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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.
| 51. |
The time required for horizontal blanking is 16% of that for each horizontal line. If horizontal time is 63.5 μs, the horizontal blanking time for each line is about |
| A. | 1 μs |
| B. | 10 μs |
| C. | 100 μs |
| D. | none of the above |
| Answer» C. 100 μs | |
| 52. |
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 | |
| 53. |
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. | |
| 54. |
If ω is the frequency of modulating voltage in FM, the modulation index is proportional to |
| A. | ω |
| B. | 1/ω |
| C. | √ω |
| D. | 1/√ω |
| Answer» C. √ω | |
| 55. |
In ionosphere incidence angle is 60°. The maximum usable frequency fm is equal to |
| A. | 2fc |
| B. | fc |
| C. | 0.5 fc |
| D. | √3 fc |
| Answer» B. fc | |
| 56. |
If Eb, the energy per bit of a binary digital signal is 10‾⁶ watt sec. and the one sided power spectral density of the white noise N0 = 10‾⁵ W/Hz, then the output SNR of the matched filter is |
| A. | 26 dB |
| B. | 10 dB |
| C. | 20 dB |
| D. | 13 dB |
| Answer» E. | |
| 57. |
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. | 0.90 |
| C. | 0.10 |
| D. | 0.05 |
| Answer» D. 0.05 | |
| 58. |
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 | |
| 59. |
Assertion (A): In AM the amplitude of carrier is made proportional to the instantaneous amplitude of modulating waveReason (R): In AM, frequency of side band = frequency carrier ± frequency of modulating wave. |
| A. | Both A and R are correct and R is correct explanation of A |
| B. | Both A and R are correct but R is not correct explanation of A |
| C. | A is correct but R is wrong |
| D. | A is wrong but R is correct |
| Answer» C. A is correct but R is wrong | |
| 60. |
A device with input x(t) and y(t) is characterized by y(t) = x²(t). An FM signal with frequency deviation of 90 kHz and modulating signal bandwidth of 5 kHz is applied to this device. The bandwidth of the output signal is |
| A. | 370 kHz |
| B. | 190 kHz |
| C. | 380 kHz |
| D. | 95 kHz |
| Answer» D. 95 kHz | |
| 61. |
The power requirement of a RADAR used in military operations is |
| A. | a few watts |
| B. | about 500 W |
| C. | about 2000 W |
| D. | a few megawatts |
| Answer» E. | |
| 62. |
If there are M equally likely and independent messages and M = 2ᴺ where N is an integer, the information in each message is equal to |
| A. | N bits |
| B. | 0.5 N bits |
| C. | 2 N bits |
| D. | 4 N bits |
| Answer» B. 0.5 N bits | |
| 63. |
In the FM wave described by equation v = 15 sin (4 x 10⁸ t + 3 sin 1100 t), the carrier frequency and signal frequency respectively are |
| A. | 63.66 MHz and 175 Hz |
| B. | 4 x 10⁸ Hz and 1100 Hz |
| C. | 175 Hz and 63.66 MHz |
| D. | 1100 Hz and 4 x 10⁸ Hz |
| Answer» B. 4 x 10⁸ Hz and 1100 Hz | |
| 64. |
Thermal noise is passed through an ideal low pass filter having cut off at fc = ω Hz. The auto-correlation value of the noise at the output of the filter is given as |
| A. | a delta function at t = 0 |
| B. | gaussian over the range -∞ ≤ t ≤ ∞ |
| C. | sin c function over the range -∞ ≤ t ≤ ∞ |
| D. | none of the above |
| Answer» D. none of the above | |
| 65. |
The most suitable method for detecting a modulated signal g(t) = (3 to 6 cos 2πfmt) cos 2πfct is |
| A. | envelope detector |
| B. | synchronous detector |
| C. | ratio detector |
| D. | both a and b |
| Answer» B. synchronous detector | |
| 66. |
Consider the following statements: In a radar system having a high value of the ratio (antenna diameter)/wavelength 1. the maximum range is large2. good target discrimination is achieved3. capture area is increased4. target acquisition is difficult Which of the above are correct? |
