Communication Systems MCQ Questions & Answers

81

Noise with double-sided power spectral density of K over all frequencies is passed through a RC low pass filter with 3 dB cut-off frequency of f_c. The noise power at the filter output is

A) K B) Kf_c C) Kπf_c D) ∞

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Answer & Solution

Answer: Option C

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82

A system has a receiver noise resistance of 50 Ω. It is connected to an antenna with an input resistance of 50 Ω. The noise figure of the system is

A) 1 B) 2 C) 50 D) 101

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Answer & Solution

Answer: Option B

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83

Noise performance of PAM is

A) better than direct base band transmission B) better than CW amplitude modulation C) poorer than direct baseband transmission D) better than that of PDM

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Answer & Solution

Answer: Option C

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84

A signal m(t) = 5cos2π100t frequency modulates a carrier. The resulting FM signal is 10cos{(2π10⁵t) + 15sin(2π100t)}. The approximate bandwidth of FM would be

A) 100 Hz B) 1000 Hz C) 3200 Hz D) 100 KHz

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Answer & Solution

Answer: Option C

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85

If transmitter bandwidth is doubled in FM, then SNR is

A) also doubled B) improved four fold C) decreased by one fourth D) unaffected

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Answer & Solution

Answer: Option C

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86

Consider the wave form V(t) = (1 + mcosω_mt)cosωt.
Show that, it the demodulated wave is to follow the envelope of V(t), it is required that at any time t₀

A) $$RC \leqslant \frac{{{\omega _n}\left( {m\sin {\omega _m}{t_0}} \right)}}{{\left( {1 + m\cos {\omega _m}{t_0}} \right)}}$$ B) $$\frac{1}{{RC}} \geqslant \frac{{{\omega _m}\left( {m\sin {\omega _m}{t_0}} \right)}}{{\left( {1 + m\cos {\omega _m}{t_0}} \right)}}$$ C) $$\frac{1}{{RC}} \leqslant \frac{1}{{\left( {m{\omega _m}} \right)}}$$ D) RC is very large

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Answer & Solution

Answer: Option B

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87

Which of the following is NOT one of the type of amplitude modulation?

A) Vestigil sideband B) Double-sideband suppressed carrier C) Single-sideband suppressed carrier D) Single-sideband with carrier

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Answer & Solution

Answer: Option D

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88

Eye diagram gives us an idea of-

A) Modulation scheme B) Clock jitter C) Signal-to-Noise Ratio D) All of the above

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Answer & Solution

Answer: Option D

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89

Power spectral density of white noise . . . . . . . . with frequency.

A) is constant B) decreases C) increases D) none of above

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Answer & Solution

Answer: Option A

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90

In a typical frequency multiplier application using a PLL, a decade counter was inserted between the VCO output and the relevant phase comparator input. If the input frequency is 10 kHz, the VCO output frequency would be

A) 10 kHz B) 100 kHz C) 1 kHz D) 11 kHz

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Answer & Solution

Answer: Option B

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Communication Systems MCQ Questions & Answers | ECE