CISPR, IEC
CISPR 25
Vehicles, boats and internal combustion engines – Radio disturbance characteristics – Limits and methods of measurement for the protection of on-board receivers
CISPR 25:2021 defines conducted and radiated emission test methods for vehicles and automotive electronic components to protect onboard radio receivers, including AM/FM, GPS, Bluetooth, Wi-Fi, and V2X systems.
Scope
CISPR 25:2021 establishes measurement methods and recommended emission limits for vehicles, boats, internal combustion engines, and associated electrical and electronic components.
The primary objective is to protect onboard radio receivers from electromagnetic disturbances generated by other systems within the same vehicle.
The standard covers disturbances between 150 kHz and 5,925 MHz, addressing interference affecting AM/FM radio, satellite navigation, mobile communications, Bluetooth, Wi-Fi, and vehicle-to-everything (V2X) communication systems.
Two evaluation approaches are provided: complete-vehicle testing, which measures disturbances received by an antenna installed on the vehicle, and component-level testing, which evaluates conducted and radiated emissions from individual electronic modules.
Important distinction: CISPR 25 addresses electromagnetic emissions affecting onboard receivers. It does not establish radiated immunity requirements or replace vehicle-level external emission requirements such as CISPR 12.
Applicable Products and Devices
CISPR 25 applies to complete vehicles and electrical/electronic components installed in automotive, marine, agricultural, and other engine-powered applications.
Typical Automotive Components
Electronic Control Units (ECUs): Engine controllers, body control modules, gateway modules, and vehicle communication interfaces.
Electric Vehicle Systems: Traction inverters, DC/DC converters, onboard chargers, battery management systems, and high-voltage power electronics.
Motors and Actuators: Electric pumps, cooling fans, wiper motors, and motor-driven automotive accessories.
Lighting and Display Electronics: LED drivers, instrument clusters, infotainment displays, and electronic lighting controllers.
Communication and Sensor Modules: Radar-related electronics, cameras, navigation modules, wireless communication units, and sensor interfaces.
Complete Vehicles: Passenger cars, commercial vehicles, motorcycles, agricultural machinery, off-road vehicles, and applicable boats or engine-powered equipment.
Key consideration: Component-level compliance does not guarantee complete-vehicle compliance. Installation position, cable routing, grounding, and antenna proximity can significantly affect emissions.
Markets and Regulatory Context
CISPR 25 is widely used by automotive manufacturers and suppliers to control electromagnetic interference within vehicles. Its application is generally driven by OEM specifications, supplier agreements, and vehicle development requirements.
Automotive OEM Requirements
Manufacturers select applicable frequency bands, emission classes, operating conditions, and measurement methods based on vehicle architecture and onboard receiver requirements.
Important: CISPR 25 provides recommended emission limits. The selected class and acceptance criteria should be documented in the agreed test plan.
European and International Markets
CISPR 25 is an international automotive EMC reference. It may be incorporated into OEM qualification programs, but compliance with CISPR 25 alone does not establish conformity with UNECE Regulation No. 10 or all applicable vehicle type-approval requirements.
North American Markets
Automotive manufacturers in Canada and the United States may specify CISPR 25 for component and vehicle qualification. FCC and ISED requirements for intentional radio transmitters remain separate from the onboard receiver protection addressed by CISPR 25.
Principal Tests and Requirements
CISPR 25:2021 establishes several measurement methods to evaluate how electromagnetic noise from automotive electronics can interfere with onboard radio reception.
Conducted Emissions – Voltage Method
Clause 6.3: Measures disturbance voltage on applicable component power connections using an Artificial Network (AN). This method helps identify noise transferred from electronic modules onto vehicle wiring.
Conducted Emissions – Current Probe Method
Clause 6.4: Measures RF disturbance current flowing through cable harnesses using a current probe. It is particularly useful for evaluating noise coupling through power and signal cables.
Radiated Emissions – ALSE Method
Clause 6.5: Measures electromagnetic fields generated by automotive components and their wiring inside an Absorber-Lined Shielded Enclosure (ALSE). Different antenna types are used across the applicable frequency bands.
Complete-Vehicle Emissions
Clause 5: Evaluates disturbances received through the vehicle’s onboard antenna system or a specified reference antenna. This approach assesses the combined effects of installed electronics, vehicle wiring, grounding, and antenna placement.
Electric and Hybrid Vehicle Testing
Annex H: Defines additional measurement arrangements for high-voltage power supply systems, including conducted and radiated emissions from EV and hybrid vehicle components.
Key distinction: Conducted measurements characterize noise on electrical connections, while radiated measurements evaluate electromagnetic fields. Both can be relevant to protecting vehicle radio reception.
Frequency Ranges and Test Levels
CISPR 25 Emission Classes (Class 1 to Class 5)
CISPR 25:2021 establishes five example emission-limit classes for automotive components. Each class defines the maximum permitted electromagnetic disturbance level for specified frequency bands and measurement methods.
The classes are distinguished by their numerical emission limits. For example, for conducted voltage emissions in the FM band (76–108 MHz), the following peak limits apply:
| Class | Peak Limit | Definition |
|---|---|---|
| Class 1 | 62 dB(uV) | Permits the highest conducted disturbance voltage among the five classes. |
| Class 2 | 56 dB(uV) | Permits 6 dB less disturbance voltage than Class 1. |
| Class 3 | 50 dB(uV) | Permits 12 dB less disturbance voltage than Class 1. |
| Class 4 | 44 dB(uV) | Permits 18 dB less disturbance voltage than Class 1. |
| Class 5 | 38 dB(uV) | Permits the lowest conducted disturbance voltage among the five classes, 24 dB below Class 1. |
Reference: CISPR 25:2021, Table 6, FM band, conducted voltage method, peak detector, 120 kHz resolution bandwidth.
