ring this book it has been necessary to seek the advice and assistance of several other people. I am indebted to many that have helped by discussing technologies, providing reference material, review- ing the work and supplying images. The support, assistance and encouragement of all has been very much appreciated, and has been invaluable in the preparation of the book. Ian Poole January 2003 An introduction to radio Radio technology is an integral part of our everyday lives. Since it was first invented, its importance has steadily increased and today we have come to accept all that radio technology offers and we take it for granted. By providing a means of sending information without wires it offers the flexibility that is becoming increasingly important in today's highly mobile world. Radio performs many functions today. One of the most established uses is domestic broadcasting. Most homes have a variety of radio sets, ranging from the relatively simple and cheap portable radios, through the more sophisticated car radios to the high fidelity systems. All of these sets offer a high degree of performance that has resulted from many years of use and development. Even SO the performance of radio sets is being improved all the time and new facilities are being introduced. The introduction of wideband FM represented a major improvement when it was first introduced. Stereo facilities are now taken for granted and other enhancements like RDS (Radio Data System) are available in many countries today. Beyond this digital radio or digital audio broadcasting has started. This brings true CD quality to radio broadcasts as well as allowing data to be broadcast at the same time. Cellular telecommunications is another technology that has been made possible by the development of radio. By the use of radio technology, telecommunications has been given considerably greater flexibility as previously only landlines were available. The flexibility offered by cellular phones has given rise to a phenomenal growth in this area. In ARCA