Modulation, demodulation, Study notes of Chemistry

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Modulation– The process of superimposing a low frequency message signal over high frequency wave is known as modulation.

Carrier wave– High frequency wave is called carrier wave.

Type of modulation - (i) Amplitude modulation (ii) Frequency modulation (iii) Phase modulation (i) (ii) (iii)

(i) Amplitude modulation :- The process of modulation in which the amplitude of carrier wave changes in accordance with the instantaneous value of the massage signal is called amplitude modulation. (i)

(ii) It requires simple and cheaper transmitters and receivers. (ii)

(iii) Its transmission requires low carrier frequencies of 0.5 – 20 MHz. (iii) (0.5 – 20 MHz)

Disadvantages of amplitude modulation : (i) Amplitude modulation suffers from noise. (ii) Quality of audio signal is poor. (iii) Efficiency of AM transmission is low. (i) (ii) (iii)

(ii) Frequency modulation :- The process modulation in which the frequency of carrier wave changes in accordance with the instantaneous value of the message signal is called frequency modulation. (ii)

(i) FM transmission is highly efficient as compared to AM. (i)

(ii) FM reception is almost immune to noise as compared to AM reception. (ii)

(i) The channel required in FM is about 10 times wider than that in A.M. (i)

(ii) F.M. receivers and transmitters are very complex and costly. (ii)

Demodulation– The process of again receiving a low frequency message signal from the modulated wave is called demodulation.

Modulation index– The ratio of the change in amplitude of carrier wave to the amplitude of original carrier wave is called modulation index or modulation factor.