, the consequences of exposure to them can transmission and the nature of electromagnetic waves confidently be stated as being very different. particularly for those from other disciplines who may Although we cannot see radio waves, most people will, otherwise find the electronic content unfamiliar. It at school or college, have done the classical experiments includes explanations of the terms relevant to this form with magnetic fields and iron filings to demonstrate the of non-ionising radiation. patterns of the fields and used an electroscope to demonstrate the presence of electrostatic charge and the force which causes the gold leaf to move. Radio frequency (RF) radiation From these early and rudimentary experiments with static fields it should at least be possible to conceive that The previous book on this subject was entitled RF such fields are not magical and are very common in any Radiation Safety Handbook, the term 'RF' covering all electrical environment. frequencies used for communications, radar, satellites, etc., up to the nominal ceiling of 300 GHz. However, it was suggested that some people regard radio frequency History of radio transmission (RF) as applying only to the lower part of this spectrum. Consequently the word 'microwave' has been added in Radio transmission is, relatively speaking, a very new this revision, although it is redundant in the context of technology which had its beginnings in the theoretical the book. It would be tedious to use both terms work of Maxwell in the nineteenth century and the throughout the book SO 'RF' is used to include 'micro- experimental work of Hertz, the German physicist, in waves' here as is understood by radio engineers. The term the last two decades of the nineteenth century. Many microwave is only specifically used when the topic in- others also made contributions, including the volves something to which the term normally attaches, development of devices which could detect the presence e.g. microwave oven, microwave antenna, etc. of radio waves. Whilst 