Modulation

The process of super-imposing a low frequency (long wave) information component on a high frequency (short wave) carrier signal is called modulation. In other words Modulation is a process by which some characteristics of a signal, called carrier, is varied in accordance with the instantaneous value of another signal, called modulating signal. With the development of modulation a whole new era of communication evolved.

Ø  The signals containing the information or intelligence are referred as modulating signals.

Ø  The carrier frequency is greater than the modulating frequency.

Ø  The signal resulting from the process of modulation is called modulated signal.

                                                         

Need of Modulation

There are many difficulties in propagation of electromagnetic wave at audio frequencies below 20 kHz.

Ø  Practicality of Antenna: With the increase of frequency the size of antenna is reduced. So we need less size of antenna for high frequency.

Ø  Reduction of Noise: Noise is one of the major limitations of any communication system. Although noise cannot be completely eliminated from the system but with the help of several modulation techniques and schemes the effect of noise can be minimized. With the increase of the transmitting frequency there is a less or minimum chance of interference of noise to the system.

Ø  Reducing the chances of interfacing between each information: All the sound in communication system are concentrated within the range from 20Hz to 20kHz and all the signals from the different sources would be inseparably mixes up. In order to separate the various signals, it is necessary to convert them all to different portions of electromagnetic spectrum.