Radio communication basics

The radio waves are actually high-frequency AC signals. An antenna wired to a high-frequency oscillator can transmit radio waves. The oscillator's frequency is usually 100 KHz or higher. In addition to transmitting high-frequency AC signals, the antenna converts the radio waves into electromagnetic waves as well. Electromagnetic waves travel at the speed of light, which is approximately 3×108 m/s. Upon an antenna receiving a transmitted electromagnetic wave, high-frequency current is created. The created current in the antenna is just a fraction of the transmitting signal. The information in this electromagnetic wave has some electrical signal data, such as frequency, voltage field, magnetic field, and waveform characteristics (sine, square, triangle, and so on). An example of an electromagnetic wave is shown here:

Modulation

In order for audio information (music, speech, and so on) to be transmitted over long distances, an electronic signal mixing technique must...