Communication Systems MCQ Questions & Answers

71

A frequency multiplier circuit

A) is usually pulse modulation B) Needs parasitic oscillations C) Operates class-A D) is tuned to harmonic of the input signal

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Answer & Solution

Answer: Option D

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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-

A) 1 B) can't be calculated unless the phase relations are known are known C) 0.5 D) 0.7

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Answer & Solution

Answer: Option C

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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?

A) Rectified output B) Pulse modulation C) Amplitude modulation D) Frequency modulation

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Answer & Solution

Answer: Option C

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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?

A) 0.999 MHz B) 0.998 MHz C) 1.002 MHz D) 1.001 MHz

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Answer & Solution

Answer: Option D

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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 ω_c. Then, the single sideband (SSB) modulated signal with the upper sideband (USB) transmitted is given as

A) $$m\left( t \right)\cos \left( {{\omega _c}t} \right) - \hat m\left( t \right)\sin \left( {{\omega _c}t} \right)$$ B) $$\hat m\left( t \right)\sin \left( {{\omega _c}t} \right)$$ C) $$m\left( t \right)\cos \left( {{\omega _c}t} \right)$$ D) $$m\left( t \right)\cos \left( {{\omega _c}t} \right) + \hat m\left( t \right)\sin \left( {{\omega _c}t} \right)$$

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Answer & Solution

Answer: Option A

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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

A) 0.95 B) 0.90 C) 0.10 D) 0.05

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Answer & Solution

Answer: Option A

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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

A) AM-DSB signal with suppressed carrier B) AM-DSB signal with carrier C) AM-SSB signal with carrier D) a sequence of exponentially decaying sine waves

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Answer & Solution

Answer: Option A

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78

In a low-level AM system, the amplifier which follow the modulated stage must be the

A) Linear device B) Harmonic device C) Class-C amplifier D) Non-linear device

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Answer & Solution

Answer: Option A

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79

If X is a zero mean Gaussian random variable, then P(X ≤ 0) is

A) 0 B) 0.25 C) 0.5 D) 1

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Answer & Solution

Answer: Option C

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80

Total bandwidth needed for an AM signal at 55.25 MHz with 0.5 MHz video modulation is

A) 0.25 MHz B) 0.5 MHz C) 1 MHz D) 10 MHz

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Answer & Solution

Answer: Option C

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Communication Systems MCQ Questions & Answers | ECE