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MCQOPTIONS
This section includes 1362 Mcqs, each offering curated multiple-choice questions to sharpen your Electronics & Communication Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
The Hilbert transform of cos ω1t + sin ω2t is |
| A. | sin ω1t + cos ω2t |
| B. | sin ω1t - cos ω2t |
| C. | cos ω1t - cos ω2t |
| D. | - sin ω1t + cos ω2t |
| Answer» C. cos ω1t - cos ω2t | |
| 2. |
Efficiency of general AM signal with em = E1 cos ω1t + E2 cos ω2 tj ec = Ec cos ωct; E1 cos ω1t with modulation index m2 is __________ . |
| A. | [A]. |
| B. | [B]. |
| C. | [C]. |
| D. | [D]. |
| Answer» B. [B]. | |
| 3. |
For a given data rate, the bandwidth βp of a BPSK signal and the bandwidth β0 of the OOK signal are related as |
| A. | [A]. |
| B. | βp = 2β0 |
| C. | [C]. |
| D. | βp = β0 |
| Answer» E. | |
| 4. |
Noise with uniform power spectral density of N0ω/Hz is passed through a filter H(ω) = 2 exp (-J ω ty) followed by an ideal low pass filter of bandwidth B Hz. The output noise power in watts is |
| A. | 2 N0B |
| B. | 4 N0B |
| C. | 8 N0B |
| D. | 16 N0B |
| Answer» C. 8 N0B | |
| 5. |
A sequence x(n) with the z transform X(z) = z4 + z2 - 2z + 2 - 3z - 4 is applied as an input to a linear, time invariant system with the impulse response h(n) = 2δ(n - 3) where The output at n = 4 is |
| A. | - 6 |
| B. | zero |
| C. | 2 |
| D. | - 4 |
| Answer» C. 2 | |
| 6. |
A signal x(t) = 100 cos (24p x 103t) is ideally sampled with a sampling period of 50 μ sec and then passed through an ideal low pass filter with cut off frequency of 15 kHz Which of the following frequencies are present at the filter output? |
| A. | 12 kHz only |
| B. | 8 kHz only |
| C. | 12 kHz and 9 kHz |
| D. | 12 kHz and 8 kHz |
| Answer» E. | |
| 7. |
If the variance σx2 of d(n) = x(n) - x(n - 1) is one-tenth the variance σx2 of a stationary zero mean discrete time signal x(n), then the normalized autocorrelation function Rxx(x)/σx2 at k = 1 is |
| A. | 0.95 |
| B. | 0.9 |
| C. | 0.1 |
| D. | 0.05 |
| Answer» D. 0.05 | |
| 8. |
In the figure , the output y(t) will be |
| A. | [A]. |
| B. | [B]. |
| C. | [C]. |
| D. | [D]. |
| Answer» D. [D]. | |
| 9. |
The F.T. of {e-1 ∪(t)} is equal to . Therefore is |
| A. | ef ∪ (f) |
| B. | e-f ∪ (f) |
| C. | ef ∪ (-f) |
| D. | e-f ∪ (-f) |
| Answer» D. e-f ∪ (-f) | |
| 10. |
Consider a sampled signal y(t) = 5 x 10-6 x(t) where x(t) = 10 cos (8p x 103)t and ts = 100 μ sec. when y(t) is passed through an ideal low-pass filter with a cut off frequency of 5 kHz, the output of the filter is |
| A. | 5 x 10-6 cos (8p x 103)t |
| B. | 5 x 10-5 cos (8p x 103)t |
| C. | 5 x 10-1 cos(8p x 103)t |
| D. | 10 cos(8p x 103)t |
| Answer» C. 5 x 10-1 cos(8p x 103)t | |
| 11. |
The PDF of a Gaussian random variable X is given by . The probability of the event {X = 4} is |
| A. | [A]. |
| B. | [B]. |
| C. | 0 |
| D. | [D]. |
| Answer» C. 0 | |
| 12. |
If k is Boltzmann's constant, T0 is standard ambient temperature, δf is bandwidth of receiver, F is noise figure, the minimum receivable signal in a radar receiver is given by |
