Basics of Communication System By Hari Mohan Rai
Basics of Communication System By: Hari Mohan Rai
Modulation: - The process of superimposing low frequency signals (Information) with high frequency is called modulation. Demodulation: - it is a technique to extract the original information signal from the modulated signal by separating out the carrier signal.
Need for Modulation Increases Reduces Improves the range the quality of height of of communi antenna reception cation Avoid the mixing of signals Allows the bandwidt h multiplexin g of signals adjustmen ts
Increase the range of communication • At low frequency radiation is poor and signal gets highly attenuated, Attenuation reduces with increase in frequency of the transmitted signals. • The frequency of baseband signal is low, hence low frequency cannot transmitted over long distance. Modulation process increases the frequency of the signal and hence the range of communication increases.
Reduces the height of antenna • For transmission of radio signals, the antenna height must be multiple of • Minimum Antenna height= • For eg. 10 k. Hz frequency is to be transmitted then Height of Antenna will be: • It is practically impossible. • Now consider frequency for modulated signal = 10 MHz • Height of Antenna: • This can be installed practically. Thus modulation reduces the Antenna height.
Improves Quality of Reception: - • With the help of modulation, the effect of noise is reduced to a great extent. Reduction of noises improves the quality of receiving signal.
Avoid mixing of signals: If baseband signals are transmitted without using a modulation by more than one transmitter, then all there signals will be in the same frequency range i. e. 0 to 20 KHz. Hence all signals gets mixed together and a receiver cannot separate them from each other. So, if each Baseband signal is use to modulate a different carrier then they will occupy different slots in the frequency domain. This avoids mixing of signals.
Allows multiplexing of signals: • Multiplexing is a process in which two or more signals can be transmitted over the same communication channel simultaneously. • Multiplexing is possible only with modulation. The multiplexing allows the same channel to be used by many signals. For eq. TV channels. • The different signals from different stations can be separated in the receiver since carrier frequencies for these signals are different
Allows adjustments in the bandwidth • Bandwidth of modulated signal may be made smaller or larger than the original signal. By controlling the bandwidth in the modulation process, the signal to noise ratio can be improved.
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- Slides: 10