McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Computer Science Engineering (CSE) .
| 1. |
If the peak message signal amplitude is half the peak amplitude of the carrier signal, the signal is modulated. |
| A. | 100% |
| B. | 2% |
| C. | 50% |
| D. | 70% |
| Answer» C. 50% | |
| Explanation: the modulation is also expressed in percentage. it is also called percentage modulation. the signal is said to be 50% modulated if the peak message signal | |
| 2. |
A percentage of modulation greater than |
| A. | 10% |
| B. | 25% |
| C. | 50% |
| D. | 100% |
| Answer» D. 100% | |
| Explanation: a percentage of modulation greater than 100% will distort the message signal if detected by an envelope detector. in this case the lower excursion of the signal will drive the carrier amplitude below zero, making it negative (and hence changing its phase). | |
| 3. |
Single sideband AM systems occupy same bandwidth as of conventional AM systems. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: single sideband (ssb) am systems transmit only one of the sidebands (either upper or lower) about the carrier. | |
| 4. |
How is the performance of SSB AM systems in fading channels? |
| A. | poor |
| B. | best |
| C. | good |
| D. | average |
| Answer» A. poor | |
| Explanation: ssb systems have the advantage of being very bandwidth efficient. but their performance in fading channels is very poor. for proper detection, the frequency of the oscillator at the product detector mixer in the receiver must be same as that of the incoming carrier frequency. | |
| 5. |
Which of the following is a disadvantage of tone-in-band SSB system? |
| A. | high bandwidth |
| B. | bad adjacent channel protection |
| C. | effects of multipath |
| D. | generation and reception of signal is complicated |
| Answer» D. generation and reception of signal is complicated | |
| Explanation: tone-in-band ssb systems has the advantage of maintaining the low bandwidth property of the ssb signals, while at the same time providing good adjacent | |
| 6. |
FFSR in AM systems stands for |
| A. | feedforward signal regeneration |
| B. | feedbackward signal regeneration |
| C. | feedbackward system restoration |
| D. | feedforward system restoration |
| Answer» A. feedforward signal regeneration | |
| Explanation: ffsr stands for feedforward signal regeneration. if the pilot tone and the information bearing signal undergo correlated fading, it is possible at the receiver to counteract the effects of fading through signal processing based on tracking of pilot tone. | |
| 7. |
AM demodulation technique can be divided into and demodulation. |
| A. | direct, indirect |
| B. | slope detector, zero crossing |
| C. | coherent, noncoherent |
| D. | quadrature detection, coherent detection |
| Answer» C. coherent, noncoherent | |
| Explanation: am demodulation techniques may be broadly divide into two main categories. they are called coherent and noncoherent demodulation. they are differentiated by the knowledge of transmitted carrier frequency and phase at the receiver. | |
| 8. |
Non coherent detection requires the knowledge of transmitted carrier frequency and phase at the receiver. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: non coherent detection does require the knowledge of phase information. however, coherent detection requires knowledge of the transmitted carrier frequency and phase at the receiver. | |
| 9. |
A product detector in AM systems is also called |
| A. | envelope detector |
| B. | differentiator |
| C. | integrator |
| D. | phase detector |
| Answer» D. phase detector | |
| Explanation: a product detector is also called a phase detector. it forms a coherent demodulator for am signals. it is a down converter circuit which converts the input bandpass signal to a baseband signal. | |
| 10. |
AM system use only product detector for demodulation. They never use envelope detectors. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: am systems can use either product detector or envelope detector for demodulation. as a rule, envelope detectors are useful when input signal power is at least 10db greater than noise power, whereas product detectors are able to process the am signals with input signal to noise ratios well below 0 db. | |
| 11. |
LCD uses |
| A. | sematic crystals |
| B. | twisted nematic crystals |
| C. | nematic crystals |
| D. | cholesteric crystals |
| Answer» B. twisted nematic crystals | |
| Explanation: lcd uses liquid crystal display. it uses twisted nematic crystals which are a type of liquid crystal, consisting of a substance called the nematic. the nematic liquid crystal is placed between two plates of polarized glass. | |
| 12. |
Which of the following stage is present in FM receiver but not in AM receiver? |
| A. | amplitude limiter |
| B. | demodulator |
| C. | am amplifier |
| D. | mixer |
| Answer» A. amplitude limiter | |
| Explanation: amplitude limiter circuit is used in fm receiver to remove the noise or any variation in amplitude present in the received signal. thus, the output of the amplitude limiter has a constant amplitude. so it is only used in frequency modulation and not in amplitude modulation. | |
| 13. |
Function of duplexer in a RADAR is to permit the use of same antenna for transmission and reception. |
