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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:
- Amplitude Modulation
- Frequency Modulation
- 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 .