hwk5_solns - ECE 300 Signals and Systems Homework 5 Due...

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Unformatted text preview: ECE 300 Signals and Systems Homework 5 Due Date: Tuesday October 9, 2007 at the beginning of class Problems: 1. Determine the complex Fourier series coefficients for the following periodic signals: a) x(t) = —1 + cos(2t) + 3 cos[4t + b) x(t) = 0052(21) (Hint: Use Euler’s identify) 0) x0)=200fl30+4sm[6hmgj 2. Find the Fourier series representation for the signal indicated using hand analysis. Clearly indicate the values of coo and the ck. Hints: (1) Draw the signal, and then use the sifting property to calculate the ck . (2) If you understand how to do this, there is very little work involved. xm=2flcw) p=—oo 3. For the periodic square wave x(t) with period To = 0.5 and 1 OSt<025 x0) -4 025$t<05 show that the Fourier series coefficients are given by :z—J—k odd ck: k7: 0 k even where x(t) = 2k ckejk4’" Fall 2007 . 4. Simplify each of the following into the form ck = a(k)e'jfl‘“sinc(/ik) ej7kfl _e—j2k7r 3) ck : . kn} e—j27rk _e—j57rk b) ck z . jk ej5k _ej2k C) Ck = k -1E tl+£ 2” ScrambledAnswers c =372'e I 2 sine 33—15 , c =3ej<2k 2)sinc % ,c =9e12k sine k—9— " 2 " 2n " 2 5. For the periodic signal shown below, with period T = 4 a) Determine the fundamental frequency (00. b) Determine the average value. 0) Determine the average power in the DC component of the signal. d) Determine an expression for the expansion coefficients, ck. You must write your expression in terms of the sine function, and possibly a leading phase term. Fall 2007 . 6. Assume x(t) has the spectrum shown below (all angles are multiples of 45 degrees): Amplitude and Phase Spectrum l l 1 _ _ _ _ _ ~ e _ _ _ _ _ _ . . ~..L—-—-_-}‘-‘_»_l_~—4—A~‘—A--l---‘~~ l g l I l l I m ‘ ' ‘ ‘ ‘ L ' ‘ ' ' ' “ ‘ ‘ ’ '4?”“‘§ ‘ ‘ ‘ ‘ “it ' ‘ ‘ ‘ ' ‘ ' ‘ ‘ “I"“" 3 i l g . i I ’ ’ ’ ’ ’ ’ ‘ ’ ’ ' ’ ’ “ “J” ’ ' ’ f ’i’ E z z l l < _ — _ — 2— e _ A A 1 7 _ ~ . . e . . — . ~-f_rv———§ — — — A —_¢+_~—--I--__V_ : E 1 -H--‘l. . . _ . _ _ _ _ _ _ _ P _ ‘ _ AA: _ _ A ‘ _..;y . A . v . _ . V v _ __|_..“_‘ I l E , l _ 7, a a .4; a We) 1 0 1 2 3 4 Index 200 I I «f. l l l I ‘5” l I 150 e e 7 , 77L 7 e 7 e ,4 r . 7 , r . . my , a e , ,1 7 , t e e iii 7 e 7 7 7 7 7 7 7 , t ,,I r 7 r , ,7 i i I l l A a j | I g: 100 ---------- "1 ~~~~ --------- --: ---- “l AAA g1 I l I I I o, 50 ~~~~~~~~~~ ~~g ———— "%"“‘r‘““‘: ~~~~ ~«3—————y———4» CD 5 I l ; I E 0» We J , a er '3- l I I l I -50 .7 L I}: r, I ,I, , l l l I g z | I I l l ’p i I .100 i L I, , i 4 3 -2 1 0 1 2 3 4 index . a) What is the average value ofx(t)? b) What is the average gower in x(t) ? 