7.1 Amplitude Modulation

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1 7. Ampliud Modulaion Samn or Q.-. An AM signal is rprsnd by v( ( 0 sin 000os( 0 6 V. Th modulaion indx is (A 0 (B (C 0. (D.5. Th oal signal powr is (A 08 (B 6 (C 00 (D. Th oal sid band powr is (A 8 (B 6 (C 0 (D. A k arrir is o b modulad o a 80% lvl. Th oal ransmid powr would b (A k (B. k (C. k (D Non o h abov 5. An AM broadas saion opras a is maximum allowd oal oupu o 00 k wih 90% modulaion. Th powr in h inllign par is (A 8.8 k (B 7. k (C 5.6 k (D Non o h abov 6. Th arial urrn o an AM ransmir is 6 A whn unmodulad bu inrass o 8 A whn modulad. Th modulaion indx is (A 0.7 (B 0.6 (C 0.89 (D Non o h abov 7. A modulaing signal is ampliid by a 80% iiny ampliir bor bing ombind wih a 0 k arrir o gnra an AM signal. Th rquird DC inpu powr o h ampliir, or h sysm o opra a 00% modulaion, would b (A 5 k (B 8.6 k (C 0 k (D 6.5 k 8. A MHz arrir is ampliud modulad by a 500 Hz modulaing signal o a dph o 60%. I h unmodulad arrir powr is k, h powr o h modulad signal is (A.8 k (B.6 k (C.8 k (D.6 k 9. An AM ransmir is oupld o an arial. Th inpu urrn is obsrvd o b 5 A. ih modulaion h urrn valu inrass o 5.9 A. Th dph o modulaion is (A 8. % (B 88.6 % (C 78. % (D 7. % 0. A arrir is ampliud modula o 00 % by a polar rangular signal as shown in ig. P7..0. Th prnag inras in signal powr is m ( - Fig. P7..0 (A 8. % (B 00 % (C 50 % (D Non o h abov. A arrir is ampliud modulad by wo sinusoidal signals o dirn rqunis wih individual modulaion dphs o 0. and 0.. Th powr in sid band would b

2 96 Ampliud Modulaion Chap 7. (A % (B 9 % (C. % (D 0 %. In 50 % modulad AM signal, h arrir is supprssd bor ransmission. Th saving in ransmid powr would b (A 88.9 % (B. % (C 7 % (D 8 %. A 0 k arrir is sinusoidally modulad by wo arrirs orrsponding o a modulaion indx o 0 % and 0 % rspivly. Th oal radiad powr is (A 5 k (B.5 k (C 0 k (D 5 k. In a broadas ransmir, h RF oupu is rprsnd as m ( K -K (A 5 % (B.8 % (C 5. % (D Non o h abov Samn or Q.8-: Th ig. P.7.8- shows h posiiv porion o h nvlop o h oupu o an AM modulaor.th mssag signal is a wavorm having zro DC valu. m ( Fig. P7..7 T x( 00[ 0. 9 os sin 9000]os( V. Th sidbands rqunis ar (A 5.99, 5.995, 6.005, MHz (B 95.5, 95., 955.7, 956. khz (C 5, 9 khz Fig. P7..8- (D 795.8,. Hz 5. A diod dor has a load o k shund by a 0000 pf apaior. Th diod has a orward rsisan o. Th maximum prmissibl dph o modulaion, so as o avoid diagonal lipping, wih modulaing signal rquny o 0 khz will b (A 0.87 (B 0.68 (C 0.7 (D Non o h abov 6. A non-linar dvi wih a ransr hararisi givn by i ( 0 vi 0. v i ma is supplid wih a arrir o V ampliud and a sinusoidal signal o 0.5 V ampliud in sris. I a h oupu h rquny omponn o AM signal is onsidrd, h dph o modulaion is (A 8 % (B 0 % (C 0 % (D. % 7. A mssag signal is priodi wih priod T, as shown in ig. P7..7. This mssag signals is applid o an AM modulaor wih modulaion indx 0.. Th modulaion iiny would b 8. Th modulaion indx is (A 0.5 (B 0.6 (C 0. (D Th modulaion iiny is (A 8.% (B.8% (C 7.69% 0. Th arrir powr is (A 60 (C 0 (D Non o h abov (B 50 (D 900. Th powr in sidbands is (A 85 (B.5 (C 56 Samn or Q.-: (D 7.5 An AM modulaor opras wih h mssag signal m ( 9os07os60. Th unmodulad arrir is givn by 00 os 00, and h sysm opras wih an indx o