| A. | k T0(δf)(F) |
| B. | k T0(δf)(F - 1) |
| C. | [C]. |
| D. | none of the above |
| Answer» C. [C]. | |
| 13. |
A 100 + j 100 Ω load is to be matched to a line with Z0 = 300 Ω to give SWR = 1. The reactance of stub is |
| A. | j 200 Ω |
| B. | -j 200 Ω |
| C. | j 100 Ω |
| D. | -j 100 Ω |
| Answer» C. j 100 Ω | |
| 14. |
A (75 - j 50) Ω load is connected to a coaxial line of Z0 = 75 Ω at 10 GHz. The best method of matching consists of using |
| A. | a capacitance at some specific distance from load |
| B. | a short circuited stub at some specific distance from load |
| C. | an inductance at load |
| D. | a short circuited stub at load |
| Answer» E. | |
| 15. |
In a phase discriminator fc, is the IF to which primary circuit is tuned. Consider the following statements: The primary and secondary voltages are exactly 90° out of phase when input frequency is fcmore than 90° out of phase when input frequency is higher than fcless than 90° out of phase when input frequency is lower than fc Which of the above statements is correct? |
| A. | 1 only |
| B. | 1 and 2 |
| C. | 1, 2 and 3 |
| D. | 2 and 3 |
| Answer» B. 1 and 2 | |
| 16. |
A device has two resistances 300 Ω and 200 Ω respectively. The noise voltages due to these two resistance calculated separately are 5.38 μV and 4.38 μV respectively. When both of them are used together, the noise voltage will be |
| A. | 9.76 V |
| B. | 1 μV |
| C. | 23.56 μV |
| D. | 6.94 μV |
| Answer» E. | |
| 17. |
An antenna has a resistance of 50 Ω and an equivalent noise resistance of 30 Ω The noise figure in decibels is |
| A. | 1.6 dB |
| B. | 2 dB |
| C. | 3.6 dB |
| D. | 6 dB |
| Answer» C. 3.6 dB | |
| 18. |
For a resistance of about 15 kΩ operating in a frequency range of a few MHz, the noise voltage is in the range of |
| A. | a few μV |
| B. | about 100 μV |
| C. | a few μV |
| D. | a few volts |
| Answer» B. about 100 μV | |
| 19. |
A resistor of 10 kΩ has an rms noise voltage of 1 mV under a certain set of conditions. A resistor of 20 kΩ under the same conditions will have an rms noise voltage of |
| A. | 1 mV |
| B. | 2 mV |
| C. | 1.414 mV |
| D. | 4 mV |
| Answer» D. 4 mV | |
| 20. |
The spectral component of noise associated with kth frequency is given, in the limit as Δf → 0 by nk(t) written as nk(t) = Ck cos (2pk Δft + θk) Consider the following statements as regards Ck and θk Ck and θk are independent of one anotherCk and θk are independent of the amplitude of a spectral component at a different frequencyCt and θk are independent of the phase of a spectral component at a different frequency Which of the above statements are correct? |
| A. | 1, 2 only |
| B. | 1, 3 only |
| C. | 1, 2, 3 |
| D. | 2, 3 only |
| Answer» D. 2, 3 only | |
| 21. |
The equation v(t) = A cos [ωct + φ(t)] where A and ωc are constant and φ(t) is a function of base signal represents Phase modulationAmplitude modulationAngle modulationFrequency modulation Which of the above are true? |
