ELEC 470, Spring 2001
Prof. Rich Kozick

Homework 7

Date Assigned: Thursday, March 1, 2001
Date Due: Tuesday, March 6 and Thursday, March 8, 2001

  1. Exam 1: Our mid-term exam was scheduled for Tuesday, March 6. We will change the exam date to Tuesday, March 27.

  2. Reading: Please read Chapter 4 in Lathi, Sections 4.1 through 4.9.

  3. Special Topic Reports: Recall from the course syllabus the "special topic reports" that students will investigate individually or in pairs and present to the class. Some possible topics for special topic reports are available at

    By March 6, please send me an email note with your topic and partner (if any). Also, specify a week in which you prefer to present: March 19, 26, or April 2, 9, 16, 23. Feel free to see me if you have questions.

  4. I have installed an interactive tutorial on amplitude modulation on the PCs in Dana 120B. The tutorial was created by Hewlett-Packard. You can find it at the following path from the Start menu:

    Programs -> Programs A-M -> Fundamentals -> AM Fundamentals -> AM Fundamentals

    Please go through these lessons before class on March 6. They include questions and animations that may help you to visualize AM concepts.

    Try to answer the following question as you study these lessons: What are the advantages and disadvantages of single sideband (SSB) modulation compared with other methods of AM? (You do not have to submit a written answer to this question.)

  5. Problems: Please solve the following problems in the Lathi text and submit your solutions on March 8.
    All students: 4.4-1, 4.5-1 (part a only), 4.5-2 (part a only).
    Graduate students: 4.5-5
    Appendix D.6 contains trigonometric identities that you might find useful.

  6. Please answer the following questions related to the Simulink programs am_env.mdl, am_env_filt.mdl, dsb_coh.mdl, costas_init.m, and costas_demo.mdl, which are available from the course home page under Demonstrations and Class Notes. Instructions for running the programs are given on the Web page.

    1. In the AM demo am_env.mdl, what are the considerations in choosing the value of the "slider gain"?
    2. In the DSB-SC demo dsb_coh.mdl, investigate the effect of a phase shift between the transmitter and receiver oscillator. Relate your observations to the analysis in problem 4.4-1.
    3. In the DSB-SC demo dsb_coh.mdl, investigate the effects of a frequency error between the transmitter and receiver oscillator. Relate your observations to the analysis in problem 4.4-1.
    4. In the DSB-SC demodulator using a Costas phase-locked loop in program costas_demo.mdl, what is the effect of the "Slider Gain" that amplifies the signal prior to being input to the VCO? What happens if this gain is too small? What happens if this gain is too large? Consider the filter that immediately precedes the Slider Gain: what signal is this filter designed to remove? Recall that in this program, you can change the phase in the "TX Carrier" to cause the Costas loop to hunt for a new phase-lock.

    Please submit answers to questions 1, 2, and 3 on March 8. You do not have to answer question 4 at this time.

  7. Graduate Students: (extra credit for undergraduates!)

    Develop a Simulink program that modulates two separate messages m1(t) and m2(t) onto a single carrier frequency using quadrature amplitude modulation (QAM) as described in Section 4.4 of the Lathi text. For example, you might make m1(t) and m2(t) sine waves with different frequencies. Demonstrate the effects of frequency and phase errors on the demodulated signals, and explain your results analytically based on problem 4.4-1.

Thank you.