Question

(a) If A and B represent the maximum amplitudes of an amplitude modulated wave, wrigte the expression for the modulation index in terms of A and B.
(b) A message signal of frequency 20 kHz and peak voltage 10 V is used to modulate a carrier of frequency 2 MHz and peak voltage of 15 V. Calculate the modulation index. Why the modulation index is generally less than one ?

Answer 1

(a) Modilation Index
`mu=(A_("max")-A_("min"))/(A_("max")+A_("min"))" "mu=(A-B)/(A+B)`
(b) `mu=(A_(M))/(AC)=10/15=0.666=0.67`
Modulation index is generally kept less than one to avoid distortion.