| A. | 3 only |
| B. | 1, 3 and 4 |
| C. | 1, 2, 3, 4 |
| D. | 3 and 4 only |
| Answer» C. 1, 2, 3, 4 | |
| 22. |
In telephone systems the relation between load r, number of calls initiated during a specified interval λ and average duration of a call (h) is |
| A. | r = λh |
| B. | r = λh2 |
| C. | λ = rh |
| D. | h = λr |
| Answer» B. r = λh2 | |
| 23. |
An amplifier has an input resistance of 10 kΩ and the noise voltage is 10 μV. If two such resistances of 10 kΩ each are connected in series at the input, the total noise voltage is about |
| A. | 20 μV |
| B. | 5μV |
| C. | 14.14 μV |
| D. | 10 μV |
| Answer» D. 10 μV | |
| 24. |
In a system an input resistance of 20 kΩ causes a noise voltage of 15μV. If two such input resistances each of 20 kΩ are used in parallel, the total noise voltage will be about |
| A. | 15 μV |
| B. | 30 μV |
| C. | 7.5 μV |
| D. | 10.6 μV |
| Answer» E. | |
| 25. |
An amplifier operating over a frequency range of 18 to 20 MHz has 10 kΩ input resistance. At a temperature of 27° C, the noise voltage at input of amplifier is (Boltzman constant k = 1.38 x 10-23 J/K) |
| A. | 18.2 μV |
| B. | 182 μV |
| C. | 16.2 μV |
| D. | 162 μV |
| Answer» B. 182 μV | |
| 26. |
For a three stage cascaded amplifier, having gains of G1, G2 and G3 and noise figures of F1, F2, F3 the overall noise figure |
| A. | [A]. |
| B. | [B]. |
| C. | [C]. |
| D. | None of the above |
| Answer» B. [B]. | |
| 27. |
If F(ω) is Fourier transform of f(t), then Fourier transform of f(t) cos2 ωct is |
| A. | F(ω) + [F(ω + 2ωc) + F(ω - 2ωc)] |
| B. | F(ω) + [F(ω + 2ωc) + F(ω - 2ωc)] |
| C. | F(ω) - [F(ω + 2ωc) + F(ω - 2ωc)] |
| D. | F(ω) - [F(ω + 2ωc) + F(ω - 2ωc)] |
| Answer» B. F(ω) + [F(ω + 2ωc) + F(ω - 2ωc)] | |
| 28. |
A carrier A cos ωct is modulated by a signal mt A cos ω1t + m2 A cos ω2t + m3 A cos ω3t. The total modulated power is |
| A. | [A]. |
| B. | A2(1 + 0.5 m12 + 0.5 m22 + 0.5 m32) |
| C. | [C]. |
| D. | [D]. |
| Answer» B. A2(1 + 0.5 m12 + 0.5 m22 + 0.5 m32) | |
| 29. |
A damped harmonic oscillator has a frequency of 5 oscillations per second. The amplitude drops to half its value for every 10 oscillations. The time it will take to drop to \(\frac{1}{{1000}}\) of the original amplitude is close to: |
| A. | 50 s |
| B. | 100 s |
| C. | 20 s |
| D. | 10 s |
| Answer» D. 10 s | |
| 30. |
For an amplitude modulated signal, ωm and ωc are angular frequency of message signal and carrier wave respectively then AM signals contains frequencies |
| A. | only ωm |
| B. | ωc and ωm |
| C. | (ωc - ωm) and ωm |
| D. | (ωc - ωm), ωc and (ωc + ωm) |
| Answer» E. | |
| 31. |
In a communication system operating at wavelength 800 nm, only one percent of source frequency is available as signal bandwidth. The number of channels accommodated for transmitting TV signals of bandwidth 6 MHz are(Take velocity of light c = 3 × 108 m/s, h = 6.6 × 10-34 J-s) |
| A. | 3.75 × 106 |
| B. | 3.86 × 106 |
| C. | 6.25 × 105 |
| D. | 4.87 × 105 |
| Answer» D. 4.87 × 105 | |
| 32. |
Encryption is |
