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Kornel Terplan, Patricia A. Morreale

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The Telecommunications Handbook

CRC Press

Chapter One

1.1 ELECTROMAGNETIC ENVIRONMENT

The electromagnetic environment is an integral part of the world in which we live. Various apparatus such as radio and television broadcast stations, communication transmitters, and other radar and navigational aids radiate electromagnetic energy during their normal operation. These are intentional radiations of electromagnetic energy into the environment. Many appliances such as automobile ignition systems and industrial control equipment used in everyday life also emit electromagnetic energy, although these emissions are not an essential part of normal operation. Several other examples of unintentional radiators are described in Chapter 3. The electromagnetic environment created by these intentional and unintentional sources, when sufficiently strong, interferes with the operation of many electrical and electronics equipment and systems.

1.2 HISTORICAL NOTES

1.2.1 Pre-World War II Era

The interference from the electromagnetic environment began to gain recognition as a subject of practical importance in the 1920s. With the beginning of radio broadcast transmissions, the interference from radio noise (also called electromagnetic noise) was viewed with concern by the manufacturers of electric power equipment and electric utility companies in the United States. This concern was serious enough to lead to the setting up of technical committees by the National Electric Light Association and the National Electrical Manufacturers Association in the United States to examine aspects of interference from radio noise. The object at that time was to evolve suitable measurement techniques and performance standards. These efforts resulted in the publication of several technical reports, a documentation of measurement methods, and evolution of test instruments for this purpose during the 1930s. Specific advances include the formulation of procedures for measuring electrical field strength near overhead power lines, measurement of field strength caused by radio broadcast stations, the development of an instrument for measuring radio noise and field strength, and an information base for determining tolerable limits for radio noise.

Across the Atlantic, at about the same time, technical papers covering various aspects of radio interference (also called electromagnetic interference [EMI]) began to appear in several countries in Europe. The papers examined not only the electromagnetic interference from radio transmissions but also interferences with radio signal reception. In England, complaints relating to more than 1000 cases of radio interference were analyzed in detail in 1934. These interferences were found to result from the operation of appliances using electric motors, switches, and automobile ignition. Interferences were also observed to originate from electric traction and electrical power lines. There was a recognition in Europe that the area of radio interference (electromagnetic interference) merits a concerted technical study at the international level and that international cooperation on matters of radio interference is necessary because radio transmissions do not know geographical or national boundaries. Further, various apparatus and appliances using electric motors and so on are likely to be marketed and used in many countries, apart from the country of manufacture; therefore these apparatus must conform to all relevant national performance standards. The International Electrotechnical Commission (IEC) and the International Union of Broadcasting joined hands in the 1930s to address relevant technical issues. Thus, the International Special Committee on Radio Interference (CISPR-Comite International Special des Perturbations Radioelectrique) was formed in 1933 and the first meeting of CISPR was held in 1934. Two important issues initially addressed by CISPR were the acceptable limits of radio interference and the methods of measuring such interference. In the next couple of years, an accepted basis for the method of measuring radio interference and measurement instrumentation in the frequency range 160 to 1605 kHz were evolved. Among the first agreements in CISPR at that time was to provide a signal-to-noise ratio of 40 dB in specifying the tolerable limits of interference for a reference field strength of 1 mV/m modulated to a depth of 20 percent.

Important milestones in progress during this period include:

* Publication of a Report in 1940 (in the United States) on methods of measuring radio noise.

* Publication of CISPR meeting proceedings and Reports RI 1-8 from 1934 to 1939 giving information on the design of measuring receivers, artificial mains networks, field measurements, and so forth. * Specification for a radio noise and field strength meter in the frequency band 0.15-18 MHz.

* Practical measurement of radio broadcast field strengths and radio noise field strength in the vicinity of overhead electric power lines.

* Development of procedures for measuring conducted radio noise from electrical apparatus and an artificial mains network for use in such measurements in the 160-1605 kHz frequency range.

* Design and limited manufacture of measuring receivers, radio noise field strength meters, and other instrumentation for use in the above measurements.

