Conducted vs. Radiated Emissions: Understanding the Differences

Electromagnetic interference (EMI) can show up as either conducted or radiated emissions, and both can cause problems for electronic devices, impacting their performance and ability to meet regulations.

This guide will walk you through the key differences between these two types of emissions, where they come from, how they’re tested, and what you can do to reduce their impact. Understanding these concepts is essential for making sure your electronic systems have electromagnetic compatibility (EMC). Emission in an electronic system can disrupt nearby systems.

There are two main types: radiated emission and conducted emission.

Radiated emission is unintentional electromagnetic radiation that can interfere with nearby systems, potentially causing them to malfunction. Radiated emissions are typically measured in the frequency range of 30 MHz to 40 GHz.

Conducted emissions, on the other hand, are currents that escape through the device’s AC power cord. These emissions enter the common electrical power network and can radiate more efficiently from there. Conducted emissions usually fall in the frequency range of 450 KHz to 30 MHz.

Digital devices, which use digital techniques and operate at clock frequencies above 9 KHz, are broadly classified into two main categories: Class A and Class B. Class A devices are intended for use in business and/or industrial environments, while Class B devices are designed for residential use. Class B radiation limits are stricter than Class A.

The FCC (Federal Communications Commission) sets limits for both conducted and radiated emissions at different frequencies for Class A and Class B devices. These limits are shown in the tables below.

FCC Limit for Radiated Emission - Class A

FCC Limit for Conducted Emission - Class A

FCC Limit for Radiated Emission - Class B

FCC Limit for Conducted Emission - Class B

Conclusion

Conducted and radiated emissions are important aspects of EMI that need careful consideration during the design and testing phases. By understanding the differences between them and using appropriate mitigation strategies, engineers can ensure that their devices comply with regulations and perform optimally in various environments.