3 Chap 7. Ampliud Modulaion 97. Th powr in normalizd mssag signal m ( n would b (A 0.69 (B 0.5 m ( x ( Squar- Law Dvi y ( Filr AM Signal (C 0.5 (D Non o h abov. Th doubl-sidd sprum o x (would b os Fig. P (A (B -60 X ( X ( Th valu o M, rquird o produ modulaion indx o 0.8, is (A 0. (B 0.6 (C 0.5 (D L b h B o mssag signal m (. AM signal would b rovrd i. (A (B (C (D (C X ( A supr hrodyn rivr is dsignd o riv ransmid signals bwn 5 and 0 MHz. High-sid uning is o b usd. Th uning rang o h loal osillaor or IF rquny 500 khz would b (A 5. MHz 9.5 MHz (B 5.5 MHz 0.5 MHz (C.5 MHz 0.5 MHz (D Non o h abov (D Non o h abov. An AM modulaor has oupu x ( 0 os 00 os 60 os 0 Th modulaion iiny is (A 0.0 (B 0.0 (C 0.0 (D An AM modulaor has oupu x ( Aos 00 Bos 80 Bos 0 Th arrir powr is 00 and h iiny is 0 %. Th valu o A and B ar (A., 8.6 (B 50, 0 (C.6,.6 (D Non o h abov Samn or Q.6-7: Considr h sysm shown in ig. P Th avrag valu o m (is zro and maximum valu o m ( is M. Th squar-law dvi is dind by y ( x ( 0x ( 9. A supr hrodyn rivr uss an IF rquny o 55 khz. Th rivr is und o a ransmir having a arrir rquny o 00 khz. High-sid uning is o b usd. Th imag rquny will b (A 855 khz (B 0 khz (C 95 khz (D 90 khz 0. A supr hrodyn rivr is o opra in h rquny rang o 550 khz 650 khz, wih h inrmdia rquny o 50 khz. Th rivr is und o 700 khz. Th apaian raio R Cmax Cmin o h loal osillaor would b (A. (B. (C (D 9. Considr a sysm shown in ig. P7... L X( and Y( dno h Fourir ransorm o x (and y ( rspivly. Th posiiv rqunis whr Y( has spral pak ar

4 98 Ampliud Modulaion Chap 7. Baland HPF Baland x ( y ( Modulaor 0 khz Modulaor (A khz and khz (C khz and khz (B khz and khz (D khz and khz sin. In ig. P7.., m (, s ( os00 and sin 99 n (. Th oupu y (is m( ~ ~ 0 khz khz X ( - - Muliplir s ( Addr n( (A sin (B sin sin os Fig. P7..b Muliplir s ( Fig. P7.. (C sin sin 05. os 5. (D sin sin os 075. (khz LPF Hz Hj ( =. In h irui shown in ig P7.. bwn h rminal and an a.. volag sour o rquny 00 Hz is onnd. Anohr a.. volag o.0 MHz is onnd bwn and. Th oupu bwn 5 and 6 onains omponns a 5 Fig. P7.. (A 00 Hz, MHz, 000. khz, khz (B MHz, 000. khz, khz 6 y( (C 00 Hz, 000. khz, khz (D 000. khz, khz. signals ah band-limid o 5 khz ar o b ransmid ovr a singl hannl by rquny division muliplxing. I AM-SSB modulaion guard band o khz is usd, hn h band widh o h muliplxd signal will b (A khz (B 8 khz (C khz (D 7 khz 5. L x ( b a signal band-limid o khz. Ampliud modulaion is prormd o produ signal g ( x (sin000. A proposd dmodulaion hniqu is illusrad in ig. P7..5. Th idal low pass ilr has uo rquny khz and pass band gain. Th y (would b (A y ( (B y ( (C y (D 0 6. Suppos w wish o ransmi h signal x ( sin00 sin00 using a modulaion ha ra h signal g ( x (sin00. I h produ g ( sin 00 is passd hrough an idal LPF wih uo rquny 00 and pass band gain o, h signal obaind a h oupu o h LPF is (A sin 00 (B (C sin 00 (D 0 sin In a AM signal h rivd signal powr is 0 0 wih a maximum modulaing signal o 5 khz. Th nois spral dnsiy a h rivr inpu is 0 8 Hz. I h nois powr is rsrid o h mssag signal bandwidh only, h signals-o-nois raio a h inpu o h rivr is (A db (B 66 db (C 56 db g( os 00 LPF Fig. P7..5 ************ y( (D db

