Radio-Frequency Interference (RFI) suppression refers to the techniques employed to minimize unwanted electromagnetic signals that can interfere with proper device operation.

RFI is a subsection of the more general electromagnetic interference (EMI) design issue. Radio frequencies involve only the higher end of the spectrum, typically ranging from 20 kHz to several GHz.

Engineers look to reduce RFI suppression in cases involving radio communication to ensure clear and unambiguous signals. In certain regulatory frameworks, new designs need to address higher frequency noise to gain compliance.

The concern about high frequency interference goes both ways: compliance testing seeks to ascertain the susceptibility of your device to external emissions and to ensure your device will not leak high frequencies that will interfere with other wireless signals or nearby hardware.

Several techniques outlined in this post serve to prevent signal degradation and interference in both directions. With EESeal®, EESeal+®, and gasket in-connector inserts, RFI can be significantly reduced without having to redesign your device.

Sources of High-End Frequencies

RFI can arise from various sources and potentially disrupt the proper functioning of electronic devices or wireless communication. While the source might originate with the wider system under development, most often interference comes from external emissions that the device encounters in various types of settings.

Some common sources include:

  • Consumer Electronics: Devices like microwave ovens, LED lights, computers, and other digital devices can emit RFI across a range of frequencies.
  • Industrial Equipment: Heavy machinery, motor controllers, and other high-power equipment can generate significant EMI, sometimes on the high end of the spectrum.
  • Communication Systems: Cell phones, Wi-Fi routers, and broadcast transmitters can produce strong signals that interfere with other wireless communications.
  • Medical Equipment: Devices such as MRI machines can create a substantial electromagnetic field that can interfere with other devices.
  • Aerospace and Automotive Contexts: The complex electronics in modern vehicles and aircraft can emit RFI that interferes with onboard communication and navigation equipment.

Engineering Techniques of RFI Suppression

The goal of RFI suppression is to eliminate or reduce influences from possible external sources in the intended environment like those listed above. Mitigation can also block parts of the spectrum emitted by your device that might prove problematic for other applications in that environment.

Methods of RFI suppression include:


To block electromagnetic fields. This involves encasing a component or entire device within a material that blocks electromagnetic fields. Shielding materials are typically metals like copper, aluminum, or alloys.


To remove more specific unwanted frequencies from entering or leaving a device. Filters can be implemented in power supply lines, signal connectors, and within circuits themselves. Filters often consist of components like capacitors and inductors, which are designed to have specific impedance characteristics at different frequencies.


To prevent loops and to provide a reference point. Effective grounding provides a reference point for current and can also act as a return path for electrical noise to the earth rather than through the device. This prevents the buildup of voltages that could cause interference.

Circuit Design Modification

To minimize the circuit’s susceptibility to and its emission of RFI. The layout of PCB traces can be shaped to minimize loop areas and the antenna effect. Other strategies include the separation of analog and digital grounds, the use of differential signaling for data transmission lines, and the implementation of decoupling capacitors to provide local noise suppression.

Advantages of Quell filter inserts for combating RFI

Quell specializes in two of these techniques to help engineers reduce RFI: filtering and grounding.

EESeal and EESeal+ Filter Inserts

While discrete filters can be soldered into boards, an innovative and easier new way to suppress undesirable high-end frequencies is through miniaturized capacitors and specialized components embedded in silicone inserts.

These inserts fit snugly onto the pins of connectors and can be installed without tools. Tested for environmental resistance and longevity, EESeal® filter inserts from Quell are by far the simplest and most cost-effective way of mitigating electromagnetic emissions.

EESeal inserts tackle EMI in general, including lower frequencies than radio waves. The newer line of filter inserts — EESeal+ — target much higher frequencies, starting around 20kHz all the way up to 1 GHz.

As a strategy, filter inserts boast several advantages:

  • More effective than discrete components
  • Easy to install — the inserts simply “pop into” connectors
  • Can be added to a design post hoc, after device is constructed or during compliance testing
  • Supply available for samples within hours or production quantities within days
  • Many varieties for targeting emissions in specific frequency ranges
  • Durable in harsh environmental conditions


In certain cases, an EMI or RFI issue can be resolved with an external grounding shield. Like filter inserts, Quell’s gaskets fit on to the pins inside a standard connector yet target the grounding pin.

Similar to EESeal filter solutions, these gaskets can be added to provide grounding after the device design is finalized, avoiding device modifications and engineering rework.

The Easier Alternative

Perhaps you have a device prototype completed. In the compliance testing lab, the analysis shows substantial spikes in the high frequency range. What should you do?

One strategy is costly in terms of time and budget — go back to the drawing board and rearrange the circuit to add an off-the-shelf filter component and grounding measures, then pay for another round of testing.

The alternative strategy is to contact Quell — Quell technicians can recommend the variety of EESeal, EESeal+ or gasket products to specifically target your RFI range.

Samples are free and can be shipped in 24 hours. You simply trade out the different samples on your device for the best attenuation while you are still at the testing facility.

For most RF projects, the answer comes through crystal clear: choose Quell.