| A. | Coding of messages to prevent unauthorised access |
| B. | Coding of computers to prevent unauthorised users |
| C. | Creating bar codes on computer peripherals |
| D. | Conversion of hard copy into soft copy |
| Answer» B. Coding of computers to prevent unauthorised users | |
| 33. |
GPRS is a : |
| A. | Wired Communication Service |
| B. | Computer Programme |
| C. | Cell Phone Device |
| D. | Wireless Communication |
| Answer» E. | |
| 34. |
A simple harmonic motion is represented by \({\rm{y}} = 5\left( {{\rm{sin\;}}3{\rm{\pi t}} + \sqrt 3 {\rm{cos\;}}3{\rm{\pi t}}} \right){\rm{cm}}.{\rm{\;}}\)The amplitude and time period of the motion are |
| A. | \(10{\rm{\;cm}},\frac{3}{2}{\rm{s}}\) |
| B. | \({\rm{\;}}5{\rm{\;cm}},\frac{2}{3}{\rm{s}}\) |
| C. | \(5{\rm{\;cm}},\frac{3}{2}{\rm{s}}\) |
| D. | \(10{\rm{\;cm}},\frac{2}{3}{\rm{g}}\) |
| Answer» E. | |
| 35. |
A signal A.cos ωt is transmitted using v0 sinω0 tas carrier wave. The correct amplitude modulated (AM) signal is: |
| A. | \({v_0}{\rm{\;sin}}{\omega _0}t + \frac{{\rm{A}}}{2}{\rm{sin}}\left( {{\omega _0} - \omega } \right)t + \frac{{\rm{A}}}{2}\left( {{\omega _0} + \omega } \right)t\) |
| B. | v0 sin [ω0 (1 + 0.01A sin ωt)t] |
| C. | v0 sin ω0 t + A cos ωt |
| D. | (v0 + A) cos ωt sinω0 t |
| Answer» B. v0 sin [ω0 (1 + 0.01A sin ωt)t] | |
| 36. |
Match the following communication channels with their distinguishing type:Set I (Communication Channel)Set II (Distinguishing Type)A) Bloggingi) Electronic MediaB) Televisionii) Print MediaC) Periodicalsiii) Social MediaD) Collection sitesiv) World wide webChoose the correct option from those given below: |
| A. | A-iv, B-ii, C-i, D-iii |
| B. | A-ii, B-iv, C-iii, D-i |
| C. | A-i, B-iii, C-iv, D-ii |
| D. | A-iii, B-i, C-ii, D-iv |
| Answer» E. | |
| 37. |
An amplitude modulates signal is given byv(t) = 10[1 + 0.3 cos (22 × 104 t)] sin (5.5 × 105 t)Here, t is in seconds. The sideband frequencies (in kHz) are (Take, \(\pi = \frac{{22}}{7}\)) |
| A. | 892.5 and 857.5 |
| B. | 89.25 and 85.75 |
| C. | 178.5 and 171.5 |
| D. | 1785 and 1715 |
| Answer» C. 178.5 and 171.5 | |
| 38. |
Given below in the left column are different modes of communication using the kinds of waves given in the right column.A. Optical Fibre CommunicationP. UltrasoundB. RadarQ. Infrared LightC. SonarR. MicrowavesD. Mobile PhonesS. Radio wavesFrom the options given below, find the most appropriate match between entries in the left and the right column. |
| A. | A-Q, B-S, C-R, D-P |
| B. | A-S, B-Q, C-R, D-P |
| C. | A-Q, B-S, C-P, D-R |
| D. | A-R, B-P, C-S, D-Q |
| Answer» D. A-R, B-P, C-S, D-Q | |
| 39. |
In a line of sight radio communication, a distance of about 50 km is kept between the transmitting and receiving antennas. If the height of the receiving antenna is 70 m, then the minimum height of the transmitting antenna should be:(Radius of the Earth = 6.4 × 106 m |
| A. | 20 m |
| B. | 51 m |
| C. | 32 m |
| D. | 40 m |
| Answer» D. 40 m | |
| 40. |
