## MCQ on Noise in Analog Communication

MCQ on Noise in Analog Communication, Objective Questions wit answer on Noise in analog communication, GATE objective questions on Noise, Noise based multiple choice questions with answers, MCQ on Noise in Digital Communication, Multiple Choice Questions on Noise in analog communication, MCQ on Noise in Analog Communication, Engineering MCQ

### Multiple-Choice Questions

Q.1. An amplifier having noise figure of 20 dB and available power gain of 15 dB is followed by a mixer circuit having noise figure of 9 dB. The overall noise figure as referred to input in dB is:

- 11.07
- 10.44
- 21.52
- 0.63

**Answer: **21.52

Q.2. Thermal noise is independent of

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

**Answer: **centre frequency

Q.3. Transistor *T _{1}* operates at 20 kHz and

*T*operates at 200 Hz. The flicker noise is

_{2}- more in
*T*_{1} - more in
*T*_{2} - equal in both
- depends on bias

**Answer: **more in *T _{2}*

Q.4. A triode has transconductance equal to 25 µυ. The equivalent noise resistance is

- 1 M ohms
- 1 k ohms
- 10 k ohms
- 100 k ohms

**Answer: **100 k ohms

Q.5. Johnson noise is

- always white
- white for all practical frequencies
- never white
- depends on temperature

**Answer: **white for all practical frequencies

Q.6. The spectrum of the white noise and an impulse function is similar in following respects

- both have similar magnitude spectrum
- both have similar phase spectrum
- both have similar magnitude and phase spectrum
- they have nothing similar

**Answer: **both have similar magnitude spectrum

Q.7. Parallel combination of a resistance R and a capacitance C develops a noise voltage source at its common terminal. The rms value of the voltage varies

- proportional to R
- inversely proportional to C
- inversely proportional to square root of C
- proportional to RC

**Answer: **inversely proportional to square root of C

Q.8. A noise voltage source has a resistance of 10 ohms. Its power density spectrum is 0.24 x 10^{-5}. The corresponding available power density is

- 2.6 x 10
^{-5} - 0.0.25
- 26 x 10
^{-5} - 6 x 10
^{-8}

**Answer: **6 x 10^{-8}

Q.9. A narrow-band noise shows

- amplitude modulation only
- frequency modulation only
- both AM and FM
- none

**Answer: **both AM and FM

Q.10. A narrow-band noise source *n(t)* has symmetrical spectrum and has power density spectrum 0.2 x 10^{-6}. The power density of quadrature component is

- 0.2 x 10
^{-6} - 0.1 x 10
^{-6} - 0.4 x 10
^{-6} - 0.05 x 10
^{-6}

**Answer: **0.1 x 10^{-6}

Q.11. In a certain system, the signal power is 13 dBm and noise power is -1 dBm. The SNR will be

- 14 dB
- -13 dB
- 12 dBm
- 12 dB

**Answer: **14 dB

Q.12. If the resistance value is doubled and temperature maintained constant, the available thermal noise power per unit bandwidth will

- increase two-fold
- increase four-fold
- remain unchanged
- decrease to half

**Answer: **increase two-fold

Q.13. The co-variance function of a band limited white noise is

- A Dirac delta function
- An exponentially decreasing function
- A sine function
- Sine
^{2}Function

**Answer: **A Dirac delta function

Q.14. Noise with uniform power spectral density of *N _{0}* W/Hz is passed through a filter

*H(ω) = 2Exp (- jωt*followed by an ideal low pass filter of bandwidth

_{d})*B*Hz. The output noise power in watts is

- 2 N
_{0}B - 4 N
_{0}B - 8 N
_{0}B - 16 N
_{0}B

**Answer: **4 N_{0}B

Q.15. Noise with double-sided power spectral density of *K* over all frequencies is passed through an RC low pass filter with 3 dB cut-off frequency of ** f_{c}**. The noise power at the filter output is

- K
- K
*f*_{c} - Kπ
*f*_{c} - ∞

**Answer: **Kπ*f _{c}*

Q.16. A white noise process *x(t)* with two-sided power spectral density of 1 x 10^{-10} W/Hz is input to a filter whose magnitude squared response is shown below.

Fig. MCQ 4.16

The power of the output process *Y(t)* is given by

- 5 x 10
^{-7}W - 1 x 10
^{-6}W - 2 x 10
^{-6}W - 1 x 10
^{-5}W

**Answer: **1 x 10^{-6} W

Q.17. A system has a receiver noise resistance of 50 Ω. It is connected to an antenna with an input resistance of 50 Ω. The noise figure of the system is

- 1
- 2
- 50
- 101

**Answer: **1

Q.18. Which one of the following types of noise gains importance at high frequency?

- Shot noise
- Random noise
- Impulse noise
- Transit-time noise

**Answer: **Transit-time noise

Q.19. **Assertion (A):** The noise generated by a resistor depends upon its operating temperature. **Reason (R):** Average noise power generated in a resistor is given by *Pn = kT Δf*, where k = Boltzmann’s constant T = temperature in degree Kelvin, Δf = bandwidth of interest

- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is NOT the correct explanation of A.
- A is true but R is false.
- A is false but R is true.

**Answer: **A is true but R is false.

Q.20. Thermal noise is passed through an ideal low-pass filter having cut-off at *f _{c }= ω* Hz. The autocorrelation value of the noise at the output of the filter is given as

- a delta function at t = 0
- Gaussian over the range -∞ ≤ t ≤ ∞.
- Sinc function over the range -∞ ≤ t ≤ ∞.
- triangular function over the range
*-1/2 ωt ≤ t ≤ 1/2 ωt*

**Answer: **Sinc function over the range -∞ ≤ t ≤ ∞.

Q.21. Which one of the following is the correct statement? If the value of a resistor creating thermal noise is doubled, the noise power generated is

- halved
- doubled
- unchanged
- slightly changed

**Answer: **doubled