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Comm Systems Lecture - Chapter 8 Communication...

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Unformatted text preview: Chapter 8. Communication Systems (Amplitude Modulation) Goal: Create a signal suitable for transmission over a communication channel. Example: Telephone. Voice 200Rz-4kflz. Communication Channel. Microwave Frequencies 200MHz—300GHz. (Amplitude) Modulation (Amplitude) Demodulation - insert info onto a high-frequency — extract info from the carrier for transmission W high-frequency carrier NH?) I Petite ‘L CL‘H ”mug“, lows; fill-hm came» sr d m4 milk v~ 1.93.1 omumw cm Time Domain Analysis =- C. “W WW I fm m) CH) *- Cow -l-' cL+1=oosw¢f A ‘ 4L moosawbt" (W3) 1 20+ cof-ZIUJZ fi «.90 Luce-TM“? \ ”3 E?) === U‘WwQH—J ‘-’- i<mu~l+ Mmmwb “5&9“ 4 . .900 Wig-3’ 1' T ”fig wayf éwawWCw) ’f Cflflblbt'bk“ “we g-+mdfaus Mg I 7% CEO is) miocb‘c. M01 (Ito) Cough %Cfim, m /fl{’ (4:013 Fémoci'C, I I " ' ' jam If (M be ViFwegeMkd Eja afiawm SW63 Chan-T616 ““ht- 4.... K6 wmmuw mum (:5) wjflwm‘mm cm W _ :::.::._'j-;;;;;n§:—3A}Qfi 3H4 Fifi HAW { Ewflgéu 500) “=== NW ‘00) R004 Beat” Eta: *1}sz $31wa @059 #CCD and Ell-9) *3(w~af):jX(9)ZZaJ-wa~9)d9 “we 715:4; I w “0 . Em) x£(w-wo =-~ §[email protected](w—mré>fi@ -=---— Sf”? Lg“) “4410‘ka v—r “.913 fire; mt M-%“9=O - Muff? 01‘ Q: M‘wb PEA” &;mf31MeJ Class Problem 1 (Modulation) mffl SL—r}*—"~ mo LOSQO *5) WW yM/w) 7%?! :9w MM? +CM'HO)I (1(7):: Gabi/lot) Suppose I -I 1 Sketch (label) jam} f2" JSMW on +— é/Ww W) L ~—>‘U Class Problem 2 (Demodulation) 5m mH-flo‘fiwi) (TL-341M- Given cm; casLt) Sketch (label) Amplitude Modulation Demodulation Example : i x(t)wcos(2m},fr: le C(I)=cos(20m} I'ZZOHZ {WWWWW :MM‘IIWIIHW‘IM ’WWW :5 l E l hj\%\/\f\/ curric: Signui moduialcd sigma!“ chIIoIIulIIIeIi Sign: I} 41h mIIcI Bulicrwonh ”LI’ fiitct lilteILd xibnai fi BWMIHZ t 2x I yr“) ‘mm‘m’ w(r):: )‘(l)<‘(t) = I'IIIcm mt . z() 4 U W 2 324(1) +%-.x(!)cos Zap WW I « mm' gum : 2 signal} I 'i‘I'aIIsmission pick a)“ < w, < w C(l)=COS(13(! : 0‘3““! CG) =cnsau + gut. >> a)“ ; I - m m mm:_fifl_m -V l i ’ [ii . Iwm=w%mmnmm . i- ::;flfli__f II If i ‘ C(jw) .._., 7r[5(w — (15)qu 6((u-I m‘. )] C(jw) = 145(0) ~€Ur } I- 5U!” m, )1 W060) '= 3L YUw) * CUM) n: 1‘ 1(1ij “Tm mmmI (U ~aji_.,____ w Synchronization fiMlua) C’coswa , “9'77“?“ ConJ-l-Q “an [owl 03“ “MW 1100,} 0.! mil [WWW bmudvvs moi" 174 Fpaée S (1.. SH”) wh~)==~ ME?) cech‘t‘ wRCML't'i-E) C. _' Lo; (”W99 ,1. i549; (”W 4— 6)) «('9 “:- 42mm we 4- 42—3494 (10$. (Mme) V f Names 5&9 (w) CG-Sldct \(gynchronous Demodulation or Coherent Detection .5043) “W“ 3331‘le *“L “L 10W SW Double Sideband “- Suppressed Carrier Moduiation (DSB—SC) Asynchronous or Envelope Detection If the “message” signal 20, then the desired output