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51.

Atmospheric noise, extraterrestrial noise and man-made noise is part of internal noise in communication.(a) True(b) FalseThe question was asked in unit test.Origin of the question is Costas Loop in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Correct OPTION is (b) False

Explanation: ATMOSPHERIC noise, extraterrestrial noise and man-made noise is part of external noise in communication. External noise are the ones which are produced by external sources, that are not part of the communication SYSTEM. INTERNAL noise are the ones which are produced by internal components of the communication system.

52.

Thermal noise is a synonym of ________(a) Atmospheric noise(b) shot noise(c) Johnson noise(d) transit time noiseThis question was posed to me in an interview for job.This is a very interesting question from Costas Loop in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Correct choice is (C) Johnson noise

Easy explanation: THERMAL noise is a type of internal noise in communication. It is produced due to thermal EXCITATION of the free electrons in the CIRCUIT. It is also KNOWN as Johnson noise.

53.

In a Vidicon camera tube, both sides of the target plate have the coating of Sno2.(a) True(b) FalseI got this question in an interview for internship.Question is from Costas Loop in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Correct option is (B) False

The BEST I can explain: A vidicon camera tube is a type of camera tube having a photoconductive surface within. In Vidicon camera tube, the side of target PLATE facing the LIGHT has a coating of Sno2 and the side facing electron gun has a coating of antimony trisulphide.

54.

Distance at which a sky wave is received back on earth ________ with an angle of incidence.(a) increases(b) decreases(c) can be increase or decrease(d) can neither be increase or decreaseI have been asked this question by my college professor while I was bunking the class.This question is from Costas Loop topic in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The correct CHOICE is (B) decreases

The best I can EXPLAIN: The distance at which a SKY wave is RECEIVED back on earth is inversely proportional to the angle of incidence. Thus, the distance at which a sky wave is received back on earth decreases with an angle of incidence.

55.

Ground wave can be used for communication upto ________(a) 5 KHz(b) 12 KHz(c) 16 KHz(d) 25 KHzThe question was asked during an interview for a job.The origin of the question is Costas Loop in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Correct option is (c) 16 KHz

For explanation I would say: GROUND wave is that wave that reaches a receiver from a transmitter DIRECTLY without reflecting from IONOSPHERE. It can be used for COMMUNICATION upto 16 KHz.

56.

A Marconi antenna has length equal to ________(a) ^ʎ⁄4(b) ^ʎ⁄2(c) 1(d) ^ʎ⁄8I had been asked this question in an online quiz.The question is from Problems of DSBSC in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The correct option is (a) ^ʎ⁄4

To elaborate: MARCONI antenna is like a vertical wire having length one fourth of the working wavelength. Thus, it is a quarter-wave monopole antenna. SINCE, it was INVENTED by Guglielmo Marconi, so it’s also called Marconi Antenna. It requires a ground plane with very GOOD conductivity. Hence it is also called as a grounded antenna.

57.

In a Vidicon camera tube, both sides of the target plate have the coating of antimony tri-sulphide.(a) True(b) FalseThis question was addressed to me in examination.I'm obligated to ask this question of Problems of DSBSC in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Right option is (b) False

For EXPLANATION: A vidicon CAMERA tube is a type of camera having a photoconductive surface within. In a Vidicon camera tube, the SIDE of target plate FACING the LIGHT has a coating of Sno2 and the side facing electron gun has a coating of antimony trisulphide.

58.

A trigonometric function is a synonym of ________(a) triangular function(b) orthogonal function(c) singular function(d) rectangular functionI got this question in an international level competition.This intriguing question comes from Problems of DSBSC topic in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Correct choice is (a) triangular FUNCTION

Best EXPLANATION: TRIGONOMETRIC function is the angle expressed as the ratio of two sides of a right-angled triangle that CONTAINS the angle. It can also be SEEN as a synonym of triangular function.

59.

Local programmes in a cable TV can be telecast at any frequency.(a) True(b) FalseThis question was addressed to me during an interview for a job.I want to ask this question from Problems of DSBSC topic in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer» CORRECT ANSWER is (a) True

The EXPLANATION is: There is not a fixed frequency range or bandwidth SET for BROADCASTING of local programs in a cable TV. It can be telecasted at any frequency, depending on the channel of bandwidth available.
60.

