the question of who first The subject of RF radiation is still regarded as transmitted radio signals is not without controversy, the mysterious and something of a black art. This is no doubt subsequent practical development of radio communica- due to the fact that it cannot be seen or touched. There tions systems is attributed to Guglielmo Marconi who was also an element of magic in some of the very early was born in Italy in 1874. experimental work, particularly that of Tesla, who seems His first British patent was taken out in 1896 and to have mixed science and showmanship. covered the use of a spark transmitter. There are many Perhaps because RF is unseen, it has also become accounts written of the experimental work carried out at confused with ionising radiation in the minds of many various locations on land and on ships during the course people. It is essential to distinguish the difference of which the range of such equipment was very much between the two since, with our present state of increased. By 1921, the thermionic transmitter tube Communications Engineering Desk Reference; ISBN: 9780123746481 Copyright © 2001, Ronald Kitchen. Published by Elsevier Ltd 2001. All rights reserved CHAPTER 2.5 Introduction to RF and microwave radiation became available and made it possible to design trans- interference has caused people to question whether they mitters to operate on a range of frequencies. The power can be harmed by it. output available increased with the development of The word 'wireless' largely passed out of use many electronic tubes which could, increasingly, handle higher years ago. Radio is now the more general term in use, powers with the aid of air or liquid cooling systems. though strangely enough in domestic use it tends not to Over the years, and stimulated by the needs of the have the same wide use, mainly being interpreted as First and Second World Wars, radio transmission has meaning sound broadcasting with the term 'television' or become an established technology which is taken for 'TV' to