5 Chap 7. Ampliud Modulaion 99 Soluions. (C v( 0[ 0. sin ( 000os( 0 6 ] V 0.. (A P P ( 0. P 00, P ( , 0.. (A P 08, P 00, P sb (B P P 5. (A P P ( ( P P 7. k P ( P P ( k i 6. (A I I (D P 0k, P 5 k, P i k 5 Th DC inpu powr 65. k (C P k, 60 % 06. ( 06. P P 9. (B I I 59. 5, 0. (B 0. or 00% 8. k. k 0886, dph 88. 6% Th modulaing signal m (assums any o h wo valus, or, wih m (bing a polr rangular signal so m (, P P[ m ( ] P % inras 00%. (C L P b h arrir powr. Toal sid band powr x ( P whr x ( 0. os 0. os x ( ( 0. os 0. os (( 0. ( P P P 0. 5P 5. P % sid-band powr 0. 5 P 5. P 50. (A ( 05. P P P. % P 5. P Saving will b P i arrir is supprssd. P Saving 5. P %. (B P P P , 0., k. (B Sid band rqunis ar, ( rad and ( rad sb 5.995, 6.005, 5.99 and MHz sb sb 955., 955., 7 95., 956. khz 5. (A m 0 khz, R 000, C 0000 pf 8 Hn m RC max ( ( (C v( os 05. os i m i 0 (os 05. os 0. (os 05. os m m Th AM signal os 0. os os ( 0. os os m m

6 00 Ampliud Modulaion Chap % Hn (B is orr opion. j ( ( j ( 7. (C Th normalizd mssag signal is m T T (, 0 T m T T d ( 0 ( 0. m ( E m ( ( % 8. (A A ( 5, A ( (C Normalizd mssag m T T n(, 0 m n E T T T d ( 0 ( 05. ( % 0. (B A ( A 0, arrir powr is P A 50. (D E P P (C Th maximum valu o m (6 mn( ( 9os0 7os 60 6 m n 9 7 ( (B x ( 00 ( 9 os 0 7 os 60 os os ( os ( os ( os( os( 60 j ( ( j ( j ( ( j ( j ( ( j ( j ( ( j (. (B x ( an b wrin as x ( ( 0 8 os 0 os 00 8 modulaion indx 0 0. P ( Th omponns a 80 Hz and 0 Hz ar sid band P sb ( ( 6 E P P sb A 5. (A Carrir powr P 00,A. E 0 P P sb B B B (D y ( ( m ( os 0( m ( os m ( os 0m ( 0m ( os 5 5 os y ( 5 m ( 0m( ( 5 m (os 5 os Th AM signal is, x( [ 5m(]os m ( Mmn( x( [ 5Mmn(]os 5M 08., M (C Th ilr hararisi is shown is ig. S7..7 Thror H ( m ( - 8. (B Sin High-sid uning is usd, + Fig. S7..7 LO m IF IF 500 khz, LOL MHz, LOU MHz 9. (B imag L IF khz

7 Chap 7. Ampliud Modulaion 0 0. (A max khz min khz LC hn rquny is minimum, apaian will b maximum R C max max (. R. C min min. (B Sin X( has spral pak a khz so a h oupu o irs modulaor spral pak will b a ( 0k k Hz and ( 0k k Hz. Ar passing h HPF rquny omponn o khz will rmain. Th oupu o nd modulaor will b ( k k Hz. So Y( has spral pak a k and khz. sin ( os ( 00. (C ms (( y ( sin ( 0 sin ( 98 sin 0 sin 98 sin 98 y( n( y( [sin 0 sin 98 sin 99] os 00 y( s( y( [sin ( 0 sin ( { sin( 98 sin ( } sin( 99 sin( ] Ar ilring sin ( sin ( sin ( y ( sin ( sin ( 05. os ( 5. sin sin 05. os 5. x (sin( 000os( 000 x (sin( 000 X j j X j X j ( ( ( 000 ( ( 000 This implis ha X ( j is zro or 000 baus m 000. hn x (is passd hrough a LPF wih uo rquny 000, h oupu will b zro. 6. (A y ( g (sin( 00 x (sin ( 00 ( os ( 800 (sin ( 00 sin ( 00 [sin ( 00 sin ( 00 os ( 800 sin ( 00 sin ( 00 os ( 800] sin ( 00 [sin ( 000 sin ( 600] sin ( 00 [sin( 00 sin ( 00] I his signal is passd hrough LPF wih rquny 00 and gain, h oupu will b sin ( (A Mssag signal B m 5 khz Nois powr dnsiy 0 8 /Hz. Toal nois powr 0 5k 5 0 Inpu signal-o-nois raio 0 0 SNR i SNR i 0log 0 db ***************. (D Th givn irui is a ring modulaor. Th oupu is DSB-SC signal. So i will onain m (os( n whr n,,... Thror hr will b only ( MHz00 Hz rquny omponn.. (D Th oal signal bandwidh 5 60 khz Thr would b guard band bwn signal. So guard band widh khz Toal band widh 60 7 khz 5. (D x ( g(os( 000

Solution of ECE 342 Test 2 S12

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