Conducted Emission vs Radiated Emission : Key Differences Explained

Electromagnetic interference (EMI) can manifest as conducted or radiated emissions, posing challenges to electronic device performance and compliance. This guide explores the key differences between these two types of emissions, their sources, testing methodologies, and strategies to mitigate their effects. Understanding these concepts is crucial for ensuring electromagnetic compatibility (EMC) in modern systems.

Emission in the electronic system leads to disturbance to the nearby other systems. There are two main types viz. radiated emission and conducted emission. Radiated emission is the unintentional electromagnetic radiation which will cause interference for the neighbouring systems. As a result they will malfunction. Radiated emission ranges from 30 MHz to 40 GHz.

Conducted emissions are those currents which are passed out through the device's AC power cord. This emission enter into common electrical power network and radiate there more efficiently. Generally conducted emission ranges from 450 KHz to 30 MHz.

The digital devices are the the devices which utilize digital techniques and operates at clock frequency above 9KHz. These digital devices are classified broadly into two major categories viz. class A device and class B device.

Class A devices are marketed to be used in the business and/or industrial environments. Class B devices are marketed to be used in residential environment.

Class B radiation limits are more stringent than the class A. The conducted emission and radiated emission limits recommended by the FCC at different frequencies for class A and class B devices are mentioned in the following tables.

FCC Limit for Radiated Emission-Class A

Frequency (MHz) µV/m
30 to 88 100
88 to 216 150
216 to 960 200
960 and above 500

FCC Limit for Conducted Emission-Class A

Frequency (MHz) µV/m
0.45 to 30 250

FCC Limit for Radiated Emission-Class B

Frequency (MHz) µV/m
30 to 88 90
88 to 216 150
216 to 960 210
960 and above 300

FCC Limit for Conducted Emission-Class B

Frequency (MHz) µV/m
0.45 to 1.705 1000
1.705 to 30 3000

Conclusion

Conducted and radiated emissions are critical aspects of EMI that require careful attention during design and testing. By understanding their differences and employing appropriate mitigation strategies, engineers can ensure device compliance and optimal performance in various environments.

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