NGR. CHARMAINE C. PAGLINAWAN
ECEA111L
Activity 5: DOUBLE-SIDEBAND SUPPRESSED CARRIER (DSB-SC)
AMPLITUDE MODULATION IN SIMULINK
Required: Simulink File
Data Sheet with Results and Answers to Questions
Proof of Activity Performance
Objectives:
1. To be able create a block diagram of a DSB-FC.
2. To be able to create a filter using Simulink transfer function block.
3. To be able to show the DSB-SC signals for different modulation index.
Introduction:
A conventional amplitude modulated signal contains the carrier signal and the
sideband frequencies. By expanding the expression for the amplitude modulated signal of a
single frequency modulated signal
𝐴(𝑡) = 𝑉𝑐 [1 + 𝑚𝑖 sin(2𝜋 𝑓𝑚 𝑡)] sin(2𝜋 𝑓𝑐 𝑡)
𝐴(𝑡) = 𝑉𝑐 sin(2𝜋 𝑓𝑐 𝑡) + 𝑉𝑐 𝑚𝑖 sin(2𝜋 𝑓𝑚 𝑡) × sin(2𝜋 𝑓𝑐 𝑡).
The second term can be simplified using the trigonometric identity,
1
1
sin 𝐴 × 𝑠𝑖𝑛 𝐵 = 𝑐𝑜𝑠(𝐴 − 𝐵) − 𝑐𝑜𝑠 (𝐴 + 𝐵)
2
2
resulting to,
𝑉
𝑉
𝐴(𝑡) = 𝑉𝑐 sin(2𝜋 𝑓𝑐 𝑡) + 2𝑚 sin[2𝜋 (𝑓𝑐 − 𝑓𝑚 )𝑡] − 2𝑚 sin[2𝜋 (𝑓𝑐 + 𝑓𝑚 )𝑡].
The frequency spectrum of the amplitude modulation of a single sinusoid contains
three distinct frequencies, the carrier frequency, the lower sideband frequency and the upper
sideband frequency.
Fig. 1 Frequency spectrum of a DSB-FC Amplitude Modulation
To reduce the power needed to transmit the signal, the magnitude of the carrier
signal or one of the sidebands can be reduced or suppressed totally. Without the carrier or
one of the sidebands, the modulating signal can still be recovered/demodulated at the receiver
side. The AM signal with suppressed carrier is called Double-Sideband, Suppressed
Carrier (DSB-SC).
To suppress the carrier frequency prior to transmission, we can apply the
DSB-FC signal to a bandstop filter centered at the carrier frequency.
Created by: Jesus Martinez
Date Modified: June 9, 2021
NGR. CHARMAINE C. PAGLINAWAN
ECEA111L
Fig. 2 Conversion of a DSB-FC to a DSB-SC using a bandstop filter
Created by: Jesus Martinez
Date Modified: June 9, 2021
NGR. CHARMAINE C. PAGLINAWAN
ECEA111L
Procedure:
1. Create the block diagram shown below on a New Blank Model.
2. Change the Block Names.
3. Click on each of the block and set the following parameters.
Sine Wave (Modulating Signal):
Sine Type:
Time (t):
Amplitude:
Bias:
Frequency (rad/sec)
Phase (rad):
Sample Time:
Time based
Use simulation time
1
0
2*pi*200
0
0
Sine Wave (Carrier Signal):
Sine Type:
Time (t):
Amplitude:
Bias:
Frequency (rad/sec)
Phase (rad):
Sample Time:
Created by: Jesus Martinez
Time based
Use simulation time
1
0
2*pi*10000
0
0
Date Modified: June 9, 2021
NGR. CHARMAINE C. PAGLINAWAN
ECEA111L
Constant (Modulation Index):
Constant Value:
0.5
Transfer Function (Bandstop Filter):
Numerator Coefficients:
Denominator Coefficients
[1 0 3.95e+09]
[1 1257 3.95e+09]
4. Set the Stop Time to 0.1 second and then Run the simulation.
5. Double click on the scope DSB-FC. Maximize the scope window.
6. Using the mouse scroll wheel, zoom out on the y-axis using the Zoom Y button until
you reach the limit.
