Electrical Communications Systems

Course No. 0909-331-01

Spring 2005 

Laboratory Project 1

Waveform Synthesis and Spectral Analysis

Objectives

This project has 4 parts. In Part 1, you will:

In Part 2, you will study the differences between the Continuous Fourier Transform (CFT) and the Discrete Fourier Transform (DFT) (this is homework!). In Part 3, you will synthesize AM and FM bandpass signals and analyze their spectra. In Part 4, you will capture and analyze the spectra of:

Equipment and Software Part 1: Digital synthesis of arbitrary waveforms with specified SNR

Background
 
  • SNR in dB = 10 log10 (ss2/sn2); where ss2:signal variance, sn2: noise variance
  • Given signal, s(t), find ss2
  • Compute required sn2
  • Generate noise signal, n(t) = snN(0,1), where N(0,1) is a Normally (Gaussian) distributed random variable with Zero mean and Unit variance
  • Message signal with desired SNR, m(t) = s(t) + n(t)

Procedure Overview

Example Matlab Code
 
%ECOMMS Lab Project 1 Example Spring 02
%S. Mandayam, Rowan University
%This program generates a 2-second duration 
%Asharp signal (466.16 Hz) with a specified SNR

%Specify SNR
snr=10;

%Generate Asharp signal
t=[0:1/8e3:2.0]';
s = 0.5*sin(2*pi*466.16*t); 
sound(s);
wavwrite(s, 'asharp.wav');
save asharp.csv -ascii s;

%Compute signal variance
var_s = cov(s);

%Calculate required noise variance
var_noise=var_s/(10^(snr/10));

%Generate noise
n=sqrt(var_noise)*randn(length(s),1);
sound(n);

%Add signal to noise and generate message
m=s+n;
sound(m);
wavwrite(m,'asharp_noise.wav');
save asharp_noise.csv -ascii m;

Part 2: Comparison between CFT and DFT (FFT)
(Uses Matlab only) (This is Homework!)

Consider the signal shown in Figure 1:

Figure 1: Time-domain signal


Part 3: Spectral Analysis of AM and FM Signals
 (Uses Matlab, Oscilloscope, Function Generator and Spectrum Analyzer)

Part 4 (a): Spectral Analysis of Composite NTSC Baseband Signal
(Uses Matlab, Oscilloscope, VCR,  and  Spectrum Analyzer/FFT Module)

Figure 2 shows a composite NTSC baseband video signal.

Figure 2: Composite baseband NTSC video signal

Part 4 (b): Spectral Analysis of ECG Signal
 (Uses Matlab, Oscilloscope, ECG Electrodes, Antiseptic Prep Pads, Isolated Power Supply/ 9 V DC batteries, 10-X Scope-Probe and  Spectrum Analyzer/FFT Module)
 
NOTE: READ THIS FIRST!!!!!!!!!!!
This experiment must be conducted with the instructor present at all times when you are obtaining the ECG readings. The procedure that has been outlined below has been determined to be safe for this laboratory. You must use an isolated power supply for powering the instrumentation amplifier. You must use a 10-X scope probe for recording the amplifier output on the oscilloscope. This objective of this experiment is compute the amplitude-frequency spectrum of real data - this experiment does not represent a true medical study; reading an ECG effectively takes considerable medical training. Therefore, do not be alarmed if your data appears"different" from those of your partners. Also, if you observe any allergic reactions when you attach the electrodes (burning sensation, discomfort), remove them and rinse the area with water. Finally, if, for any reason, you do not want to participate in this experiment, obtain  recorded ECG data from your instructor.

Figure 3: Components of a typical ECG signal



Figure 4: Experimental set-up for taking ECG measurements.


Click here for required lab project report format.

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References:


 
 
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