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Electromagnetic interference (EMI) is

[a]ny electromagnetic disturbance that interrupts, obstructs, or otherwise degrades or limits the effective performance of electronics and electrical equipment. It can be induced intentionally, as in some forms of electronic warfare, or unintentionally, as a result of spurious emissions and responses, intermodulation products, and the like.[1]


EMI occurs when magnetic force lines generated by radio waves, electrical current in other phone lines, or events in outer space, such as sunspots, intersect with a telephone wire, generating a slight variation in the electrical current that (“static”). Magnetic interference is a major obstacle to higher modem speeds because it changes the very precisely modulated analog signal that modems use to transmit and receive data.

EMI impedes operations and hinders mission accomplishment by degrading essential systems that utilize the electromagnetic spectrum. The timely and accurate identification, reporting, and resolution of EMI are key functions of electromagnetic spectrum management. Decisive resolution of EMI plays a crucial role in assuring vital information is exchanged quickly and accurately. Therefore, EMI resolution is an important foundation of information operations and an essential factor in obtaining and maintaining information superiority during military operations in war, operations other than war, and peacetime. Since EMI can be caused by enemy, neutral, friendly, or natural sources, it generally must be resolved on a case-by-case basis.[2]


  1. U.S. Department of Defense, Joint Pub. 1–02: DOD Dictionary of Military and Associated Terms (Nov. 8, 2010, as amended through May 15, 2011) (full-text).
  2. Joint Spectrum Interference Resolution (JSIR) Procedures, at A-1.

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