Electromagnetic environmental measurement system employing frequency level selective process

Abstract

IntroductionThis paper describes a method of measuring quasistationary electromagnetic waves, whose level, generation time, radiation points, and rates of the incidents are not always constant. Those quasi-stationary waves radiated from the amateur radio, the land mobile station, and so on, sometimes cause electromagnetic interference (EMI) and are rather difficult to detect. The frequency and the electromagnetic field level of those waves can be detected effectively by frequency domain measurements using a high-resolution spectrum analyzer. This measurement system detects EM1 waves whose peak level is above a threshold line set in the specific frequency range. Measurements were also carried out in urban areas to investigate the environment for citizen-band. Results indicate that there is a close relationship between the occurrence rates and the human activities. This system is useful for detecting the cause of EM1 and establishing countermeasures against electromagnetic waves.With advances in semiconductor devices, signals carrying information have become faster and weaker. As a result, the immunity level of electrical equipment against electromagnetic interference (EMI) waves has fallen. Moreover, as the numbers and types of electrical equipment increase, the amount of man-made noises increases so that the prevention of EM1 is being recognized as an important issue [I]. In this situation, by means of the methods for statistical measurement of the electromagnetic environment in urban areas, the characteristics of the interference waves and the EMI-generating mechanisms have been investigated [2-41. On the other hand, with a view to finding the cause of the interference, a report is available on the time domain measurement system that interlocks with a malfunction of electrical equipment [5]. The method is particularly effective for detection of the transient phenomena such as the impulsive EM1 waves [6-81.Key words: Electromagnetic interference (EMI); electromagnetic environment; frequency spectrum; electromagnetic environmental adaptability; CB radio. However, in order to proceed with the prevention methods for EMI, it is also important to carry out the frequency domain measurement which is effective for 100 ISSN8756-6621/95/0005-0100 @