I hope, you are doing well. I want to ask question about baseband conversion.

Background:

• I generated two AM signals in MATLAB, which one of them is shifted in time.
• I multiply the signals with $$\cos(2\pi f_c t)$$ in order to obtain IF signal.
• I filtered the IF signals with $$f_c$$ cut-off frequency.

In this way, I aim to downconverted to signal to baseband.

My problem is, when I try to cross-correlated the baseband signals, my result peaks at zero.

I expect to see the delay, but I could not. Am I missing something?

Notes: I am exact sure, my cross-correlation function works perfectly. I tried this function before baseband process. Also, in order to obtain both I and Q components, I try to multiply my signals with sin(2pifc*t). Nothing changes. MessageSignal: Audio Signal.

If you mix up to $$f_c$$, but then use a filter with cut-off frequency of $$f_c$$, you're not downconverting your signal to baseband at all. You're just cutting off half the signal.