It is a common misunderstanding that radio waves are sound waves. In fact, they are part of the electromagnetic spectrum—just another type of light, with a long wavelength. The clever bit is that if the waves are varied in height or length, they can carry information. Of course the most common example of this is to carry audio information, which is then deciphered by your radio and turned back into sound.
There are two ways of varying radio waves and these are called AM (amplitude modulation) and FM (frequency modulation), which are the two most common modes on radio. The first changes the intensity of the transmission—or if you think in terms of waves, it changes their height—and it was this method that Canadian inventor Reginald Fessenden (1866-1932) came up with in 1906.
Fessenden's set-up used a microphone to convert sound into an electric signal that was then combined with continuous radio waves. These modulated waves were transmitted through an antenna and received by a second antenna some distance away. To hear the original sound, the waves were turned back into electric signals. This process is called demodulation. Finally the signal was sent to a loudspeaker, which converted it back to sound for ears to hear.
It was on Christmas Eve of 1906 that Fessenden made the world's first radio broadcast using his amplitude modulation technique, He transmitted his voice and recorded music over several hundred miles from Brant Rock, Plymouth County, Massachusetts, to ships in the Atlantic Ocean. This was the start of broadcasting, and it was not long before every self- respecting household was gathering around the radio in the evenings to listen to broadcasts.
