Modulation :-

Transmission of information by communication systems over large distances is quite a feat of human ingenuity. We can talk, video chat and text anyone on this planet! The communication system uses a very clever technique called Modulation to increase the reach of the signals. Two signals are involved in this process.

Types of Modulation -

There are three types of Modulation:

1. Amplitude Modulation
2. Frequency Modulation
3. Phase Modulation

Need of Modulation :-

• Reduction in the height of antenna - For the transmission of radio signals, the antenna height must be multiple of λ/4 ,where λ is the wavelength .

  λ = c /f

  where c : is the velocity of light

  f: is the frequency of the signal to be transmitted

• Avoids mixing of signals - If the baseband sound signals are transmitted without using the modulation by more than one transmitter, then all the signals will be in the same frequency range i.e. 0 to 20 kHz . Therefore, all the signals get mixed together and a receiver can not separate them from each other .

  Hence, if each baseband sound signal is used to modulate a different carrier then they will occupy different slots in the frequency domain (different channels). Thus, modulation avoids mixing of signals .

• Increase the Range of Communication - The frequency of baseband signal is low, and the low frequency signals can not travel long distance when they are transmitted . They get heavily attenuated .

  The attenuation reduces with increase in frequency of the transmitted signal, and they travel longer distance .

  The modulation process increases the frequency of the signal to be transmitted . Therefore, it increases the range of communication.

• Multiplexing is possible - Multiplexing is a process in which two or more signals can be transmitted over the same communication channel simultaneously .

  This is possible only with modulation.

  The multiplexing allows the same channel to be used by many signals . Hence, many TV channels can use the same frequency range, without getting mixed with each other or different frequency signals can be transmitted at the same time .

• Improves Quality of Reception - With frequency modulation (FM) and the digital communication techniques such as PCM, the effect of noise is reduced to a great extent . This improves quality of reception .