Radio technology was originally called the wireless telegraphy. The prefix radio- in the sense of wireless transmission was first recorded in the word radioconductor, coined by the French physicist Edouard Branly in 1897 and based on the verb to radiate. When radio waves pass an electrical conductor, the oscillating electric or magnetic field induces an alternating current and voltage in the conductor. This can be transformed into audio or other signals that carry information. The word 'radio' is used to describe this phenomenon, and television, radio, radar, and cell phone transmissions are all classed as radio frequency emissions.
Early radios ran the entire power of the transmitter through a carbon microphone. While some early radios used some type of amplification through electric current or battery, until the mid 1920s the most common type of receiver was the crystal set. In the 1920s, amplifying vacuum tube radio receivers and transmitters came into use. In 1878 David E. Hughes was the first to transmit and receive radio waves when he noticed that his induction balance caused noise in the receiver of his homemade telephone. Between 1886 and 1888 Heinrich R. Hertz first validated Maxwell's theory through experiment, demonstrating that radio radiation had all the properties of waves (now called Hertzian waves), and discovering that the electromagnetic equations could be reformulated into a partial differential equation called the wave equation.
Between 1894 and 1900 the Indian physicist Jagdish Chandra Bose performed pioneering research on radio waves and created waves as short as 5 mm. In November 1894, Bose ignited gunpowder and rang a bell at a distance using electromagnetic waves, confirming that communication signals could be sent without using wires, but he too did not patent his work.
The New Zealander Ernest Rutherford, 1st Baron Rutherford of Nelson was instrumental in the development of radio. In 1895 he was awarded an Exhibition of 1851 Science Research Scholarship to Cambridge. He arrived in England with a reputation as an innovator and inventor, and distinguished himself in several fields, initially by working out the electrical properties of solids and then using wireless waves as a method of signalling. Rutherford was encouraged in his work by Sir Robert Ball, who had been scientific adviser to the body maintaining lighthouses on the Irish coast; he wished to solve the difficult problem of a ship’s inability to detect a lighthouse in fog. Sensing fame and fortune, Rutherford increased the sensitivity of his apparatus until he could detect electromagnetic waves over a distance of several hundred metres. Thomson quickly realised that Rutherford was a researcher of exceptional ability and invited him to join in a study of the electrical conduction of gases. The commercial development of wireless technology was thus left for Guglielmo Marconi.
In 1893 in St. Louis, Missouri, Tesla made devices for his experiments with the electricity. Addressing the Franklin Institute in Philadelphia and the National Electric Light Association, he described and demonstrated in detail the principles of his work. The descriptions contained all the elements that were later incorporated into radio systems before the development of the vacuum tube. He initially experimented with magnetic receivers, unlike the coherers used by Marconi and other early experimenters. Tesla is usually considered the first to apply the mechanism of electrical conduction to wireless practices.
Further information and links:History of Radio
History of Radio
USA AMATEUR RADIO HISTORY AND LICENSING