Modulation

In earlier times, the most widely used form of communication was a system based on the transmission of a continuous-wave (CW) signal. With this system, the signal was interrupted periodically (Morse code) to produce a coded message. The CW systems required tremendous training and expertise on the part of the persons involved in transmitting and receiving the messages. So, the field was limited to a few experts. With the development of modulation, a whole new era of communications evolved. Its results can be seen all round us to day.

Can electricity carry intelligence?

A steady current (DC) cannot carry any intelligence. This is because there is no variation in it. However, if it can be changed in some meaningful sequence, then it can be made to carry information (or intelligence).

A continuous as wave as such also cannot carry intelligence. This is because it is made up of a series of identical sine waves having same amplitude, same period, same frequency etc., there are no meaningful variations. Every cycle of sine wave looks exactly the same.

A continuous ac wave can be made to carry intelligence if it is interrupted in such a way that it becomes a series of pulses. These pulses can correspond to some known code.

A high frequency carrier wave is used to carry the audio signal. The audio signal is superposed over the carrier wave. The process is called modulation and may be defined as under:

The process of changing some characteristic e.g. amplitude, frequency or plane of a carrier wave in accordance with the intensity of the signal is known as modulation.

The literal meaning of the modulation is "to change". In modulation, some characteristic of carrier wave is changed in accordance with the intensity (i.e., amplitude) of the signal. The resultant wave is called modulated ware or radio wave and contains the audio signal. Modulation permits the transmission to occur at high frequencies while it simultaneously allows the carrying of the audio signal.