In an amplitude modulator circuit, the carrier wave is given by, C(t) = 4 sin (20000πt) while modulating signal is given by, m(t) = 2 sin (2000πt). The values of modulation index and lower side band frequency are: |
| A. | 0.5 and 10 kHz |
| B. | 0.4 and 10 kHz |
| C. | 0.3 and 9 kHz |
| D. | 0.5 and 9 kHz |
| Answer» E. | |
| 41. |
A TV transmission tower has a height of 140 m and the height of the receiving antenna is 40 m. What is the maximum distance up to which signals can be broadcasted from this tower in LOS (Line of Sight) mode? (Take, radius of earth = 6.4 × 106 m). |
| A. | 65 km |
| B. | 80 km |
| C. | 40 km |
| D. | 48 km |
| Answer» B. 80 km | |
| 42. |
Match List-I with List-IIList IList IIA) 50 in decimali) 0110010 in binaryB) 102 in decimalii) 1100110 in binaryC) Real - Time video conferencingiii) Synchronous communicationD) SMS textingiv) Asynchronous communication Choose the correct option from those given below: |
| A. | A-ii, B-i, C-iii, D-iv |
| B. | A-ii, B-i, C-iv, D-iii |
| C. | A-i, B-ii, C-iii, D-iv |
| D. | A-ii, B-iii, C-iv, D-i |
| Answer» D. A-ii, B-iii, C-iv, D-i | |
| 43. |
Immediacy of cues in communication is dependent upon one's own |
| A. | Economic preferences |
| B. | Cultural background |
| C. | Physical fitness |
| D. | Social expectations |
| Answer» C. Physical fitness | |
| 44. |
The HV supply to a TV receiver is 25 kV and the total beam current for the three electron guns is 2000 μA. The power handled by IHVT is |
| A. | 5W |
| B. | 0.5 W |
| C. | 50 W |
| D. | 500 W |
| Answer» D. 500 W | |
| 45. |
The modulation index is, if fm = 500 Hz, Δf = 2.25 kHz |
| A. | 2.25 |
| B. | 4.5 |
| C. | 9 |
| D. | 18 |
| Answer» C. 9 | |
| 46. |
Some sources of TV programs are 1. TV camera2. Telecine3. VTR4. External signal Which of the above are actually present in a TV studio? |
| A. | 1, 2, 3 and 4 |
| B. | 1, 2, 3 |
| C. | 1 and 3 |
| D. | 1 2 and 4 |
| Answer» B. 1, 2, 3 | |
| 47. |
Some multiplexing arrangements for telephone system are 1. Space multiplexing2. Time division multiplexing3. Frequency division multiplexing Which of the above allow transmission of many independent signals over a single channel? |
| A. | 1 only |
| B. | 2 and 3 only |
| C. | 1, 2, 3 |
| D. | 1 and 3 only |
| Answer» C. 1, 2, 3 | |
| 48. |
If F(ω) is Fourier transform of f(t), then the Fourier transform of f(t) cos ωct is |
| A. | F(ω + ωc) + F(ω - ωc) |
| B. | 1/2 [F(ω + ωc) + F(ω - ωc)] |
| C. | F(ω + ωc) - F(ω - ωc) |
| D. | 1/2 [F(ω + ωc) - F(ω - ωc)] |
| Answer» C. F(ω + ωc) - F(ω - ωc) | |
| 49. |
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 ω is message bandwidth and ωc is carrier frequency both in rad sec, |
| A. | Rc < 1/ω |
| B. | Rc > 1/ω |
| C. | Rc < 1/ωc |
| D. | Rc > 1/ωc |
| Answer» B. Rc > 1/ω | |
| 50. |
If k is Boltzmann's constant, T₀ is standard ambient temperature, δf is bandwidth of receiver, F is noise figure, the minimum receivable signal in a radar receiver is given by |
| A. | k T₀(δf)(F) |
| B. | k T₀(δf)(F - 1) |
| C. | k T₀(δf) / (F - 1) |
| D. | none of the above |
| Answer» C. k T₀(δf) / (F - 1) | |