Electrical
Communications Systems
Course No. ECE.09.433
Laboratory
Project 3
Frequency Modulation and Detection
Objectives
This project has 2 parts. In Part 1, you will investigate the performance of the slope detector. In Part 2, you will model an FM communications systems using the Matlab Simulink Communications Systems Toolbox.
In both parts, you will test the system with single-tone FM (w and w/o added Gaussian noise).
Equipment
and Software
·
You
will be synthesizing waveforms in Matlab and creating
their corresponding electrical signals using the Arbitrary Waveform Generator.
In order to do this, you will need the Keysight IO
Libraries Suite.
Instructions have been created by Yang Qi with sample Matlab code.
·
You
will be capturing signals from the Oscilloscope/Spectrum Analyzer and will be
analyzing them in Matlab.
·
You
will use electronic components to breadboard the slope detector circuit.
·
You
will use Matlab Simulink Communications Systems
Toolbox to model an FM communications system.
Project Requirements
Part 1
- Design the slope detector circuit shown in Figure 1.
The slope detector is nothing but a frequency-to-voltage converter
followed by an AM envelope detector.The design
equation for the frequency-to-amplitude converter is fco1 = 1/(2piR1C1) where fco1
is the cut-off frequency of the low-pass filter R1C1
. fco1 is chosen to be at the carrier
frequency of the FM signal. The design equation for the envelope detector
circuit is similar and was provided in Lab Project 2.
As before, C3 is a coupling capacitor, chosen such that C3
>> C2 . As part of your
initial design parameters, you can choose an FM carrier frequency of 30kHz and a maximum modulating frequency of 15 KHz to
design your circuit.
Figure 1: Slope detector circuit.
- Using the HP Arb. Function Generator, generate an FM
wave with carrier frequency of 30 kHz and
modulation frequency 1 kHz (single tone).
- Vary the frequency
deviation and observe the input and output waveforms.
- Vary the modulating
frequency and observe the input and output waveforms.
- Determine the range of performance
of the slope detector, in terms of modulation frequency and modulation
index.
- Digitally capture
samples of the input and output waveforms in this range
- Perform a spectral
analysis of these input and output waveforms.
- Listen to the output
signal using the PC speakers. Compare with the pure tone of the same
frequency.
- Repeat the experiment by digitally synthesizing FM
signals with varying SNR. Figure 2 shows the overall block diagram for
this part of the lab project.
- At each stage, note your observations and conclusions.
Part
2: FM Communication System
The objective is to observe (in time and spectral domains) & listen as audio tones progresses along a modulation-demodulation system, both in the presence and absence of added Gaussian noise.
Develop a Matlab Simulink simulation of an FM system that includes a source, modulator, channel, demodulator and sink. Test the system with single-tone audio frequency message inputs. Note down observations in the time and spectral domains, and listen to the audio signals and the input and output.
Bonus: Demonstrate the Carrier-Null effect for the correct frequency-modulation indices.
Click here for required lab project report
format.