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Unformatted text preview: ECE4111 — MIDTERM 3
(UTEB. Room 175, 9:009:50AM Wednesday, November 18‘". 2009) This is a closedbook exam, with three “cheatsheets". 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; = 20kllz/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/lIz. 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 {0'313) 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 illphase and quadrature components. misuming a carrier
frequency of 100MHz. Label your axes. lel’l .414 v/
IO [1: 7°) ‘9' (HMl 3. (15 marks) An FM system without prc~/tlce111phasis 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 “11 (Lurktwcl ucrgon at crué; ‘5 “hiL‘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 quchr’ {)‘r‘hJ 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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 Spring '09
 Burrs

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