the British Empire in contact with London by being able An introduction to radio 13 Figure 1.6 A superhet radio receiver from the early 1930s to receive at least one transmission a day. This was the forerunner of today's BBC World Service. With short wave broadcasting well established attention was soon turned to the possibility of using ultra short waves for communication. Initially this posed problems with suitable devices for operation at these frequencies. However, these problems were slowly overcome and in March 1931 Standard Telephones and Cables Limited gave a demonstra- tion of telephony across the Straits of Dover using a wavelength of just 18 cm. The British Post Office also installed some services on these frequencies. In 1932 they opened a telephone circuit across the Severn on 5 metres which saved having to use a much longer cable route through the Severn Tunnel. The idea of modulating the frequency of a signal instead of its amplitude had been known from the earliest days of radio. Early experiments had been undertaken in 1902 to investigate its viability. Later ones as well had treated it in a similar way to AM. In attempts to reduce the levels of background noise and interference the bandwidth had been reduced and this had only served to impair its performance. However, Edwin Armstrong, who was already a millionaire from his previous inventions, turned traditional thinking around. Instead of reducing the bandwidth, he increased it. Early interest in the idea was very limited and SO Armstrong set up his own transmitter and receiver to demonstrate the idea in 1935. Using a frequency of 110 MHz he was able to conclusively prove that wideband FM gave significant improvements over traditional AM systems for high quality transmissions. Also using 14 Newnes Guide to Radio and Communications Technology higher frequencies he would be able to reduce the congestion on the long and medium wave bands which were already overcrowded. Despite the success of the demonstration, interest from broadcasters was very l