| A. | 1, 2, 3, 4 |
| B. | 1, 2, 3 |
| C. | 1, 2 |
| D. | 1, 3, 4 |
| Answer» C. 1, 2 | |
| 67. |
Some features of advanced mobile phone service are 1. To provide telephone communication to a large number of telephone users within the area of a metropolitan only2. To use minimum amount of frequency spectrum3. To permit hand held as well as vehicle operation of telephone Which of the above are true? |
| A. | 1 and 2 only |
| B. | 1, 2, 3 |
| C. | 1 and 3 only |
| D. | 2 and 3 only |
| Answer» C. 1 and 3 only | |
| 68. |
If M (jω) = £[m(t)] where £ denotes Fourier transform, then £[m(t) cos ωct] = |
| A. | M (jω + jωc) |
| B. | M (jω - jωc) |
| C. | M (jω + jωc) + M (jω - jωc) |
| D. | 1/2 [M (jω + jωc) + M (jω - jωc)] |
| Answer» E. | |
| 69. |
Consider the following 1. Generation of SSB signals2. Design of minimum phase type filters3. Representation of band pass signals Which of the above applications is Hilbert transform used? |
| A. | 1 only |
| B. | 1, 2 and 3 |
| C. | 1, 2 only |
| D. | 1 and 3 |
| Answer» C. 1, 2 only | |
| 70. |
A superheterodyne receiver is to operate in the frequency range 550 kHz - 1650 kHz, with the intermediate frequency of 450 kHz. Let R = Cmin/Cmax denote the required capacitance ratio of the local oscillator and I denote the image frequency (in kHz) of the incoming signal. If the receiver is tuned to 700 kHz, then |
| A. | R = 4.41 J =1600 |
| B. | R = 2.10 J =1150 |
| C. | R = 3.0 J =1600 |
| D. | R = 9.0 J =1150 |
| Answer» B. R = 2.10 J =1150 | |
| 71. |
An analog signal is band limited to B Hz sampled at Nyquist rate and samples are quantized into 4 levels each with probability 1/4. The information rate is |
| A. | 4 bits/s |
| B. | B bits/s |
| C. | 4 B bits/s |
| D. | 0.25 B bits/s |
| Answer» D. 0.25 B bits/s | |
| 72. |
In a reactance FET, gm = 9 x 10‾³ Siemens, gate to source resistance is one-ninth of reactance of gate to drain capacitor and frequency is 4 MHz. The capacitive-reactance is |
| A. | 1000 Ω |
| B. | 1/1000 Ω |
| C. | 36 x 10³ Ω |
| D. | 4/9 x 10³ Ω |
| Answer» B. 1/1000 Ω | |
| 73. |
When number of quantization levels are two, then the average transmission power in NRZ polar signalling is __________ that of NIRZ unipolar signalling. |
| A. | 1/2 |
| B. | 1/4 |
| C. | 1/8 |
| D. | None |
| Answer» D. None | |
| 74. |
Some desirable features of a computer communication network are 1. It should accept an intended transmission without excessive delay2. The data arriving at a receiving point should be processed rapidly3. When a transmission calls for a response, the delay of response should be minimum. Which of the above are true? |
| A. | 1 and 2 only |
| B. | 1 and 3 only |
| C. | 1, 2, 3 |
| D. | 2 and 3 only |
| Answer» D. 2 and 3 only | |
| 75. |
Some features of RF stage in good radio receivers is 1. It increases sensitivity by providing amplification to RF signal2. It eliminates image frequency interference3. It increases selectivity4. It reduces noise level Which of the above are true? |
| A. | 1, 2 and 3 only |
| B. | 1, 2 and 4 only |
| C. | 2, 3, 4 only |
| D. | 1, 2, 3, 4 |
| Answer» E. | |
| 76. |
In TV transmitter, visual exciter may consist of 1. Video processing unit2. Visual modulator3. VSB filter4. Delay equaliser5. Frequency converter Which of the above are actually a part of visual exciter? |
| A. | 1, 2 and 3 |
| B. | 2, 3 and 4 |
| C. | 1, 2, 3 and 4 |
| D. | 1, 2, 3, 4 and 5 |
| Answer» E. | |
| 77. |
In a single tone AM the power of carrier is P and modulation index is m. The powers of each of the two side bands are |
| A. | Pm² / 4 |
| B. | Pm² / 2 |
| C. | Pm² / 8 |
| D. | Pm² / 16 |
