Communication Systems MCQ Questions & Answers

21

In a superheterodyne receiver, rejection of the image signal can be achieved by using a

A) higher local oscillator frequency B) crystal oscillator C) narrow band IF filter D) narrow band filter at RF stage

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Answer & Solution

Answer: Option D

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22

In Amplitude Modulation, . . . . . . . . of total transmitted power is used for carrying message signal under best conditions.

A) 25% B) 33% C) 50% D) 78%

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Answer & Solution

Answer: Option B

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23

Consider the following:
1. Filter system
2. Phase-shift method
3. Third method
4. Balanced modulator
Which of these can be used to remove unwanted side-bands in SSB?

A) 1, 2 and 4 B) 1, 2 and 3 C) 2, 3 and 4 D) 1, 3 and 4

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Answer & Solution

Answer: Option B

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24

x(t) = A cosωt + B sinωt, the BW of A cosωt is 10 kHz, BW of B sinωt is 15 kHz the BW of the signal x(t) is . . . . . . . .

A) 5 kHz B) 10 kHz C) 15 kHz D) 25 kHz

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Answer & Solution

Answer: Option C

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25

Which of the following is angle modulation

A) Amplitude modulation B) Phase modulation C) PCM D) None of these

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Answer & Solution

Answer: Option B

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26

The diagonal clipping in Amplitude Demodulation (using envelope detector) can be avoided if RC time-constant of the envelope detector satisfies the following condition, (here W is message bandwidth and ω is carrier frequency both in rad/sec)

A) $$RC < \frac{1}{W}$$ B) $$RC > \frac{1}{W}$$ C) $$RC < \frac{1}{\omega }$$ D) $$RC > \frac{1}{\omega }$$

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Answer & Solution

Answer: Option A

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27

An antenna pointing in a certain direction has a noise temperature of 50 K. The ambient temperature is 290 K. The antenna is connected to a pre-amplifier that has a noise figure of 2 dB and an available gain of 40 dB over an effective bandwidth of 12 MHz. The effective input noise temperature T_e for the amplifier and the noise power P_a0 at the output of the preamplifier, respectively, are

A) T_e = 169.36 K and P_a0 = 3.37 × 10^-10 W B) T_e = 170.8 K and P_a0 = 4.56 × 10^-10 W C) T_e = 182.5 K and P_a0 = 3.85 × 10^-10 W D) T_e = 160.62 K and P_a0 = 4.6 × 10^-10 W

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Answer & Solution

Answer: Option A

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28

As the modulation index of an FM signal with sinusoidal modulation is increased from zero to three, the power in the carrier component will

A) Increase continuously B) Decrease continuously C) First increase, attain a maximum and then decrease D) First deceases, become zero and then increase

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Answer & Solution

Answer: Option B

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29

In an amplitude modulated system, if the total power is 600 W and the power in carrier is 400 W, then the modulation index is

A) 0.5 B) 0.75 C) 0.9 D) 1

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Answer & Solution

Answer: Option D

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30

For an angle modulated signal x(t) = 3cos[2π10⁶t + 2sin(2π10³t)], what is the maximum frequency deviation?

A) 2,000 Hz B) 1,000 Hz C) 5,000 Hz D) 10,000 Hz

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Answer & Solution

Answer: Option A

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Communication Systems MCQ Questions & Answers | ECE