1. LOCAL RADIO (AM & FM)
In the late 19th century it was clear to various scientists and experimenters that wireless communication was possible. Many people worked on developing the devices and improvements.
In 1878, David E. Hughes noticed that sparks could be heard in a telephone receiver when experimenting with his carbon microphone.
Marconi equipped ships with lifesaving wireless communications and established the first transatlantic radio service. Tesla developed means to reliably produce radio frequency electrical currents, publicly demonstrated the principles of radio, and transmitted long distance signals.
In 1901, Marconi conducted the first successful transatlantic experimental radio communications.
The invention of amplitude-modulated (AM) radio, is attributed to Reginald Fessenden and Lee de Forest. On Christmas Eve 1906, Reginald Fessenden used an Alexanderson alternator and rotary spark-gap transmitter to make the first radio audio broadcast, from Brant Rock, Massachusetts.
Inventor Edwin Howard Armstrong is credited with developing regeneration, the super heterodyne circuit and wide-band frequency modulation or FM. FM gave listeners a static-free experience with better sound quality and fidelity than AM.
Frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency (contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant).
Edwin Howard Armstrong (1890–1954) was an American electrical engineer who invented frequency modulation (FM) radio. He patented the regenerative circuit in 1914, the super heterodyne receiver in 1918 and the super-regenerative circuit in 1922.
Today there are 10’s of thousands for commercial radio stations. Revenues of these stations reached $21.2 billion in 2006.
2. HD radio
Radio hasn't really changed much in the past 80 years or so. The last "big thing" was...