1.2.2 World War II and the Next Twenty-Five Years

The advent of World War II provided a damper and at the same time a new impetus for understanding and controlling radio noise. During the years of war, technical work under the aegis of CISPR came to a complete standstill.

With extensive interest in using telecommunication and radar facilities by the military during World War II, the concerns of the military about radio interference became very strong. The military was also interested in frequency bands higher than the normal radio broadcast frequencies. These interests of the military gave rise to the development of military standards and instrumentation for reliable measurement of electromagnetic interferences up to 20 MHz during the 1940s, progressing up to 30 MHz during the 1950s, and at frequencies of up to 1000 MHz during the 1960s. Right from the beginning, the military performance standards were more stringent and demanding. In the aerospace systems and satellite technologies also, the concepts of electromagnetic interference, and effective steps to combat such interference, are of paramount importance. This resulted in a great deal of practically oriented technical work. The results of this work, however, remained classified for a long time.

CISPR meetings resumed after World War II. The United States, Canada, and Australia joined in the CISPR deliberations at this time. The CISPR forum was used as a technical gathering for reaching an agreement on radio interference measurement methodologies and the instrumentation to be used for this purpose. With the progressive use of higher frequencies, the thrust was invariably to develop measurement procedures, standard schematics, and instrumentation for higher frequencies. More and more countries from Asia and other parts of the world, and several international organizations such as Comite Consultatif International des Radio communication (CCIR) with an interest in radio sciences, also started participating in CISPR meetings. With the increased international participation and growth of technical areas being addressed, the CISPR meetings became important vehicles in the development of international understanding and cooperation in electromagnetic interference. Thus, measurement techniques and detailed experimental schematics for use at higher frequencies were evolved in this forum. Precise details of measurement procedures covering frequencies up to 1000 MHz were also discussed and agreed upon in these meetings.

With the increasing use of radio communications for nonmilitary applications in the post-World War II period, the subject of electromagnetic interference and the associated need to exercise certain design discipline in building various telecommunication products became apparent. Thus, several major technical studies covering interference mechanisms and their effects, measurement techniques, and design procedures to minimize electromagnetic interference became subjects of serious study in many parts of the world, including the United States and Europe. Many practical measurements were done during this period to evaluate the radio frequency noise emitted by several electrical and electronics apparatus and systems. As part of the technical background for deliberations in CISPR, detailed measurements of the electromagnetic noise emitted by radio and television, electrical power transmission lines, household appliances, motor vehicles, and industrial/scientific/medical (ISM) instruments were made, reported, and extensively discussed in CISPR meetings. The emphasis was initially on obtaining an agreement on measurement procedures and details of instrumentation, while leaving the more difficult subject of acceptable performance limits to a later date. Separate from these developments, but closely following on them, national regulatory agencies such as the Federal Communications Commission (FCC) in the United States and the British Standards Institution (BSI) in the United Kingdom started promulgating interference control limits applicable in their respective countries.

The important milestones in progress during this period include:

* The first Joint Army-Navy specification JAN-I-225 in 1945 covering the method of measuring radio interference for the armed forces up to 20 MHz (which became document C 63.1 in 1946); a revised standard covering measurements up to 30 MHz called C 63.2 in 1963; and standard C 63.3 covering instruments for frequencies up to 1000 MHz in 1964.

* Publication of military standards MIL-STD-462 "Measurement of EMI characteristics" in 1967 and MIL-STD-461 "Electromagnetic emission and susceptibility requirements for the control of electromagnetic interference" in 1968.

* Progressive standardization of measurement techniques and instrumentation (specifically for nonmilitary applications) by CISPR covering frequency bands up to 30 MHz by 1958, 300 MHz by 1961, and 1000 MHz by 1968.

* Invention of the ferrite clamp method of measuring the electromagnetic emissions generated by household appliances in the frequency range 30-300 MHz.

* Publication by the CISPR of CISPR-4 "Measuring set specifications for the frequency range 300-1000 MHz" in 1967 and also CISPR-5 "Radio interference measuring apparatus having detectors other than quasi-peak" in 1967.

