EMI Line Filters | RFI Line Filters

Electromagnetic Interference Filters (EMI Filters) & Radio Frequency Interference Filters (RFI Filters)

Curtis Industries, a leading manufacturer of superior quality electronic and electrical components and assemblies for more than 70 years, offers a complete line of RFI power line filters designed to help your equipment meet FCC and CE requirements on conducted EMI.

Radio Frequency Interference (RFI) is unwanted noise generated by almost all electronic and electrical devices. Any electronic device that generates radio frequency energy greater than 10 kHz must comply with international safety requirements (FCC docket 20780 in the U.S. and VDE 0871 and 0875 in Germany). At Curtis Industries, our product design, controlled assembly, and constant testing ensure our RFI power line filters meet all governmental emissions and safety requirements.

Manufacturers of ISO 9001:2015 Certified Filters

These EMI and RFI power line filters are available in an assortment of configurations and styles which can be customized to meet your exact requirements. Our design capabilities are unmatched, consistently creating innovative solutions to your toughest electrical component challenges. We are committed to total customer satisfaction, providing world-class quality to each of our clients.

EMI/RFI Power Line Filters

RF Interference Filters Designed for Safety and Performance

Curtis designs quality into every RFI filter product and then tests for quality by specification compliance—including hipot, component value, grounding and leakage—on a 100% production basis. We employ a rigorous component qualification program with thorough incoming and on-line inspection procedures. Our computer controlled 100% safety and performance testing to demanding customer requirements is your assurance of the highest quality RFI filters available today.

Three Phase Filters to Protect and Prevent

Your network will not protect your sensitive equipment from Radio Frequency Interference (RFI) originating from external sources, nor will it prevent the RFI emitted by your devices from reaching other electronic equipment.

Curtis Industries’ three-phase power line filters are designed to protect your equipment from outside interference originating from other devices and to prevent the RFI given off by your device from interfering with other electronic equipment.

Filters Targeting 150kHz – 30 MHz Range

Our F3480/F3600 three-phase filters provide noise suppression in the critical 150 kHz – 30 MHz range—which is more than sufficient to prevent televisions, radios, and other valuable electronic equipment from being damaged or otherwise impaired. These filters will ensure your equipment meets all FCC and CE requirements on conducted EMI. They contain a 2-stage filter line, so your power network will be supported regardless of whether it is a 3-wire Delta structure or a 4-wire Wye structure.

As a leader in manufactured electrical components for over 70 years, Curtis Industries’ products are in full compliance with all government emissions and safety requirements. We focus on quality; every EMI | RFI filter product is fully tested to assure you of the highest-quality standards.

Three Phase Filter Applications include:

EMI | RFI Line Filter Manufacturer

Curtis Industries is a globally recognized manufacturer of a wide variety of high-quality power line filters, including custom models. We have earned a solid reputation for designing, engineering, and manufacturing superior radio frequency interference filters for a wide variety of industries and are a proud supplier of top notch, custom built, EMI | RFI filters.

Our highly skilled and experienced engineers provide precise, customized filters for your specific applications. All of our products are expertly designed, meeting, and exceeding industry standards and requirements.

• Single Phase Filters
• Power Entry Modules
• Medical Filters
• DC Filters
• Three-Phase Filters

EMI | RFI Filter Resources:

Information (as PDF downloads) available on our RFI power line filter products below.

How Line Filters Work

There are multiple different types of RFI filters on the market, but at their core they all operate in the same fashion. EMI (electromagnetic interference) emissions can greatly hinder circuit performance and impact the effectiveness of your electronic devices. EMI emissions are radiated from a wide variety of sources, but some notorious platforms for EMI interference include power lines, cellular phones, radio transmissions, and various other electronic outlets. This is where RFI filters come in. RFI filters help to allow only certain frequencies to pass through, effectively eliminating most common sources of EMI emission. Different RFI filters serve different purposes, and some of the most basic types include:

• RFI Noise Filters
• Military RFI Filters
• RFI Suppression Filters
• RFI Filters for Radios
• Medical RFI Filters

We supply RFI filters to a wide variety of industries including the military, radio broadcasting industries, telecommunications, and more!

Line Filter Technical Considerations

Meeting Emissions Standards

The emissions limits that a piece of equipment must meet will depend on the intended market for that piece of equipment. If there is more than one market, more than one emission standard may have to be met. This can have a substantial effect on the circuit, size, and cost of a filter. Standards like the CISPR’s or the FCC Rules Part 15 have frequency limits of 150 kHz to 30 MHz.

EMI measurements are generally made using Spectrum Analyzers with Average or Quasi-Peak detectors in accordance with methods described in CISPR 16. Quasi-Peak differs from Average measurements by weight-averaging the peaks into the total.

Equipment meeting these specifications can utilize a filter with a fairly high cutoff frequency. Other standards like FCC 18 with a low frequency limit of 10 kHz will result in the equipment using lower cutoff filters. As might be expected, the lower the cutoff frequency, the larger the physical size and the higher the cost of the filter.

