Modulation Process in Communication

WHY MODULATION?

(i) Long distance communication

The purpose of a modulation is to convert the message signal into a suitable form that matches to the transmission medium. This is necessary because the message signal is a low frequency signal that cannot be transmitted effectively over the transmission channel directly. These channels are best suited for high frequency signal transmission  for long distance.

(ii) Interface

In radio communication, signals from various sources are transmitted through a common media, that is, the open space. This causes interference among various signals, and no useful message is received or recovered by the receiver. The problem of interference is solved by translating the message signals to different radio frequency spectra, which is called as frequency translation in communication.

These main problems can be overcomed by the transmitter by using a process known as modulation.

MODULATION PROCESS

• Modulation may be defined as the process by which some parameters (amplitude, frequency & phase) of a high frequency signal termed as carrier signal, is varied in accordance with the instantaneous amplitude value of the information signal, which is a low frequency signal to achieve long distance communication.
• Signals containing information or intelligence to be transmitted are referred to as modulating signals or low frequency signals or information signals or base band signals.
• The term base band designates the band of frequencies representing the signal supplied by the source of information.
• The carrier signal is nothing but high frequency signal which supposed to carry the message signal from the transmitter to receiver. The carrier signal frequency is much greater than the modulating signal frequency.

The signal resulting from the process of modulation is called modulated signal. At the  receiver side,  this modulated signal is received and the  carrier is removed and discarded and the low-frequency information signal is retained.

The process of extracting a modulating signal from the modulated signal is called demodulation or detection and the device used for this is called as demodulator or detector.