Question

What is the modulation index of an AM signal if the peak voltage goes from Emax to Emin?

(a) \(\frac{E_{min}}{E_{max}}\)

(b) \(\frac{E_{max}}{E_{min}}\)

(c) \(\frac{E_{max} – E_{min}}{E_{max} + E_{min}}\)

(d) \(\frac{E_{max} + E_{min}}{E_{max} – E_{min}}\)

This question was addressed to me during a job interview.

My query is from Spectrum of AM SC Waves in section Side Band Techniques of Analog Communications

Answer 1

Correct answer is (c) \(\frac{E_{max} – E_{min}}{E_{max} + E_{min}}\)

Best explanation: Modulation index tells us the amount by which the carrier wave is varied with respect to the message signal. It is defined as \(\frac{E_{max} – E_{min}}{E_{max} + E_{min}}\) where Emax and Emin are respectively the maximum and minimum voltage of the modulated wave.