Radio

Energy is required to create a radio signal. Radio signals use the energy from the transmitter that accelerates electric charge in the transmitting antenna. A radio signal carries this energy from the transmitting antenna Radio towers on Elden Mountain above Flagstaff, Arizona. Each transmitting antenna has a size that matches the wavelength of the signal it transmits. Photograph by Tom Bean. Stock Market. Reproduced by permission.

to the receiving antenna. Only a small fraction of the transmitter's power is normally intercepted by any one receiving antenna, but even a vanishingly-small received signal can be amplified electronically millions of times as required.