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NCERT Class XII Chapter
Communication Systems
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Question : 7 of 8
Marks: +1, -0
For an amplitude modulated wave, the maximum amplitude is found to be 10 V while the minimum amplitude is found to be 2 V. Determine the modulation index, µ. What would be the value of µ if the minimum amplitude is zero volt?
Solution:  
We know
Modulation index, µ = AmAc\frac{A_m}{A_c}
Also, minimum amplitude, AminA_{min} = AcA_c (1− m)
Maximum amplitude, AmaxA_{max} = AcA_c (1+ m)
So, modulation index
µ = Amax−AminAmax+Amin\frac{A_{max}-A_{min}}{A_{max}+A_{min}}
or µ = 10−210+2\frac{10-2}{10+2} = 812\frac{8}{12} = 2/3 = 0.67
If AminA_{min} = 0, then modulation index,
µ = Amax−AminAmax+Amin\frac{A_{max}-A_{min}}{A_{max}+A_{min}} = 10−010+0\frac{10-0}{10+0} = 1010\frac{10}{10} = 1
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