71. A frequency multiplier circuit
72. A carrier is simultaneously modulated by two sine waves with modulation indices of 0.3 and 0.4. The total modulation index will be-
73. A circuit produces an output y(t) = a + bx2(t) where x(t) is its input. This circuit can produce which one of the following?
74. The signal m(t) = sinc (2 × 104t) is frequency modulated with K = 103 Hz/V. What is the maximum instantaneous frequency of the modulated signal when carrier frequency is 1 MHz?
75. Let m(t) denote a message signal and $$\hat m\left( t \right)$$ denote the Hilbert transform of m(t). Let the carrier frequency by ωc. Then, the single sideband (SSB) modulated signal with the upper sideband (USB) transmitted is given as
76. If the variance $$\sigma _x^2$$ of d(n) = x(n) - x(n - 1) is one-tenth the variance $$\sigma _x^2$$ of a stationary zero-mean discrete-time signal x(n), then the normalized autocorrelation function $$\frac{{{R_{xx}}\left( K \right)}}{{\sigma _x^2}}$$ at K = 1 is
77. An arbitrary signal m(t) has zero average value and it is band-limited to 3.2 kHz. It is sampled at the rate of 8 k samples/s. The samples are passed through an ideal band-pass filter with centre frequency of 32 kHz and bandwidth of 6.4 kHz. The output of the band-pass filter is
78. In a low-level AM system, the amplifier which follow the modulated stage must be the
79. If X is a zero mean Gaussian random variable, then P(X ≤ 0) is
80. Total bandwidth needed for an AM signal at 55.25 MHz with 0.5 MHz video modulation is
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