This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Power Calculation”.

1. If peak voltage of a carrier wave is 10V, what is the peak voltage of modulating signal if modulation index is 50%?

a) 10V

b) 20V

c) 8V

d) 5V

View Answer

Explanation: Using relation, μ =

^{Am}⁄

_{Ac}we have 0.5 =

^{Am}⁄

_{10}which gives A

_{m}= 5V

2. Maximum Amplitude of an amplitude modulated 10V and minimum amplitude is 5V. Find its modulation index?

a) 0.65

b) 0.9

c) 0.33

d) 1

View Answer

Explanation: A

_{c}+ A

_{m}= 10 and A

_{c}– A

_{m}= 5 are the two given equations. By adding these two equations we have A

_{c}= 15/2 and A

_{m}= 5/2 . We know μ =

^{Am}⁄

_{Ac}so μ = 0.33.

3. 24 channels, each band limited to 3.4 KHz, are to be time division multiplexed. Find the bandwidth required for 128 quantization level? (Given that sampling frequency is 8 KHz)

a) 2436 KHz

b) 1002 KHz

c) 1536 KHz

d) 1337 KHz

View Answer

Explanation: We know, 2

^{n}= 128 which gives number of bits, n = 7. f

_{s}= 2f

_{m}= 2 x3.4 =6.8 KHz. Bandwidth = [24(7 + 1)] x 8 = 1536 KHz.

4. Sampling frequency of a signal is 6 KHz and is quantized using 7 bit quantizer. Find its bit rate?

a) 48kbPs

b) 64kbPs

c) 16kbPs

d) 8kbPs

View Answer

Explanation: Bit rate, R

_{b}=

^{1Tb where so bit rate = n × fs = 7 x 6 = 48kbPs.}

5. Calculate power in each sideband, if power of carrier wave is 96W and there is 40% modulation in amplitude modulated signal?

a) 11.84W

b) 6.84W

c) 3.84W

d) 15.84W

View Answer

6. For 50% modulation, power in each sideband is ________ of that of carrier?

a) 10%

b) 4.32%

c) 5%

d) 6.25%

View Answer

7. For 100% modulation, total power is ________

a) 1.5P_{c}

b) 2P_{c}

c) 3.75P_{c}

d) 1.25P_{c}

View Answer

Explanation: Total power, P

_{t}= P

_{c}(1 +

^{m2}⁄

_{2}) where m is equal to 1 so P

_{t}= P

_{c}(1 +

^{12}⁄

_{2}). On solving it we get P

_{t}= 1.5P

_{c}.

8. If each element of signal occupies 70ms, what will its speed?

a) 11.23 bauds

b) 14.28 bauds

c) 17.39 bauds

d) 13.33 bauds

View Answer

9. Power of carrier wave is 300W and modulation index is 0.75. Find its total power?

a) 465W

b) 384W

c) 323W

d) 502W

View Answer

10. If a wave is modulated by two waves. One of them has modulation index equal to 0.75 and other has 0.2, the total modulation index will be ________

a) 0.67

b) 0.58

c) 0.77

d) 0.35

View Answer

Explanation: Given that m1 = 0.75 and m2 = 0.2. Total modulation index will be equal to By substituting values we have which is equal to 0.77.

11. Find the power saving for DSB-SC wave with 100% modulation?

a) 66%

b) 86%

c) 50%

d) 33%

View Answer

Explanation: In DSB-SC power is suppressed by two third. So power saving is

^{2}⁄

_{3}x 100 = 66%

12. If power transmitted is 45kW, field at a distance of 23km will be ________

a) 0.02

b) 0.75

c) 0.05

d) 0.03

View Answer

13. Find the number of pulses, if the number of level is 128 in PCM?

a) 3

b) 6

c) 4

d) 7

View Answer

Explanation: 2

^{n}= 128, so n = 7.

**Sanfoundry Global Education & Learning Series – Analog Communications.**

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