0) Write an expression for x(t) in terms of cosines (Assume (00 =1). Your expression must be real. Special Note: We will be using the code you write in the next part for the next few homeworks and labs, so be sure you do this and understand what is going on! 7. (Matlab/PreLab Problem) Read the Appendix and then do the following: a) Copy the file Trigonometric_Fourier_Series.m (you wrote this for homework 4) to file Complex_Fourier_Series.m. b) Modify Complex_Fourier_Series.m so it computes the average value ea 0) Modify Complex_Fourier_Series.m so it also computes ck for k =1 to k = N Fall 2007 d) Modify Complex_Fourier_Series.m so it also computes the Fourier series estimate using the formula N x(t) z CD + Z 2 l ck | cos(ka)at + lick) k:l You will probably need to use the Matlab functions abs and angle for this. e) Using the code you wrote in part d, find the complex Fourier series representation for the following functions (defined over a single period) fi0)=ah40 OSt<3 t OSZ<2 fxn= 3 23t<3 0 3St<4 0 —2$t<—1 1 —13t<2 ZSt<3 t : f3() 3 0 3St<4 These are the same functions you used for the trigonometric Fourier series. Use N = 10 and turn in your plots for each of these functions. Also, turn in your Matlab program for one of these. Note that the values of low and high will be different for each of these functions! Fall 2007 Appendix In the majority of this course we will be using the complex (or exponential) form of the Fourier series, since it is really easier to do various mathematical things with it once you get used to it. Exponential Fourier Series If x(t) is a periodic function with fundamental period T, then we can represent x(t) as a Fourier series 00 00 .k , x(t): E cke’ “’“’= E )(ke’W k——oo k=—ao where ma :2;— is the fundamental period, c0 is the average (or DC, i.e. zero frequency) value, and l T c0 = 51— 6[x(t)dt T ck :% Ix(t)e‘jkw"'dt 0 |fx(t) is a real function, then we have the relationships [ck |=i c_k | (the magnitude is even) and do, = —z(ck (the phase is odd). Using these relationships we can then write x(t) = c, + 2 2| c, lcos(ka)0t + ac, ) k~1 This is usually a much easier form to deal with, since it lends itself easily to thinking of a phasor representation of x(t). This will be particularly useful when we starting filtering periodic signals. Fall 2007 :4/ FE/ CK fifflié/flwéflu 7, 6/) W5) 5 4* “SK—2;“) fng/Vz‘r‘ CD 77:9) : QwS/gg) 7: 794/“, m a) W24) 7 ’/%wS‘/2é) + 3 MEI/yZQ—QB . . Q If ” .u J. 5% l “119 L )3 L ’ /"'(2€ +36 4’3 26, f >6 mfimxw gm 3;sz % 2 33$ 9: SEN Qwrfiwww wkmmmm aw Selma 50 SHEETS 22-142 100 SHEETS 23‘} $HEE§TS§ 22441 5E} SHEETS 22442 ‘IQO SHEETS 2M) 3HEETS 22441 «144 22 «657 . ‘ 6. Assume x(t) has the spectrum shown below (all angles are multiples of 45 degrees): Amplitude and Phase Spectrum a) What is the average value Ofx(t) ? b) What is the average Qwer in x(t) ? c) Write an expression for x(t) in terms of cosines (Assume mo =1). Your expression must be real. a) 32:340/0" r *3 32‘ I») a: Mom Woman/z meg/3— 21m -: 21+2'22 +2./2: 9+9f2:im (91(17): 00‘!’ Z {CK} KZi \ : -34— 2.199030“: ~‘?o°)+ 2. \ w:(?'<*+‘i50) MW,/\ A W“ \ (We) = '3+ Rw§LKH¢200> r1w§<QKE NS") ...
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This note was uploaded on 11/04/2008 for the course ECE 300 taught by Professor Throne during the Fall '07 term at Rose-Hulman.

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hwk5_solns - ECE 300 Signals and Systems Homework 5 Due...

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