How can i get frequency of the modulated signal

[question]

All my questions are showed in the picture.

[Jim_Kring]

Answer: By demodulating it.

That was easy, now let's try a multiple choice question:

Will you get in trouble for (A) cheating on your homework, or (B) infringing on your text-book's copyright by scanning it's artwork and posting it to the Internet?

Take a guess, it's a 50-50 shot!

[question]

Sorry,I don't know how to demodulate it.
It is one of my friends'question.He knows I am using Labview,He want to know whether Labview can demodulate the signal easily or not and how? Is there any example show me how to do in NI's website?
thanks!

[Jim_Kring]

"Well, since it is for a "friend"...

An FFT (or Power Spectrum) will tell you all of the fundamental frequencies of your signal. This is pretty easy and there are functions in LabVIEW to do this. However, since you are only trying to determine the frequency of one square wave mixed with many sine waves, you can just look at the first dirivitive of the signal (dS/dt) and look for discontinuities (dS/dt = +/- Inf). This discontinuity is only due to the square wave signal component. Find the frequency of the discontinuities of the first dirivitive and you have your answer.


-Jim"