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प्रश्न
Answer the following question.
If A and B represent the maximum and minimum amplitudes of an amplitude-modulated wave, write the expression for the modulation index in terms of A and B.
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उत्तर
Modulation index for an AM wave for which the maximum amplitude is 'a' while the minimum amplitude id 'b'.
Modulation index,
`a_m = (E_m)/(E_c)` ...(1)
The maximum amplitude of the modulated wave, a = Ec + Em ...(2)
The minimum amplitude of the modulated wave, b = Ec - Em ....(3)
From the above equations,
`E_c = (a + b)/2 , E_m = (a - b)/2`
From Equation 1 we get,
Thus, the modulation index is `a_m = E_m/E_c = (((a - b))/2)/(((a + b))/2) = ((a - b))/((a + b))`.
संबंधित प्रश्न
Explain any two factors that justify the need of modulating a low-frequency signal.
The frequencies of two side bands in an AM wave are 640 kHz and 660 kHz respectively. Find the frequencies of carrier and modulating signal. What is the bandwidth required for amplitude modulation?
Write three important factors which justify the need of modulating a message signal. Show diagrammatically how an amplitude modulated wave is obtained when a modulating signal is superimposed on a carrier wave.
What is meant by term ‘modulation’? Draw a block diagram of a simple modulator for obtaining an AM signal.
Why is frequency modulation preferred over amplitude modulation for transmission of music?
Define amplitude modulation in a communication system.
In amplitude modulation, the modulation index m, is kept less than or equal to 1 because ______.
- m > 1, will result in interference between carrier frequency and message frequency, resulting into distortion.
- m > 1 will result in overlapping of both side bands resulting into loss of information.
- m > 1 will result in change in phase between carrier signal and message signal.
- m > 1 indicates amplitude of message signal greater than amplitude of carrier signal resulting into distortion.
The maximum amplitude of an A.M. wave is found to be 15 V while its minimum amplitude is found to be 3 V. What is the modulation index?
An amplitude modulated wave is as shown in figure. Calculate
- the percentage modulation
- peak carrier voltage and
- peak value of information voltage.
The maximum and minimum voltage of an amplitude modulated signal are 60 V and 20 V respectively. The percentage modulation index will be ______.