White noise is a synonym of ________(a) partition noise(b) shot noise(c) johnson noise(d) transit time noiseI had been asked this question in an internship interview.This is a very interesting question from Problems of DSBSC topic in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The correct choice is (c) johnson noise

Explanation: White noise is an INTERNAL noise of communication SYSTEM having different frequencies present with EQUAL intensities. It can also be CALLED Thermal noise or Johnson noise.

61.

Minimum viewing angle of resolution of human eye is ________(a) \(\frac{ʎ}{d}\)(b) \(\frac{1.22ʎ}{d}\)(c) \(\frac{3ʎ}{d}\)(d) \(\frac{2ʎ}{d}\)I have been asked this question in an internship interview.The above asked question is from Problems of DSBSC in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The correct ANSWER is (b) \(\frac{1.22ʎ}{d}\)

The EXPLANATION is: Minimum resolution of human eye for clear OBSERVATION is GENERALLY \(\frac{1.22ʎ}{d}\). The DIAMETER of human eye is about 25mm.

62.

Power density spectrum of a resistor R can be expressed as ________(a) 2 kTR(b) 1 kTR(c) 0.75 kTR(d) 3 kTRThis question was addressed to me during an online interview.Enquiry is from Problems of DSBSC in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The correct option is (a) 2 kTR

Explanation: Power Spectral DENSITY is the quantity of power present in a signal in the frequency DOMAIN. The Power Density SPECTRUM of a resistor R can be expressed as 2 kTR where k is Boltzmann’s constant, T is temperature and R is GIVEN RESISTANCE.

63.

VSB is generally used in ________(a) television production(b) radio transmission(c) telephonic conversations(d) long distance conversationsI had been asked this question during an internship interview.This interesting question is from Problems of DSBSC in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Correct answer is (a) television production

Explanation: VESTIGIAL Sideband Modulation (VSB) is a type of amplitude modulation in which the carrier and only ONE sideband are completely transmitted and the other sideband is PARTLY transmitted. THUS, television production is done using VSB modulation.

64.

What is the typical bandwidth of a 2-wire telephone line?(a) 20 Hz to 6 KHz(b) 300 Hz to 3.4 KHz(c) 20 Hz to 20 KHz(d) 200 Hz to 6.5 KHzI got this question in an international level competition.My question is based upon Problems of DSBSC topic in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The correct option is (b) 300 Hz to 3.4 KHz

Explanation: A HELICAL ANTENNA is an antenna made of one or more conducting wires wound in the form of a helix. It produces circular polarization, because of which it is highly USED in radio telemetry. It is mainly used for satellite tracking DUE to its good front to back ratio.

65.

A helical antenna is used for satellite tracking due to its __________(a) broad bandwidth(b) circular polarization(c) linear polarization(d) good front to back ratioI got this question during an online exam.My doubt is from Problems of DSBSC topic in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer» RIGHT answer is (d) GOOD front to back ratio

To explain: Helical antenna consists conducting wire. These conducting wire is WOUND around it in the form of helix. It is mainly used for satellite TRACKING due to its good front to back ratio.
66.

Television transmission is possible through ________(a) DSB-SC(b) SSB-SC(c) VSB(d) AMThe question was posed to me in final exam.My question is based upon Quadrature Carrier Multiplexing in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Right answer is (c) VSB

Explanation: We generally use VESTIGIAL sideband (VSB) for television production. In VSB, ONE of the SIDEBANDS is completely TRANSMITTED whereas the other sideband is partly transmitted, along with the carrier. VSB is used as it reduces the required bandwidth to half.

67.

The output stage in a television transmitter is likely to be ________(a) screen modulated(b) plate modulated(c) rectangular modulated(d) grid modulatedI have been asked this question in an online quiz.My question is taken from Quadrature Carrier Multiplexing topic in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The CORRECT option is (d) grid modulated

The best I can explain: We generally use vestigial SIDEBAND modulation (VSB) for television PRODUCTION as it reduces the required bandwidth. However, the output stage in a television transmitter is generally grid modulated using a Class C amplifier, In grid modulation, the carrier wave to the message signal is provided by the grid CIRCUIT of the ELECTRON tube.

