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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...