Electronic – Amplitude Modulation Concepts

MATLABModulation

I am currently learning about telecommunications but I have some concept issues.

Firstly, does it matter if I am using cosine or sine in the equation? I understand that they are basically the same thing but there is a phase shift difference between them. Should I account for that phase shift?

For instance if I am making a computer program (matlab) that is going to generate an amplitude modulated signal, should I use cosine or sine?

My equation for the program is as follows:

output = amplitude * (1 + depth * cos(2 * pi * modu * (i / exp_rate)));

Where:

  • modu is the modulating frequency
  • exp_rate is the carrier frequency
  • i is the ith pulse
  • depth is the depth I want in the modulated frequency

Is it correct?

Note: I am trying to apply amplitude modulation to a train of biphasic pulses. So in the end it should be a train of biphasic pulses going up and down periodically. The amplitude of the ith pulse will follow the modulation waveform and there is no carrier term.

Best Answer

I don't understand I in your formula.

Normally (traditionally) AM is: -

y(t) = [A + M cos(ωm t + φ)] . sin(ωc t)

where

  • y(t) is the final modulated signal
  • M is the amplitude of the modulating cosine (or sine to answer your question)
  • A is the amplitude of the carrier sine (or cosine to reinforce the answer!!)
  • φ is the phase displacement of the modulating sinewave but is irrelevant all but mathematically
  • ωm and ωc are the frequencies of modulation and carrier.

Maybe I just don't recognize your formula but the answer is, like Jim Dearden implies swap them up or use the same because carrier and modulator are not going to be the same frequency when dealing with AM.

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