68.

The advantage of using mechanical filter in filter system of sideband suppression is good band pass.(a) True(b) FalseThis question was posed to me by my school principal while I was bunking the class.The origin of the question is Quadrature Carrier Multiplexing in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The CORRECT answer is (a) True

The explanation: GENERALLY, the filters have sharp cut-off FREQUENCY as a result of which EITHER of the sidebands are not completely suppressed. Thus, the advantage of using mechanical filter in filter system of SIDEBAND suppression is smaller size, good band pass and good attenuation characteristics.

69.

The rms value of a thermal noise voltage is proportional to (where k is Boltzmann’s constant) _______(a) √k(b) k(c) k^2(d) k^^1⁄3I have been asked this question in an online quiz.Question is taken from Quadrature Carrier Multiplexing topic in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Correct answer is (a) √k

The best I can explain: THERMAL noise is the noise generated in electronic DEVICES at frequencies below a few kilohertz, due to thermal EXCITATION of electrons. The root mean square value of thermal noise is proportional to root k TIMES, where k represents Boltzmann’s CONSTANT.

70.

For a human eye the minimum viewing angle of resolution should be ^ʎ⁄D where D is iris opening and ʎ is wavelength of light.(a) True(b) FalseThe question was asked in my homework.My question comes from Quadrature Carrier Multiplexing topic in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The CORRECT option is (B) False

For explanation: For a human eye the minimum VIEWING angle of RESOLUTION should be 1.22ʎ/D. The diameter of human eye is about 25MM.

71.

Noises which get generated within the receiver is called ________(a) Internal noise(b) External noise(c) Man-made noise(d) Extraterrestrial noiseThe question was asked in an internship interview.My question is taken from Quadrature Carrier Multiplexing in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer» RIGHT CHOICE is (a) Internal noise

Best EXPLANATION: Internal noise in communication is the noise that gets generated within the RECEIVER or communication SYSTEM.
72.

In amplitude modulation, magnitude of side bands is ________ times the carrier amplitude.(a) ^ma⁄2(b) 4ma(c) ma(d) 2maThis question was posed to me at a job interview.My question comes from Quadrature Carrier Multiplexing in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Right answer is (b) 4ma

The explanation is: In amplitude MODULATION, for a good transmission and reception, the magnitude of side bands must be 4ma times the amplitude of CARRIER wave, (where, m = Modulation Index and a =Amplitude of Message SIGNAL).

73.

Autocorrelation function of white noise is ________(a) an impulse function(b) a step function(c) a constant(d) a variableThe question was posed to me in my homework.This question is from Quadrature Carrier Multiplexing topic in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The correct choice is (c) a constant

The explanation: WHITE noise is an internal noise of COMMUNICATION system having different frequencies present with EQUAL intensities. It has a peak only at zero and are zero at all points. THUS, the AUTOCORRELATION function of white noise is a constant.

74.

In a Vidicon camera tube, the side of target plate facing the light has a coating ofSno2 (tin oxide) and the side facing electron gun has a coating of antimony trisulphide.(a) True(b) FalseThe question was posed to me in semester exam.My question is based upon Quadrature Carrier Multiplexing topic in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The correct answer is (a) True

For explanation: A VIDICON camera tube is a type of camera having a photoconductive surface within. In a Vidicon camera tube, the side of TARGET plate facing the light has a COATING of Sno2 and the side facing electron GUN has a coating of antimony trisulphide.

75.

Marconi antenna ________(a) is a grounded antenna(b) is an ungrounded antenna(c) can either be grounded or ungrounded antenna(d) can neither be grounded nor ungrounded antennaI got this question during an interview.I need to ask this question from Quadrature Carrier Multiplexing in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Right answer is (a) is a grounded antenna

For explanation I WOULD say: Marconi antenna is like a vertical wire having length one fourth of the WORKING WAVELENGTH. Thus, it is a quarter wave MONOPOLE antenna. Since it was invented by GUGLIELMO Marconi, so it’s also called Marconi Antenna. It requires a ground plane with very good conductivity. Hence it is also called as a grounded antenna.