* Formal organization of technical information including measurement methodologies and sources of interference covering ISM equipment, electric power lines, automobiles, radio/television receivers, and household appliances.

* Publication of national regulatory measures concerning electromagnetic interference by agencies such as the Federal Communications Commission, for example, FCC Rules and Regulations Vol. II, Part 18 for "Industrial, scientific, and medical equipment" in 1968.

1.2.3 The Last Twenty-Five Years

The field of electrical and electronics engineering has rapidly advanced during the past 25 years. Major advances include developments in the field of digital computers, information technology, instrumentation, telecommunications, and semiconductor technologies. Electromagnetic noise and techniques to surmount problems caused by electromagnetic interference are important in all these areas. The result has been a great deal of technical activity worldwide in the field of electromagnetic noise.

Continuing deliberations in CISPR resulted in CISPR Publication 16, which integrated various measurement procedures in this field, and the recommended limits for electromagnetic interference, into one self-contained publication. The deliberations in CISPR also yielded publications covering electromagnetic noise and its measurement for radio and television receivers, industrial/scientific/medical instruments, automobiles, and fluorescent lighting. In tune with the developments in information technology and digital electronics products, an important emerging technology during the 1980s, CISPR also brought out CISPR Publication 22 covering information technology equipment.

Military interest in the field of electromagnetic noise also resulted in much progress in the field of electromagnetic interference and techniques to measure and control it. Several important advances in understanding EMI and technologies to achieve electromagnetic compatibility (EMC) are a direct result of the work done for the U.S. military in this area. Much of the technological activity on individual products remained classified for both military and commercial reasons. Important military documents published include MIL-STD-463 covering definitions and units of measurement in EMI technology and updated versions of MIL-STD-461 and MIL-STD-462. The armed forces in several countries documented and published their own standards for limiting electromagnetic interference. The work and standards published by the U.S. military, however, continue to lead the way in this field. Apart from basic military standards MIL-STD-461 /462/463, the U.S. military also published several other standards covering system electromagnetic compatibility and design and performance requirements for a variety of equipment such as radar, aircraft power supplies, space systems, naval platforms, mobile communications, and so forth.

Worldwide growth in digital technologies, including the applications of these in industrial automation, heavily affected developments in electromagnetic noise-related issues during the 1980s. Digital instruments and equipment are easily susceptible to electromagnetic noise because such instruments and equipment cannot distinguish between a pulse signal and transient noise. They are prone to malfunction as a result of electromagnetic noise. At the same time, digital circuits and equipment generate a great deal of electromagnetic noise, which is essentially a broadband noise arising from the very short pulse rise time used in digital equipment. The clock frequencies used in digital circuits and apparatus also result in electromagnetic noise. Digital electronic equipment makes extensive use of solid-state devices and integrated circuits. The integrated circuits and solid-state devices are easily damaged by transient electromagnetic disturbances. Thus, special design and engineering methods are necessary to protect the sensitive semiconductor devices from electromagnetic environment. This area received considerable attention during the past two decades, and many papers were published on this subject worldwide. Discussions on these techniques and technologies continue to dominate many national and international conferences.

Several countries devoted special attention to formulate the permissible limits of electromagnetic noise for emissions by various electrical and electronic appliances and the immunity limits which these instruments and equipment must withstand before they can be marketed. Thus, organizations such as the Federal Communications Commission, Fernmelde Technisches Zentralamt (FTZ) in Germany, British Standards Institution, Voluntary Control Council for Interference (VCCI) in Japan, and similar institutions in other countries promulgated performance standards governing electromagnetic noise emissions and immunity requirements. Specialized agencies within governments such as the National Aeronautics and Space Administration (NASA) and the National Telecommunication and Information Agency (NTIA) in the United States and similar organizations in other countries have also published performance standards governing electromagnetic emissions and immunity. International organizations such as the International Civil Aviation Organization (ICAO) and the International Maritime Consultative Organization (IMCO) have also devoted considerable attention to electromagnetic noise and its allowable limits.

Continues...

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