Communication Systems MCQ Questions & Answers

1

A DSB-SC signal can be demodulated using:

A) a synchronous detector B) a phase shift discriminator C) a low pass filter D) an envelope detector

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Answer & Solution

Answer: Option A

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2

Determine the bandwidth occupied by a sinusoidal frequency modulated carrier for which the modulation index is 2.4.

A) 4.8 f_m B) 6.8 f_m C) 2.4 f_m D) 3.8 f_m

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Answer & Solution

Answer: Option B

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3

A receiver has poor IF selectivity. It will therefore also have poor-

A) blocking B) double-spotting C) diversity reception D) sensitivity

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Answer & Solution

Answer: Option A

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4

The carrier of an AM signal obtained by sinusoidal modulation to a depth of modulation equal to 1, carries.

A) 33.33% power B) 50% power C) 66.66% power D) 100% power

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Answer & Solution

Answer: Option C

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5

Consider a message signal whose spectrum is given by $$M\left( f \right) = 1 - \frac{{\left| f \right|}}{{{{10}^4}}},\,\left| f \right| \leqslant {10^4}$$ and zero elsewhere. The message signal amplitude modulates a carrier f_c = 1 MHz. The bandwidth of the modulated signal is:

A) 20 KHz B) 1.01 MHz C) 1.02 MHz D) 10 KHz

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Answer & Solution

Answer: Option A

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6

A probability density function is given by $$P\left( x \right) = K\exp \left( { - \frac{{{x^2}}}{2}} \right),\, - \infty < x < \infty $$
The value of K should be

A) $$\frac{1}{{\sqrt {2\pi } }}$$ B) $$\sqrt {\frac{2}{\pi }} $$ C) $$\frac{1}{2}\sqrt \pi $$ D) $$\frac{1}{{\pi \sqrt 2 }}$$

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Answer & Solution

Answer: Option A

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7

A uniformly distributed random variable X with probability density function $${f_x}\left( x \right) = \frac{1}{{10}}\left( {u\left( {x + 5} \right) - u\left( {x - 5} \right)} \right)$$
Where u(⋅) is the unit step function is passed through a transformation given in the figure below. The probability density function of the transformed random variable Y would be
Communication Systems mcq question image

Communication Systems mcq question image

A) $${f_Y}\left( y \right) = \frac{1}{5}\left( {u\left( {y + 2.5} \right) - u\left( {y - 2.5} \right)} \right)$$ B) $${f_Y}\left( y \right) = 0.5\delta \left( y \right) + 0.5\delta \left( {y - 1} \right)$$ C) $${f_Y}\left( y \right) = 0.25\delta \left( {y + 2.5} \right) + 0.25\delta \left( {y - 2.5} \right) + 0.5\delta \left( y \right)$$ D) $${f_Y}\left( y \right) = 0.25\delta \left( {y + 2.5} \right) + 0.25\delta \left( {y - 2.5} \right) + \frac{1}{{10}}\left( {u\left( {y + 2.5} \right) - u\left( {y - 2.5} \right)} \right)$$

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Answer & Solution

Answer: Option B

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8

Consider the following statements regarding signals:
1. Deterministic signal is a signal about which there is no uncertainty with respect to its value at any time.
2. Each signal within the ensemble has a certain probability of occurrence and the ensemble of signals is referred to as a random process.
3. EEG signal is an example of random signal.
Which of the above statements are correct?

A) 1 and 2 only B) 1 and 3 only C) 2 and 3 only D) 1, 2 and 3

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Answer & Solution

Answer: Option D

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9

In a communication system, the signal power is 13 dBm and noise power is -1 dBm. The SNR will be:

A) 14 dB B) -13 dB C) 12 dBm D) 12 dB

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Answer & Solution

Answer: Option A

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10

A carrier of frequency 1 MHz is amplitude modulated by a signal of frequency 1 kHz to a depth of 60%. This is passed through a filter of characteristics shown in the given Figure-I and Figure-II. If the filter output is fed to an envelope detector, the detector output will be
Communication Systems mcq question image

A) zero B) dc C) dc + 1 kHz signal D) 1 kHz signal

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Answer & Solution

Answer: Option B

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Communication Systems MCQ Questions & Answers | ECE