t be widely available for a number of years, devices which were at the forefront of technology some years ago are now in widespread use enabling many of the systems which we take for granted to function. These developments represent just a few of the areas where radio technology is moving forwards. However, they are not the only areas. In view of the importance of radio in today's society, there are many areas where new developments are being sought to enable new radio applications to be implemented and others to be able to operate it more effectively. All of them are an indication of the importance that the electronics industry attaches to radio. This means that it is a technology for the future. Radio waves and propagation The properties of radio waves and the way in which they travel or propagate are of prime importance in the study of radio technology. These waves can travel over vast distances enabling communication to be made where no other means is possible. Using them communication can be established over distances ranging from a few metres to many thousands of miles. This enables telephone conversations and many other forms of communication to be made with people on the other side of the world using short wave propagation or satellites. Radio waves can be received over even greater distances. Radio telescopes pick up minute signals from sources many light years away. Radio waves are a form of radiation known as electromagnetic waves. As they contain both electric and magnetic elements it is first necessary to take a look at these fields before looking at the electromagnetic wave itself. Electric fields Any electrically charged object whether it has a static charge or is carrying a current has an electric field associated with it. It is a commonly known fact that like charges repel one another and opposite charges attract. This can be demonstrated in a number of ways. Hair often tends to stand up after it has been brushed or combed. The brushing action generates an electrostatic charge on the hairs, and a