This publication applies to radio noise from overhead power lines and high voltage equipment which may cause interference to radio reception, excluding the fields from power line carrier signals. The frequency range covered is 0.15 MHz to 300 MHz. The purpose of Part 1 is to discuss the physical phenomena involved in the generation of electromagnetic noise fields; it also includes the main properties of such fields and their numerical values. The data should facilitate the use of the recommendations given in CISPR 18-2 and 18-3.