NCERT Physics Class 12 Exemplar Ch 15 Communication Systems Part 6

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Frequencies present are

+

+

1. Plot of amplitude versus is shown in the Figure.

Plot of amplitude versus ωis

Plot of Amplitude Versus Ωis

Plot of amplitude versus ωis

  • As can be seen frequency spectrum is not symmetrical about . Crowding of spectrum is present for .

  • Adding more modulating signals lead to more crowding in w < w c and more chances of mixing of signals.

  • Increase band-width and to accommodate more signals. This shows that large carrier frequency enables to carry more information (more ) and which will in turn increase bandwidth.

Q 30 An audio signal is modulated by a carrier wave of 20MHz such that the bandwidth required for modulation is 3 kHz. Could this wave be demodulated by a diode detector which has the values of R and C as

(i) .

(ii) .

(iii) .

Ans:

So , is satisfied

(ii) .

Here too

So this too can be demodulated

(iii)

Here so this cannot be demodulated

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