| Answer» B. Pm² / 2 | |
| 78. |
A message signal with bandwidth 10 kHz is lower sideband SSB modulated with carrier frequency fc1 = 10⁶ Hz. The resulting signal is then passed though a narrow band frequency modulator with carrier frequency fc2 = 10⁹ Hz. The bandwidth of the output would be |
| A. | 4 x 10⁴ Hz |
| B. | 2 x 10⁶ Hz |
| C. | 2 x 10⁹ Hz |
| D. | 2 x 10¹⁰ Hz |
| Answer» C. 2 x 10⁹ Hz | |
| 79. |
Consider the following features of monochrome TV 1. Number of lines per picture - 6252. Interlace ratio - 2 : 13. Aspect ratio - 4 : 34. Channel bandwidth - 8 MHz As regards CCIR system B, which of the above are correct? |
| A. | 1, 2, 3, 4 |
| B. | 1, 2, 3 |
| C. | 1, 2, 4 |
| D. | 2, 3, 4 |
| Answer» C. 1, 2, 4 | |
| 80. |
Consider the following statements in amplitude modulation 1. The harmonic and intermodulation distortion may occur in audio and RF amplifiers2. The sum and difference frequencies are present in the output of mixer3. The diode detector has audio frequencies in its output4. A balanced modulator cannot produce an AM with suppressed carrier Which of the above are true? |
| A. | 1, 2, 3, 4 |
| B. | 1, 2, 3 |
| C. | 1, 2 |
| D. | 3, 4 |
| Answer» C. 1, 2 | |
| 81. |
Consider the following statements as regards DPSK and DEPSK 1. DPSK demodulator requires a device which operates at carrier frequency and provides a delay of bit time Tb2. In DPSK, synchronous demodulation recovers the signal b(t) and the decoding of b(t) to generate d(t) is done at base band3. In both DPSK and DEPSK errors always occur in pairs Which of the above statements are correct? |
| A. | 1 and 3 |
| B. | 1 and 2 |
| C. | 2 and 3 |
| D. | 1, 2 and 3 |
| Answer» C. 2 and 3 | |
| 82. |
The minimum viewing angle of resolution of human eye is (D is iris opening and λ is wavelength of light) |
| A. | λ/D radians |
| B. | 1.22λ/D radians |
| C. | 5λ/D radians |
| D. | λ²/D radians |
| Answer» C. 5λ/D radians | |
| 83. |
Which of the following are useful in comparing the noise performance of receivers? 1. Input noise voltage2. Noise figure3. Noise resistance4. Noise temperature Select answer as per the following codes: |
| A. | 1, 2 and 3 |
| B. | 1, 3 and 4 |
| C. | 2, 3, 4 |
| D. | 1, 2, 4 |
| Answer» D. 1, 2, 4 | |
| 84. |
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 | |
| 85. |
If the amplitude of the voltage is kept constant, but its frequency is raised to 6 kHz, the new deviation will be for the modulation index is, if fm = 500 Hz, Δf = 2.25 |
| A. | 6 kHz |
| B. | 12 kHz |
| C. | 27 kHz |
| D. | 54 kHz |
| Answer» D. 54 kHz | |
| 86. |
Consider the following statements as regards noise1. If Gaussian noise is applied at input of a rectifier, the output is not gaussian2. The noise encountered on a telephone line consists of short, pulse type disturbances whose amplitude distribution is not Gaussian3. Shot noise results from random emission of electrons from a cathode4. Shot noise results from phenomenon associated with the flow of current across semi conductor junctions Which of the above are correct? |
| A. | 1, 2, 3, only |
| B. | 1, 2, 4 only |
| C. | 1, 2, 3, 4 |
| D. | 2, 3 only |
| Answer» D. 2, 3 only | |
| 87. |
Consider the following statements about loop antenna 1. It is suitable for direction finding application2. It is a single turn or multiturn coil carrying RF current3. The loop is surrounded by a magnetic field everywhere perpendicular to the loop Which of the above statements are correct? |
| A. | 1 and 2 only |
| B. | 1 only |
| C. | 1, 2, 3 |
| D. | 2 and 3 only |
| Answer» D. 2 and 3 only | |
| 88. |
A 1 MHz sinusoidal carrier is amplitude modulated by a symmetrical square wave of period 100 μ sec. Which of the following frequencies will not be in the modulated signal? |
