Maximum voltage of an AM wave: Vmax Minimum voltage of an AM wave: V‌min ‌ Amplitude of the modulating signal is calculated as: Am=‌
Vmax−Vmin
2
Amplitude of the carrier signal is calculated as: AC=‌
Vmax+Vmin
2
The modulation index or modulation factor m is defined as the ratio of the amplitude of the modulating signal to the amplitude of the carrier signal: m=‌
Am
AC
Substituting the expressions for Am and AC, the modulation index becomes: m=‌