## MCQ on Noise in Analog Communication (Part-2)

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MCQ on Noise in Analog Communication (Part-1)

### Multiple-Choice Questions

Q.1. _____________ noise is often called static noise.

- Equipment
- Atmospheric
- Space
- Thermal

**Answer: **Atmospheric

Q.2. Lightning, which is a static electricity discharge is a physical source of noise.

- cosmic
- sky
- solar
- atmospheric

**Answer: **atmospheric

Q.3. ______________ noise can be serious problem for satellite reception.

- Atmospheric
- Solar
- Thermal
- Shot

**Answer: ** Solar

Q.4. __________ noise is sometimes called white noise.

- Thermal
- Atmospheric
- Transit-time
- Flicker

**Answer: **Thermal

Q.5. Typical values of SNR range from ______ for hardly intelligible speech signals to __________ or more for CD audio systems.

- 0 dB: 10 dB
- 10 dB: 20 dB
- 10 dB: 90 dB
- 50 dB: 120 dB
**Answer:**10 dB: 90 dB

Q.6. A receiver produces a noise power of 500 mW with no signal. Its output power increases to 5 W when a signal is applied. Its (S+N)/N ratio is

- 100
- 10
- 1l
- 1

**Answer: **10

Q.7. The signal power at the input to an amplifier is 100 µW and the noise power is 1 µW. At its output. the signal power is 1W and the noise power is 10 mW. The noise figure of the amplifier (in ratio) will be

- 1000
- 100
- 10
- 1

**Answer: **1

Q.8. The signal at the input of an amplifier has a SNR of 30 dB. If the amplifier has a noise figure of 3 dB, the SNR at the output of the amplifier will be

- 3 dB
- 27 dB
- 30 dB
- 33 dB

**Answer: **27 dB

Q.9. Equivalent noise temperatures of low-noise amplifiers are often

- less than 100 K
- more than 100 K
- about 1000 K
- about 0 K

**Answer: **less than 100 K

Q.10. An amplifier has a noise figure of 1.6. Its equivalent noise temperature is

- 754 K
- 290 K
- 174 K
- 0 K

**Answer: **174 K

Q.11. A three-stage amplifier has individual power gain of 10, 25, and 30 respectively. The overall power gain of the amplifier is

- 65
- 280
- 760
- 7500

**Answer: **7500

Q.12. If the noise figure of three individual amplifier stages is 2, 4, and 5. The respective power gains are 10, 25, and 30. The overall noise figure of the system is

- 11
- less than 2
- between 2 and 4
- more than 5

**Answer: **between 2 and 4

Q.13. If the cutoff frequency of a low-pass RC filter is doubled, its output noise power (assuming same white noise at its input)

- remains unchanged
- is halved
- is doubled
- increases 4 limes

**Answer: **is doubled

Q.14. ______________ is preferred in characterizing a two-port network operating near room temperature.

- Equivalent noise temperature
- Equivalent noise bandwidth
- SNR
- Noise figure

**Answer: **Noise figure

Q.15. Thermal noise is independent of

- Boltzmann’s constant
- temperature
- bandwidth
- centre frequency

**Answer: **centre frequency

Q.16. Thermal noise is

- white noise for all practical purposes
- never white noise
- always white noise
- sometimes pink noise

**Answer: **white noise for all practical purposes

Q.17. Transistor Q1 operates at 100 Hz and transistor Q2 operates at 10 kHz. The flicker noise is

- more in Q1
- more in Q2
- same in Q1 and Q2
- less in Q1 and more in Q2

**Answer: **more in Q1

Q.18. A resistor having resistor R is connected with a capacitor of capacitance C in shunt. The square of the rms value of the noise voltage across the circuits varies

- inversely proportional to square root of C
- inversely proportional to C
- directly proportional to square root of C
- directly proportional to C

**Answer: **inversely proportional to C

Q.19. A narrowband noise exhibits

- both amplitude and frequency modulation
- phase modulation
- amplitude modulation
- frequency modulation

**Answer: **both amplitude and frequency modulation

Q.20. In a particular system, the signal power is 10 dBm and noise power is -1 dBm. The SNR will be

- 11 dB
- 9 dB
- -10dB
- -11 dB

**Answer: **11 dB

Q.21. A narrowband noise source has symmetrical power density spectrum. If it has power density spectrum 0.1 x l0^{-6}, then the power density spectrum of in-phase components is

- 0.1 x 10
^{-6} - 0.2 x 10
^{-6} - 0.05 x 10
^{-6} - 0.025 x 10
^{-6}

**Answer: **0.05 x 10^{-6}

Q.22. The available thermal noise power per unit bandwidth will ______ if the value of resistance is doubled while maintaining ambient temperature constant.

- remain unchanged
- be doubled
- be halved
- be increased four-fold

**Answer: **be doubled

Q.23. An amplifier has an output signal power of 10 W and an output noise power of 0.01 W. The signal-to-power power ratio is

- 10 dB
- 20 dB
- 30 dB
- 60 dB

**Answer: **30 dB

Q.24. An amplifier has an input SNR of 100 and output SNR of 50. Its noise figure is

- 2 dB
- 3 dB
- 6 dB
- 10 dB

**Answer: **3 dB

Q.25. An amplifier has an output SNR of 16 dB and noise figure of 5.4 dB. Its input SNR is

- 10.4 dB
- 21.4 dB
- 16 dB
- 5.4 dB

**Answer: **21.4 dB

Q.26. Theoretical power of white noise

- is infinite
- is finite
- is zero
- depends on the frequency of the signal

**Answer: **depends on the frequency of the signal

Q.27. The spectral density of white noise

- is constant
- varies with bandwidth
- varies with amplitude
- varies with frequency

**Answer: **is constant

Q.28. The available power depends on resistive as well as reactive component of the source impedance.

- True
- False

**Answer: **False

Q.29. The available power spectral density at the output of two-port network is the product of the source power spectral density and available gain.

- True
- False

**Answer: **True

Q.30. An amplifier with a noise figure 4 dB means that the signal-to-noise ratio at the output is 4 dB more than it was al its input.

- True
- False

**Answer: **False