is the “envelope” Io Modulation Index (Text 8.2.2) M + SW = (B +M (+1) up; m + B \v N (3%) (93%{3 W1” 8‘ 0 @6936. B So “(’Qx‘r B+MLF)'P;0 m? H E Mal!” 5 :4. Example. Suppose MH)=K£o$meC. m SCH?" (Bi-Mm) (103603" fi # E, r“ 7% Mm) 31“”) 7:3 r3 ““ My: Eli)“. Mia-”Wm At 100% modulation, ”5] “=u h «7 B =-- K Therefore, keep ju (:5, £10 +1, 6152 l2... Circuits for Moduiation + MZH') + 2mm Col wfl—L assay-t l3 * m m. 2mm wswdr-r- iced: msfliof) Tuned Radio Frequency (TRF Receiver) LC Bandpass Filter Ml + E1 L C ‘5?“ E; as... TRF Receiver Selectivity Q __._ AM Band 550 kHz 1000 kHz 2. Tune here (Q~constant) BU) "fir SSD'C‘H‘s am” 69*”“7'BTW L BM) "be sum,” r 1. _ Tune 1550 kHz Seperheterodyne Receiver 64m gmflfléj Advantage —— constant selectivity over a wide range of received frequencies Audio & Power Ampls IF Amplifier Constant BW over entire band “Oscillator (L0) L9 always 455 kHz above incoming carrier frequency Example: tune to 590 kHz. L0 ~ 590 kHz 3 455 kHz m> L0 = 1045 kHz Trimmers I—-——-————-————-——— Figure3~9 Variable ganged capacitor. H 10, The tie-multiplexing and demedulation of redie and teievision signals is generally done using a system called the superheterodyne receiver, which is equivalent re a tunable filter. The basic system is MI} -oa:‘se tunable 2“) Fixed selective r0) fiiter H —a)) filter H ( 160) T0 demodulater ECos(w + mgr ‘9 i (a) The mput signal ya) consists of the superposition of many amplitude—modulated signals {hat have been multiplexed using frequeneywdivision multiplexing, 30 that each signal occupies a different frequency channel (or radio station) Consider one sect: channel that contains the amplitude-modulated signal $01) xl(t)eosw t, with spectrum 3” (w) as shown In the top half of the next figure We want to demuitipiex and demoéulate the timed. signal 350) to recover the modulating signal x16), using the system above. The coarse innable filter has the spectrum H] (w) , shown below. Desermine the speCtrum 2(a)) of the input signal to the fixed selective filter 113(0)). Sketch and label Z(w) for w>0. input signal 1 (DC - 50!“ (BC + wk, Cesrse tunable filter (b) The fixed frequency-selective filter is a bandpass type centered mund the fixed frequency a)! , as shown below. We would like the eutput of the filter with spectrum ”2(0) to be r(t} m x; (000sz1. in terms of can and COM, what constraint must a)? satisfy to guarantee that the undistorted spectrum of 2:10} is centered around a} a (of? Hi; (£0) E i i i I 3 i a air fl Fixed selective filter G (C) Whatmust {3,9243 be so that r0} = x,(z)ceswfl ? {4&3 Cos [w¢+wac"j{- i?) W. Coarse _nabke “(59X 3(1) Fixed scheme r6} 2% (.4) (10$!ch ) film: H u?» mm H3050) To demodulator €me 2% mm E mania} +5913: >i< i i I ‘ i ...
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