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  • (i) Draw the plot of amplitude versus ω for an amplitude modulated wave whose carrier wave omega > omega _c carrying two modulating signals

 (i) Draw the plot of amplitude versus ω for an amplitude-modulated wave whose carrier wave \left ( \omega >\omega _c \right ) is carrying two modulating signals,\omega _1 \: and \: \omega _2\left ( \omega _2 >\omega _1 \right )
(ii) Is the plot symmetrical about \omega _c? Comment especially about the plot in the region \left ( \omega <\omega _c \right )
(iii) Extrapolate and predict the problems one can expect if more waves are to be modulated.
(iv) Suggest solutions to the above problem. In the process can one understand another advantage of modulation in terms of bandwidth?

Answers (1)

Explanation:-

For an amplitude-modulated wave with two modulating signals, the carrier wave’s spectrum will consist of a central frequency at the carrier frequency.

ii)  The USB and LSB for each modulating frequency are mirror images on either side of the carrier frequency. No, the plot of the frequency spectrum is not symmetrical due to the crowding for \left ( \omega <\omega _c \right ) the present in the spectrum

iii) Each modulating signal adds a pair of sidebands, increasing the bandwidth requirement. If too many signals are modulated, sidebands can overlap, leading to intermodulation distortion. Closely spaced modulating frequencies can cause crosstalk, where information from one signal interferes with another.

The probability of mixing of signals is very high due to the crowding at \left ( \omega <\omega _c \right )

iv) Use filters to confine each modulating signal to its designated frequency band, preventing sideband overlap. Allocate specific frequency ranges for different modulating signals (frequency-division multiplexing). An easy way to accommodate more signals would be to increase the bandwidth and frequency of the carrier waves.

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