Power Efficiency of Amplitude Modulation

modulation parameters

µ

0.8

f

c

(hz)

7000

f

m

(hz)

500

modulated carrier plot options

show carrier

show message

This Demonstration illustrates the effect of changing the modulation factor

μ

(also called the modulation depth) on the power efficiency of ordinary amplitude modulation (AM) technique. A modulation factor

μ

greater than 1 results in envelope distortion, causing difficulties during demodulation. Hence

μ

must be kept less than 1.

At 100% modulation (

μ=1)

, the power efficiency of AM is 33.33%, that is, the total power carried by the sidebands is 1/3 of the total power. The middle graph shows the modulated carrier

s(t)=(1+μm(t))cos(2π

f

c

t)

, where

m(t)=cos(2tπ

f

m

)

is the message signal and

μ

is the modulation factor. For simplicity, the amplitude of the carrier signal and the amplitude of the message signal are both kept equal to 1.