Modulation index

The modulation index (or modulation depth) of a modulation scheme describes by how much the modulated variable of the carrier signal varies around its unmodulated level. It is defined differently in each modulation scheme. See:

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if we visualize that some distortion will occur if Em > Ec.

                 the relationship between ampls. of m(t) and c(t) is known as modulation co-officent or degree of modulation.

m=Em/Ec it should be always <1