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ECE :: Signals and Systems

  1. A.
    True
    B.
    False

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  2. If

  3. A.
    -j sgn (f) x X(f)
    B.
    j2pf x ejptf X(f)
    C.
    D.

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  4. Which of the following is/are not a property/properties power spectral density function Sx(ω)?

  5. A.
    Sx(ω) is real function of ω
    B.
    Sx(ω) is a even function of ω
    C.
    Sx(ω) is non-positive function of ωSx(ω) ≤ 0 for all ω
    D.
    All of the above

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  6. A casual LTI system is described by the difference equation
    2y[n] = ay[n - 2] - 2x[n] + βx[n -1]
    The system is stable only if

  7. A.
    |a| = 2 |β| < 2
    B.
    |a| > 2 |β| > 2
    C.
    |a| < 2 any value of β
    D.
    |β| < 2, any value of a

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  8. Which of the following can be impulse response of a casual system?

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  10. An excitation is applied to a system at t = T and the response in zero for -∞ < t < T. This system is

  11. A.
    non casual
    B.
    stable
    C.
    casual
    D.
    unstable

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  12. For the wave i = I0 + I1m sin ωt + I3m sin 3ωt, the rms value is

  13. A.
    I = (I20 + I21m + I23m)0.5
    B.
    C.
    I = 0.707 (I20 + I21m + I23m)0.5
    D.
    none of these

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  14. The Laplace transform of sin ∝t is

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  16. The signumm function written as [sgn(t)] is defined as

  17. A.
    sgn(t) = - 1 for t < 0, = 0 for t = 0 and = 1 for t > 0
    B.
    sgn(t) = 1 for t < 0, = 0 for t = 0 and = - 1 for t > 0
    C.
    sgn(t) = 0 for t < 0, = 1 for t = 0 and = 0 for t > 0
    D.
    sgn(t) = 0 for t < 0, = 1 for t3 0

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  18. Fourier transform of the unit step function (i.e., u(t) = 1 for t ≥ 0 and u(t) = 0 for t < 0) is

  19. A.
    pδ (ω)
    B.
    C.
    D.

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