| A. | 990 kHz |
| B. | 1010 kHz |
| C. | 1020 kHz |
| D. | 1030 kHz |
| Answer» D. 1030 kHz | |
| 89. |
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 | |
| 90. |
An antenna having a length of λ/4 and grounded at one end is called |
| A. | Marconi antenna |
| B. | Yagi antenna |
| C. | Turnstile antenna |
| D. | None of the above |
| Answer» B. Yagi antenna | |
| 91. |
In a two tone AM system the two modulating frequencies are 2000 π and 4000 π rad/sec. If carrier frequency is 2π x 10⁶ rad/sec the frequencies of upper sidebands are |
| A. | 1.002 MHz and 1.004 MHz |
| B. | 1.001 MHz and 1.002 MHz |
| C. | 1.001 MHz and 1.004 MHz |
| D. | 1.002 MHz and 1.008 MHz |
| Answer» C. 1.001 MHz and 1.004 MHz | |
| 92. |
A signal m(t) amplitude modulates a carrier Ac cos ωct. The final signal will be |
| A. | [Ac m(t)] cos ωct] |
| B. | Ac . [1 + m(t)] cos ωct |
| C. | Ac + [m(t)] cos ωct |
| D. | Ac cos ωct + m(t) |
| Answer» C. Ac + [m(t)] cos ωct | |
| 93. |
In single tone FM discriminator (S₀/N₀) is |
| A. | proportional to deviation |
| B. | proportional to cube of deviation |
| C. | proportional to square of deviation |
| D. | none of the above |
| Answer» E. | |
| 94. |
If γ = (S0/N0)/(Si/Nm) where S0 and S1 are signal power output and signal power input and N0 and Nm are noise power output and noise power input, the value of γ for SSB-SC and DSB-SC amplitude modulated system respectively are |
| A. | 1 and 1 |
| B. | 1 and 2 |
| C. | 2 and 1 |
| D. | 0.5 and 0.5 |
| Answer» B. 1 and 2 | |
| 95. |
Consider the following types of distortions in diode detectors 1. Distortion is caused due to the reason that dc and ac load impedances are unequal2. Distortion is caused because ac load impedance has a reactive component at high audio frequencies3. Audio frequency diode current is less than dc current Which of the above are true? |
| A. | 1, 2 and 3 |
| B. | 1 and 2 |
| C. | 1 and 3 |
| D. | 2 and 3 |
| Answer» C. 1 and 3 | |
| 96. |
The characteristics of H and V sync pulses in a colour TV receiver are1. H sync, pulses are narrow and have frequency of 15625 Hz2. V sync, pulses are much wider and have frequency of 50 Hz3. H and V pulses have almost the same size but frequencies of 15625 and 50 Hz respectively4. V sync, pulses are very narrow but H sync, pulses are wide and their frequencies are 15625 Hz and 50 Hz respectively Which of the above are correct? |
| A. | 1 and 2 only |
| B. | 1 only |
| C. | 3 only |
| D. | 4 only |
| Answer» B. 1 only | |
| 97. |
In a two stage cascade amplifier, each stage has a gain of 10 dB and noise figure of 10 dB. The overall noise factor is |
| A. | 10 |
| B. | 1.09 |
| C. | 1 |
| D. | 10.9 |
| Answer» E. | |
| 98. |
A horizontal output stage is cutoff for retrace and 40% of trace. If time for each horizontal line is 64 μs and retrace time is 12 μs, the transistor is conducting for about |
| A. | 64 μs |
| B. | 6.4 μs |
| C. | 31 μs |
| D. | 3.1 μs |
| Answer» D. 3.1 μs | |
| 99. |
c(t) and m(t) are used to generate an FM signal. If the peak frequency deviation of the generated FM signal is three times the transmission bandwidth of the AM signal, then the coefficient of the term cos [2π(1008 x 10³t)] in the FM signal (in terms of the Bessel Coefficients) is |
| A. | 5 J₄(3) |
| B. | 5/2 J₈(3) |
| C. | 5/2 J₈(4) |
| D. | 5 J₄(6) |
| Answer» E. | |
| 100. |
Consider the following statements about PCM 1. PCM is not noise resistant2. PCM requires complex encoding and quantizing circuitry3. PCM requires large bandwidth Which of the above are correct? |
| A. | 1 only |
| B. | 1, 2, 3 |
| C. | 2, 3 |
| D. | 1 and 3 |
| Answer» D. 1 and 3 | |