dwell Time: The duration a test signal is applied at a specific frequency during a scan.

Dynamic Range: The span between a system's noise floor and its maximum distortion-free level.

E-Field: The electric component of an EM wave, measured in Volts per metre (V/m).

Effective Aperture: The area over which an antenna extracts energy from a passing wave.

EFT (Electrical Fast Transient): Rapid voltage spikes simulating switching events or inductive load changes.

EMC (Electromagnetic Compatibility): The ability of a system to function without causing or suffering from interference.

EMI (Electromagnetic Interference): Disruption caused by unwanted electromagnetic interactions.

ERP (Effective Radiated Power): Total power radiated by an antenna in its direction of maximum gain.

ESD (Electrostatic Discharge): A sudden flow of electricity between two objects (simulated with an "ESD Gun").

Far-Field: The region far from an antenna where the wave acts as a plane wave.

FCC: The Federal Communications Commission, regulating EMC in the USA.

Ferrite Bead: A passive component used to suppress high-frequency noise on cables.

Filter: A device used to pass desired frequencies while blocking others.

Gain: The ratio of output power to input power, usually expressed in dB.

GTEM Cell: A specialized chamber providing OATS-equivalent results for emissions and immunity.

H-Field: The magnetic component of an EM field, measured in Amps per metre (A/m).

Harmonics: Integer multiples of a fundamental frequency.

High-Pass Filter: A filter that allows frequencies above a specific cutoff to pass.

Immunity (Susceptibility): A device's ability to function correctly when exposed to external interference.

Impedance (Z): The total opposition to current flow in a circuit, measured in Ohms (Ω).

Inductive Coupling: Energy transfer between circuits via a shared magnetic field.

In-Situ Testing: Testing performed at a customer's site rather than in a lab.

Insertion Loss: Signal strength reduction caused by placing a component in a circuit.

Intermodulation: Unwanted frequencies caused by the mixing of two or more signals.

Isotropic: Radiating or receiving energy equally in all directions.

Limit Line: The maximum allowable emission level defined by an EMC standard.

LISN (Line Impedance Stabilization Network): A filter used to provide defined impedance and isolate noise in conducted tests.

Log-Periodic Antenna: A wideband antenna covering a large frequency range.

Loop Antenna: A closed-circuit antenna used for measuring low-frequency magnetic fields.

Low-Pass Filter: A filter that allows frequencies below a specific cutoff to pass.

Magnetic Flux Density: The strength of a magnetic field, expressed in Tesla (T).

Mains Dropout: A brief AC power interruption used to test product resilience.

Modulation: Varying a carrier wave (amplitude, frequency, or phase) to transmit a signal.

Narrowband: A signal with a very small bandwidth relative to its centre frequency.

Near-Field: The region close to an antenna where fields do not yet act as a plane wave.

Noise Floor: The lowest detectable signal level above a system's internal noise.

Non-Ionising Radiation: EM radiation that does not carry enough energy to ionise atoms (includes all RF).

NSA (Normalised Site Attenuation): A measurement used to validate that a test site is suitable for radiated emissions.

OATS (Open Area Test Site): An outdoor reference site for radiated emission standards.

Octave: A frequency ratio of 2:1 (e.g., 1 GHz to 2 GHz).

Overshoot: The amount by which a signal exceeds its steady-state value during a transition.

Passband: The range of frequencies a filter allows to pass with minimal loss.

Peak Detector: A receiver mode capturing the highest instantaneous signal value.

Permeability: The ability of a material to support a magnetic field.

Permittivity: The ability of a material to store energy in an electric field.

Radiated Emissions (RE): Unwanted EM energy emitted through the air from a device.

Radiated Immunity (RI): A test of a device's function when exposed to external radiated fields.

Radio Frequency (RF): Electromagnetic oscillations from approx. 20 kHz to 300 GHz.

Reflection Coefficient: A measure of how much a wave is reflected by an impedance mismatch.

Return Loss: The ratio of power sent down a line to the power reflected back.

Semi-Anechoic Chamber (SAC): A shielded room with a reflective floor and absorbent walls.

Self-Certification: Declaring a product compliant based on the manufacturer's own test data.

Shielding Effectiveness (SE): The ratio of field intensity before and after shielding is applied.

Step Size: The frequency increment used between measurement points in a scan.

Transient: A sudden, high-energy change in voltage or current of very short duration.

UKCA Marking: The product mark for goods placed on the market in Great Britain.

UKAS: The United Kingdom Accreditation Service; ensures the competence of testing and calibration.

Voltage Surge: A high-energy transient on power lines, often caused by lightning or switching.

VSWR (Voltage Standing Wave Ratio): A measure of how efficiently RF power is transmitted into a load.

Wavelength (λ): The physical distance between wave crests, related to frequency and light speed.

WEMEC Ltd: Technical partner of EMC Hire, providing specialist engineering consultancy.

White Noise: A signal containing all frequencies in a given range at equal power.

Yagi Antenna: A directional antenna consisting of a dipole and additional parasitic elements.

Z-Axis: Often refers to the vertical height adjustment of an antenna mast during a scan.

Zero Span: A spectrum analyser mode where the frequency is fixed to show time-domain changes.