Modulation the process of changing some characteristic (e.g. amplitude, frequency or phase) of a carrier wave in accordance with the intensity of the signal is known as modulation. Modulation means to “change”. In another word, it can be said that-“it is the process of combining an audio-frequency (AF) signal with a radio-frequency (RF) carrier wave”. The audio-frequency (AF) signal is also called amodulating wave and the resultant wave produced is called modulated wave. During modulation, some characteristic of the carrier wave is varied in time with the modulating signal and accomplished by combining the two.
Modulator is a one kind of device that performs the modulation. Modulator is necessary for to transmit signal. It can also modify the signal based on the input signal or audio-frequency (AF) signal. Modulators determines at what frequency the system transmits.
Need for modulation:
Modulation is particularly essential in communication system due to the following reason:
- Mutual Interference reduction:
The main purpose of modulation is the reduction of mutual interference. When the signal fed to the transmitter via modulator to the air, the signals are overlap, and then interference occurs. So, modulation is needs to reduce the interference.
- Practical antenna length:
The length of the transmitting antenna should be approximately equal to the wavelength of the wave. Now,
As the audio frequencies range from 20 Hz to 20 KHz, therefore if they are transmitted directly into space, the length of the transmitting antenna required would be extremely large. For instance, to radiate a frequency of 20 KHz directly into space, we would need an antenna length of
This is too long antenna to be constructed practically. For this reason, it isimpracticable to radiate audio signal directly into space. On the other hand, if a carrier wave say of 1000 KHz is used to carry the signal, we need an antenna length of 300 meters only and this size can be easily constructed.
- Operating range:
The energy of a wave depends upon its frequency. The greater the frequency of the wave, the greater the energy the energy possessed by it. As the audio signalfrequencies are small, therefore, these can’t be transmitted over longer distances if radiated directly into space. The only practical solution is to modulate a high frequency carrier wave with audio signal and permits the transmission to occur at this high frequency.
- Wireless Communication:
One popular feature of radio transmission is that it should be carried without wires i.e. radiated into space. At audio frequencies, radiation is not practicable because the efficiency of radiation is poor. However, efficient radiation of electrical energy is possible at high frequencies (>20 Hz).For this reason, modulation is always done in communic
Source: From Google