7. Using the Zoom X icon, zoom in until the graph shows about three periods of the
envelope.
8. Double click on the scope DSB-SC. Maximize the scope window.
9. Using Zoom X and Zoom Y commands, adjust the viewing options until the graph
shows a similar waveform shown below.
Created by: Jesus Martinez
Date Modified: June 9, 2021
NGR. CHARMAINE C. PAGLINAWAN
ECEA111L
10. Copy the figures (Ctrl+C) and paste it inside the boxes.
DSB-FC (𝑚𝑖 = 0.5)
Created by: Jesus Martinez
Date Modified: June 9, 2021
NGR. CHARMAINE C. PAGLINAWAN
ECEA111L
DSB-SC (𝑚𝑖 = 0.5)
11. Change the modulation index to 0.25, 0.75, and 1.00.
12. Repeat (10) for modulation indices of 0.25, 0.75, and 1.00. Paste the waveforms and
properly label them below.
DSB-FC (𝑚𝑖 = 0.25)
Created by: Jesus Martinez
Date Modified: June 9, 2021
NGR. CHARMAINE C. PAGLINAWAN
ECEA111L
DSB-SC (𝑚𝑖 = 0.25)
DSB-FC (𝑚𝑖 = 0.75)
Created by: Jesus Martinez
Date Modified: June 9, 2021
NGR. CHARMAINE C. PAGLINAWAN
ECEA111L
DSB-SC (𝑚𝑖 = 0.75)
DSB-FC (𝑚𝑖 = 1.00)
Created by: Jesus Martinez
Date Modified: June 9, 2021
NGR. CHARMAINE C. PAGLINAWAN
ECEA111L
DSB-SC (𝑚𝑖 = 1.00)
13. Measure the peak-to-peak values for each modulation index. Tabulate your
measurements.
Modulation Index
0.25
0.50
0.75
1.00
Peak-to-Peak
-1.25 to 1.25
-1.50 to 1.50
-1.75 to 1.75
-2 to 2
14. Write all your answers on this .docx file and then save as .pdf. This will serve as
your Data sheet/Activity Results.
15. Save Simulink file and video file for validation. Separate files in Google drive by
Folder or by activity.
Created by: Jesus Martinez
Date Modified: June 9, 2021
NGR. CHARMAINE C. PAGLINAWAN
ECEA111L
INTERPRETATION OF RESULTS
This experiment has told us to build a circuit regarding the DoubleSideband Suppressed Carrier. And for this circuit it is like the third activity
and with the additional transfer function and a scope. And from observing
the results of the graphs for the DSB-FC its peak to peak is just 1 plus the
modulating index for example the 0.5 modulating index has a peak to peak
of -1.5 to 1.5 and the 0.25 also has the same pattern which is -1.25 to 1.25.
The rest also has the same pattern this just proves that DSB-FC does not have
any effect it only adds 1 in each modulating index value. Meanwhile for
the DSB-SC it all kind of the different but the order of it is all ascending from
the lowest modulating index to the highest value. The 0.25 has a DSB-SC of
0.225 while the 0.5 has 0.45, and the 0.75 has 0.65, and finally the 1
modulating index has a DSB-SC of 0.9. And from the observation of me the
values of the DSB-SB values have been near the modulating index with the
slightly difference. These are the results of the circuits and the interpretation
of the results.
Created by: Jesus Martinez
Date Modified: June 9, 2021
NGR. CHARMAINE C. PAGLINAWAN
ECEA111L
CONCLUSION
In conclusion of all the data, the circuits have been executed properly
with the help of the guides in the activity. And the each of the data has
been presented and interpreted above. All the interpretation has been
based on the observation with the results. The goal of the study also has
been done by creating the block diagram, also creating a transfer
function, and showing it with the DSB-SC signals in different modulating
index. The results of the DSB-SC signals have been also shown in the activity
not just that also the DSB-FC has been also shown. And with all the
objectives has been done, we have ensured that our activity has been
done and executed properly by the researcher.
Created by: Jesus Martinez
Date Modified: June 9, 2021