Bode diagram of poor input/output signal

Hello,

I have an input signal u and an output signal y. The frequency range of the system on which I want to focus is 0-5 Hz.

Let's assume that my input signal u is a sinusoidal excitation but only at two frequencies: 1 and 2 Hz. After having filtered my signal to remove measurement noise, I can plot the Bode diagram thanks to the functions iddata and spa. I will than obtain a Bode Diagramm for the frequencies 0-5 Hz. But as the input signal only contains ~2 different frequencies, how does Matlab proceed to plot the Bode diagram for the other frequencies? I think that the result must be wrong for the frequencies not contained in the input signal.

In this case, I don't want to plot a continous Bode diagramm but a discrete Bode diagram only containing the system response for the frequencies which actually are in the input signal.

Is that possible ? Thank you and good evening.

Answer 1

[Rajiv Singh]

bode(sys,[w1 w2],'.'), where w1 and w2 are your two input frequencies and sys is the identified model.