communication-systems Question 29
Question: Q. 3. (i) Give three reasons why modulation of a message signal is necessary for long distance transmission.
(ii) Show graphically an audio signal, a carrier wave and an amplitude modulated wave.
R [Delhi/Outside Delhi 2018 Set I, II, III] OR
Why is the baseband signal not transmitted directly? Give any two reasons.
[2016-OD, North]
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Solution:
Ans. (i) If base band signal were to be transmitted directly
(a) The height of the antenna needed will be impractically large.
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(b) The effective power radiated would be too low.
(c) There would be a high probability of different signals getting mixed up with one another. 1 Kindly refer ‘Revision Notes’ of topic-2 for diagram.
[CBSE Marking Scheme, 2016]
Detailed Answer :
(i) (a) Modulation allows us to send a signal over a bandpass frequency range. If every signal gets its own frequency range, then we can transmit multiple signals simultaneously over a single channel.
(b) It allows the use of smaller antenna.
(c) Low frequency signals get attenuated in space while high frequency do not get attenuated in space as fast as low frequency and can travel long distances.
