[LabVIEW]The Analysis of Amplitude Modulation

Introduction:

In this lab, I have learnt the basic concepts and steps of AM. At the same time, I understand deeply the difference between envelope detection and coherent detection by construct the LabVIEW program. After complete the tasks which were required by Lab, I start to try to output the shape of the envelope and use Hilbert transform to compute the envelope directly. 

Lab results & Analysis:

1. The principle of amplitude modulation and demodulation:

Modulation is actually the shift of the spectrum (so the simplest implementation is based on signal multiplication), while demodulation is the opposite (so the simplest is still signal multiplication). However, in the shift process, because of the characteristics of signal multiplication, the intermodulation spectrum is generated, so the unfavorable frequency need to be filtered out.

1. Amplitude modulation:

Let the modulating signal be,

m(t)=Amcos(2πfmt)

and the carrier signal be,

c(t)=Accos(2πfct)

Where,

Am and Ac are the amplitude of the modulating signal and the carrier signal respectively.

fm and fc are the frequency of the modulating signal and the carrier signal respectively.

Then, the equation of Amplitude Modulated wave will be

s(t)=[Ac+Amcos(2πfmt)]cos(2πfct)s(t)

 

1. Amplitude demodulation:

1. Envelope detector is used to detect (demodulate) high level AM wave. Following is the block diagram of the envelope detector.

1. Coherent demodulation

P(t) = s(t) cos(2πfct)

   Then we can let the signal p(t) p