A radio is much more than a device that provides communication and entertainment. Its invention led to a revolution in technology.

Although turning on a radio produces sound, radio waves themselves can not be "heard" and have nothing to do with sound waves. Sound waves are a vibration of the air; radio waves are a part of the electromagnetic spectrum. They have long wavelengths and are located below the red and infrared portion of the spectrum. As history has shown, radio waves have the excellent property to act as a "carrier," carrying the information which a radio detector ( receiver) then decodes and amplifies.

The existence of radio waves was first predicted by James Clerk Maxwell (1831-1879). Maxwell, who had worked out the laws concerning electromagnetism in 1865, had predicted that an oscillating current would produce radiation with an extremely long wavelength.

In 1890 Elihu Thomson discovered the principal of alternating...