Important: These numerical values apply only to the specified frequency band, detector, and measurement method. Other frequency bands and conducted or radiated emission methods have different numerical limits.
Class Selection: CISPR 25 does not assign a fixed emission class to every automotive component. The OEM and supplier establish the required class in the test plan, considering the vehicle installation, wiring configuration, and onboard receiver protection requirements.
Limit Overview
6. CISPR 25 Emission Limit Overview
CISPR 25:2021 provides five emission limit classes (Class 1 to Class 5), with Class 5 representing the most stringent requirements. The applicable class is established by the vehicle manufacturer or agreed upon between the OEM and supplier.
The following tables provide selected examples from CISPR 25:2021. They illustrate the differences between emission classes without reproducing the complete frequency-dependent limit tables.
Conducted Emissions – Voltage Method
Conducted voltage emissions are measured using an Artificial Network (AN). Results are expressed in dB(uV).
| Frequency Band | Class 5 Peak / Average | Class 3 Peak / Average |
|---|---|---|
| MW: 0.53–1.8 MHz | 54 / 41 dB(uV) | 70 / 57 dB(uV) |
| FM: 76–108 MHz | 38 / 25 dB(uV) | 50 / 37 dB(uV) |
Reference: CISPR 25:2021, Table 6. Values are example limits for component-level conducted voltage measurements.
Conducted Emissions – Current Probe Method
This method evaluates RF disturbance currents flowing along automotive cable harnesses. Results are expressed in dB(uA).
| Frequency Band | Class 5 Peak / Average | Class 3 Peak / Average |
|---|---|---|
| MW: 0.53–1.8 MHz | 26 / 13 dB(uA) | 42 / 29 dB(uA) |
| FM: 76–108 MHz | 4 / -9 dB(uA) | 16 / 3 dB(uA) |
Reference: CISPR 25:2021, Table 7. Negative dB(uA) values are valid logarithmic measurement levels.
Radiated Emissions – ALSE Method
Radiated emissions are measured inside an Absorber-Lined Shielded Enclosure (ALSE) using antennas appropriate to the frequency range. Results are expressed in dB(uV/m).
| Frequency Band | Class 5 Peak / Average | Class 3 Peak / Average |
|---|---|---|
| MW: 0.53–1.8 MHz | 40 / 27 dB(uV/m) | 56 / 43 dB(uV/m) |
| FM: 76–108 MHz | 38 / 25 dB(uV/m) | 50 / 37 dB(uV/m) |
Reference: CISPR 25:2021, Table 8.
How Compliance Is Determined
Average Limit: The equipment must satisfy the applicable average emission limit.
Peak or Quasi-Peak Limit: The equipment must also satisfy the peak or quasi-peak requirement selected in the test plan, subject to the conformance provisions of Clause 4.1.3.
OEM Requirements: The vehicle manufacturer may specify different emission classes for different frequency bands or establish additional requirements.
Important: The values above are selected examples, not universal CISPR 25 limits. Formal compliance must be assessed using the applicable frequency bands, detector settings, bandwidths, emission classes, and approved test plan.
Equipment Configuration and Operating Modes
Automotive emission measurements are strongly influenced by the physical arrangement of the equipment under test (EUT). CISPR 25 therefore specifies controlled test configurations to support repeatable measurements.
Component-Level Test Configuration
Reference Ground Plane: Components are arranged on or above a conductive reference ground plane according to the applicable test method.
Cable Harness: Harness length, routing, height, and termination are controlled because wiring can act as an important coupling and radiation path.
Artificial Networks: ANs provide defined electrical impedance for conducted disturbance measurements and isolate the test setup from external RF noise.
Load Simulator: Representative loads and auxiliary equipment are used to reproduce the intended electrical operating conditions.
Operating Conditions
Testing should consider relevant modes such as motor operation, communication activity, switching states, and maximum or representative electrical loading.
For electric and hybrid vehicles, charging and propulsion-related operating modes may require additional test arrangements.
Practical consideration: An emission failure observed in one operating mode may disappear in another. Accurate documentation of the EUT state is essential for identifying the disturbance source and reproducing results.
Engineering and Pre-Compliance Guidance
Automotive emission failures frequently originate from interactions between switching electronics, cable harnesses, and vehicle grounding structures. Identifying the coupling mechanism is often more effective than applying filtering without first locating the source.
Typical Sources of Interference
Motor Drives and Inverters: High-speed switching generates common-mode currents that can propagate along power cables and couple into nearby vehicle wiring.
DC/DC Converters: Switching frequencies and their harmonics can produce conducted emissions that extend into sensitive radio bands.
Digital Electronics: Clock signals, processors, and communication interfaces may generate narrowband emissions at fundamental frequencies and harmonics.
Cable Harness Resonances: Harness geometry and grounding arrangements can increase radiation at particular frequencies, even when the electronic module itself has relatively low emissions.
Diagnostic Approaches
Near-Field Investigation: Identify localized emission sources around switching devices, PCB traces, connectors, and cable interfaces.
Current Probe Measurements: Locate common-mode currents traveling along power and communication harnesses.
Operating Mode Comparison: Correlate emission peaks with switching frequency, motor speed, load changes, or digital activity.
Corrective Action Verification: Evaluate the effectiveness of cable shielding, grounding improvements, filtering, or layout changes through repeat measurements.
Engineering Insight: A filter that reduces conducted emissions may not adequately reduce radiated emissions if the dominant interference path is common-mode current on the harness. Identifying the actual coupling mechanism is essential for effective EMC troubleshooting.
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