Radio

I

Introduction

Radio, system of communication using electromagnetic waves propagated through space. Radio waves are used in wireless telegraphy, telephone transmission, television, radar, navigation systems, and space communication. They are also used in radio broadcasting; the term “radio” is therefore most popularly applied to sound broadcasting in general.

II

History

In the last quarter of the 19th century many scientists were attempting to transmit messages over distances without wires. They were not searching for a means of mass-communication, but simply exploring the possibility of using electromagnetic waves in order to communicate between two fixed points. Nevertheless, the history of “wireless” communication eventually became largely the history of broadcasting.

Radio had no single inventor, but grew out of several international developments. The pioneers of radio drew on the work of the British physicist James Clerk Maxwell, who published his theory of electromagnetic waves in 1873. However, it was the German physicist Heinrich Rudolf Hertz who first generated such waves electrically. Hertz managed to create an oscillating electric discharge, which radiated some of its energy in the form of electromagnetic waves. However, the waves produced were incapable of travelling great distances, and the problem of creating effective transmitters and receivers remained.

A

Marconi

It was the Italian electrical engineer and inventor Guglielmo Marconi who then took the most significant steps, combining technical inventiveness with business acumen. He succeeded in developing both a suitable receiver, or “coherer”, and an improved spark oscillator, which was connected to a crude but effective antenna to transmit radio waves over significant distances. His transmitter was modulated with an ordinary telegraph key, and a crude amplification relay activated a telegraphic instrument at the receiving end.

In 1896 Marconi transmitted signals for a distance exceeding 1.6 km (1 mi) and applied for his first British patent. Within a year of his first demonstration he transmitted signals from shore to a ship at sea 29 km (18 mi) away. In 1899 he established commercial communication between England and France, and in 1901 he succeeded in sending a simple message across the Atlantic. He had demonstrated that radio waves could travel beyond the horizon, and had used his flair for the dramatic to bring the concept of radio to the attention of governmental agencies and business interests.

B

Transmission of Sound

This was still only wireless telegraphy (the transmission of signals) rather than wireless telephony (the transmission of sound itself). However, on Christmas Eve in 1906 an American, Reginald Fessenden, managed to transmit both speech and music over several hundred miles out to sea from the Massachusetts coast. Over the next few years other demonstrations followed in the United States, Britain, and Europe.

The creation of the “vacuum tube oscillator” helped the steady transition from telegraphy to telephony, since it provided a continuous signal that was effective for transmitting speech, rather than just the short bursts of radio waves generated for early telegraphic messages.

It was, however, the development of the radio valve that proved to be crucial in advancing the transition from wireless to broadcasting. In 1904 the British electrical engineer John Ambrose Fleming experimented with the first thermionic two-electrode valve, or diode; a triode was created by the American Lee de Forest by inserting a third electrode into the valve. This device meant that a weak signal could be amplified. More sensitive wireless receivers could now be made, and radio-telephone messages picked up at far greater distances than had earlier been thought possible.