76.

Flyback switched mode is used in television because it can supply many voltage outputs.(a) True(b) FalseI have been asked this question during an internship interview.I would like to ask this question from Carrier Acquistion Techniques in DSB-SC in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Correct OPTION is (B) False

To explain: In frequency modulation, POWER is determined from CARRIER amplitude and as carrier amplitude does not change, thus power remains constant. So if we increase the modulation index, then also it does not affect power and it will REMAIN constant.

77.

What will be the effect on power if the modulation index of a frequency modulated signal is increased?(a) increases(b) decreases(c) remains constant(d) first increases and then decreasesThis question was posed to me during an online interview.Enquiry is from Carrier Acquistion Techniques in DSB-SC topic in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Right CHOICE is (c) remains constant

To explain I would SAY: In frequency modulation, power remains constant. So if we increase the modulation index then ALSO it does not affect power, it will remain constant.

78.

The equation 20sin⁡(10^8 t + 3 sin⁡ 10^9 t) represents which modulation?(a) AM(b) DSB-SC(c) PM(d) FMI had been asked this question in class test.This interesting question is from Carrier Acquistion Techniques in DSB-SC in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Correct ANSWER is (d) FM

To explain I would say: On comparing with the GENERAL equation of each MODULATION, we found that it represents Frequency modulation.

FM (t) = Ac sin (2πfct + βsin(2πfmt)), where symbols have their USUAL MEANING.

79.

Monopole antenna is a type of travelling wave antenna.(a) True(b) FalseThis question was posed to me in quiz.Asked question is from Carrier Acquistion Techniques in DSB-SC in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Correct choice is (b) False

Explanation: MONOPOLE antenna is a type of WIRE antenna like Marconi antenna, ALSO known as quarter-WAVE antenna. Travelling wave antenna makes use of a travelling wave as a radiating guide and they consist of helical antenna, SPIRAL antenna.

80.

In which modulation, frequency of carrier signal is varied with the amplitude of modulating signal?(a) FM(b) AM(c) PM(d) VSBThe question was asked in a job interview.My doubt is from Carrier Acquistion Techniques in DSB-SC in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Right answer is (a) FM

For explanation I would say: In Frequency Modulation, the frequency of CARRIER wave is VARIED with the INSTANTANEOUS amplitude of modulating signal. The general FM modulated expression is :

FM (t) = Ac sin (2πfct + βsin(2πfmt)), where SYMBOLS have their usual meaning.

81.

In Phase Modulation the phase of carrier signal is varied.(a) True(b) FalseI got this question in examination.The above asked question is from Carrier Acquistion Techniques in DSB-SC topic in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The correct option is (a) True

For explanation I would SAY: In phase modulation, the phase shift of carrier WAVE is varied with respect to the instantaneous amplitude of modulating signal. The general PM MODULATED expression is:

PM (t) = Ac sin (2πfct + βsin(2πfmt)), where SYMBOLS have their usual meaning.

82.

Power spectral density of thermal noise remains uniform upto frequency ___________(a) 10^15 HZ(b) 10^5 HZ(c) 10^2 HZ(d) 10^13 HZI had been asked this question in an internship interview.This key question is from Carrier Acquistion Techniques in DSB-SC topic in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The correct ANSWER is (d) 10^13 HZ

Explanation: Power Spectral Density is the quantity of power PRESENT in a signal in the frequency domain. Power spectral density of thermal or white noise gets affected when the frequency becomes greater than 10^13 Hz and THUS, it remains uniform UPTO 10^13 Hz.

83.

Carrier frequency remains constant in cell communication.(a) True(b) FalseI had been asked this question during an online interview.Enquiry is from Carrier Acquistion Techniques in DSB-SC in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The correct answer is (b) False

The best explanation: In cell communication, the carrier frequency does not remain CONSTANT. INSTEAD, the carrier frequency get CHANGES continuously with RESPECT to the INSTANTANEOUS amplitude of the message signal.