| A. | true |
| B. | false |
| Answer» A. true | |
| Explanation: a duplexer is being an electronic unit, allows bi-directional communication over the same path. the transmitter and receiver can communicate simultaneously. in radar, the duplexer isolates the receiver from the transmitter while allowing them to share a common antenna. | |
| 14. |
Single Sideband Modulation (SSB) is generally reserved for point-to-point communication. |
| A. | true |
| B. | false |
| Answer» A. true | |
| Explanation: a point-to-point communication refers to bidirectional communication between only one transmitter and one receiver. in ssb-sc modulation technique, the carrier is suppressed and only one of the two side-bands are transmitted. | |
| 15. |
For an AM transmitter, class C amplifier can be used after the modulation stage. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: in an am transmitter, the required transmission power is obtained from class c amplifier, as it is a power amplifier, for low-level or high-level modulation. so it is not used after the modulation stage. | |
| 16. |
For which of the modulated system, the linear amplified modulated stage is used? |
| A. | low level amplitude modulated system |
| B. | high level amplitude modulated system |
| C. | high level frequency modulated system |
| D. | low level frequency modulated system |
| Answer» A. low level amplitude modulated system | |
| Explanation: in low-level modulation, the generation of amplitude modulated signal takes place at low power levels. the generated am signal is then amplified using a chain of linear amplifiers, which are required to avoid waveform distortion. thus, linear amplified modulated stage is used in low level amplitude modulated system. | |
| 17. |
When noise is passed through a narrow band filter, the output of filter should be? |
| A. | triangular |
| B. | square |
| C. | parabolic |
| D. | sinusoidal |
| Answer» D. sinusoidal | |
| Explanation: narrow band filter is used to isolate a narrow band of frequencies from a wider bandwidth signal. it is a combination of band pass and band reject filter. when noise gets passed through it, the output of it should be sinusoidal. | |
| 18. |
A narrow band noise can exist in |
| A. | am only |
| B. | pcm only |
| C. | fm only |
| D. | am and fm both |
| Answer» D. am and fm both | |
| Explanation: narrow band filter is used to isolate a narrow band of frequencies from a wider bandwidth signal. it is a combination of band pass and band reject filter. so it can be used in both am and fm to pass a band of frequencies or to attenuate a band of frequencies. | |
| 19. |
The upper and lower sideband frequencies for 5KHz amplitude modulation with a 30KHz carrier frequency will be? |
| A. | 35khz and 25khz |
| B. | 34khz and 24khz |
| C. | 25khz and 35khz |
| D. | 0.35khz and 0.25khz |
| Answer» A. 35khz and 25khz | |
| Explanation: upper sideband frequency will be (30 + 5) = 35 khz and lower sideband frequency will be (30 – 5) = 25 khz. | |
| 20. |
Phase array radar can track many targets together. |
| A. | true |
| B. | false |
| Answer» A. true | |
| Explanation: a phased array radar is an array of radiating elements, with each having a phase-shifter. the phase of the signal being emitted from the radiating element is changed to produce beams, thereby producing constructive or destructive interference for steering the beams in the required direction. | |
| 21. |
A duplex arrangement use separate frequencies for transmission. |
| A. | true |
| B. | false |
| C. | topic 1.3 ssbsc |
| Answer» A. true | |
| Explanation: in duplex communication, two- way interaction is favourable simultaneously. thus, a cordless telephone is duplex which uses separate frequencies for transmission in base and portable units. | |
| 22. |
VSB modulation is used in televisions because it avoids phase distortion at low frequencies. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: vestigial sideband modulation (vsb) is a type of amplitude modulation in which the carrier and only one sideband is completely transmitted and the other sideband is partly transmitted. thus, television production is done using vsb modulation as it reduces bandwidth to half. | |
| 23. |
A cordless telephone that uses separate frequencies for transmission in base and portable units is called |
| A. | half duplex |
| B. | duplex |
| C. | simplex |
| D. | one-way communication |
| Answer» B. duplex | |
| Explanation: in duplex communication, two- way interaction is favourable simultaneously. thus, a cordless telephone is duplex which uses separate frequencies for transmission in base and portable units. | |
| 24. |
Which polarization is used to reduce the depolarization effect on received waves? |
| A. | circular polarization |
| B. | linear polarization |
| C. | atomic polarization |
| D. | dipolar polarization |
| Answer» A. circular polarization | |
| Explanation: in circular polarization at each point the electric field of electromagnetic wave has a constant magnitude but its | |
| 25. |
