exam 3 - ECE4111 — MID-TERM 3(UTEB Room 175 9:00-9:50AM...

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Unformatted text preview: ECE4111 — MID-TERM 3 (UTEB. Room 175, 9:00-9:50AM Wednesday, November 18‘". 2009) This is a closed-book exam, with three “cheat-sheets". You have 50 minutes. Questions are worth the nmrks shown. Points will be deducted for answers not in simplest form. Put a box around your final answers. 1. (25 marks) You are asked to design an 1" M system for a message that has bandwidth W = l5kHz, modulation sensitivity k; = 20kl-lz/Volt, maximum message amplitude Im(l,)|,,.,.I = 2Volts. loss of [OMB from transmitter to receiver and noise power spec- tral density No/2=10""'\Vz1tts/l-Iz. Which. from the list below. is the lowwt transmitted power that will work? (b) 2 x 103 Watts (c) l x 10" Watts ((1) 8 x 105 Watts (0) none of the above will work (Tku is A SKMP‘JHJ wt/stuh oi {0'3-13) P“ >1°Nuer -—> (mum) > 2° No CW + 2 k9 NHL“) —> P > (Io’°3(zo)(2xuo““;"%}((1i(tswo41(1°“-“$)(2V\l T HCMU (G\ 'S (oleh- I OH S017“ CH Ail ler (e\, +0 +k05J~ ()le j MudeIsJNurl ‘HA clu9t+|uu hull JAJ ROI“ reel vhul tel saw» an semeMv‘ l ccl‘kouvl 2. (20 marks) A real bandpass noise process X (t) has a power spectral density that is 10"“W/Hz (i.e., flat) between 991MHz mu! 100MHz, and zero elsewhere. Sketch the power spectral density of the ill-phase and quadrature components. misuming a carrier frequency of 100MHz. Label your axes. lel’l .414 v/ IO [1: 7°) ‘9' (HM-l 3. (15 marks) An FM system without prc~/tlc-e111phasis operates with an SNR of 52dB. A pre-[de—emplmsis system is added, and its improvement factor is 40. What is the new SNE? (b) 92(113 (c) 208dI3 (d) 76(113 (0) none 01' the above (T1415 :5 a “1-1 (Lurktwcl u-crg-on at crué; ‘5 “hi-L‘Nk'k) 40 new 50 8m: = 51+ '5 = 69‘”? x1. (25 Hunks) Let :03) = v(t) —- v(t — ’1‘), where v(t) is a white noise with unity power spectral density. Choose the power spectral density of z(t) from the list below. (a) 04!) = Two—,1 (b) ow) = HI? (6) G:(f) = 2jsinc(f) (d) GzU) = 4si112(7rfT) (0) none of the above (Thu, is a «mph verum J‘9.1—‘J.) (luv: [Hm L Cum — [mm] ‘1 -d'lfii’l‘ll = - e I 1- 5“” 50M quch-r’ {)‘r‘h-J CfiéLf 419 (el ska “Kiln «JAR gem» {march wk, juL duck 5. (I5 marks) Given a DSB system with P" = 100W, Pm = 0.9. SNR=30dB, what must Pu be for an equivalent 388 system? an sovv (b) sovv (d) lllVV ((2) none of the above (Thus as Q U—Ct‘btuk .L '0‘1‘Vt 59 fund)‘; 44‘0“ '.+ MA. MI, arm-“3 4m shah) TH SN“ exfrefiiavw a; D§B‘§( 4A1 S’CB are ‘RA some. So +5 Nu‘gqu FHA”! “ 'H'~ 569”- CH ...
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