The antenna current of an AM broadcast transmitter, modulated to a depth of 40% by an audio sine wave is 11 A. It increases to 12 A as result of simultaneous modulation by another audio sine wave. What is the modulation index due to this second wave? -

Mumbai University > Computer Engineering > Sem 3 > Electronic Circuits and Communication Fundamentals

Marks: 10 Marks

Year: May 2014

We know that

$$I_t=I_c(1+m^2/2)^{1/2} \\ I_c=I_t(1+m^2/2)^{1/2} \\ =11/(1+(0.4)^2/2^{1/2} \\11/(1+0.08)^{1/2} \\ Ic=10.58Amp$$

Mt=Total modulation index

$$Mt=\{[It/Ic]^2-1\}^{1/2} \\ =0.757 \\ \\ M^2=M_t^2-M_1^2 \\ =(0.423)^{1/2}$$

M=0.643=Modulation Index due to second wave