7-valve 'superhet' heterodyne radio receiver, 1924.
© Science Museum / Science & Society Picture Library
The radio receiver has valves and is battery operated. It is shown with its frame aerial and headphones. In 1917, Edward Howard Armstrong (1890-1954) developed the superheterodyne electronic circuit, which significantly improved the sensitivity and selectivity of radio receivers over a wide range of frequencies, making amplifier tuning unnecesary. This made the task of tuning the radio receiver to different stations much more simple and straightforward. 'Superhet' radios had to use an indoor frame aerial because such sets used an oscillator which was capable of radiating interference if the incoming signal was too strong. This was a big problem for several years, before better circuit design largely eliminated it.