This chapter discusses wireless theory. At the transmitter, the radio signals have two main elements: (1) a high-frequency radio carrier wave generated by a valve oscillator, and (2) the low-frequency audio information impressed on this carrier. At the receiver there are again two elements: (1) a tuned aerial system to intercept the wanted radiated signal, and (2) a detector to extract the-low frequency modulation.

During the 1924-34 period, fundamental changes took place in radio valves: manufacturing methods, types and designs were all completely transformed. There was also a realization that different valve characteristics were more suitable for different positions in a receiver, e.g. a power output valve was more efficient if it had a reasonably low anode impedance; there was competition to produce detector valves which were not a prolific source of 'microphonic' noises; and there were one or two odd 'special' types - perhaps with an extra grid incorporated - but these were in many cases only partly understood and saw little commercial use.

This chapter presents a complete transformation of the British wireless industry during the year 1924-34; it is the purpose of this chapter to consider some of the influences bearing on that transformation. As we have seen, so far as the purchaser of equipment was concerned, the situation in 1924 had not changed in any essential way since the inception of broadcasting. We have already looked at the changes in transmitting conditions over the following decade and briefly at techno logical change; but we must remember that this was also an era of great social, economic and political change; the time of the 'slump', the General Strike and the 'great depression'. These events, also, affected the development of wireless throughout this short period; some historical background is necessary if we are to attempt to understand the sequence of events. One reliable method of examining the growth of the wireless industry is available to us; the number of wireless receiving licences in operation at any given time. A graph is appended showing this chart of progress over these ten years. It is clear that this graph shows a largely unbroken climb from about 600,000 in January 1924 to 6,600,000 by December 1934; it is also clear that it is by no means a uniform growth.