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CCIT4076: Introduction to Engineering
Laboratory 4: Demodulating Radio Signals
In this laboratory we are going to demodulate an audio signal on Octave. You are given with
an audio file radio signal.wav, which is a modulated radio signal in coherence to what I showed
back in the very first lecture. You are also given with the following functions:
1. IE spectrum(x, fs). This is an Octave function written to visualise the frequency spectrum
of an audio signal x, whose sampling frequency is fs. Note that we do not have an output
argument here.
2. y = IE Filter(x, fs, fl, fh). This is the same function given in Lab 2 when we had
our first attempt on filtering. The only difference is that it no longer automatically visualises
the plot of the spectrum of the filtered y. You may view that by using IE spectrum instead.
3. y = IE ProdMod(x, fs, fc). This is a product modulator that returns an output of
y(t) = x(t) · cos(2pifct)
where fc is assumed to be smaller than half of the sampling frequency.
Your task is to retain as much information from the given file as possible. Good luck and enjoy!
