Radio Frequency Interference Definition & Jargon

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Helping to Understand Radio Frequency Interference (RFI) Filters

For anyone who isn’t well-versed in the area of radio frequency interference, we’ve put together a short list of definitions to help you out. If you come across a word whose meaning you don’t readily know while reading our product specifications, return to this page for some guidance.

For those of you who know what you’re looking for and what the terms mean, have a look through our product catalog, and see if you can’t find the specifications you’re looking for. But don’t give up if it’s not there. At Curtis Industries, we manufacture:

to fit your exact needs and specifications.


  • The decrease in intensity or absorption of electromagnetic energy
  • Expressed in decibels – dB
  • Sometimes referred to as loss

Conducted Interference:

  • Electromagnetic signals entering a device through direct connection
  • Requires a physical connection


  • The level of electromagnetic disturbances equipment causes to its environment
  • Also referred to as electromagnetic radiation


  • Remove electrical noise or interference from the power line by cleaning up the sine wave
  • The sine wave is a curve in mathematics describing a smooth and repetitive oscillation


  • The level to which equipment is not affected by electromagnetic disturbances in its environment


  • Opposition to the flow of electrical current when a given voltage is applied


  • Passive component that produces a voltage proportional to the change in current
  • Measured in Henrys – H

Insertion Loss:

  • The electromagnetic signal loss resulting from the insertion of a filter in a transmission line
  • Expressed in decibels – dB

Radio Frequency Interference (RFI):

  • A type of electromagnetic interference (EMI) causing unwanted signals (noise) in other circuits, either through radiation or conduction—interferes with information transportation and data transfers

What is RFI?

Radio frequency interference (RFI) is the radiation or conduction of radio frequency energy (or electronic noise) produced by electrical and electronic devices at levels that interfere with the operation of adjacent equipment. Frequency ranges of most concern are 10 kHz to 30 MHz (conducted) and 30 MHz to 1 GHz (radiated).

What causes RFI?

The most common sources include components such as switching power supplies, relays, motors and triacs. These devices are found in a wide variety of equipment used in industrial, medical, white goods, and building HVAC equipment.

What are the types of RFI?

An electrical or electronic device emits RFI in two ways:

  • Radiated RFI is emitted directly into the environment from the equipment itself.
  • Conducted RFI is released from components and equipment through the power line cord into the AC power line network. This conducted RFI can affect the performance of other devices on the same network.

How can RFI be controlled?

  • Radiated RFI is usually controlled by providing proper shielding in the enclosure of the equipment.
  • Conducted RFI can be attenuated to satisfactory levels by including a power line filter in the system.

The filter suppresses conducted noise leaving the unit, reducing RFI to acceptable levels. It also helps to lower the susceptibility of the equipment to incoming power line noise that can affect its performance.

What is the Government’s Role in Regulating RFI?

Governments and safety agencies of major industrial countries, including the United States, Canada and the European Union have established noise emission regulations that are focused on digital and other electronic equipment. The most important of these guidelines are FCC CFR 47 (Parts 15 and 18) in the United States and CISPR 11, 14 and 22 in the European Union.

FCC CFR 47 (Part 15) regulates the RF interference of electronic computing devices, defined as any electronic device or system that generates and uses timing signals or pulses at a rate in excess of 10,000 pulses (cycles) per second and uses digital techniques. This definition includes telephone equipment that utilizes digital techniques and any device or system that generates and uses radio frequency energy for the purpose of performing dataprocessing functions such as electronic computations, operations, transformations, recording, filing, sorting, storage, retrieval or transfer.

FCC regulations are broken down into Class A computing devices marketed for use in commercial, industrial or business environments, and Class B devices intended for use in a residential environment.

The European Union has harmonized the various national regulations and has established the international standards CISPR 11, 14 and 22. CISPR 11 covers industrial, scientific and medical equipment. CISPR 14 covers electrical and thermal appliances and tools. CISPR 22 covers information technology equipment.

In addition to governmental regulations, safety agencies worldwide have established guidelines for all electrical/electronic components. These include UL, CSA and TUV. They are designed to protect against shock and fire hazard.

How do RFI Power Line Filters Work?

Consisting of a multiple-port network of passive components arranged as a dual low-pass filter, the RFI filter attenuates radio frequency energy to acceptable levels, while permitting the power frequency current to pass through with little or no attenuation. Their function, essentially, is to trap noise and to prevent it from entering or leaving your equipment.

RFI is conducted through a power line in two modes. Asymmetric or common mode noise occurs between the line and ground. Symmetric or differential mode is measured from line to line.

Leading Resource for RFI Filter Information and Products

Our goal is to be one of the leading resources for information about RFI filters, standardized RFI filters, and custom-made RFI filters. We’ll be adding more definitions to continue our quest to be the best and most helpful RFI filter resource on the web. Send us your questions, concerns, comments, or product specifications, and we’ll be in touch. Also, feel free to look through the Frequently Asked Questions–chances are likely that if you have a question, someone else has it too.

Product turnaround time takes only 1-2 weeks for the initial design to get sent back to you for approval. From there, it’s all smooth sailing. We’re a reliable power supplies manufacturer who knows what we’re doing in this business.

5 Focus Areas for Customer Satisfaction

Curtis Industries focuses on a few key areas to ensure customer satisfaction in our business dealings.

  • Customer Satisfaction – is a company wide goal. Customer interface with our friendly and knowledgeable Customer Service Representatives where all the information needed for order entry, processing, shipping, pricing, and order expediting are immediately available electronically.
  • Design Engineering – is able to create new designs to solve our OEM customers’ requirements. Using the Solid Works modeling technology enables our engineers to design the optimum terminal blocks or custom control package.
  • Quality Control- uses proprietary techniques with semi and full automation to build in quality and reduce thru-put. We deliver 99.9% reliable product to meet our customers’ quality objectives.
  • Manufacturing – uses Cellular and Lean manufacturing technologies to maintain high quality, short lead times, and lower costs. We deliver 99.9% reliable products to meet our customers’ quality objectives.
  • On-Time Delivery – is a focus for everyone at Curtis Industries, and has resulted in an on-time delivery rate greater than 98%.
Get your power supplies and RFI filters from Curtis Industries, the dependable power people.

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