MCQOPTIONS
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MCQOPTIONS
This section includes 83 Mcqs, each offering curated multiple-choice questions to sharpen your Electronic Devices Circuits knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
For which of the following reasons, amplitude modulation is used for broadcasting? |
| A. | It is more immune to noise |
| B. | Its use avoids receiver complexity |
| C. | It requires less transmitting power |
| D. | Only the positive peak of the carrier wave varies with the modulating signal |
| Answer» C. It requires less transmitting power | |
| 52. |
Determine the percentage power saved when carrier and one of the sidebands are suppressed in an AM wave modulated to a depth of 50%. |
| A. | 76% |
| B. | 83.3% |
| C. | 55% |
| D. | 94.4% |
| Answer» E. | |
| 53. |
If modulation index of an AM was is changed from 0 to 1, then the transmitted power |
| A. | increase by 50% |
| B. | increase by 75% |
| C. | increase by 100% |
| D. | remains unaffected |
| Answer» B. increase by 75% | |
| 54. |
Amplitude modulation is used for broadcasting because |
| A. | It is more noise immune than other modulation systems |
| B. | Compared with other systems it requires less transmitting power |
| C. | Its use avoids receiver complexity |
| D. | No other modulation system can provide the necessary BW for high fidelity |
| Answer» D. No other modulation system can provide the necessary BW for high fidelity | |
| 55. |
A 240 kHz, 10 Vpp carrier is amplitude modulated using a 1 kHz sine wave of 3 Vpp. What is the modulation index? |
| A. | 3.3 |
| B. | 0.3 |
| C. | 0.54 |
| D. | 0.6 |
| Answer» C. 0.54 | |
| 56. |
Given a carrier frequency of 100 kHz and a modulating frequency of 5 kHz, the bandwidth of AM transmission is |
| A. | 5 kHz |
| B. | 200 kHz |
| C. | 10 kHz |
| D. | 20 kHz |
| Answer» D. 20 kHz | |
| 57. |
In TV, Video signals are transmitted through |
| A. | Amplitude modulation |
| B. | Frequency modulation |
| C. | Either amplitude or frequency modulation |
| D. | Neither amplitude nor frequency modulation |
| Answer» B. Frequency modulation | |
| 58. |
In a 50% modulated signal, the carrier is suppressed for transmission. The saving in transmitter power would be |
| A. | 88.9% |
| B. | 11% |
| C. | 72% |
| D. | 18% |
| Answer» B. 11% | |
| 59. |
An AM signal with a carrier of 1 kW has 200 W in each side band. The percentage of modulation is: |
| A. | 20% |
| B. | 89.4% |
| C. | 49.7% |
| D. | 40% |
| Answer» C. 49.7% | |
| 60. |
A carrier voltage is simultaneously modulated by two sine waves causing modulating indexes of 0.4 and 0.3. The overall modulation index is |
| A. | 0.35 |
| B. | 0.7 |
| C. | 0.5 |
| D. | cannot be calculated unless the phase relations are known |
| Answer» D. cannot be calculated unless the phase relations are known | |
| 61. |
In a Frequency Division Multiplexed (FDM) system, cross talk occurs due to |
| A. | Imperfect time synchronization between transmitter and receiver |
| B. | Imperfect filtering at the receiver front-end |
| C. | Imperfect carrier recovery at the receiver |
| D. | Channel noise |
| Answer» C. Imperfect carrier recovery at the receiver | |
| 62. |
A signal with frequency fm modulates a carrier fc (where fc fm). Then the output of the AM - DSB-SC signal will contain frequencies: |
| A. | 2 fc and fc ± fm |
| B. | fc and fc ± 2 fm |
| C. | fc ± fm |
| D. | fc and fc ± fm |
| Answer» D. fc and fc ± fm | |
| 63. |
Modulation is used to1. Separate different transmissions2. Reduce the bandwidth requirement3. Allow the use of practicable antennas4. Ensure that intelligence may be transmitted over long distancesWhich of the above statements are correct? |
| A. | 1, 2 and 3 only |
| B. | 1, 3 and 4 only |
| C. | 2 and 4 only |
| D. | 1, 2, 3 and 4 |
| Answer» C. 2 and 4 only | |
| 64. |
In an amplitude modulated system, a sinusoidal carrier signal of 1 MHz is modulated by a 10 kHz sinusoidal signal. If the lower sideband and the carrier are suppressed and if the amplitude modulated signal is sampled for further processing, what should be the minimum sampling frequency for baseband sampling? |
| A. | 1000 kHz |
| B. | 990 kHz |
| C. | 1980 kHz |
| D. | 2020 kHz |
| Answer» E. | |
| 65. |
In an Amplitude Modulate (AM) wave with 100% modulation (m), the carrier is suppressed. The percentage of power saving will be: |
| A. | 100% |
| B. | 50% |
| C. | 25% |
| D. | 66.7% |
| Answer» E. | |
| 66. |
One of the following cannot be used to remove the unwanted side band in SSB |
| A. | filter system |
| B. | balanced modulator |
| C. | third method |
| D. | phase shift method |
| Answer» B. balanced modulator | |
| 67. |
If two tones f1 and f2 are amplified by a non-linear amplifier, which frequency components would be present in output? |
