EEE30004 Digital Signal Processing
Lab 2: Spectrograms of AM and FM Signals
Name : Barry Belian
ID Number : 100078049
Lab Group : Friday 10:30
... [Show More] a.m.
Lab Date : 5
th of October 2018
Lab Demonstrator : Mr. Ling Ting Soon
Contents
Objective...............................................................................................................................................3
Pre-Lab..................................................................................................................................................3
Beat Control GUI................................................................................................................................3
MATLAB Synthesis of Chirp Signals....................................................................................................4
Spectrogram of an FM Signal: Sinusoidal Modulation.......................................................................7
Lab Exercise...........................................................................................................................................9
2.1 Beat Notes and Frequency Resolution.........................................................................................9
Beat Note Spectrogram.................................................................................................................9
Inverse Relationship: Section Length vs. Frequency Resolution...................................................11
Comments...................................................................................................................................11
2.2 Spectrogram for a Chirp with Negative Instantaneous Frequency.............................................12
Section Length in Chirp Spectrogram...........................................................................................12
Comments...................................................................................................................................13
Lab Homework: Matching Unknown Spectrograms.............................................................................13
Conclusion...........................................................................................................................................14
P a g e 2 | 16
Objective
Lab 2 studies signal synthesis for amplitude modulation (AM) and frequency modulation (FM) signals,
and their time-frequency content as shown in spectrogram. An underlying objective of the lab is to
learn more about the spectrogram. there are several specific steps that will be considered in this lab:
1. Synthesize a beat-note signal with a MATLAB M-file and display its spectrogram.
2. Study the frequency resolution of the spectrogram for two closely spaced sinusoids.
3. Spectrogram: Male empirical observations of the spectrogram as the section length is
changed.
4. Synthesize a linear-FM chirp with a MATLAB M-file and display its spectrogram.
5. Spectrogram: Create a spectrogram that displays negative frequencies, as well as positive
ones.
6. Synthesize a frequency-modulated (FM) signal to match a given spectrogram. i.e, match
specific time-frequency spectral content.
Pre-Lab
Beat Control GUI
A basic signal shapes for beat signals can be created using the ‘beatcon’ which is MATLAB GUI tool. It
is a part of the DSP-First Toolbox. Elements of the signal can be edited in the user interface. The tool
can be invoked by typing “beatcon” in the command prompt of MATLAB.
Figure 1: Beat signal with 690 Hz
The beat signal was created using the beatcon which has a user interface to allow users to input data
easily. The above signal was created using a 690 Hz centre frequency. The signal below is created
using 700 Hz centre frequency. [Show Less]