Frequency-time analysis of the interferences in a 220 V network

The paper proposes an approach to investigate the fine structure of the voltages circulating in the industrial network within the range of 300 kHz-20 MHz, which serves to do some measurements of real lines in real operating mode. It is shown that the interferences can be divided into basic- with spectral density changing slowly with frequency alteration and narrow-band (frequency-pulse). It is also indicated that the frequency concentrated interferences occupy usually 1-5% of the frequency range studied and their intensity is deeply modulated with the doubled frequency of the power supply voltage. There are areas with distinctly expressed low interferences around the zero transitions. The study is motivated by the search for sophisticated methods of high-speed data exchange through the power network.