Fundamentals of Communication Systems ECOM 360  Spring 2017  Dr. Atef Abdrabou
Mini Project
Determining the Bandwidths of for Gated Modulator & Synchronous Demodulator Filters
1- Purpose
The purpose of this project is to get familiar with the design of the Gated modulator and synchronous
demodulators for DSB-SC signals.
2- Given Signals and Parameters
Your information signal is a square wave with a fundamental frequency = 100 rad/sec. The switching
signal has a fundamental frequency of 10,000 rad/sec. The center frequency of the BPF is set to 10,000
rad/sec. The carrier frequency at the receiver is set to 10,000 rad/sec.
3- Requirements
(a)  Find the correct bandwidths for the BPF at the transmitter side (the modulator) and the LPF at
the receiver side (the demodulator) by trial and error. This can be done by changing the pass
band of the both filters until the received signal looks very close to the information signal.
(b)  Explain by doing the necessary calculations why the bandwidth you get in part (a) is sufficient to
make the received signal looks very close to the information signal.
(c)  Change the center frequency of the BPF to 30,000 rad/sec and the receiver carrier frequency
accordingly without changing any bandwidth and explain if there are any changes in the output
signal.
(d)  Can we replace the Carrier Rx block by a Switching Signal? Explain and do this change then
observe the output.
3- Deliverables
1-  A project report that contains your answers to (a), (b), and (c) above.
Please Note:
Fundamentals of Communication Systems ECOM 360  Spring 2017  Dr. Atef Abdrabou
1-  When you double click any block, it will give you the parameters of the block. Do not change any
other parameters that are not required to be changed.
2-  The project is implemented in Matlab Simulink, which does not need any previous knowledge of
Matlab coding.
3-  In order to observe the information or received signal, it is better to wait for the simulation to
stop.
4-  The project Simulink file is posted on the Blackboard.
5-  Copying the report from other students will lead to a deduction of 50% of your project grade.

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