Circular polarization involves critical alignment between transmitting and receiving antenna. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: in circular polarization at each point the electric field of the electromagnetic wave has a constant magnitude but its direction changes as it rotates with time at a steady rate, in a plane perpendicular to the direction of propagation of the wave. it is used to reduce depolarization effect on received waves. it does not involve alignment between transmitting and receiving antenna. | |
| 26. |
It is only the reflected color that decided the color of an object. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: color of any object is decided by the reflected color for opaque object and wavelength transmitted through it for transparent object, while both reflector color and wavelength transmitted are considered for a translucent object. | |
| 27. |
What do you understand by the term “carrier” in modulation? |
| A. | voltage to be transmitted |
| B. | resultant wave |
| C. | voltage for which amplitude, phase or frequency can be varied |
| D. | voltage for which amplitude, phase or frequency remains constant |
| Answer» C. voltage for which amplitude, phase or frequency can be varied | |
| Explanation: carrier wave is the wave with frequency higher than the message signal, | |
| 28. |
Carrier wave in modulation is a resultant wave. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: carrier wave is the wave with frequency higher than the message signal, whose certain characteristics like amplitude, phase or frequency are varied with respect to the instantaneous amplitude of the message signal. thus forming the modulated wave which is the wave to be transmitted. | |
| 29. |
For a low level AM system, amplifier modulated stage must have |
| A. | harmonic devices |
| B. | linear devices |
| C. | non-linear devices |
| D. | class a amplifiers |
| Answer» B. linear devices | |
| Explanation: in low-level modulation, the generation of amplitude modulated signal takes place at low power levels. the generated am signal is then amplified using a chain of linear amplifiers, which are required to avoid waveform distortion. thus, linear devices are used in low level amplitude modulated system. | |
| 30. |
Which is the greatest disadvantage of Pulse Code Modulation? |
| A. | highly prone to noise |
| B. | cannot travel long distances |
| C. | its inability to handle analog signals |
| D. | large bandwidth is required for it |
| Answer» D. large bandwidth is required for it | |
| Explanation: pulse code modulation (pcm) is a digital form of communication. for demodulation of pcm, it is necessary to convert it into pam. quantization noise occurs in pcm only. its greatest disadvantage is its requirement for large bandwidth. | |
| 31. |
Inductance and capacitance of a line is 0.8 |
| A. | 158 |
| B. | 166 |
| C. | 143 |
| D. | 127 |
| Answer» A. 158 | |
| 32. |
Quantization noise occurs in |
| A. | frequency division multiplexing |
| B. | time division multiplexing |
| C. | delta modulation |
| D. | amplitude modulation |
| Answer» D. amplitude modulation | |
| Explanation: quantisation is the process | |
| 33. |
What the main advantage of PCM? |
| A. | can travel small distances |
| B. | higher bandwidth |
| C. | lower noise |
| D. | good reception |
| Answer» C. lower noise | |
| Explanation: pulse code modulation is a technique in which the amplitude of an analogue signal is converted to a binary value represented as a series of pulses. it is less prone to noise and can travel through long distances without loss of data. | |
| 34. |
In AM pilot carrier, transmission has |
| A. | carrier and part of one side band |
| B. | two side bands and a carrier |
| C. | two side bands |
| D. | carrier, one side band and part of other side band |
| Answer» B. two side bands and a carrier | |
| Explanation: in amplitude modulated wave, the transmitted wave has two side bands and a carrier. thus it’s bandwidth is twice the maximum modulating frequency. | |
| 35. |
Quantization noise depends upon both sampling rate and number of quantization levels. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: quantization noise in pulse code modulation (pcm) depends upon only on number of quantization levels. | |
| 36. |
Which of the following frequency is not transmitted in AM transmission? |
| A. | upper side band frequency |
| B. | carrier frequency |
| C. | lower side band frequency |
| D. | audio frequency |
| Answer» D. audio frequency | |
| Explanation: audio frequency is the frequency that is not transmitted in am transmission. | |
| 37. |
Companding is used in PCM transmitters to allow amplitude limiting in the receivers. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: companding is the process through which the signal to noise ratio of a wave is reduced by compressing and expanding the signal. it decreases the number of bits required to record the strongest signal. companding also improves signal to noise ratio. | |
| 38. |
What is the use of Companding? |
| A. | in pcm transmitters to allow amplitude limiting in the receivers |
| B. | in pcm receiver to overcome impulse noise |
| C. | to overcome quantizing noise in pcm |
| D. | to protect small signals in pcm from quantizing distortion |
| Answer» D. to protect small signals in pcm from quantizing distortion | |
