Modulation Index Calculator

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Amplitude modulation varies the carrier amplitude; frequency modulation varies the carrier frequency; phase modulation varies the carrier phase.
Use signal amplitudes if you know the message and carrier peak amplitudes separately. Use envelope peaks if you measured the modulated waveform directly.
Peak amplitude of the modulating (message) signal in volts.
V
Peak amplitude of the unmodulated carrier signal in volts.
V
The highest peak of the AM waveform envelope.
V
The lowest trough of the AM waveform envelope (must be >= 0).
V
Power of the unmodulated carrier. Used to compute total transmitted power and sideband power.
W
Frequency of the carrier wave in hertz.
Hz
Frequency of the modulating (message) signal in hertz.
Hz
Modulation indexUnder-modulated
0.6

Dimensionless ratio expressing the depth of modulation

Modulation depth60%%
Signal bandwidth10,000Hz
Total transmitted power118W
Sideband power (each)9W
Upper sideband (USB)1,005,000Hz
Lower sideband (LSB)995,000Hz
Power efficiency15.3%
Modulation statusUnder-modulated (m < 1): valid, no distortion
0.6 m
Low<0.5Optimal0.5-1Over1-1.5Severe1.5+

Modulation index: 0.6000 (60.0% depth)

  • Your AM modulation depth is 60.0%. A depth of 100% (index = 1.0) maximises sideband power without distortion.
  • Only 15.3% of total transmitted power is in the sidebands (the useful signal). The rest is carrier power, which conveys no information.

Next stepTo improve power efficiency, consider switching to single-sideband (SSB) or double-sideband suppressed-carrier (DSB-SC) modulation, which eliminate the wasted carrier power.

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