北邮考研信号与系统专业课试卷及答案2004B

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1、(B)B73211.y(t)=x(t)*h(t),a>0(a)Aaxt(a)*ht()Bxt()*ht(a)Cxt(a)*ht(a)Daxt(a)*ht(a)2.f(t)F(j)=(-)f(t)0A1ej0tu()tB1e-j0t22C1ej0tD1e-j0tu()t223.u(t)-u(t-2)-2s-2s1e1eAF()s=-Re[S]>0BF()s=-Re[S]>2ssss-2s-2s1e1eCF()s=-sDF()s=-0

2、eætö5.f(t)BHzfç÷,è2øætöfç÷,è2ø1111A:s,BHz;B:s,2BHz;C:s,BHz;D:s,2BHz2BBB2B6.f(n)=2-nu(n)ZFZ()-1zz2z2zA:B:C:D:2z-12z-12z-12z+1æ1ö7.x()n=Asinçn+÷è84ø1ABC16D8849327¥1.òsint(2t-1)dt=-¥:n*2.xøn÷ã¥0,2,4,2£x9)=s82(3.f(t){4.T(t)ã;øtónT1÷,nãó{2(B)5.f(t),y(t),H(j)=Z6.F()Z=f(n)1Z-2111Z>f(n)=2Z

3、23ó1ó27.xøn÷ZXøz÷ã4zõ1õzõ6zx(n)x(n)=_____________________________________8.x(n)=(n-3)u(n-2)zX(z)=__________________9.H(s)S5840æ1ö1.f(t)fç-t-2÷è2øo2.f(t)=2+6cos(24t-120)+4cos(40t)-2cos(56t)(1)f1(2)Fnønf1÷ønf1÷0sint3.ø÷2ftãt3(B)f(t)02O22tó00¥jnt4.f()t=åe(-¥

4、,B,Cf(t)By(t)Hø÷ACcostz5.Hø÷zãzõ0.57624$4$1.8x1ø÷nã30,1,2,3,4#x2ø÷nã311,1,1,0,0#ss2nã0"2nã0"x(n)=x(n)*x(n)122ø÷ø÷ø÷dytdytdft2.8õ4õ3yø÷tãõ5fø÷t2dtdtdtó2th(t)føt÷ãeuøt÷y(t)zsYøs÷3.8Hø÷sãã41H(s)2ø÷2Es4(B)H(s)K2()+Es+k+Y(s)åå2sõ1+H(s)24.13LTIHøs÷,Hø0÷ãó0.5,(1)Høs÷høt÷;(2);(3),Høj÷,sinøt÷uøt÷,

5、;j´2ó2o2´ó25.15x(n)y(n)Sz-1S0.2ó0.8-1z123{26.10føt÷ã2Saøt÷Saø2t÷,.fø÷tdt(ó{)5(B)(B)73211.D2.C3.C4.C5.C6.C7.C932711.2.¥0,0,2,0,4,0,2£2s{:*223.4.T(t)ã;99ón))T1nãó{8T1(nnójt0æ1öæ1ö()5.Høj÷ãke6.ç÷u()n-ç÷u-n-1è2øè2ø7.xøn÷ã4ønõ3÷õøn÷õønó1÷õ6ønó2÷2óz8.9.2zøzó1÷58401(B)ætöfç--2÷è2ø¥(2)Ot1.2.:f0=G

6、CD(12,20,28)=4HzGCDFn3322211-28-20-12O122028fn()180120-2812-12O28f-120-180Fø÷13.ó0O022¥{4.:f()tÛF()=2å(-n)fø÷tIcostE;øónó1÷n=-¥nãó{{fø÷tIcostöhø÷tEHøj÷;2øónó1÷nãó{ãøõ2÷õ2øõ1÷õ3ø÷õ2øó1÷õøó2÷F()F[f(t)×cost]2LLLø÷L-2-1012-2-10122(B)Y()(3)()(2)(2)()ó2-1012je115.:Høj÷ãããj..ójø1õ0.5cos÷ó0.5sine

7、õ051õ05ej1Høj÷ã1.25õcosjH(e)jIm[z]2-0.5o1Re[z]23ó2óo27624$1.xø÷nã3136,109,7,4#s2nã0"G:1ót1ó3t*-t-3t2.h(t)ã9eóe)uø÷th(t)=(2e-e)u(t)822(()ótó3tó2tyt=f(t)*h(t)=ø2eõeó3e÷uøt÷zs6sõ3óK13.:1H2ø÷sã2Kâó8sõ4kõ42Aøsó2÷Aøsó2÷Aøsó2÷4.:(1)Hø÷sãããøsõ2ó2j÷øsõ2õ2j÷22øsõ2÷õ4sõ4sõ8ó2A