Conducted RFI Susceptibility

The problem of susceptibility can be extremely difficult to deal with because the amplitude and frequency of the offending RF noise are seldom known and are often intermittent. If the malfunction can be duplicated by isolating the equipment from the power line with LISN’s (Line Impedance Stabilization Network) and using signal generators to inject RF of varying amplitude and frequency, some insight can be gained as to the nature of the problem. However, the criteria for acceptable performance will have to be decided upon so that a filter yielding this level of performance can be obtained from the test procedure. Unfortunately, this still does not eliminate the need for final testing in the actual operating environment which, in many cases, occurs in the field.

Selection of a suitable filter can best be based on the type of power supply or input impedance of the equipment and on the mode of the offending RFI noise.

Noise Modes

Power line filters attenuate noise in two different modes.

Common Mode: Also known as line-to-ground noise measured between the power line and ground potential.
Differential Mode: Also known as line-to-line noise measured between the lines of power.

Power line filters are designed to attenuate either one or both modes of noise. The need for one design over another will depend on the magnitude of each noise type present. The attenuation is measured in dB (decibels) at various frequencies of signal.

Circuit Configuration

Power line RFI filters are generally built with two or three-pole filter networks. As the number of poles and the corresponding component count increases, the cost will increase also. Trying to typify an equipment’s impedance as either high or low for purposes of filter selection may not be successful. If it is a complex impedance, it could probably be low at some frequencies, high at others, and some intermediate value at still other frequencies.

Although we have been generally successful in recommending a two-pole network for linear power supplies and three-pole networks for switching power supplies and synchronous motors, you should not limit your testing to just one circuit type if either additional circuit performance or lower cost is desired. Consider the following: If the equipment looked strictly capacitive, the performance of a two-pole network would be reduced to that of a single-pole filter.

Obviously a three-pole filter would be preferred for maximum performance. Likewise, if the equipment looked strictly inductive, the performance of a threepole network would be reduced to that of a two-pole network.

Undoubtedly the two-pole filter would be a more economical choice with probably equal performance in this application. Since the equipment is not likely to be equivalent to either one of these simple cases, the only way to find the best cost-effective solution is to test the filters in your equipment and base your judgement on these test results.

Leakage Current

The maximum leakage current that a device is allowed depends on the requirements of the particular safety agency involved. Here, selection of the filter is quite easy since either the filter is designed to meet a given level or it is not. Although there is no compromise when it comes to safety specifications, it should be understood that for a given level of performance, as the leakage current is reduced, the physical size of the package will increase. Curtis medical filters have a very low leakage current.

Insertion Loss

DO NOT use the insertion loss specifications to make your final decision. Power line filters are two-terminal pair passive networks whose attenuation characteristics can be defined by a complex transfer function. How that transfer function will react in a particular system and at specific frequencies will depend on the complex impedances connected to each side of the filter. The equipment impedance and the impedance of the power line, even if a 50 ohm LISN (Line ImpedanceStabilization Network) is being used during emission testing, will not generally be equal to the resistive 50 ohms used during insertion loss measurements. Therefore, the performance of the filter in the equipment cannot be related to the published insertion loss data.

Minimum Insertion Loss

Do not be alarmed that the insertion loss figures we have published may be of lower value than those of our competition. You will only find guaranteed minimum insertion loss figures in this catalog, without any mention of typical values.Insertion loss test data measured in a 50 ohm system is a valuable incoming inspection tool to assure you that consistent product is being shipped. The only figures of any importance are those that specify the criteria for acceptance or rejection of that product, and those figures are the minimum values.

RFI | EMI Conducted Emissions Testing

Curtis offers full RFI | EMI conducted emissions testing  services for manufacturers who must produce equipment in accordance with FCC and CE standards.

Curtis testing facilities consist of a laboratory equipped to test and evaluate EMI characteristics of equipment that must comply with FCC Part 15 and/or CISPR standards. With these facilities, Curtis can provide manufacturers with greater assistance in the selection of RFI | EMI filters to help them meet the necessary emission levels.

Isolated Environment Enhances Test Capabilities

• Totally isolated environment for both equipment under test and test instrumentation provided by separate chambers.
• RF screen room shielded against magnetic, electric and plane wave field per MIL-STD-285.
• Specially constructed line impedance stabilization networks (LISN) for FC Part 15 and CISPR testing.
• Sensitive, reliable automatic measurement and recording of conducted emissions data from 10 KHz to 1 GHz.
• Computer-controlled Agilent E7402A Spectrum Analyzer with associated amplifiers and attenuators.
• Agilent E7402A graphics capabilities allow quick generation of hard copies of emissions test results.

Fast Pre-Compliance Test Results

Computer-generated graphics and test reports provide the customer with fast turnaround on all testing.

On-site RFI filter design/applications engineers are available to assist in evaluating test results and to determine cost-effective solutions to conducted emissions problems before going to agencies.

Please contact your local Curtis representative or the factory sales staff to coordinate pre-compliance testing of your equipment at Curtis Industries.