Television evolved from early experiments in the 1920s to becoming a widespread mass medium by the 1950s. Key developments included the invention of the electric television tube in the 1920s, early broadcasts in the UK and US in the 1930s, the development of coaxial cable and mass production of affordable TV sets in the late 1940s enabling national networks and the spread of television to over half of US households by 1952. In India television was introduced in 1959 in Delhi and expanded slowly at first before gaining momentum in the 1970s with the launch of regional stations and a satellite broadcast network, leading to the establishment of private broadcasters in the 1990s.