Introduction to Simulink & Double Sideband
Modulation/Demodulation
Bibek Karki
EE 2170
Lab #6
Introduction:
The goal of this section of the lab is to introduce the concept of Simulink and provide the handson experience of Simulink. Simulink is a tool for model-based design in which one can design a
system with continuous, discrete, or a combination of both characteristics. Another important
concept introduced in this lab was the process of Double sideband Modulation and
Demodulation.
Command platform for Simulink
There are 5 cycles of the square wave.
Period is 2 seconds.
In the above graph there are spikes in 50 Hz (i.e. fundamental frequency) and on respective
harmonics. But in the theoretical Fourier Transform magnitude for a sine wave, we only see one
spike at fundamental frequency.
The Fourier Transform magnitude computed with Simulink has values only in the positive Xaxis in comparision to the theoretical value which would have values in both positive and
negative X-axes.
When the sample time of the “power spectral density” plot is changed to 0.001 and re-run the
simulation, the graph gets magnified (zoomed in) in comparison to the previous.
The obtained graph is after the modulation of the signal, the graph is the magnitude of the
Fourier transform of the sine wave with respect to the frequency domain.
In the above graph, we got the square wave graph as we entered before the modulation and
demodulation process but with the top and bottom squares with rough edges. This happens
because some portion of wave is lost during the process as the modulation and demodulation
process not 100% perfect.
MATLAB codes.
B=[1]
B=
1
>> A = [1/500^2 , sqrt(2)/500 , 1]
A = 0.0000
0.0028
1.0000
>> freqs(B,A)
The filter is low-pass filter because it passes all signals having frequency less frequency
(multiplies all signals with lower frequency by 10^0 i.e. 1) as shown in the magnitude graph
above.
Conclusion:
The main purpose of the lab was to gain an understanding of the Simulink and perform
modulation/demodulation in the Simulink in MATLAB which was done well by implementing
the given assignment using Simulink. Square sine wave was used to simulate and verify the
concept of modulation and demodulation. The concept of Fourier transform was used along with
various graphing techniques to obtain the desired output.