te at Cape Cod was abandoned in favour of one at St Johns in Newfoundland. Finally on 12 December 1901 the first transmission was received when the letter 'S' was detected in the receiver and Marconi became a legend in his own time. This was a major success, and it ably proved the value of wireless as a means of providing long-distance communications. However, it also Figure 1.3 Marconi after his transmission (courtesy Marconi plc) Newnes Guide to Radio and Communications Technology highlighted the many shortcomings of the systems in use at the time. The most noticeable problem was the lack of sensitivity of the detector in the receiver. It was this problem that occupied much of the thought of Professor Ambrose Fleming. He had played a significant part in the transatlantic success, designing many parts of the equipment including the trans- mitter. For a number of years he had known about a phenomenon called the Edison effect. It was found that when a second element was introduced into a light bulb, current would only pass in one direction between the two elements. Both Edison and Fleming had observed the effect, but neither had been able to think of a use for it. However, one day as Fleming was walking down Gower Street in London, he had what he later described as 'a sudden very happy thought'. He realized the possibilities of using the Edison effect in detecting Hertzian waves. Fleming quickly instructed his assistant to set up an experiment to see if the idea worked and to their delight it proved very successful. Fleming patented the idea on 16 November 1904, calling the device his oscillation valve because of its unidirectional properties with electrical oscillations. In many respects this was the first major component of the electronic era. The oscillation valve consisted of a filament heated to white heat. This caused electrons to leave the filament because of an effect known as Figure 1.4 Fleming's early oscillation valves (courtesy Marconi plc) An introduction to radio 9 Current Anode Electrons attracted b