communication-systems Question 33
Question: Q. 8. A carrier wave of peak voltage $15 \mathrm{~V}$ is used to transmit a message signal. Find the peak voltage of the modulating signal in order to have a modulation index of $60 %$.
[CBSE Delhi &All India-2018]
Short Answer Type Questions-II
Q. 1. Define the term ‘amplitude modulation’. Explain any two factors which justify the need for modulating a low frequency base band signal.
R [2017-DelhiSet-I, II, III]
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Solution:
Ans. It is the process of superposition of information / message signal over a carrier wave in such a way that the amplitude of carrier wave is varied according to the information signal / message signal.
Direct transmission, of the low frequency base band information signal, is not possible due to the following reasons : (i) Size of Antenna : For transmitting a signal, minimum height of antenna should be $\frac{\lambda}{4}$, with the help of modulation wavelength of signal decreases, hence height of antenna becomes manageable.
(ii) Effective power radiated by an antenna :
Effective power radiated by an antenna varies inversely as $\lambda^{2}$, hence effective power radiated into the space, by the antenna, increases. $1 / 2+1 / 2$
(iii) To avoid mixing up of signals from different transmitters.
(Any two)
[CBSE Marking Scheme, 2017]
