Radio-frequency interference (RFI) is unwanted radio-frequency energy that degrades, distorts, or disrupts reception in a radiocommunication system. The key is its effect on a receiver: a nearby electronic device is not automatically an interference source just because it is close.
What does radio-frequency interference mean?
The International Telecommunication Union (ITU) defines interference in Radio Regulations No. 1.166 as the effect of unwanted energy from emissions, radiations, or inductions on reception in a radiocommunication system. It may appear as degraded performance, misinterpreted information, or information loss that would not occur without that energy. The definition is about what happens to reception, not simply the presence of radio energy.
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In everyday use, RFI commonly refers to unwanted radio-frequency energy affecting a radio signal or another communications system. The formal ITU definition is broader: it covers the effect of unwanted energy on reception, regardless of whether the source is an emission, radiation, or induction. The ITU Radio Regulations provide the general regulatory definition.
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Not every interference event meets the regulatory threshold for harmful interference. The ITU distinguishes permissible, acceptable, and harmful interference. Under Radio Regulations No. 1.169, harmful interference is interference that endangers radionavigation or another safety service, or seriously degrades, obstructs, or repeatedly interrupts a radiocommunication service operating in accordance with the Radio Regulations. Whether a problem is harmful in this formal sense depends on its effects and the service involved.
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Interference can be accidental or intentional. Its effects may reach beyond broadcast radio: broadcasting, mobile and fixed communications, scientific services, and radionavigation can all be affected. Positioning and timing services used by aircraft, ships, cars, and telecommunications networks are among the systems where disruption can have serious consequences. For cross-border cases, the ITU describes a formal process in which its Radiocommunication Bureau can investigate cases brought to it and forward findings and recommendations to the administrations involved; national regulatory authorities are part of the reporting route.
Where can RFI matter beyond everyday radio?
Communications and navigation
Interference can degrade or interrupt communications, or affect information used for navigation and timing. The practical consequence depends on the receiver and service: a disruption to a routine broadcast is not equivalent to interference that endangers a safety service.
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Radio astronomy
Radio astronomy uses a specialized framing. ITU-R Report RA.2126-2, published in March 2026, describes RFI as an unwanted addition to the cosmic signal with the potential to degrade or prevent a successful observation. It groups mitigation into preventing interference from entering the data, removing it in real time, and reducing or removing its effects after observation. This describes the needs of astronomical observation; it does not replace the general Radio Regulations definition.
Mission-critical systems
Electromagnetic disturbances can also matter in safety- and mission-sensitive equipment. NASA Johnson Space Center’s EMI/EMC engineering overview describes electromagnetic compatibility work as part of ensuring reliable spaceflight hardware and protecting mission-critical communications.
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How to investigate a suspected interference problem
Start by checking whether there is a repeatable reception problem and whether a suspected source is actually connected to it. The ITU-T’s Recommendation K.37 (January 2024) focuses on electromagnetic-compatibility mitigation for telecommunications installations and systems. Its troubleshooting guidance emphasizes identifying the cause before selecting a remedy.
- Record when the problem occurs. Note when it began, what changed around that time, and whether the issue is continuous or intermittent. New, moved, damaged, or malfunctioning equipment may be relevant, but proximity alone does not prove causation.
- Check for a repeatable link to equipment. Where practical, monitor the affected radio or television while switching suspected nearby equipment on and off. If the problem changes consistently with one device, that is useful evidence to investigate further.
- Inspect the installation. Check for damaged cable screening, loose or poor connections, and cable routes that pass close to suspected equipment. In telecommunications installations, a broadband radio receiver can be used to monitor for possible sources where appropriate.
- Match the correction to the cause. Depending on the mechanism, options may include repairing screening or connections, rerouting a cable, separating equipment, or applying suitable screening or filtering. The right option depends on the system, installation, and frequencies involved.
Which mitigation approach fits the problem?
There is no universal RFI accessory or fix. ITU-T K.37 discusses sound electromagnetic-compatibility installation practices, including appropriate equipment, earthing and bonding, power distribution, cabling, environmental controls, and keeping disturbing equipment away from sensitive telecommunications equipment. If a problem occurs, it also discusses checking screening and connections, cable rerouting, separation, screening, and filtering.
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- Cable-related or conducted currents: A ferrite choke may be appropriate when common-mode current on a cable is the identified mechanism. It is not a general-purpose cure for every reception problem.
- Coupling between equipment: Increasing separation or using suitable screening may help when the diagnosis points to radiation or coupling between a source and an affected system.
- Interference entering through a cable or connection: Inspecting and repairing screening, connections, or cable routing may address the path more directly than adding an unrelated accessory.
- Interference in measurement data: In radio astronomy, mitigation may occur before data collection, in real time, or during later processing, depending on the observation and the interference.
These approaches address different paths and targets: reducing emissions at the source, reducing a receiver’s susceptibility, or managing interference in data after reception. The relevant frequency range and installation context also matter; K.37 is specifically focused on telecommunications installation and maintenance.
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