Electromagnetic Compatibility EMC

the capability of electronic equipment intended for various purposes to be operated simultaneously in such a way that the radio interference that arises during the operation of such equipment results in only a slight degradation of the equipment’s ability to perform its functions (see alsoNOISE IMMUNITY). The radio interference that arises includes the effects of sources of industrial interference.

Radio interference is unavoidable during the simultaneous operation of electronic equipment or of electrical equipment that radiates electromagnetic waves. The level of the interference is determined by, for example, the number of radiators, the power of the radiators, the spatial distribution of the radiators, the shape of the radiation pattern, and the conditions under which the radio waves propagate. The achievement of EMC entails the establishment of conditions for the normal simultaneous operation of all types of electronic equipment.

Efforts at the achievement of EMC were first undertaken at almost the same time that radio waves were first used for practical purposes, such as radio communication. Gradually, the problem became more complicated. Finally, in the 1950’s, it developed into a challenging problem, mainly because of such factors as increased congestion in the radio-frequency bands in use, continuous increases in the number and power of radiating devices, improvements in receiver sensitivity, imperfections of electronic equipment, and greater complication of the functions and operating conditions of such equipment. The imperfections of electronic equipment include emissions outside the allocated band and spurious emissions from radio transmitters and the presence of channels for the reception of such emissions in radio receivers. The functions and operating conditions of electronic equipment became more complicated as a result of, for example, frequent switching on and off, frequency tuning, and portability.

A distinction is made between management measures and technical measures for the achievement of EMC. The management measures include the spatial separation of electronic equipment and the use of time division or frequency division. Spatial separation entails the use of the same frequency bands in different regions of the earth if such use does not result in mutual interference between systems. Time division is the successive, operation of electronic equipment at a single carrier frequency in accordance with a specific time program. Frequency division is the simultaneous operation of electronic equipment at different carrier frequencies.

The technical measures for the achievement of EMC include the development of electrical equipment and radio transmitters that are improved from the viewpoint of a reduction in disturbing emissions and the development of radio receivers that are less sensitive to such emissions.

In the USSR, the achievement of EMC is the task of the State Commission on Radio Frequencies of the USSR, which was established in 1958 (until 1972, it was called the Interdepartmental Commission on Radio Frequencies). The commission implements a uniform technical policy with respect to problems associated with the efficient allocation and use of the radio spectrum. It sets standards for the parameters of the radio emissions and radio reception of electronic equipment and deals with other aspects of EMC. The standards approved by the State Commission on Radio Frequencies of the USSR include all-Union standards for the width of radio-frequency bands, for the spectra of emissions outside the allocated band from radio transmitters, for permissible transmitter frequency deviations, for permissible levels of spurious emissions from transmitters, and for permissible levels of industrial radio interference. Such standards are binding on all ministries and departments that develop, fabricate, purchase abroad, or use either electronic equipment for any purpose or electrical equipment that produces industrial radio interference.

Internationally, recommendations aimed at the achievement of EMC are made by the International Telecommunication Union.