| Explanation: companding is the process through which the signal to noise ratio of a wave is reduced by compressing and expanding the signal. it decreases the number of bits required to record the strongest signal. companding also improves signal to noise ratio. it is mainly used to protect small signals in pcm from quantizing distortion. | |
| 39. |
5 PSD MODULATORS AND DEMODULATORS |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: modern mobile communication systems use digital modulation techniques. | |
| 40. |
Which of the following is not an advantage of digital modulation? |
| A. | greater noise immunity |
| B. | greater security |
| C. | easier multiplexing |
| D. | less bandwidth requirement |
| Answer» D. less bandwidth requirement | |
| Explanation: digital modulation offer many advantages over analog modulation. some advantages include greater noise immunity and robustness. they provide easier multiplexing of various forms of information and greater security. | |
| 41. |
The performance of modulation scheme is not measured in terms of |
| A. | power efficiency |
| B. | bandwidth efficiency |
| C. | cost and complexity |
| D. | transmitted power |
| Answer» D. transmitted power | |
| Explanation: the performance of modulation scheme is often measured in terms of its power efficiency and bandwidth efficiency. | |
| 42. |
In digital communication system, in order to increase noise immunity, it is necessary to increase |
| A. | signal power |
| B. | signal amplitude |
| C. | signal frequency |
| D. | signal magnitude |
| Answer» A. signal power | |
| Explanation: in digital communication system, in order to increase noise immunity, it is necessary to increase signal power. | |
| 43. |
Which of the following is the ratio of signal energy per bit to noise power spectral density? |
| A. | bandwidth efficiency |
| B. | spectral density |
| C. | power efficiency |
| D. | power density |
| Answer» C. power efficiency | |
| Explanation: power efficiency is often expressed as the ratio of signal energy per bit to noise power spectral density required at the receiver input for a certain probability of error. power efficiency is a measure of how favourably the trade-off between fidelity and signal power is made. | |
| 44. |
Increasing the data rate implies the increase in pulse width of digital symbol. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: there is an unavoidable relationship between data rate and bandwidth occupancy. increasing the data rate implies decreasing the pulse width of a digital symbol, which increases the bandwidth of the signal. | |
| 45. |
Which of the following is the ratio of the throughput data rate per Hertz? |
| A. | bandwidth efficiency |
| B. | spectral density |
| C. | power efficiency |
| D. | power density |
| Answer» A. bandwidth efficiency | |
| Explanation: bandwidth efficiency reflects how efficiently the allocated bandwidth is utilized. it is defined as the ratio of throughput data rate per hertz in a given bandwidth. it describes the ability of a modulation scheme to accommodate data within a limited bandwidth. | |
| 46. |
Which of the following is defined as the range of frequencies over which the signal has a non zero power spectral density? |
| A. | null to null bandwidth |
| B. | half power bandwidth |
| C. | 3 db bandwidth |
| D. | absolute bandwidth |
| Answer» D. absolute bandwidth | |
| Explanation: the absolute bandwidth is defined as the range of frequencies over which the signal has a non-zero power spectral density. for symbols represented as rectangular baseband pulses, the psd profile extends over an infinite range of frequencies, and has an absolute bandwidth of infinity. | |
| 47. |
is equal to width of main spectral lobe. |
| A. | null to null bandwidth |
| B. | half power bandwidth |
| C. | 3 db bandwidth |
| D. | absolute bandwidth |
| Answer» A. null to null bandwidth | |
| Explanation: null to null bandwidth is a simpler and more widely accepted measure of bandwidth. it is equal to the width of main spectral lobe. | |
| 48. |
Half power bandwidth is also called |
| A. | absolute bandwidth |
| B. | null to null bandwidth |
| C. | 3 db bandwidth |
| D. | zero db bandwidth |
| Answer» C. 3 db bandwidth | |
| Explanation: half power bandwidth is also called the 3 db bandwidth. it is defined as the interval between frequencies at which the psd has dropped to half power, or 3 db below the peak value. | |
| 49. |
FM is a part of general class of modulation known as |
| A. | angle modulation |
| B. | phase modulation |
| C. | amplitude modulation |
| D. | frequency modulation |
| Answer» A. angle modulation | |
| Explanation: fm is a part of general class of modulation known as angle modulation. | |
| 50. |
Frequency modulated signal is regarded as the phase modulated signal in which the modulating wave is differentiated before modulation. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: frequency modulated signal is regarded as the phase modulated signal in which the modulating wave is integrated before modulation. this means that an fm signal can be generated by first integrating the message signal and then using the result as an input to a phase modulator. | |
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