For models operating in the linear range, the input amplitude A 1 in y(t) must be larger
than the amplitudes of other harmonics, A 2 and A 3.
u(t) =A 1 sin(ω 1 +φ 1 )
y(t) =A 1 sin(ω 1 +φ 1 )+A 2 sin(ω 2 +φ 2 )+A 3 sin(ω 3 +φ 3 )+...How Do I Fix It?
Adjust the amplitude of your input signal to decrease the impact of other harmonics, and
repeat the estimation. Typically, you should decrease the input amplitude level to keep
the model operating in the linear range.
For more information about modifying signal amplitudes, see one of the following:
Troubleshooting Frequency Response Estimation