84.

Waves of which frequency can penetrate the atmosphere?(a) higher than 10 MHz(b) higher than 20 MHz(c) higher than 30 MHz(d) higher than 100 MHzI got this question by my school principal while I was bunking the class.My question comes from Carrier Acquistion Techniques in DSB-SC topic in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The correct answer is (c) HIGHER than 30 MHz

Explanation: Most RADIO Waves penetrate the atmosphere.Thus, any wave having frequency greater than 30 MHz can penetrate the atmosphere. The waves having frequency LESS than it cannot penetrate the atmosphere and GET absorbed into it.

85.

Armstrong modulator can only generate FM signal.(a) True(b) FalseI had been asked this question in an international level competition.My question is based upon Carrier Acquistion Techniques in DSB-SC topic in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Correct option is (B) False

To elaborate: Armstrong Modulator can also generate PM along with FM. So the STATEMENT is incorrect. THUS, collectively Armstrong modulator is an Angle Modulator, where the angle of the CARRIER wave is varied with respect to the instantaneous AMPLITUDE of modulating signal.

86.

Flyback switched mode is used in television because it does not require a filter choke.(a) True(b) FalseI have been asked this question in my homework.This is a very interesting question from Demodulation of DSB-SC topic in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The correct CHOICE is (a) True

To explain I would say: Flyback SWITCHED MODE is used in television because it does not require FILTER choke. It is also cheap as compared to others.

87.

Waves of frequency 60MHz can penetrate the atmosphere.(a) True(b) FalseI got this question during an online exam.The above asked question is from Demodulation of DSB-SC in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The correct CHOICE is (a) True

The EXPLANATION is: Most Radio Waves penetrate the atmosphere.Thus, FREQUENCIES above 30MHz can penetrate the atmosphere. So 60 MHz can penetrate the atmosphere.

88.

Ground wave travels along surface of ground.(a) True(b) FalseThis question was posed to me during an interview.My question is based upon Demodulation of DSB-SC topic in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

The correct answer is (a) True

For EXPLANATION: Ground wave propagation occurs in the area between the surface of the Earth and the Ionosphere. The wave TRAVELS parallel or ALONG the surface of the ground. It is usually used for transmission of low frequency SIGNALS.

89.

In which of the modulation, the waveform is modified resulting in a signal where each quarter cycle is transposed.(a) AM(b) FM(c) PM(d) TMI had been asked this question in a job interview.My question is from Demodulation of DSB-SC in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Correct answer is (d) TM

The explanation is: In TM, the message signal is modulated by inserting inflections in the original waveform. The waveform is MODIFIED resulting in a modulated signal where each QUARTER cycle is TRANSPOSED in MODULATION process.

90.

TM stands for _________(a) Trans positional Modulation(b) Time Multiplexing(c) Transit Modulation(d) Tuned ModulationThis question was addressed to me in class test.Enquiry is from Demodulation of DSB-SC in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Right answer is (a) Trans positional Modulation

The explanation: TM stands for Transpositional Modulation. In TM, the message signal is MODULATED by inserting inflections in the original waveform. The waveform is modified resulting in a modulated signal where each QUARTER CYCLE is TRANSPOSED in modulation process.

91.

Which of the following is a reflector antenna?(a) Marconi reflector antenna(b) Corner reflector antenna(c) Helical antenna(d) Bow tie antennaThis question was addressed to me in a job interview.My doubt is from Demodulation of DSB-SC in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer» RIGHT option is (b) CORNER reflector antenna

To explain I would say: It is corner reflector antenna that comes under reflector antenna. HELICAL antenna and BOW tie antenna comes under travelling wave antenna and log antenna respectively. Marconi reflector antenna comes under grounded antenna.
92.

Carbon microphone has a bidirectional feature.(a) True(b) FalseI have been asked this question in an online interview.Question is from Demodulation of DSB-SC topic in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer» RIGHT option is (b) False

The best I can explain: CARBON microphone does not have a bidirectional feature. It is ribbon microphone that has bidirectional feature.