RF Interference (RFI)

 

Introduction

Interference occasionally occurs in most of the radio equipment including wireless microphones. It may disrupt the device’s operation or cause system failure. Interference can be categorized into three basic types - radio frequency interference, electrical interference, and intermodulation. Let’s understand radio frequency interference (or  RFI) in detail.

RFI

Mostly, electronic and electrical devices such as industrial controls, switching power relays, and medical instrumentation emit radio frequency interference (RFI). These devices can emit radio frequency interference in two ways: 

• Radiated RFI, and

• Conducted RFI

When a device directly transmits the interference to the environment, then this phenomenon is known as radiated RFI. Whereas, when a device uses its power cord to transmit interference to the AC power line through, then this phenomenon is known as conducted RFI. 

Radiated radio frequency interference can be controlled by proper shielding in the enclosure of a device, while conducted radio frequency interference can be controlled to satisfactory and acceptable levels using a power line filter.

Radio frequency interference can occur due to natural sources (like different forms of space weather including solar storms) or man-made sources (like any electronic device). In the case of satellite communications, radio frequency interference can occur due to both sources (natural and man-made).  So, high directional antennas and strong end filtering are used to prevent narrow band radio frequency interference while sources are modified to lower the broadband interference. 

RF interference is increasing with the increasing usage of mobile phones or any consumer electronics. There are various factors causing radio frequency interference such as the concentration of electronic devices in a spectrum, the flaw in the design, and poor enclosure design with low absorption loss.

RF interference is a critical factor in the manufacturing of electronic devices. It must be considered in each stage of product development from the design phase to the pre-compliance testing phase. Hence, electronic devices must comply with electromagnetic compatibility, EMC.

Standards and Regulations

Government bodies and safety agencies have established norms for radio frequency interference and noise emissions. They also have rules and regulations for radio frequency communication.

In North America, there are clear standards and regulations for RFI that are also applied by other parts of the world. The United States follows OET65 standards, i.e., FCC (Federal Communications Commission) policy on human exposure to radio-frequency electromagnetic fields, and Canada follows Safety Code 6 (similar to OET65 in the US). In 1996, the FCC adopted the ICNIRP and ANSI/IEEE C95.1-1992 standards that focus on human health and safety. ICNIRP guidelines recommend maximum permissible exposure limits for field strength and power density for transmitters operating at 300 kHz to 100 GHz frequencies, and ANSI/IEEE C95.1-1992 guidelines recommend the specific absorption rate, SAR limits for devices that operate within the close proximity to the body.