| A. | f1, f2 |
| B. | f1, f2, f1 + f2, f1 – f2 |
| C. | f1 + f2, f1 – f2 |
| D. | nf1 ± mf2, where n and m are integers |
| Answer» E. | |
| 68. |
A 1 MHz sinusoidal carrier is amplitude modulated by a symmetrical square wave of period 100 μs. Which of the following frequencies will not be present in the modulated signal? |
| A. | 990 kHz |
| B. | 1010 kHz |
| C. | 1020 kHz |
| D. | 1030 kHz |
| Answer» D. 1030 kHz | |
| 69. |
A carrier is modulated to a depth of 40%. The percentage increase in the transmitted power is |
| A. | 40% |
| B. | 20% |
| C. | 16% |
| D. | 8% |
| Answer» E. | |
| 70. |
If two signals modulate the same carrier with different modulation depths of 0.3 and 0.9, the resulting modulation signal will |
| A. | be over-modulated |
| B. | have the resultant modulation limit to 1.0 |
| C. | have the resultant modulation index around 0.82 |
| D. | have the resultant modulation index around 0.95 |
| Answer» E. | |
| 71. |
A broadcast AM transmitter radiates 50 kW of carrier power. The radiation power at 85% of modulation is |
| A. | 68.1 kW |
| B. | 60.8 kW |
| C. | 61.8 kW |
| D. | 62.0 kW |
| Answer» B. 60.8 kW | |
| 72. |
Modulation system used for video modulation in TV transmission is |
| A. | DSB |
| B. | VSB |
| C. | SSB |
| D. | SSBBC |
| Answer» C. SSB | |
| 73. |
A broadcasting AM transmitter radiates 10 kW. If the modulation is 60%, how much power is contained in the side band? |
| A. | 8.47 kW |
| B. | 1.53 kW |
| C. | 5 kW |
| D. | 3.06 kW |
| Answer» C. 5 kW | |
| 74. |
A 360 W carrier is simultaneously modulated by two audio waves with modulation percentages of 55 and 65 respectively. The effective modulation index and the total power radiated are |
| A. | 0.85 and 490.5 W |
| B. | 0.65 and 490.5 W |
| C. | 0.85 and 450.5 W |
| D. | 0.65 and 450.5 W |
| Answer» B. 0.65 and 490.5 W | |
| 75. |
Consider the following features of FM vis-à-vis AM:1. Better noise immunity is provided2. Lower bandwidth is required3. The transmitted power is better utilized4. Less modulating power is required Which of the above are advantages of FM over AM? |
| A. | 1, 2 and 3 only |
| B. | 1, 3 and 4 only |
| C. | 2 and 4 only |
| D. | 1, 2, 3 and 4 |
| Answer» C. 2 and 4 only | |
| 76. |
A message signal given by \(m\left( t \right) = \frac{1}{2}\cos {\omega _1}\left( t \right) - \frac{1}{2}\sin {\omega _2}t\)is amplitude modulated with carrier of frequency \({\omega _c}\) to generate \(s\left( t \right) = \left[ {1 + m\left( t \right)} \right]\cos {\omega _c}t\) .What is the power efficiency achieved by this modulation scheme? |
| A. | 8.33% |
| B. | 11.11% |
| C. | 20% |
| D. | 25% |
| Answer» D. 25% | |
| 77. |
A non-periodic composite signal has a bandwidth of 440 kHz. With a middle frequency of 600 kHz and a peak amplitude of 100 V. The two extreme frequencies have an amplitude of 20 V Determine the lowest and the highest frequencies. |
| A. | 450 kHz and 890 kHz, respectively. |
| B. | 360 kHz and 800 kHz, respectively. |
| C. | 380 kHz and 820 kHz, respectively. |
| D. | 400 kHz and 840 kHz, respectively. |
| Answer» D. 400 kHz and 840 kHz, respectively. | |
| 78. |
Consider the following statements with regard to a PLL:i. The 'capture range' of a PLL primarily depends upon the slope of transition band edge of the low-pass filter.ii. The 'look range' is not affected by the slope of transition band of the low-pass filter.Which of the above statements is/are correct? |
| A. | Both i and ii |
| B. | i only |
| C. | ii only |
| D. | Neither i nor ii |
| Answer» B. i only | |
| 79. |
An amplitude-modulated amplifier has a radio frequency output of 60 W at 100% modulation. The internal loss in the modulator is 6W. What is the unmodulated carrier power? |
| A. | 33 W |
| B. | 36 W |
| C. | 40 W |
| D. | 44 W |
| Answer» E. | |
| 80. |
If a modulating signal with frequency fm amplitude modulates a carrier of frequency fc (where fc fm), the frequencies present at the output of AM is/are (with carrier). |
| A. | fc, fc ± fm |
| B. | ± fm only |
| C. | fc + 2 fm |
| D. | fc - fm only |
| Answer» B. ± fm only | |
| 81. |
A TV system has BW of 240 MHz, how many TV signals could be transmitted using FDM of 4 MHz wide? |
| A. | 20 |
| B. | 30 |
| C. | 150 |
| D. | 60 |
| Answer» E. | |
| 82. |
In AM modulation, the equation of the modulating signal is given by f(t) = Am cos ωmt. If the amplitude of the carrier wave is A and there is no over-modulation, the modulation efficiency will be |
| A. | 33.33% |
| B. | 38.6% |
| C. | 48.3% |
| D. | 48.6% |
| Answer» B. 38.6% | |
| 83. |
A 20 kHz carrier is amplitude modulated a speech band of 300 to 3300 Hz. The range of LSB will be: |
| A. | 20.3 to 23.3 kHz |
| B. | 50.3 to 52.25 kHz |
| C. | 52.25 to 55.25 kHz |
| D. | 16.7 to 19.7 kHz |
| Answer» E. | |