Overview

Radio broadcasting has made a significant contribution to humankind by shrinking the time needed to communicate between distant places. It has provided the timely distribution of news and public service messages, and offered mass entertainment at no cost to the listener. It has also helped to save lives by speeding up responses to natural and humanmade emergencies. The first radio communications were commercial message traffic transmitted across oceans or between shore stations and ships at sea. When regular sponsored radio broadcasts began, radio became the first worldwide mass media. Millions of people at all levels of society could hear the news, be entertained, hear storm warnings, and even get the right time.

Private citizens soon became radio amateurs who were able to communicate with other amateurs elsewhere in the world. These amateur links proved helpful in informing the rest of the world about wars and disasters that cut off other forms of communication.

Despite the popularity of broadcast and cable television, radio remains popular with many people, especially those engaged in other activities such as driving automobiles or working. Radio talk shows became the first interactive media when listeners were able to telephone the radio station with comments and criticisms. Music broadcasts programmed to appeal to different groups of listeners have also helped to keep radio alive and competitive.

The first radio stations broadcast with amplitude-modulated (AM) signals, which can be heard over wide listening areas, but they are subject to humanmade and natural interference. The later development of...