Communication Systems MCQ Questions & Answers

1

The line code that has zero dc component for pulse transmission of random binary data is

A) Non-return to zero (NRZ) B) Return to zero (RZ) C) Alternate mark inversion (AMI) D) None of these

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Answer & Solution

Answer: Option C

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2

An amplitude modulated signal is given by:
S(t) = 10cos(2π × 10⁶t) + 5cos(2π × 10⁶t)cos(2π × 10³t) + 2cos(2π × 10⁶t)cos(4π × 10³t)
The effective modulation index is:

A) 0.538 B) 0.5 C) 0.2 D) 0.7

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Answer & Solution

Answer: Option A

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3

A PLL can be used to demodulate

A) PAM signals B) PCM signals C) FM signals D) DSB-SC signals

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Answer & Solution

Answer: Option C

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4

Noise voltage varies in a resistor as

A) $$4KTRB$$ B) $$\sqrt {4KTRB} $$ C) $$\sqrt {2eIp\beta } $$ D) $$\sqrt {2eIp\beta R} $$

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Answer & Solution

Answer: Option B

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5

Ratio between SNR and $$\frac{{{{\text{E}}_{\text{b}}}}}{{{{\text{N}}_{\text{o}}}}}$$ of a signal is as follows

A) R_b B) 2R_bW C) $$\frac{{{{\text{R}}_{\text{b}}}}}{{\text{W}}}$$ D) $$\frac{{{\text{2}}{{\text{R}}_{\text{b}}}}}{{\text{W}}}$$

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Answer & Solution

Answer: Option C

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6

Determine the bandwidth of the FM signal for 5kHz audio signal modulated by a carrier of 50 MHz causing a frequency deviation of 25 kHz?

A) 60 kHz B) 90 kHz C) 30 kHz D) 80 kHz

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Answer & Solution

Answer: Option A

Solution:

In Frequency Modulation (FM), the bandwidth of the signal is determined by Carson's Rule.
Carson's Rule states: Bandwidth (BW) ≈ 2 * (Δf + fm), where:
Δf is the frequency deviation, which is 25 kHz in this case.
fm is the highest frequency in the modulating signal, which is 5 kHz in this case.
Plugging in the values: BW ≈ 2 * (25 kHz + 5 kHz).
BW ≈ 2 * (30 kHz).
BW ≈ 60 kHz.
Therefore, the bandwidth of the FM signal is approximately 60 kHz.

7

In a super heterodyne receiver, if the intermediate frequency is 10.7 MHz and the carrier frequency is 89.6 MHz, the image frequency is:

A) 78.9 MHz B) 100.3 MHz C) 111 MHz D) 121 MHz

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Answer & Solution

Answer: Option C

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8

FM discriminator changes the FM signal into

A) AM signal B) FM signal C) PM signal D) None of these

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Answer & Solution

Answer: Option A

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9

X(t) is a stationary process with the power spectral density S_x(f) > 0 for all f. The process is passed through a system shown below.
Let S_Y(f) be the power spectral density of Y(t). Which one of the following statements is correct?
Communication Systems mcq question image

Communication Systems mcq question image

A) S_Y(f) > 0 for all f B) S_Y(f) = 0 for |f| > 1 KHz C) S_Y(f) = 0 for f = nf₀, f₀ = 2 kHz, n any integer D) S_Y(f) = 0 for f = (2n + 1)f₀, f₀ = 1 kHz, n any integer

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Answer & Solution

Answer: Option D

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10

An AM broadcast station transmits modulating frequencies up to 6 kHz. If the AM station is transmitting on a frequency of 894 kHz, the values for maximum and minimum upper and lower sidebands and the total bandwidth occupied by the AM station are:

A) 900 kHz, 888 kHz, 12 kHz B) 894 kHz, 884 kHz, 12 kHz C) 894 kHz, 888 kHz, 6 kHz D) 900 kHz, 888 kHz, 6 kHz

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Answer & Solution

Answer: Option A

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Communication Systems MCQ Questions & Answers | ECE